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Impact of unmodified (PGV) and modified (Cloisite20A) nanoclays into biodegradability and other properties of (bio)nanocomposites
Applied Clay Science 186 (2020) 105453
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Research paper
Impact of unmodified (PGV) and modified (Cloisite20A) nanoclays into biodegradability and other properties of (bio)nanocomposites
T
Paulo Henrique Camania, José Paulo Machado Toguchia, Ana Paula S.M. Fiorib, ⁎ Derval dos Santos Rosaa, a b
Center for Engineering, Modeling and Applied Social Sciences - CECS, Federal University of ABC (UFABC), São Paulo 09210-580, Brazil Federal Institute of Education, Science and Technology of Alagoas (IFAL) - Marechal Deodoro Campus, Alagoas 57160000, Brazil
A R T I C LE I N FO
A B S T R A C T
Keywords: Bionanocomposites Organic modification Nanoclays Biodegradability PBAT [poly(butylene adipate-coterephthalate)]
The production of bionanocomposites using nanoclays are in constant development to improve the mechanical, gas barrier and thermal properties, and the biodegradability of the polymeric materials. In this study, two different nanoclays: non-treated (hydrophilic sodium-montmorillonite nanoclay - PGV) and treated with organomodification (montmorillonite nanoclay - Cloisite 20A) were incorporated (2%wt.) into PBAT [poly(butylene adipate-co-terephthalate)] by melting process. The composites properties were evaluated by SEM/EDS, XRD, mechanical properties, contact angle, TGA, and aerobic biodegradation (Sturm test). The SEM/EDS showed the presence of sodium in PGV, which characterize it as sodic montmorillonite, while the Cloisite 20A, as montmorillonite organo-modified, by the high occurrence of carbon percentage. The patterns of X-ray diffraction (XRD), about the d-spacing of the bionanocomposites, indicates high intercalation of the matrix with nanoclay Cloisite 20A and a decrease in the crystallinity index. The elasticity modulus of the bionanocomposites had a slight increase, while maximum elongation was decreased, corroborating with the intercalation, as seen in XRD results. The contact angle results have shown high hydrophilicity for PBAT/PGV, by the presence of sodium ions. Besides, an increase in thermal stability for PBAT/Cloisite 20A was observed. However, the CO2 produced during the degradation of the PBAT/PGV was higher than PBAT/Cloisite20A only at the beginning of the process. Besides, better exfoliation of nanoclay Cloisite 20A in PBAT promoted an increase in the biodegradation process rate. Therefore, these properties can contribute to possible soil stabilizer application, hitching surface hydrophilicity, and good biodegradability, by its water retention ability.
1. Introduction In the world, plastic production has increased exponentially in the last fifty years, carrying a substantial environmental impact, possibly caused by the high plastic waste volume and its high environmental stability (Agarski et al., 2019). In this scenario, applications with biodegradable polymers have gained more attention (Marichelvam et al., 2019). Among them, poly(butylene adipate-co-terephthalate) (PBAT) is a copolymer obtained from 1,4-butanediol, adipic acid, terephthalic acid, that is a biodegradable polymer with higher flexibility compared to other biodegradable polyesters (Sangroniz et al., 2019). However, PBAT has application limitations due to low mechanical resistance, low modulus of elasticity, and low barrier properties for gas and humidity, which are necessary for use in the packaging (one of the main applications of biodegradable polymers). (Pinheiro et al., 2017; Sarkar et al.,
2018; Kim et al., 2018). One possibility for enhancement in any material properties is the combination of two materials having desirable characteristics, as it occurs through the production of composites and nanocomposites (Zdiri et al., 2017; Pinheiro et al., 2017; Alves et al., 2019). In recent years, composites of biodegradable polymers with clay and nanoclay have generated considerable interest in materials engineering (Ramya et al., 2017; Hasani et al., 2019). Nanoclays such as sodium-montmorillonite are widely used in the preparation of various nanocomposite products, and the structure of nanoclays and the preparation method are fundamental for the properties of produced materials (Tunç and Duman, 2010; Lvov et al., 2019). The addition of nanoclays within a polymer matrix causes an improvement in the thermal, mechanical and gas barrier properties of nanocomposite (Tunç and Duman, 2011; Tunc et al., 2016) Even with the addition of small amounts of these nanoclays (generally less than
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Corresponding author. E-mail addresses: [email protected] (P.H. Camani), [email protected] (J.P.M. Toguchi), anapaula.fi[email protected] (A.P.S.M. Fiori), [email protected] (D.d.S. Rosa). https://doi.org/10.1016/j.clay.2020.105453 Received 29 July 2019; Received in revised form 13 January 2020; Accepted 16 January 2020 Available online 12 February 2020 0169-1317/ © 2020 Elsevier B.V. All rights reserved.
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Fig. 1. SEM/EDS images of analyzed area: (a) Cloisite 20A Nanoclay and (b) PGV Nanoclay with the magnification of 1000×.
Southern Clay Products provided the nanoclays [hydrophilic sodiummontmorillonite nanoclay (Nanomer PGV) and montmorillonite nanoclay (Cloisite 20A)]. Nanomer PGV has a higher cation exchange capacity (CEC), 145 meq/100 g, and Cloisite 20A is an organically modified nanoclay, containing modifier agents as dimethyl, dehydrogenated tallow, quaternary ammonium.
5%, in mass), it promotes high level of reinforcement establishing and high-performance in polymer nanocomposites (Gul et al., 2016a; Tan and Thomas, 2016; Adrar et al., 2017; Ajmal et al., 2018; Hasani et al., 2019). Moreover, nanoclay can contribute positively to retain water, in applications as a soil stabilizer, thus controlling water released in the soil, especially when this material is discarded (Syakir et al., 2016). The compatibility between polymer and clay can enhance the physical properties of the nanocomposite. Therefore, to improve the compatibility between polymers and nanoclays, they usually are treated with organic surfactant-containing chemical groups as quaternary ammonium cations, quaternary phosphonium cations, diamines, and amino acids (Gul et al., 2016b; Malik et al., 2018). Besides, this compatibility can cause better dispersion of the clay's lamellae for all polymeric matrix (Gul et al., 2016b; Guo et al., 2018). Many studies have contributed to an understanding of nanocomposites with different nanoclay and its influence on the properties of the polymeric matrix (Wu et al., 2018. Olivato and coworkers have studied the effects of sepiolite addition (0, 1, 3 and 5 wt%) on dynamicmechanical behavior, water uptake, thermal and optical properties of thermoplastic starch (TPS)/(PBAT) nano-biocomposites, with different TPS/PBAT (w/w) ratios and nanofiller contents. The results highlighted the improvement of the dynamic-mechanical behavior and decreased the water absorption rate and water adsorption capacity with the addition of sepiolite (Olivato et al., 2017). Besides, Nofar and coworkers prepared blends of an amorphous polylactide (PLA) with 25 wt% poly [(butylene adipate)-co-terephthalate] (PBAT) containing 1 and 5 wt% Cloisite 30B (C30B) Nanoclay, by processing in an internal batch mixer. With 1 wt% C30B, the nanoparticles were located at the PLA-PBAT interface for all mixing routes, which was favorable for morphology stabilization. Another consideration is that in the blends containing 5 wt% C30B, the location of the nanoparticles and the occurrence of coalescence depended on the mixing strategy used (Nofar et al., 2016). Other authors also observed an increase in mechanical properties by the addition of montmorillonite clays in the PBAT matrix (Livi et al., 2014), as well as the thermal properties improved significantly with modified montmorillonite dispersion (Adrar et al., 2017). Besides of biodegradable polymers, nanoclays can be used to improve mechanical properties of biodegradable nanocomposites as PP/natural fibers, as described by Islam and coworkers, acting on interfacial interaction and adhesion of fiber–polymer matrix and improving biodegradability by higher water absorption (Islam et al., 2017). Therefore, the work aim was to prepare and characterize of PBAT nanocomposites with unmodified (PGV) and organo-modified (Cloisite20A) nanoclays, evaluating the impact of these nanoclays on the mechanical, thermal and mainly the aerobic biodegradation properties.
2.2. Preparation of nanocomposites The PBAT/nanoclay nanocomposites (PBAT/PGV and PBAT/ Cloisite20A), as well as, control sample (Pure PBAT), were prepared using K-Mixer (model MH 100, MH equipment Ltda). First, the PBAT was homogenized, and after the nanoclays (PGV or Cloisite20A) were added (2% wt.). The samples were shaped using a press (Model SL11, Solab) at 110 °C, 8 tons for 3 min. 2.3. Experimental section 2.3.1. Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) To qualify and quantify the possible atomic components of the nanoclays samples, it was used SEM/EDS images in an equipment model JSM-6010LA, JEOL, with an increase of 1000× and resolution of 4.0 nm (Singh and Bhowmick, 2019), as shown in Fig. 1. For sample preparation, the nanoclays were placed in aluminum stubs with carbon tape, uncoated with a thin conductive layer. 2.3.2. X-ray diffraction (XRD) To obtain the d-spacing of nanoclays and nanocomposites, and also its crystallinity index (%), were used X-ray diffraction. Therefore, it was used a diffractometer STOE-STADI P, varying the range in 2θ, from 2 to 80.735°, pass of the 0.0015°, using curve monochromator of Germanium (111) and radiation of CuKα1, with a wavelength of 1.54060 nm and an integration time of the 60s for kind of 1.05°. 2.3.3. Tensile properties The tensile test was realized in a universal testing machine, model 3369, Instron. Samples were prepared in the heating press (Model SL 11, Solab Equipments, SP, Brazil), using spacers delimiting thickness of 1 mm, at 160 °C and 7 tons. According to ASTM D638-14, tests (in quintuplicate) were realized with the test speed of 50 mm/min, cell load of 50 kN, and using test specimens type V, with a thickness of 1.4 mm. 2.3.4. Contact angle measurements The contact angle measurements were realized in triplicate, using the method of the micro drop, type Sesil, using distilled water. A tensiometer (SEO), model Phoenix 300 and a system of three-phase air/ water/sample with water drop volume of ~7 μL were used, under environmental temperature, for determining water angle in the sample, by the method of static contact angle with needle diameter 0.019″, using the Young-Laplace equation to data treatment (Liao et al., 2016).
2. Materials and methods 2.1. Materials Poly(butylene adipate-co-terephthalate) (PBAT) was supplied by Basf S.A., with the commercial name as Ecoflex® F Blend C1200, Brazil. 2
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characterize the nanoclay type and differences of the organo-modification, chemical composition by energy dispersive spectroscopy (EDS) measurements were conducted. Table 1 presents these results. From Table 1, it could observe that the nanoclay PGV presents sodium as a chemical element, with 2.9 ± 0.1 of mass percentage, characterizing a sodic nanoclay type, probably with the presence of the sodium cation between the lamellae, and also with other cations as magnesium. On the other hands, it suggests more polarity to PVG than Cloisite 20A, because of the presence of sodium and magnesium between lamellae promotes this polarity, different of modification, which there is a disappearance of mass percentage for sodium, that it becomes a possible interaction between polymer and nanoclay, as seen by Čèsniene and coworkers (Čèsniene et al., 2018). Besides, lower values of dspacing can be seen for PGV, because of polarity between its lamellae, than Cloisite 20A, with higher d-spacing, by organo-modification. The results presented in Table 1 already show the non-presence of sodium into Cloisite 20A, and higher mass (molar percentage) of the carbon and lower mass (molar percentage) of the silicon into Cloisite 20A. Probably, these results were by the presence of the surfactant structure into treated nanoclay. This modification makes the structure of the nanoclay more “non-polar,” which makes it more hydrophobicity, allowing more significant interaction of this with the polymers, which can increase the nanocomposite properties (Guo et al., 2018).
2.3.5. Thermal gravimetric analysis (TGA) The thermal gravimetric analysis was realized in the equipment of thermal analysis model 2950, TA Instruments, with a heating rate of 10 °C/min, under the nitrogen atmosphere (flow rate of 60 mL/min) and initial temperature from 30 °C to 800 °C. The data were treated by software Origin 8.0. 2.3.6. Biodegradation test The biodegradable test proposed in this article consists of the measurement of the production of carbon dioxide during biodegradation by acid-base titration (Azevedo et al., 2016). The samples (Pure PBAT, PBAT/PGV, and PBAT/Cloisite20A) were ground with liquid nitrogen in grind type croton, model TE-625, Tecnal, Brazil. The granulometry of the samples was around 1.19 mm (D80) (80% of total milled material). The test was realized adapting ASTM D5338-15 (American Society for Testing and Materials, 2015, following the model of the Sturm test. The inoculum for this test was a dark earth compost, in aqueous solution, maintained at 58 ± 2 °C, with ideal C/N relation of 1:4, pH of 7.0, with diary measurements of the produced CO2. The samples (Pure PBAT, PBAT/PGV, and PBAT/Cloisite20A) were used in grain form (40 g of material), added in organic compost. To observe the biodegradation process, Sturm Test occurred around 108 days until the total transformation of carbon (mineralization) for carbon dioxide. According to Fig. 2, the formation of carbon dioxide consists of the air injection on the first reactor containing barium hydroxide (left), connected to a second reactor (containing dark earth compost). From mineralized carbon (produced during biodegradation), these carbon reacts with oxygen, producing carbon dioxide. Produced carbon dioxide is moved to the third reactor. The solution in the third reactor is titrated by acid-base titration (Araque et al., 2018). The CO2 mass production calculus (mCO2) is described in Eq. 1, following:
mCO2 mBaCO3 = MCO2 MBaCO3
3.2. X-ray Diffraction (XRD) When nanoclays are incorporated in the polymeric matrix, the XRD helps to comprehend how the lamellae are dispersed in the polymer, using type morphology that the nanocomposite can present. Fig. 3a and b have presented the diffractograms, comparing the curves of pure PBAT, PGV, PBAT/PGV, and PBAT, Cloisite 20A, PBAT/Cloisite 20A, respectively. In Fig. 3a, it is observed that in the nanoclay Cloisite 20A, it is found a characteristic peak for nanoclay Cloisite 20A around to 2θ = 3.4°, with d-spacing of 1.79 nm, according to Bragg Law, having dislocation for PBAT/Cloisite 20A for 2θ = 2°, with d-spacing of 3.08 nm. In Fig. 3b, for nanoclay PGV, there was the appearance of peaks in 2θ = 6.9°, with d-spacing of 0.89 nm, but in PBAT/PGV, the presence of the peak occurred around to 2θ = 6.7°, with d-spacing of 0.92 nm, and having the same behavior as Fig. 3b, explained by a scheme in Fig. 4. The extinction and intensity decreasing of peaks for low angles at the diffractograms show exfoliation processes in the nanocomposites because the ordinated structure of nanoclay was modified with the appearance of a disorganized structure, indication the exfoliation (Torin et al., 2017). Thus, in S.1, it is possible to illustrate that removal of Sodium by the treatment of clay increases the spacing of the lamellae, which increases the interaction between nanoclay and the polymer chains. According to literature, the dislocation of the peaks for lower angles and increase in d-spacing indicate that there was an increase in the distance between nanoclay lamellae structure, showing an intercalation process of the clay into the matrix (Torin et al., 2017). Another critical point is the difference of the intercalation process, higher for treated nanoclay than in nature nanoclay. The organic treatment in the nanoclay generates better compatibility with the polymeric matrix, caused by the insertion of strong nonpolar groups present in organo-modification, being more susceptible to the same nonpolar nature of the polymer (Falcão et al., 2017). For the crystallinity index, Pure PBAT showed 14.2%, and the crystallinity values of the PBAT/PGV and PBAT/Cloisite 20A were 12.1% and 12.5%, respectively. These results were corroborating with Livi and co-workers, who found that the organic chains in the modified nanoclays results decrease in crystallinity (Livi et al., 2014). Moreover, the same phenomenon can be observed with composites of the PBAT with nanoclay Cloisite 20A (Falcão et al., 2017). The small decrease in the crystallinity index can contribute to facilitating the biodegradation
(1)
Where: m = Mass (g) and M = Molar Mass. 3. Results and discussions 3.1. Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) Fig. 1 showed the photomicrographs of the nanoclay PGV and nanoclay Cloisite 20A. For Cloisite 20A, which is an organo-modified nanoclay, according to Fig. 1a, it is possible to observe lower particles, differently from the Nanoclay PGV, in Fig. 1. The nanoclay PGV is a natural type of montmorillonite, on the other hand, without modification, differently of Cloisite 20A (Staroszczyk et al., 2017). To
Fig. 2. Illustrative scheme showing the used experimental apparatus, described in the literature as the Sturm Test (Biodegradation Test). 3
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Table 1 Surface chemical composition of all samples. Chemical elements Sample
Carbon
Oxygen
PGV [Mass percentage (%)] PGV [Molar percentage (%)] Cloisite 20A [Mass percentage (%)] Cloisite 20A [Molar percentage (%)]
8.0 ± 0.0 12.4 ± 0.3 43.7 ± 1.0 55.7 ± 0.6
53.8 62.4 34.0 32.5
± ± ± ±
0.0 0.3 0.1 0.2
Sodium
Magnesium
Aluminum
Silicon
2.9 ± 0.1 2.3 ± 0.0 – –
1.5 ± 0.0 1.16 ± 0.0 0.8 ± 0.0 0.5 ± 0.0
9.5 6.5 5.7 3.2
22.7 ± 1.0 17.0 ± 2.0 13.5 ± 1.8 7.3 ± 1.1
± ± ± ±
0.2 0.2 0.1 0.1
69.6 ± 1.1° and 60.8 ± 2.0° for pure PBAT, PBAT Cloisite20A, and PBAT/PGV, respectively. These results suggest high hydrophilicity for nanocomposites compared to pure PBAT. The lower values of contact angle were obtained due the nanoclay promotes a possible increase in surface roughness, being a more visible effect for nanoclay PGV that it is less exfoliated (Fukushima et al., 2013a; Fukushima et al., 2013b). As described by several authors, this increase in roughness may facilitate the access of microorganisms in the material by helps them in the process of adhesion and facilitating the hydrolysis process, increasing the rates of biodegradation process (Rodrigues et al., 2015; Stloukal et al., 2015). Besides the superficial characteristics, the presence of sodium ion between lamellae of the nanoclay, promotes hydrophilic character in the nanocomposites surface, as for sample PBAT/PGV, which resulted in high sodium percentage, observed in SEM/EDS. This fact may also facilitate the degradation process of the polymeric matrix (Chen and Yang, 2015; Naderi-Samani et al., 2017). Different behavior was observed for PBAT/Cloisite20A, with a slighter decrease of contact angle values, with 69.6°, in comparison to PBAT/PGV. This phenomenon can be attributed to the presence of organically modified clay nanoparticles (Cloisite20A) on the surface of PBAT, as seen by Kumar, Mishra, and Chatterjee for nanocomposite systems PCL/Cloisite30B (Kumar et al., 2014). Moreover, as the nanocomposites have high hydrophilicity than the pure PBAT, by a decrease of contact angle, these materials could be applied as absorbent materials in agricultural applications, especially when these materials were discarded, because of its interaction with water polarity (Syakir et al., 2016).
process since the amorphous region is more susceptible to the microbial attack (Stloukal et al., 2015). 3.3. Tensile test (mechanical properties) Table 2 shows elasticity modulus (E), maximum elongation (εmax), and tensile strength at break (σrup) results of all samples. The nanocomposite samples showed an increase in elasticity modulus (E) for PBAT/Cloisite20A around to 19% and PBAT/PGV of 18%. Moreover, there was a decrease in maximum elongation of 36% in both nanocomposite systems (with PGV and Cloisite 20A), and tensile strength at the break did not have significant differences between all samples, so causing reinforcement in the matrix (Livi et al., 2014). These results corroborate with literature, where Livi and contributors presented the same behavior with PBAT/nanoclay Nanofil 757 composites, by increasing the elasticity modulus and decreasing the maximum elongation and tensile strength (Livi et al., 2014). Seyidoglu and Yilmazer had observed the effect of inorganic particles in elongation, and they concluded that a decrease in tensile strength and maximum elongation occurred. The authors suggest that it happened because nanoclay acts as a tensile concentrator. However, when these particles were better dispersed in the polymeric matrix by an exfoliation/intercalation process, there was an improvement in mechanical properties, with the increase in the contact area between matrix and filler (Seyidoglu and Yilmazer, 2013; Amanpour and Sharifi-Sanjani, 2017). Therefore, the treated nanoclay, with non-polar structure added during organo-modification may promote improvement in mechanical properties due to possible partial exfoliation and improved chemical interaction with the polymer as observed in XRD results with a decrease in peak intensity for PBAT/Cloisite20A than PBAT/PGV (Amanpour and Sharifi-Sanjani, 2017).
3.5. Thermal gravimetric analysis (TGA) In Fig. 4a and b, it is presented the loss weight curve and DTG curves, respectively, for all the samples obtained by TGA. Besides, in Table 3, it was shown temperatures with 10% and 50% of the weight loss of Fig. 4a (T10% and T50%) and maximum temperature of thermal events obtained by the DTG curves of Fig. 4b (Tmax 1 and Tmax 2). As seen in Fig. 4a and Table 3, there were no significant changes in
3.4. Contact angle measurements The values for static contact angle measurements were 76.9 ± 0.8°,
Fig. 3. (a) X-ray diffraction patterns of PBAT, Cloisite 20A nanoclay and PBAT/Cloisite 20A, and (b) X-ray diffraction patterns of PBAT, PGV nanoclay, and PBAT/ PGV. 4
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Fig. 4. Thermal decomposition for all samples: Weight-loss curves (a) and DTG curves (b), obtained by TGA. Table 2 Crystallinity index, elasticity modulus, maximum elongation, and tensile strength at break value, respectively, for pure PBAT, PBAT/Cloisite20A, and PBAT/PGV. Sample
Crystallinity index (%)
Elasticity modulus (E) (MPa)
Maximum elongation (εmax) (mm/mm)
Tensile strength at break (σrup) (MPA)
Pure PBAT PBAT/Cloisite20A PBAT/PGV
14.2 ± 0.2 12.5 ± 0.2 12.1 ± 0.2
50 ± 1 59 ± 3 59 ± 2
1684 ± 438 1083 ± 152 1078 ± 69
26 ± 3 23 ± 3 25 ± 1
comprehended the first phase of the degradation for samples PBAT/ PGV, followed by PBAT/Closite20A and Pure PBAT. This behavior can be explained by the hydrophilicity of the polar groups between lamellae of the nanoclays, more specifically, by the presence of terminal hydroxyl groups interlayer of modifier nanoclays, corroborating with contact angle results (Castro-Aguirre et al., 2018). On the other hand, the presence of nanoclay improves water diffusion on the polymeric matrix, promoting hydrolytic degradation of the nanocomposite (Mohanty and Nayak, 2010). As cited before, the excellent dispersion of nanoclays, observed by XRD results, and possible roughness, suggested by contact angle values, may help in the abiotic process, and the microbial action (Rodrigues et al., 2015). In literature, many works obtained similar results with composites of PBAT with treated or non-treated nanoclays, showing that the nanoclay presence in the polymer causes surface erosion, which increases the possibility for biodegradation. Moreover, XRD results showed that good dispersion by intercalation/exfoliation promotes the biodegradation process (Mondal et al., 2014). In the nanoclay PGV, d-spacing was from 0.89 to 0.92 nm. This fact shows its low exfoliation capacity of the biodegradable polymer. However, the nanoclay Cloisite 20A, an organo-modified, it obtained great exfoliation, by high initial lamellae distance, leading a great exfoliation of the polymer in the nanoclay, from 1.79 to 3.08 nm. This great exfoliation does not change the crystallinity significantly but leads to high interaction of the water molecule, which furthers its high biodegradation. This result can be seen in Fig. 6 that corroborate to show its high CO2 production for the nanocomposite Cloisite 20A than with PGV (Staroszczyk et al., 2017; Jurca et al., 2019). Other factors, as crystallinity, described by Sousa and coworkers that found a relationship between hydrolytic degradation and crystallinity index for composites of PLA and organo-modified nanoclays corroborates with results for PBAT/Cloisite 20A showing that high intercalation and lower crystallinity, favoring high biodegradability (Souza et al., 2013). This property, joined with hydrophilicity, can help in soil stabilizer when composted, providing controlled release of absorbed water in the soil (Syakir et al., 2016).
Table 3 Temperatures at 10% and 50% of weight loss (T10% and T50%) values for thermogravimetry curves (TG) and maximum temperature 1 and 2 (Tmax1 and Tmax2) for derivative curves (DTG). Sample
T10% (°C)
T50% (°C)
Tmax1 (°C)
Tmax2 (°C)
Pure PBAT Cloisite20A PGV PBAT/Cloisite20A PBAT/PGV
367 291 62 369 366
400 362 82 400 399
388 93 310 390 388
504 691 625 – 504
the loss of the mass for values in T10% and T50% for the pure PBAT and PBAT/PGV, showing that there was not a loss of thermal stability, being proved by Tmax 1 and Tmax 2, obtained by DTG curves of Fig. 4b. The addition of natural nanoclay, corroborating with literature results (Livi et al., 2014) that said with a minor degree of intercalation, there is a lower increase in d-spacing, obtained by XRD results. Observing that with treated nanoclays, as Cloisite 20A, that it promoted high intercalation and, it occurred a slight increase in thermal stability (NaderiSamani et al., 2017). Also, it was observed the disappearance of Tmax 2 of PBAT/Cloisite20A, obtained in the DTG curve of Fig. 4b. This effect can also be explained by high intercalation and the presence of ammonium quaternary salt of organo-modified nanoclay (Puglia et al., 2014). Improvement in thermal stability can be due to the presence of exfoliation or a similar condition that promotes the higher surface area, acting as the heat barrier, and then modifying the thermal stability of the system (Mohanty and Nayak, 2012; Iturrondobeitia et al., 2017). 3.6. Biodegradation test In Fig. 5, it is presented the CO2 mass production curve during 108 days of biodegradation for Pure PBAT and nanocomposites samples (PBAT/PGV and PBAT/Cloisite20A). In Fig. 5, for all the samples, there was a high production of CO2, that produced negative values of carbon gas quantity, due variation in inoculum composition. Theoretically, it is considered as a negative pattern the polyethylene, to measure the biodegradation process for the other formulations (according to ASTM D5338-15), since the polyethylene structure has high stability to microbial action (MartínezRomo et al., 2015). Between 15 and 20 days of degradation, it
4. Conclusions The SEM/EDS results showed that there was the presence of sodium 5
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Fig. 5. Evaluation of biodegradation by CO2 mass production versus days curves, obtained for all samples.
the presence of the sodium ions between the nanoclay lamellae. This promotes an increase of the polarity and consequently, the increase of the hydrophilicity, which can increase the biodegradation. Probably, there was a possible increase in surface roughness, and it creates higher accessibility of the microorganism in the surface of the materials. In biodegradation, PBAT/Cloisite20A had better results and higher CO2 production during the test. The treatment of the nanoclay and its excellent dispersion (seen by XRD results) helps in the biodegradable process.
ions for nanoclay PGV, characterizing sodic nanoclay. However, for Cloisite20A, the mass percentage of carbon and oxygen was higher (43.7 ± 1.0% and 34.0 ± 0.1%, respectively) than PGV (8.03 ± 0.02% and 53.84 ± 0.03%, respectively), and there was the disappearance of mass percentage for sodium. This justifies that the treatment changed the hydrophilicity of nanoclay, which provided higher compatibility between treated nanoclay with PBAT. The organomodification of Cloisite20A caused high values of the d-spacing (1.79 nm), which could promote higher dispersion of the nanoclay lamellae. Besides, the crystallinity index decreased from 14.2% (Pure PBAT) for 12.5% and 12.1% (PBAT/Cloisite20A and PBAT/PGV), respectively. The nanocomposite samples showed an increase in elasticity modulus for PBAT/Cloisite20A and PBAT/PGV around to 19% and 18%, respectively. Also, there was a decrease in the maximum elongation of 36%, in both bionanocomposites. The results of weight loss showed slightly higher thermal stability for PBAT/Cloisite 20A, possibly because there was significant intercalation between nanoclay and the polymeric matrix, which increasing thermal stability. Already, in the contact angle results, there was increased hydrophilicity for nanocomposites, proved by a decrease in contact angle values. This was observed, more significant for PBAT/PGV, with 60.8 ± 2.0°, caused by
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq (n° 305819/2017-8), UFABC and FAPESP (2017/25039-8 and 2018/11277-7). The authors
Fig. 6. General scheme to understand differences between nanoclays and its incorporation in PBAT and biodegradation. 6
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thank the technical support of the Multiuser Experimental Center of UFABC (CEM-UFABC).
Adv. 4, 26452–26461. Lvov, Y., Panchal, A., Fu, Y., Fakhrullin, R., Kryuchkova, M., Batasheva, S., Stavitskaya, A., Glotov, A., Glotov, A., Vinokurov, V., 2019. Interfacial self-assembly in halloysite nanotube composites. Langmuir 35 (26), 8646–8657. Malik, N., Kumar, P., Ghosh, S.B., Shrivastava, S., 2018. Organically modified nanoclay and aluminum hydroxide incorporated bionanocomposites towards enhancement of physico-mechanical and thermal properties of lignocellulosic structural reinforcement. J. Polym. Environ. 26, 3243–3249. Marichelvam, M.K., Jawaid, M., Asim, M., 2019. Corn and rice starch-based bio-plastics as alternative packaging materials. Fibers 7 (32), 1–14. Martínez-Romo, A., González-Mota, R., Soto-Bernal, J.J., Rosales-Candelas, I., 2015. Investigating the degradability of HDPE, LDPE, PE-BIO, and PE-OXO films under UVB radiation. J. Spectrosc. 2015, 1–6. Mohanty, S., Nayak, S.K., 2010. Aromatic-aliphatic poly(butylene adipate-co-terephthalate) bionanocomposite: influence of organic modification on structure and properties. Polym. Compos. 31 (7), 1194–1204. Mohanty, S., Nayak, S.K., 2012. Biodegradable nanocomposites of poly(butylene adipateco-terephthalate) (PBAT) and organically modified layered silicates. J. Polym. Environ. 20, 195–207. Mondal, D., Bhowmick, B., Mollick, M.M.R., Maity, D., Saha, N.R., Rangarajan, V., Rana, D., Sen, R., Chattopadhyay, D., 2014. Antimicrobial activity and biodegradation behavior of poly (butylene adipate-co-terephthalate)/clay nanocomposites. J. Appl. Polym. Sci. 131 (40079), 1–9. Naderi-Samani, H., Loghman-Estarki, M.R., Razavi, R.S., Ramazani, M., 2017. The effects of organoclay on the morphology, thermal stability, transparence and hydrophobicity properties of polyamide – imide/nanoclay nanocomposite coatings. Prog. Org. Coat. 112, 162–168. Nofar, M., Heuzey, M.-C., Carreau, P.J., Kamal, M.R., 2016. Effects of nanoclay and its localization on the morphology stabilization of PLA/PBAT blends under shear flow. Polymer 98, 353–364. Olivato, J.B., Marini, J., Yamashita, F., Pollet, E., Grossmann, M.V.E., Avérous, L., 2017. Sepiolite as a promising nanoclay for nano-biocomposites based on starch and biodegradable polyester. Mater. Sci. Eng. C 70, 296–302. Pinheiro, I.F., Ferreira, F., Souza, D.H.S., Gouveia, R.F., Lona, L.M.F., Morales, A.R., Mei, L.H.I., 2017. Mechanical, rheological and degradation properties of PBAT nanocomposites reinforced by functionalized cellulose nanocrystals. Eur. Polym. J. 97, 356–365. Puglia, D., Fortunati, E., D’Amico, D.A., Manfredi, L.B., Cyras, V.P., Kenny, J.M., 2014. Influence of organically modified clays on the properties and disintegrability in compost of solution cast poly(3-hydroxybutyrate) films. Polym. Degrad. Stab. 99, 127–135. Ramya, E., Rajashree, C., Nayak, P.L., Rao, D.N., 2017. New hybrid organic polymer montmorillonite/chitosan/polyphenylenediamine composites for nonlinear optical studies. Appl. Clay Sci. 150, 323–332. Rodrigues, C.A., Tofanello, A., Nantes, I.L., Rosa, D.S., 2015. Biological oxidative mechanisms for degradation of poly(lactic acid) blended with thermoplastic starch. ACS Sustain. Chem. Eng. 3 (11), 2756–2766. Sangroniz, A., Sangroniz, L., Gonzalez, A., Santamaria, A., Rio, J., Iriarte, M., Etxeberria, A., 2019. Improving the barrier properties of a biodegradable polyester for packaging applications. Eur. Polym. J. 115, 76–85. Sarkar, N., Sahoo, G., Das, R., Swain, S.K., 2018. Three-dimensional rice straw-structured magnetic nanoclay-decorated tripolymeric nanohydrogels as superadsorbent of dye pollutants. ACS Appl. Nano Mater. 1 (3), 1188–1203. Seyidoglu, T., Yilmazer, U., 2013. Production of modified clays and their use in polypropylene-based nanocomposites. J. Appl. Polym. Sci. 127 (2), 1257–1267. Singh, H., Bhowmick, H., 2019. Influence of nanoclay on the thermophysical properties and lubricity characteristics of mineral oil. Mater Today-Proc. 18, 1058–1066. Souza, P.M.S., Corroqué, N.A., Morales, A.R., Marin-Morales, M.A., Mei, L.H.I., 2013. PLA and organoclays nanocomposites: degradation process and evaluation of ecotoxicity using Allium cepa as test organism. J. Polym. Environ. 21 (4), 1052–1063. Staroszczyk, H., Malinowska-Panczyk, E., Gottfried, K., Kołodziejska, I., 2017. Fish gelatin-nanoclay films. Part I: effect of a kind of nanoclays and glycerol concentration on mechanical and water barrier properties of nanocomposites. J. Food Process. Preserv. 41, 13211. Stloukal, P., Pekarová, S., Kalendova, A., Mattausch, H., Laske, S., Holzer, C., Chitu, L., Bodner, S., Maier, G., Slouf, M., Koutny, M., 2015. Kinetics and mechanism of the biodegradation during thermophilic phase of composting process. Waste Manag. 42, 31–40. Syakir, M.I., Nurin, N.A., Zafirah, N., Kassim, Mohd Asyraf, Abdul Khalil, H.P.S., 2016. Nanoclay Reinforced on Biodegradable Polymer Composite: Potential as a Soil Stabilizer. Springer Singapore, pp. 329–356. Tan, B., Thomas, N.L., 2016. A review of the water barrier properties of polymer/clay and polymer/graphene nanocomposites. J. Membr. Sci. 514, 595–612. Torin, R.F.S., Camani, P.H., Silva, L.N., Sato, J.A.P., Ferreira, F.F., Rosa, D.S., 2017. Effect of clay and clay/essential oil in packaging films. Polym. Compos. 1–7. Tunç, S., Duman, O., 2010. Preparation and characterization of biodegradable methyl cellulose/montmorillonite nanocomposite films. Appl. Clay Sci. 48 (3), 414–424. Tunç, S., Duman, O., 2011. Preparation of active antimicrobial methyl cellulose/carvacrol/montmorillonite nanocomposite films and investigation of carvacrol release. LWT-Food Sci. Technol. 44 (2), 465–472. Tunc, S., Duman, O., Polat, T.G., 2016. Effects of montmorillonite on properties of methyl cellulose/carvacrol based active antimicrobial nanocomposites. Carbohydr. Polym. 150, 259–268. Wu, D., Tan, Y., Han, L., Zhang, H., Dong, L., 2018. Preparation and characterization of acetylated maltodextrin and its blend with poly (butylene adipate-co-terephthalate). Carbohydr. Polym. 181, 701–709. Zdiri, K., Elamri, A., Hamdaoui, M., 2017. Advances in thermal and mechanical behaviors of PP/clay nanocomposites. Polym. Plast Technol. 56 (8), 824–840.
Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.clay.2020.105453. References Adrar, S., Habib, A., Ajji, A., Grohens, Y., 2017. Combined effect of epoxy functionalized graphene and organomontmorillonites on the morphology, rheological and thermal properties of poly (butylenes adipate-co-terephthalate) with or without a compatibilizer. Appl. Clay Sci. 146, 306–315. Agarski, B., Vukelic, D., Micunovic, M.I., Budak, I., 2019. Evaluation of the environmental impact of plastic cap production, packaging, and disposal. J. Environ. Manag. 245, 55–65. Ajmal, A.W., Masood, F., Yasin, T., 2018. Influence of sepiolite on thermal, mechanical and biodegradation properties of poly-3-hydroxybutyrate-co-3-hydroxyvalerate nanocomposites. Appl. Clay Sci. 156, 11–19. Alves, J.L., Rosa, P.T.V., Realinho, V., Antunes, M., Velasco, J.I., Morales, A.R., 2019. Influence of chemical composition of Brazilian organoclays on the morphological, structural and thermal properties of PLA-organoclay nanocomposites. Appl. Clay Sci. 180, 105–186. Amanpour, J., Sharifi-Sanjani, N., 2017. Mechanical and thermal properties of poly(tetrahydrofurfuryl methacrylate) nanocomposites. J. Macromol. Sci. B. 56 (10), 775–789. American Society for Testing and Materials, 2015. ASTM D 5338-15. Determining Aerobic Biodegradation of Plastic Materials Under Controlled Composting Conditions, Incorporating Thermophilic Temperatures. ASTM International, West Conshohocken, PA. Araque, L.M., Alves, T.S., Barbosa, R., 2018. Biodegradation of polyhydroxybutyrate and hollow glass microspheres composite films. J. Appl. Polym. Sci. 47195, 1–10. Azevedo, J.B., Carvalho, L.H., Canedo, E.L., Barbosa, J.D.V., Silva, M.W.S., 2016. Avaliação da biodegradação em compósitos com fibras naturais através de perda de massa e produção de CO2. Rev. Virtual Quim. 8 (4), 1115–1129. Castro-Aguirre, E., Auras, R., Selke, S., Rubino, M., Marsh, T., 2018. Impact of nanoclays on the biodegradation of poly(lactic acid) nanocomposites. Polymers 10 (202), 1–21. Čèsniene, J., Baltušnikas, A., Lukošiute, I., Brinkiene, K., Kalpokaite-Dičkuviene, R., 2018. Influence of organoclay structural characteristics on properties and hydration of cement pastes. Constr. Build. Mater. 166, 59–71. Chen, J.-H., Yang, M.-C., 2015. Preparation and characterization of nanocomposite of maleated poly(butylene adipate-co-terephthalate) with organoclay. Adv. Mater. ResSwitz. 46, 301–308. Falcão, G.A.M., Vitorino, M.B.C., Almeida, T.G., Bardi, M.A.G., Carvalho, L.H., Canedo, E.L., 2017. PBAT/organoclay composite films: preparation and properties. Polym. Bull. 74 (11), 4423–4436. Fukushima, K., Rasyida, A., Yang, M.-C., 2013a. Biocompatibility of organically modified nanocomposites based on PBAT. J. Polym. Res. 20 (302), 1–12. Fukushima, K., Rasyida, A., Yang, M.-C., 2013b. Characterization, degradation and biocompatibility of PBAT based nanocomposites. Appl. Clay Sci. 80, 291–298. Gul, S., Kausar, A., Muhammad, B., Jabeen, S., 2016a. Research progress on properties and applications of polymer/clay nanocomposite. Polym. Plast. Technol. 55 (7), 684–703. Gul, S., Kausar, A., Muhammad, B., Jabeen, S., 2016b. Technical relevance of epoxy/clay nanocomposite with organically modified montmorillonite: a review. Polym. Plast. Technol. 1393–1415. Guo, F., Aryana, S., Han, Y., Jiao, Y., 2018. A review of the synthesis and applications of polymer–nanoclay composites. Appl. Sci. 1696 (8), 1–29. Hasani, Z., Youssefi, M., Borhani, S., Mallakpour, S., 2019. Structure and properties of nylon-6/amino acid modified nanoclay composite fibers. Text. Inst. 110 (9), 1336–1342. Islam, M.S., Talib, Z.A., Hasan, M., Ramli, I., Haafiz, M.K.M., Jawaid, M., Islam, A., Inuwa, I.M., 2017. Evaluation of mechanical, morphological, and biodegradable properties of hybrid natural fiber polymer nanocomposites. Polym. Compos. 38 (3), 583–587. Iturrondobeitia, M., Guraya, T., Okariz, A., Srot, V., Aken, P.A., Ibarretxe, J., 2017. Quantitative electron tomography of PLA/clay nanocomposites to understand the effect of the clays in the thermal stability. J. Appl. Polym. Sci. https://doi.org/10. 1002/APP.44691. Jurca, M., Julinová, M., Slavik, R., 2019. Negative effect of clay fillers on the polyvinyl alcohol biodegradation: technical note. Sci. Eng. Compos. Mater. 26 (1), 97–103. Kim, T., Jeon, H., Jegal, J., Kim, J.H., Yang, H., Park, J., Oh, D.X., Hwang, S.Y., 2018. Trans-crystallization behavior and strong reinforcement effect of cellulose nanocrystals on reinforced poly(butylene succinate) nanocomposites. RSC Adv. 8 (38) 21636. Kumar, S., Mishra, A., Chatterjee, K., 2014. Effect of organically modified clay on mechanical properties, cytotoxicity and bactericidal properties of poly(ε-caprolactone) nanocomposites. Mater. Res. Express. 1, 1–20. Liao, L., Li, X., Wang, Y., Fu, H., Li, Y., 2016. Effects of surface structure and morphology of nanoclays on the properties of jatropha curcas oil-based waterborne polyurethane/ clay nanocomposites. Ind. Eng. Chem. Res. 55 (45), 11689–11699. Livi, S., Sar, G., Bugatti, V., Espuche, E., Duchet-Rumeau, J., 2014. Synthesis and physical properties of new layered silicates based on ionic liquids: improvement of thermal stability, mechanical behavior and water permeability of PBAT nanocomposites. RSC
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Applied Clay Science journal homepage: www.elsevier.com/locate/clay
Research paper
Impact of unmodified (PGV) and modified (Cloisite20A) nanoclays into biodegradability and other properties of (bio)nanocomposites
T
Paulo Henrique Camania, José Paulo Machado Toguchia, Ana Paula S.M. Fiorib, ⁎ Derval dos Santos Rosaa, a b
Center for Engineering, Modeling and Applied Social Sciences - CECS, Federal University of ABC (UFABC), São Paulo 09210-580, Brazil Federal Institute of Education, Science and Technology of Alagoas (IFAL) - Marechal Deodoro Campus, Alagoas 57160000, Brazil
A R T I C LE I N FO
A B S T R A C T
Keywords: Bionanocomposites Organic modification Nanoclays Biodegradability PBAT [poly(butylene adipate-coterephthalate)]
The production of bionanocomposites using nanoclays are in constant development to improve the mechanical, gas barrier and thermal properties, and the biodegradability of the polymeric materials. In this study, two different nanoclays: non-treated (hydrophilic sodium-montmorillonite nanoclay - PGV) and treated with organomodification (montmorillonite nanoclay - Cloisite 20A) were incorporated (2%wt.) into PBAT [poly(butylene adipate-co-terephthalate)] by melting process. The composites properties were evaluated by SEM/EDS, XRD, mechanical properties, contact angle, TGA, and aerobic biodegradation (Sturm test). The SEM/EDS showed the presence of sodium in PGV, which characterize it as sodic montmorillonite, while the Cloisite 20A, as montmorillonite organo-modified, by the high occurrence of carbon percentage. The patterns of X-ray diffraction (XRD), about the d-spacing of the bionanocomposites, indicates high intercalation of the matrix with nanoclay Cloisite 20A and a decrease in the crystallinity index. The elasticity modulus of the bionanocomposites had a slight increase, while maximum elongation was decreased, corroborating with the intercalation, as seen in XRD results. The contact angle results have shown high hydrophilicity for PBAT/PGV, by the presence of sodium ions. Besides, an increase in thermal stability for PBAT/Cloisite 20A was observed. However, the CO2 produced during the degradation of the PBAT/PGV was higher than PBAT/Cloisite20A only at the beginning of the process. Besides, better exfoliation of nanoclay Cloisite 20A in PBAT promoted an increase in the biodegradation process rate. Therefore, these properties can contribute to possible soil stabilizer application, hitching surface hydrophilicity, and good biodegradability, by its water retention ability.
1. Introduction In the world, plastic production has increased exponentially in the last fifty years, carrying a substantial environmental impact, possibly caused by the high plastic waste volume and its high environmental stability (Agarski et al., 2019). In this scenario, applications with biodegradable polymers have gained more attention (Marichelvam et al., 2019). Among them, poly(butylene adipate-co-terephthalate) (PBAT) is a copolymer obtained from 1,4-butanediol, adipic acid, terephthalic acid, that is a biodegradable polymer with higher flexibility compared to other biodegradable polyesters (Sangroniz et al., 2019). However, PBAT has application limitations due to low mechanical resistance, low modulus of elasticity, and low barrier properties for gas and humidity, which are necessary for use in the packaging (one of the main applications of biodegradable polymers). (Pinheiro et al., 2017; Sarkar et al.,
2018; Kim et al., 2018). One possibility for enhancement in any material properties is the combination of two materials having desirable characteristics, as it occurs through the production of composites and nanocomposites (Zdiri et al., 2017; Pinheiro et al., 2017; Alves et al., 2019). In recent years, composites of biodegradable polymers with clay and nanoclay have generated considerable interest in materials engineering (Ramya et al., 2017; Hasani et al., 2019). Nanoclays such as sodium-montmorillonite are widely used in the preparation of various nanocomposite products, and the structure of nanoclays and the preparation method are fundamental for the properties of produced materials (Tunç and Duman, 2010; Lvov et al., 2019). The addition of nanoclays within a polymer matrix causes an improvement in the thermal, mechanical and gas barrier properties of nanocomposite (Tunç and Duman, 2011; Tunc et al., 2016) Even with the addition of small amounts of these nanoclays (generally less than
⁎
Corresponding author. E-mail addresses: [email protected] (P.H. Camani), [email protected] (J.P.M. Toguchi), anapaula.fi[email protected] (A.P.S.M. Fiori), [email protected] (D.d.S. Rosa). https://doi.org/10.1016/j.clay.2020.105453 Received 29 July 2019; Received in revised form 13 January 2020; Accepted 16 January 2020 Available online 12 February 2020 0169-1317/ © 2020 Elsevier B.V. All rights reserved.
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Fig. 1. SEM/EDS images of analyzed area: (a) Cloisite 20A Nanoclay and (b) PGV Nanoclay with the magnification of 1000×.
Southern Clay Products provided the nanoclays [hydrophilic sodiummontmorillonite nanoclay (Nanomer PGV) and montmorillonite nanoclay (Cloisite 20A)]. Nanomer PGV has a higher cation exchange capacity (CEC), 145 meq/100 g, and Cloisite 20A is an organically modified nanoclay, containing modifier agents as dimethyl, dehydrogenated tallow, quaternary ammonium.
5%, in mass), it promotes high level of reinforcement establishing and high-performance in polymer nanocomposites (Gul et al., 2016a; Tan and Thomas, 2016; Adrar et al., 2017; Ajmal et al., 2018; Hasani et al., 2019). Moreover, nanoclay can contribute positively to retain water, in applications as a soil stabilizer, thus controlling water released in the soil, especially when this material is discarded (Syakir et al., 2016). The compatibility between polymer and clay can enhance the physical properties of the nanocomposite. Therefore, to improve the compatibility between polymers and nanoclays, they usually are treated with organic surfactant-containing chemical groups as quaternary ammonium cations, quaternary phosphonium cations, diamines, and amino acids (Gul et al., 2016b; Malik et al., 2018). Besides, this compatibility can cause better dispersion of the clay's lamellae for all polymeric matrix (Gul et al., 2016b; Guo et al., 2018). Many studies have contributed to an understanding of nanocomposites with different nanoclay and its influence on the properties of the polymeric matrix (Wu et al., 2018. Olivato and coworkers have studied the effects of sepiolite addition (0, 1, 3 and 5 wt%) on dynamicmechanical behavior, water uptake, thermal and optical properties of thermoplastic starch (TPS)/(PBAT) nano-biocomposites, with different TPS/PBAT (w/w) ratios and nanofiller contents. The results highlighted the improvement of the dynamic-mechanical behavior and decreased the water absorption rate and water adsorption capacity with the addition of sepiolite (Olivato et al., 2017). Besides, Nofar and coworkers prepared blends of an amorphous polylactide (PLA) with 25 wt% poly [(butylene adipate)-co-terephthalate] (PBAT) containing 1 and 5 wt% Cloisite 30B (C30B) Nanoclay, by processing in an internal batch mixer. With 1 wt% C30B, the nanoparticles were located at the PLA-PBAT interface for all mixing routes, which was favorable for morphology stabilization. Another consideration is that in the blends containing 5 wt% C30B, the location of the nanoparticles and the occurrence of coalescence depended on the mixing strategy used (Nofar et al., 2016). Other authors also observed an increase in mechanical properties by the addition of montmorillonite clays in the PBAT matrix (Livi et al., 2014), as well as the thermal properties improved significantly with modified montmorillonite dispersion (Adrar et al., 2017). Besides of biodegradable polymers, nanoclays can be used to improve mechanical properties of biodegradable nanocomposites as PP/natural fibers, as described by Islam and coworkers, acting on interfacial interaction and adhesion of fiber–polymer matrix and improving biodegradability by higher water absorption (Islam et al., 2017). Therefore, the work aim was to prepare and characterize of PBAT nanocomposites with unmodified (PGV) and organo-modified (Cloisite20A) nanoclays, evaluating the impact of these nanoclays on the mechanical, thermal and mainly the aerobic biodegradation properties.
2.2. Preparation of nanocomposites The PBAT/nanoclay nanocomposites (PBAT/PGV and PBAT/ Cloisite20A), as well as, control sample (Pure PBAT), were prepared using K-Mixer (model MH 100, MH equipment Ltda). First, the PBAT was homogenized, and after the nanoclays (PGV or Cloisite20A) were added (2% wt.). The samples were shaped using a press (Model SL11, Solab) at 110 °C, 8 tons for 3 min. 2.3. Experimental section 2.3.1. Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) To qualify and quantify the possible atomic components of the nanoclays samples, it was used SEM/EDS images in an equipment model JSM-6010LA, JEOL, with an increase of 1000× and resolution of 4.0 nm (Singh and Bhowmick, 2019), as shown in Fig. 1. For sample preparation, the nanoclays were placed in aluminum stubs with carbon tape, uncoated with a thin conductive layer. 2.3.2. X-ray diffraction (XRD) To obtain the d-spacing of nanoclays and nanocomposites, and also its crystallinity index (%), were used X-ray diffraction. Therefore, it was used a diffractometer STOE-STADI P, varying the range in 2θ, from 2 to 80.735°, pass of the 0.0015°, using curve monochromator of Germanium (111) and radiation of CuKα1, with a wavelength of 1.54060 nm and an integration time of the 60s for kind of 1.05°. 2.3.3. Tensile properties The tensile test was realized in a universal testing machine, model 3369, Instron. Samples were prepared in the heating press (Model SL 11, Solab Equipments, SP, Brazil), using spacers delimiting thickness of 1 mm, at 160 °C and 7 tons. According to ASTM D638-14, tests (in quintuplicate) were realized with the test speed of 50 mm/min, cell load of 50 kN, and using test specimens type V, with a thickness of 1.4 mm. 2.3.4. Contact angle measurements The contact angle measurements were realized in triplicate, using the method of the micro drop, type Sesil, using distilled water. A tensiometer (SEO), model Phoenix 300 and a system of three-phase air/ water/sample with water drop volume of ~7 μL were used, under environmental temperature, for determining water angle in the sample, by the method of static contact angle with needle diameter 0.019″, using the Young-Laplace equation to data treatment (Liao et al., 2016).
2. Materials and methods 2.1. Materials Poly(butylene adipate-co-terephthalate) (PBAT) was supplied by Basf S.A., with the commercial name as Ecoflex® F Blend C1200, Brazil. 2
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characterize the nanoclay type and differences of the organo-modification, chemical composition by energy dispersive spectroscopy (EDS) measurements were conducted. Table 1 presents these results. From Table 1, it could observe that the nanoclay PGV presents sodium as a chemical element, with 2.9 ± 0.1 of mass percentage, characterizing a sodic nanoclay type, probably with the presence of the sodium cation between the lamellae, and also with other cations as magnesium. On the other hands, it suggests more polarity to PVG than Cloisite 20A, because of the presence of sodium and magnesium between lamellae promotes this polarity, different of modification, which there is a disappearance of mass percentage for sodium, that it becomes a possible interaction between polymer and nanoclay, as seen by Čèsniene and coworkers (Čèsniene et al., 2018). Besides, lower values of dspacing can be seen for PGV, because of polarity between its lamellae, than Cloisite 20A, with higher d-spacing, by organo-modification. The results presented in Table 1 already show the non-presence of sodium into Cloisite 20A, and higher mass (molar percentage) of the carbon and lower mass (molar percentage) of the silicon into Cloisite 20A. Probably, these results were by the presence of the surfactant structure into treated nanoclay. This modification makes the structure of the nanoclay more “non-polar,” which makes it more hydrophobicity, allowing more significant interaction of this with the polymers, which can increase the nanocomposite properties (Guo et al., 2018).
2.3.5. Thermal gravimetric analysis (TGA) The thermal gravimetric analysis was realized in the equipment of thermal analysis model 2950, TA Instruments, with a heating rate of 10 °C/min, under the nitrogen atmosphere (flow rate of 60 mL/min) and initial temperature from 30 °C to 800 °C. The data were treated by software Origin 8.0. 2.3.6. Biodegradation test The biodegradable test proposed in this article consists of the measurement of the production of carbon dioxide during biodegradation by acid-base titration (Azevedo et al., 2016). The samples (Pure PBAT, PBAT/PGV, and PBAT/Cloisite20A) were ground with liquid nitrogen in grind type croton, model TE-625, Tecnal, Brazil. The granulometry of the samples was around 1.19 mm (D80) (80% of total milled material). The test was realized adapting ASTM D5338-15 (American Society for Testing and Materials, 2015, following the model of the Sturm test. The inoculum for this test was a dark earth compost, in aqueous solution, maintained at 58 ± 2 °C, with ideal C/N relation of 1:4, pH of 7.0, with diary measurements of the produced CO2. The samples (Pure PBAT, PBAT/PGV, and PBAT/Cloisite20A) were used in grain form (40 g of material), added in organic compost. To observe the biodegradation process, Sturm Test occurred around 108 days until the total transformation of carbon (mineralization) for carbon dioxide. According to Fig. 2, the formation of carbon dioxide consists of the air injection on the first reactor containing barium hydroxide (left), connected to a second reactor (containing dark earth compost). From mineralized carbon (produced during biodegradation), these carbon reacts with oxygen, producing carbon dioxide. Produced carbon dioxide is moved to the third reactor. The solution in the third reactor is titrated by acid-base titration (Araque et al., 2018). The CO2 mass production calculus (mCO2) is described in Eq. 1, following:
mCO2 mBaCO3 = MCO2 MBaCO3
3.2. X-ray Diffraction (XRD) When nanoclays are incorporated in the polymeric matrix, the XRD helps to comprehend how the lamellae are dispersed in the polymer, using type morphology that the nanocomposite can present. Fig. 3a and b have presented the diffractograms, comparing the curves of pure PBAT, PGV, PBAT/PGV, and PBAT, Cloisite 20A, PBAT/Cloisite 20A, respectively. In Fig. 3a, it is observed that in the nanoclay Cloisite 20A, it is found a characteristic peak for nanoclay Cloisite 20A around to 2θ = 3.4°, with d-spacing of 1.79 nm, according to Bragg Law, having dislocation for PBAT/Cloisite 20A for 2θ = 2°, with d-spacing of 3.08 nm. In Fig. 3b, for nanoclay PGV, there was the appearance of peaks in 2θ = 6.9°, with d-spacing of 0.89 nm, but in PBAT/PGV, the presence of the peak occurred around to 2θ = 6.7°, with d-spacing of 0.92 nm, and having the same behavior as Fig. 3b, explained by a scheme in Fig. 4. The extinction and intensity decreasing of peaks for low angles at the diffractograms show exfoliation processes in the nanocomposites because the ordinated structure of nanoclay was modified with the appearance of a disorganized structure, indication the exfoliation (Torin et al., 2017). Thus, in S.1, it is possible to illustrate that removal of Sodium by the treatment of clay increases the spacing of the lamellae, which increases the interaction between nanoclay and the polymer chains. According to literature, the dislocation of the peaks for lower angles and increase in d-spacing indicate that there was an increase in the distance between nanoclay lamellae structure, showing an intercalation process of the clay into the matrix (Torin et al., 2017). Another critical point is the difference of the intercalation process, higher for treated nanoclay than in nature nanoclay. The organic treatment in the nanoclay generates better compatibility with the polymeric matrix, caused by the insertion of strong nonpolar groups present in organo-modification, being more susceptible to the same nonpolar nature of the polymer (Falcão et al., 2017). For the crystallinity index, Pure PBAT showed 14.2%, and the crystallinity values of the PBAT/PGV and PBAT/Cloisite 20A were 12.1% and 12.5%, respectively. These results were corroborating with Livi and co-workers, who found that the organic chains in the modified nanoclays results decrease in crystallinity (Livi et al., 2014). Moreover, the same phenomenon can be observed with composites of the PBAT with nanoclay Cloisite 20A (Falcão et al., 2017). The small decrease in the crystallinity index can contribute to facilitating the biodegradation
(1)
Where: m = Mass (g) and M = Molar Mass. 3. Results and discussions 3.1. Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) Fig. 1 showed the photomicrographs of the nanoclay PGV and nanoclay Cloisite 20A. For Cloisite 20A, which is an organo-modified nanoclay, according to Fig. 1a, it is possible to observe lower particles, differently from the Nanoclay PGV, in Fig. 1. The nanoclay PGV is a natural type of montmorillonite, on the other hand, without modification, differently of Cloisite 20A (Staroszczyk et al., 2017). To
Fig. 2. Illustrative scheme showing the used experimental apparatus, described in the literature as the Sturm Test (Biodegradation Test). 3
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Table 1 Surface chemical composition of all samples. Chemical elements Sample
Carbon
Oxygen
PGV [Mass percentage (%)] PGV [Molar percentage (%)] Cloisite 20A [Mass percentage (%)] Cloisite 20A [Molar percentage (%)]
8.0 ± 0.0 12.4 ± 0.3 43.7 ± 1.0 55.7 ± 0.6
53.8 62.4 34.0 32.5
± ± ± ±
0.0 0.3 0.1 0.2
Sodium
Magnesium
Aluminum
Silicon
2.9 ± 0.1 2.3 ± 0.0 – –
1.5 ± 0.0 1.16 ± 0.0 0.8 ± 0.0 0.5 ± 0.0
9.5 6.5 5.7 3.2
22.7 ± 1.0 17.0 ± 2.0 13.5 ± 1.8 7.3 ± 1.1
± ± ± ±
0.2 0.2 0.1 0.1
69.6 ± 1.1° and 60.8 ± 2.0° for pure PBAT, PBAT Cloisite20A, and PBAT/PGV, respectively. These results suggest high hydrophilicity for nanocomposites compared to pure PBAT. The lower values of contact angle were obtained due the nanoclay promotes a possible increase in surface roughness, being a more visible effect for nanoclay PGV that it is less exfoliated (Fukushima et al., 2013a; Fukushima et al., 2013b). As described by several authors, this increase in roughness may facilitate the access of microorganisms in the material by helps them in the process of adhesion and facilitating the hydrolysis process, increasing the rates of biodegradation process (Rodrigues et al., 2015; Stloukal et al., 2015). Besides the superficial characteristics, the presence of sodium ion between lamellae of the nanoclay, promotes hydrophilic character in the nanocomposites surface, as for sample PBAT/PGV, which resulted in high sodium percentage, observed in SEM/EDS. This fact may also facilitate the degradation process of the polymeric matrix (Chen and Yang, 2015; Naderi-Samani et al., 2017). Different behavior was observed for PBAT/Cloisite20A, with a slighter decrease of contact angle values, with 69.6°, in comparison to PBAT/PGV. This phenomenon can be attributed to the presence of organically modified clay nanoparticles (Cloisite20A) on the surface of PBAT, as seen by Kumar, Mishra, and Chatterjee for nanocomposite systems PCL/Cloisite30B (Kumar et al., 2014). Moreover, as the nanocomposites have high hydrophilicity than the pure PBAT, by a decrease of contact angle, these materials could be applied as absorbent materials in agricultural applications, especially when these materials were discarded, because of its interaction with water polarity (Syakir et al., 2016).
process since the amorphous region is more susceptible to the microbial attack (Stloukal et al., 2015). 3.3. Tensile test (mechanical properties) Table 2 shows elasticity modulus (E), maximum elongation (εmax), and tensile strength at break (σrup) results of all samples. The nanocomposite samples showed an increase in elasticity modulus (E) for PBAT/Cloisite20A around to 19% and PBAT/PGV of 18%. Moreover, there was a decrease in maximum elongation of 36% in both nanocomposite systems (with PGV and Cloisite 20A), and tensile strength at the break did not have significant differences between all samples, so causing reinforcement in the matrix (Livi et al., 2014). These results corroborate with literature, where Livi and contributors presented the same behavior with PBAT/nanoclay Nanofil 757 composites, by increasing the elasticity modulus and decreasing the maximum elongation and tensile strength (Livi et al., 2014). Seyidoglu and Yilmazer had observed the effect of inorganic particles in elongation, and they concluded that a decrease in tensile strength and maximum elongation occurred. The authors suggest that it happened because nanoclay acts as a tensile concentrator. However, when these particles were better dispersed in the polymeric matrix by an exfoliation/intercalation process, there was an improvement in mechanical properties, with the increase in the contact area between matrix and filler (Seyidoglu and Yilmazer, 2013; Amanpour and Sharifi-Sanjani, 2017). Therefore, the treated nanoclay, with non-polar structure added during organo-modification may promote improvement in mechanical properties due to possible partial exfoliation and improved chemical interaction with the polymer as observed in XRD results with a decrease in peak intensity for PBAT/Cloisite20A than PBAT/PGV (Amanpour and Sharifi-Sanjani, 2017).
3.5. Thermal gravimetric analysis (TGA) In Fig. 4a and b, it is presented the loss weight curve and DTG curves, respectively, for all the samples obtained by TGA. Besides, in Table 3, it was shown temperatures with 10% and 50% of the weight loss of Fig. 4a (T10% and T50%) and maximum temperature of thermal events obtained by the DTG curves of Fig. 4b (Tmax 1 and Tmax 2). As seen in Fig. 4a and Table 3, there were no significant changes in
3.4. Contact angle measurements The values for static contact angle measurements were 76.9 ± 0.8°,
Fig. 3. (a) X-ray diffraction patterns of PBAT, Cloisite 20A nanoclay and PBAT/Cloisite 20A, and (b) X-ray diffraction patterns of PBAT, PGV nanoclay, and PBAT/ PGV. 4
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Fig. 4. Thermal decomposition for all samples: Weight-loss curves (a) and DTG curves (b), obtained by TGA. Table 2 Crystallinity index, elasticity modulus, maximum elongation, and tensile strength at break value, respectively, for pure PBAT, PBAT/Cloisite20A, and PBAT/PGV. Sample
Crystallinity index (%)
Elasticity modulus (E) (MPa)
Maximum elongation (εmax) (mm/mm)
Tensile strength at break (σrup) (MPA)
Pure PBAT PBAT/Cloisite20A PBAT/PGV
14.2 ± 0.2 12.5 ± 0.2 12.1 ± 0.2
50 ± 1 59 ± 3 59 ± 2
1684 ± 438 1083 ± 152 1078 ± 69
26 ± 3 23 ± 3 25 ± 1
comprehended the first phase of the degradation for samples PBAT/ PGV, followed by PBAT/Closite20A and Pure PBAT. This behavior can be explained by the hydrophilicity of the polar groups between lamellae of the nanoclays, more specifically, by the presence of terminal hydroxyl groups interlayer of modifier nanoclays, corroborating with contact angle results (Castro-Aguirre et al., 2018). On the other hand, the presence of nanoclay improves water diffusion on the polymeric matrix, promoting hydrolytic degradation of the nanocomposite (Mohanty and Nayak, 2010). As cited before, the excellent dispersion of nanoclays, observed by XRD results, and possible roughness, suggested by contact angle values, may help in the abiotic process, and the microbial action (Rodrigues et al., 2015). In literature, many works obtained similar results with composites of PBAT with treated or non-treated nanoclays, showing that the nanoclay presence in the polymer causes surface erosion, which increases the possibility for biodegradation. Moreover, XRD results showed that good dispersion by intercalation/exfoliation promotes the biodegradation process (Mondal et al., 2014). In the nanoclay PGV, d-spacing was from 0.89 to 0.92 nm. This fact shows its low exfoliation capacity of the biodegradable polymer. However, the nanoclay Cloisite 20A, an organo-modified, it obtained great exfoliation, by high initial lamellae distance, leading a great exfoliation of the polymer in the nanoclay, from 1.79 to 3.08 nm. This great exfoliation does not change the crystallinity significantly but leads to high interaction of the water molecule, which furthers its high biodegradation. This result can be seen in Fig. 6 that corroborate to show its high CO2 production for the nanocomposite Cloisite 20A than with PGV (Staroszczyk et al., 2017; Jurca et al., 2019). Other factors, as crystallinity, described by Sousa and coworkers that found a relationship between hydrolytic degradation and crystallinity index for composites of PLA and organo-modified nanoclays corroborates with results for PBAT/Cloisite 20A showing that high intercalation and lower crystallinity, favoring high biodegradability (Souza et al., 2013). This property, joined with hydrophilicity, can help in soil stabilizer when composted, providing controlled release of absorbed water in the soil (Syakir et al., 2016).
Table 3 Temperatures at 10% and 50% of weight loss (T10% and T50%) values for thermogravimetry curves (TG) and maximum temperature 1 and 2 (Tmax1 and Tmax2) for derivative curves (DTG). Sample
T10% (°C)
T50% (°C)
Tmax1 (°C)
Tmax2 (°C)
Pure PBAT Cloisite20A PGV PBAT/Cloisite20A PBAT/PGV
367 291 62 369 366
400 362 82 400 399
388 93 310 390 388
504 691 625 – 504
the loss of the mass for values in T10% and T50% for the pure PBAT and PBAT/PGV, showing that there was not a loss of thermal stability, being proved by Tmax 1 and Tmax 2, obtained by DTG curves of Fig. 4b. The addition of natural nanoclay, corroborating with literature results (Livi et al., 2014) that said with a minor degree of intercalation, there is a lower increase in d-spacing, obtained by XRD results. Observing that with treated nanoclays, as Cloisite 20A, that it promoted high intercalation and, it occurred a slight increase in thermal stability (NaderiSamani et al., 2017). Also, it was observed the disappearance of Tmax 2 of PBAT/Cloisite20A, obtained in the DTG curve of Fig. 4b. This effect can also be explained by high intercalation and the presence of ammonium quaternary salt of organo-modified nanoclay (Puglia et al., 2014). Improvement in thermal stability can be due to the presence of exfoliation or a similar condition that promotes the higher surface area, acting as the heat barrier, and then modifying the thermal stability of the system (Mohanty and Nayak, 2012; Iturrondobeitia et al., 2017). 3.6. Biodegradation test In Fig. 5, it is presented the CO2 mass production curve during 108 days of biodegradation for Pure PBAT and nanocomposites samples (PBAT/PGV and PBAT/Cloisite20A). In Fig. 5, for all the samples, there was a high production of CO2, that produced negative values of carbon gas quantity, due variation in inoculum composition. Theoretically, it is considered as a negative pattern the polyethylene, to measure the biodegradation process for the other formulations (according to ASTM D5338-15), since the polyethylene structure has high stability to microbial action (MartínezRomo et al., 2015). Between 15 and 20 days of degradation, it
4. Conclusions The SEM/EDS results showed that there was the presence of sodium 5
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Fig. 5. Evaluation of biodegradation by CO2 mass production versus days curves, obtained for all samples.
the presence of the sodium ions between the nanoclay lamellae. This promotes an increase of the polarity and consequently, the increase of the hydrophilicity, which can increase the biodegradation. Probably, there was a possible increase in surface roughness, and it creates higher accessibility of the microorganism in the surface of the materials. In biodegradation, PBAT/Cloisite20A had better results and higher CO2 production during the test. The treatment of the nanoclay and its excellent dispersion (seen by XRD results) helps in the biodegradable process.
ions for nanoclay PGV, characterizing sodic nanoclay. However, for Cloisite20A, the mass percentage of carbon and oxygen was higher (43.7 ± 1.0% and 34.0 ± 0.1%, respectively) than PGV (8.03 ± 0.02% and 53.84 ± 0.03%, respectively), and there was the disappearance of mass percentage for sodium. This justifies that the treatment changed the hydrophilicity of nanoclay, which provided higher compatibility between treated nanoclay with PBAT. The organomodification of Cloisite20A caused high values of the d-spacing (1.79 nm), which could promote higher dispersion of the nanoclay lamellae. Besides, the crystallinity index decreased from 14.2% (Pure PBAT) for 12.5% and 12.1% (PBAT/Cloisite20A and PBAT/PGV), respectively. The nanocomposite samples showed an increase in elasticity modulus for PBAT/Cloisite20A and PBAT/PGV around to 19% and 18%, respectively. Also, there was a decrease in the maximum elongation of 36%, in both bionanocomposites. The results of weight loss showed slightly higher thermal stability for PBAT/Cloisite 20A, possibly because there was significant intercalation between nanoclay and the polymeric matrix, which increasing thermal stability. Already, in the contact angle results, there was increased hydrophilicity for nanocomposites, proved by a decrease in contact angle values. This was observed, more significant for PBAT/PGV, with 60.8 ± 2.0°, caused by
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq (n° 305819/2017-8), UFABC and FAPESP (2017/25039-8 and 2018/11277-7). The authors
Fig. 6. General scheme to understand differences between nanoclays and its incorporation in PBAT and biodegradation. 6
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thank the technical support of the Multiuser Experimental Center of UFABC (CEM-UFABC).
Adv. 4, 26452–26461. Lvov, Y., Panchal, A., Fu, Y., Fakhrullin, R., Kryuchkova, M., Batasheva, S., Stavitskaya, A., Glotov, A., Glotov, A., Vinokurov, V., 2019. Interfacial self-assembly in halloysite nanotube composites. Langmuir 35 (26), 8646–8657. Malik, N., Kumar, P., Ghosh, S.B., Shrivastava, S., 2018. Organically modified nanoclay and aluminum hydroxide incorporated bionanocomposites towards enhancement of physico-mechanical and thermal properties of lignocellulosic structural reinforcement. J. Polym. Environ. 26, 3243–3249. Marichelvam, M.K., Jawaid, M., Asim, M., 2019. Corn and rice starch-based bio-plastics as alternative packaging materials. Fibers 7 (32), 1–14. Martínez-Romo, A., González-Mota, R., Soto-Bernal, J.J., Rosales-Candelas, I., 2015. Investigating the degradability of HDPE, LDPE, PE-BIO, and PE-OXO films under UVB radiation. J. Spectrosc. 2015, 1–6. Mohanty, S., Nayak, S.K., 2010. Aromatic-aliphatic poly(butylene adipate-co-terephthalate) bionanocomposite: influence of organic modification on structure and properties. Polym. Compos. 31 (7), 1194–1204. Mohanty, S., Nayak, S.K., 2012. Biodegradable nanocomposites of poly(butylene adipateco-terephthalate) (PBAT) and organically modified layered silicates. J. Polym. Environ. 20, 195–207. Mondal, D., Bhowmick, B., Mollick, M.M.R., Maity, D., Saha, N.R., Rangarajan, V., Rana, D., Sen, R., Chattopadhyay, D., 2014. Antimicrobial activity and biodegradation behavior of poly (butylene adipate-co-terephthalate)/clay nanocomposites. J. Appl. Polym. Sci. 131 (40079), 1–9. Naderi-Samani, H., Loghman-Estarki, M.R., Razavi, R.S., Ramazani, M., 2017. The effects of organoclay on the morphology, thermal stability, transparence and hydrophobicity properties of polyamide – imide/nanoclay nanocomposite coatings. Prog. Org. Coat. 112, 162–168. Nofar, M., Heuzey, M.-C., Carreau, P.J., Kamal, M.R., 2016. Effects of nanoclay and its localization on the morphology stabilization of PLA/PBAT blends under shear flow. Polymer 98, 353–364. Olivato, J.B., Marini, J., Yamashita, F., Pollet, E., Grossmann, M.V.E., Avérous, L., 2017. Sepiolite as a promising nanoclay for nano-biocomposites based on starch and biodegradable polyester. Mater. Sci. Eng. C 70, 296–302. Pinheiro, I.F., Ferreira, F., Souza, D.H.S., Gouveia, R.F., Lona, L.M.F., Morales, A.R., Mei, L.H.I., 2017. Mechanical, rheological and degradation properties of PBAT nanocomposites reinforced by functionalized cellulose nanocrystals. Eur. Polym. J. 97, 356–365. Puglia, D., Fortunati, E., D’Amico, D.A., Manfredi, L.B., Cyras, V.P., Kenny, J.M., 2014. Influence of organically modified clays on the properties and disintegrability in compost of solution cast poly(3-hydroxybutyrate) films. Polym. Degrad. Stab. 99, 127–135. Ramya, E., Rajashree, C., Nayak, P.L., Rao, D.N., 2017. New hybrid organic polymer montmorillonite/chitosan/polyphenylenediamine composites for nonlinear optical studies. Appl. Clay Sci. 150, 323–332. Rodrigues, C.A., Tofanello, A., Nantes, I.L., Rosa, D.S., 2015. Biological oxidative mechanisms for degradation of poly(lactic acid) blended with thermoplastic starch. ACS Sustain. Chem. Eng. 3 (11), 2756–2766. Sangroniz, A., Sangroniz, L., Gonzalez, A., Santamaria, A., Rio, J., Iriarte, M., Etxeberria, A., 2019. Improving the barrier properties of a biodegradable polyester for packaging applications. Eur. Polym. J. 115, 76–85. Sarkar, N., Sahoo, G., Das, R., Swain, S.K., 2018. Three-dimensional rice straw-structured magnetic nanoclay-decorated tripolymeric nanohydrogels as superadsorbent of dye pollutants. ACS Appl. Nano Mater. 1 (3), 1188–1203. Seyidoglu, T., Yilmazer, U., 2013. Production of modified clays and their use in polypropylene-based nanocomposites. J. Appl. Polym. Sci. 127 (2), 1257–1267. Singh, H., Bhowmick, H., 2019. Influence of nanoclay on the thermophysical properties and lubricity characteristics of mineral oil. Mater Today-Proc. 18, 1058–1066. Souza, P.M.S., Corroqué, N.A., Morales, A.R., Marin-Morales, M.A., Mei, L.H.I., 2013. PLA and organoclays nanocomposites: degradation process and evaluation of ecotoxicity using Allium cepa as test organism. J. Polym. Environ. 21 (4), 1052–1063. Staroszczyk, H., Malinowska-Panczyk, E., Gottfried, K., Kołodziejska, I., 2017. Fish gelatin-nanoclay films. Part I: effect of a kind of nanoclays and glycerol concentration on mechanical and water barrier properties of nanocomposites. J. Food Process. Preserv. 41, 13211. Stloukal, P., Pekarová, S., Kalendova, A., Mattausch, H., Laske, S., Holzer, C., Chitu, L., Bodner, S., Maier, G., Slouf, M., Koutny, M., 2015. Kinetics and mechanism of the biodegradation during thermophilic phase of composting process. Waste Manag. 42, 31–40. Syakir, M.I., Nurin, N.A., Zafirah, N., Kassim, Mohd Asyraf, Abdul Khalil, H.P.S., 2016. Nanoclay Reinforced on Biodegradable Polymer Composite: Potential as a Soil Stabilizer. Springer Singapore, pp. 329–356. Tan, B., Thomas, N.L., 2016. A review of the water barrier properties of polymer/clay and polymer/graphene nanocomposites. J. Membr. Sci. 514, 595–612. Torin, R.F.S., Camani, P.H., Silva, L.N., Sato, J.A.P., Ferreira, F.F., Rosa, D.S., 2017. Effect of clay and clay/essential oil in packaging films. Polym. Compos. 1–7. Tunç, S., Duman, O., 2010. Preparation and characterization of biodegradable methyl cellulose/montmorillonite nanocomposite films. Appl. Clay Sci. 48 (3), 414–424. Tunç, S., Duman, O., 2011. Preparation of active antimicrobial methyl cellulose/carvacrol/montmorillonite nanocomposite films and investigation of carvacrol release. LWT-Food Sci. Technol. 44 (2), 465–472. Tunc, S., Duman, O., Polat, T.G., 2016. Effects of montmorillonite on properties of methyl cellulose/carvacrol based active antimicrobial nanocomposites. Carbohydr. Polym. 150, 259–268. Wu, D., Tan, Y., Han, L., Zhang, H., Dong, L., 2018. Preparation and characterization of acetylated maltodextrin and its blend with poly (butylene adipate-co-terephthalate). Carbohydr. Polym. 181, 701–709. Zdiri, K., Elamri, A., Hamdaoui, M., 2017. Advances in thermal and mechanical behaviors of PP/clay nanocomposites. Polym. Plast Technol. 56 (8), 824–840.
Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.clay.2020.105453. References Adrar, S., Habib, A., Ajji, A., Grohens, Y., 2017. Combined effect of epoxy functionalized graphene and organomontmorillonites on the morphology, rheological and thermal properties of poly (butylenes adipate-co-terephthalate) with or without a compatibilizer. Appl. Clay Sci. 146, 306–315. Agarski, B., Vukelic, D., Micunovic, M.I., Budak, I., 2019. Evaluation of the environmental impact of plastic cap production, packaging, and disposal. J. Environ. Manag. 245, 55–65. Ajmal, A.W., Masood, F., Yasin, T., 2018. Influence of sepiolite on thermal, mechanical and biodegradation properties of poly-3-hydroxybutyrate-co-3-hydroxyvalerate nanocomposites. Appl. Clay Sci. 156, 11–19. Alves, J.L., Rosa, P.T.V., Realinho, V., Antunes, M., Velasco, J.I., Morales, A.R., 2019. Influence of chemical composition of Brazilian organoclays on the morphological, structural and thermal properties of PLA-organoclay nanocomposites. Appl. Clay Sci. 180, 105–186. Amanpour, J., Sharifi-Sanjani, N., 2017. Mechanical and thermal properties of poly(tetrahydrofurfuryl methacrylate) nanocomposites. J. Macromol. Sci. B. 56 (10), 775–789. American Society for Testing and Materials, 2015. ASTM D 5338-15. Determining Aerobic Biodegradation of Plastic Materials Under Controlled Composting Conditions, Incorporating Thermophilic Temperatures. ASTM International, West Conshohocken, PA. Araque, L.M., Alves, T.S., Barbosa, R., 2018. Biodegradation of polyhydroxybutyrate and hollow glass microspheres composite films. J. Appl. Polym. Sci. 47195, 1–10. Azevedo, J.B., Carvalho, L.H., Canedo, E.L., Barbosa, J.D.V., Silva, M.W.S., 2016. Avaliação da biodegradação em compósitos com fibras naturais através de perda de massa e produção de CO2. Rev. Virtual Quim. 8 (4), 1115–1129. Castro-Aguirre, E., Auras, R., Selke, S., Rubino, M., Marsh, T., 2018. Impact of nanoclays on the biodegradation of poly(lactic acid) nanocomposites. Polymers 10 (202), 1–21. Čèsniene, J., Baltušnikas, A., Lukošiute, I., Brinkiene, K., Kalpokaite-Dičkuviene, R., 2018. Influence of organoclay structural characteristics on properties and hydration of cement pastes. Constr. Build. Mater. 166, 59–71. Chen, J.-H., Yang, M.-C., 2015. Preparation and characterization of nanocomposite of maleated poly(butylene adipate-co-terephthalate) with organoclay. Adv. Mater. ResSwitz. 46, 301–308. Falcão, G.A.M., Vitorino, M.B.C., Almeida, T.G., Bardi, M.A.G., Carvalho, L.H., Canedo, E.L., 2017. PBAT/organoclay composite films: preparation and properties. Polym. Bull. 74 (11), 4423–4436. Fukushima, K., Rasyida, A., Yang, M.-C., 2013a. Biocompatibility of organically modified nanocomposites based on PBAT. J. Polym. Res. 20 (302), 1–12. Fukushima, K., Rasyida, A., Yang, M.-C., 2013b. Characterization, degradation and biocompatibility of PBAT based nanocomposites. Appl. Clay Sci. 80, 291–298. Gul, S., Kausar, A., Muhammad, B., Jabeen, S., 2016a. Research progress on properties and applications of polymer/clay nanocomposite. Polym. Plast. Technol. 55 (7), 684–703. Gul, S., Kausar, A., Muhammad, B., Jabeen, S., 2016b. Technical relevance of epoxy/clay nanocomposite with organically modified montmorillonite: a review. Polym. Plast. Technol. 1393–1415. Guo, F., Aryana, S., Han, Y., Jiao, Y., 2018. A review of the synthesis and applications of polymer–nanoclay composites. Appl. Sci. 1696 (8), 1–29. Hasani, Z., Youssefi, M., Borhani, S., Mallakpour, S., 2019. Structure and properties of nylon-6/amino acid modified nanoclay composite fibers. Text. Inst. 110 (9), 1336–1342. Islam, M.S., Talib, Z.A., Hasan, M., Ramli, I., Haafiz, M.K.M., Jawaid, M., Islam, A., Inuwa, I.M., 2017. Evaluation of mechanical, morphological, and biodegradable properties of hybrid natural fiber polymer nanocomposites. Polym. Compos. 38 (3), 583–587. Iturrondobeitia, M., Guraya, T., Okariz, A., Srot, V., Aken, P.A., Ibarretxe, J., 2017. Quantitative electron tomography of PLA/clay nanocomposites to understand the effect of the clays in the thermal stability. J. Appl. Polym. Sci. https://doi.org/10. 1002/APP.44691. Jurca, M., Julinová, M., Slavik, R., 2019. Negative effect of clay fillers on the polyvinyl alcohol biodegradation: technical note. Sci. Eng. Compos. Mater. 26 (1), 97–103. Kim, T., Jeon, H., Jegal, J., Kim, J.H., Yang, H., Park, J., Oh, D.X., Hwang, S.Y., 2018. Trans-crystallization behavior and strong reinforcement effect of cellulose nanocrystals on reinforced poly(butylene succinate) nanocomposites. RSC Adv. 8 (38) 21636. Kumar, S., Mishra, A., Chatterjee, K., 2014. Effect of organically modified clay on mechanical properties, cytotoxicity and bactericidal properties of poly(ε-caprolactone) nanocomposites. Mater. Res. Express. 1, 1–20. Liao, L., Li, X., Wang, Y., Fu, H., Li, Y., 2016. Effects of surface structure and morphology of nanoclays on the properties of jatropha curcas oil-based waterborne polyurethane/ clay nanocomposites. Ind. Eng. Chem. Res. 55 (45), 11689–11699. Livi, S., Sar, G., Bugatti, V., Espuche, E., Duchet-Rumeau, J., 2014. Synthesis and physical properties of new layered silicates based on ionic liquids: improvement of thermal stability, mechanical behavior and water permeability of PBAT nanocomposites. RSC
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