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PE biocomposites properties
Composites: Part B 68 (2015) 310–316
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Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Manufacture and research of TPS/PE biocomposites properties q _ a, Krzysztof Formela b Jerzy Korol a,⇑, Joanna Lenza a b
Central Mining Institute, Department of Material Engineering, Pl. Gwarkow 1, 40-166 Katowice, Poland Gdansk University of Technology, Faculty of Chemistry, Department of Polymer Technology, ul. Narutowicza 11/12, 80-233 Gdansk, Poland
a r t i c l e
i n f o
Article history: Received 22 February 2014 Received in revised form 15 July 2014 Accepted 25 August 2014 Available online 6 September 2014 Keywords: E. Extrusion B. Environmental degradation D. Mechanical testing E. Thermal analysis
a b s t r a c t In this paper the process of native starch preparing for modification by extrusion and manufacture of biocomposites is presented. The first aim of this study was to determine the mixing and granulating condition of native starch to obtain granulated native starch. For mixing and granulation of native starch Intensive Mixer manufactured by Maschinenfabrik Gustav Eirich was used. Mixing and granulation in a single process is a new method of preparation of powders for other processing. The main task of granulation is the elimination of dust emissions and the increase in density of powders. Granules are easy for dosage and more handy for transport and storage than powders, which is important from a technological point of view. The second aim of this study was to manufacture TPS/PE biocomposites. At first thermal modification of waxy maize starch was carried out with the use of a co-rotating twin screw extruder. During extrusion native starches have been deprived of their crystallinity and the obtained starch (TPS) has fully amorphous structure. XRD analysis revealed that semi crystalline phase of native starch after extrusion disappeared. During extrusion crystal structure of native starch is transformed into amorphous structure of thermoplastic starch (TPS), which was confirmed by XRD analysis. Reactive extrusion of obtained thermoplastic starch and high density polyethylene (HDPE) in the presence of polyethylene-grafted maleic anhydride (PE-g-MA) was done. To modify properties of TPS/PE blend polycaprolactone (PCL) was added in amount of 5 and 10 wt.%. The mass flow rate, static mechanical properties, thermal properties and morphology of obtained biocomposites were examined. The results show that the increased amount of TPS caused an increase in tensile strength and modulus of elasticity of prepared biocomposites. Addition of PCL to TPS/PE blends decreased tensile strength and modulus of elasticity. Moreover, higher amount of TPS and PCL in TPS/PE blends caused decrease of the elongation at break. On the other hand, using of PE-g-MA in TPS/PE blends cause increasing phase compatibility, which was confirmed by mechanical properties and morphology measurements. Biocomposites filled with higher TPS content (45 and 60 wt.%) possess lower resistance to hydrolytic degradation, which cause decrease of mechanical properties. It was found that higher amount of TPS in TPS/PE blends have small effect on mass flow rate and thermal properties estimated by differential scanning calorimetry (i.e. melting temperature, degree of crystallinity, melting enthalpy). This phenomenon have significant influence on processing of obtained biocomposites. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction The development of environmentally friendly materials has attracted extensive interest because of environmental pollution problems caused by using crude oil for synthetic polymers q The results of this work have been presented at the 4th Conference of Natural Fibre Composites, Rome 17–18 October 2013. ⇑ Corresponding author. _ E-mail addresses: [email protected] (J. Korol), [email protected] (J. Lenza), kformela. [email protected] (K. Formela).
http://dx.doi.org/10.1016/j.compositesb.2014.08.045 1359-8368/Ó 2014 Elsevier Ltd. All rights reserved.
production [1–4]. Recently the development of partially or totally biodegradable materials based on starch, in combination with synthetic thermoplastic polymers has been the subject of considerable research effort [5]. Starch, owing to its reproducibility, availability, and relatively low price, becomes a key raw material for the production of biopolymers and biocomposites. Native starch should be modified by plasticization to improve its processability. Common way of plastification is extrusion of native starch in presence of plasticizers, mostly glycerine and water [7–9]. Use of plasticizers decreases the glass transition
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temperature (Tg) of native starch improving its polymer chain mobility. It is necessary during processing, because Tg of native starch is higher than its decomposition temperature. However, starch-based plastics have some drawbacks, including limited long-term stability caused by water absorption, ageing caused by retrogradation, poor mechanical properties and bad processability. To overcome these weaknesses, the association of plasticized starch with another biodegradable polymer is a way to obtain compostable material. For example TPS is widely used in blends with other polymers, such as polycaprolactone. Also blending TPS with synthetic polymers such as polyethylene has been commonly used, leading to non fully biodegradable materials. [10–12]. In this paper native starch before extrusion was mixed with glycerine and granulated with use of Intensive Mixer manufactured by Maschinenfabrik Gustav Eirich (Germany). With use of intensive mixer we can carry out the two process steps: mixing and granulation. Obtained granules are dense and more useful for further technological operation (transport, storage, dosage) than powders, which is important from a technological point of view. Thermoplastic starch (TPS) (obtained in own way from disposal starch with expiry date of use as a food product) is introduced into HDPE at a variable weight percentage up to 60 wt.%. To modify some properties (i.e. processing) of TPS/PE blends, polycaprolactone (PCL) was added in an amount 5 wt.% and 10 wt.%. PCL was chosen for this purpose because of its good mechanical properties, biodegradability and compatibility with many types of polymers [7]. The use of disposal starch (expired date of use expired date of use as a food product), can reduce environmental impact of obtained material by using renewable resources and also increase eco-efficiency of polymer composites. As a result, the consumption of non-renewable fossil materials is reduced.
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2. Experimental The first aim of this study was to determine the mixing and granulating condition of native starch to obtain granulated native starch before extrusion. The second aim of this study was to manufacture TPS/PE biocomposites based on TPS, obtained during twin screw extrusion and on PE with addition of PCL, to modify properties of TPS/PE. The static tensile mechanical properties, structure and thermal properties of obtained biocomposites were examined. Also the effect of hydrolytic degradation on structure, mechanical and thermal properties of biocomposites was examined. 2.1. Materials used in the research Basic materials for research were: HDPE M300054, MFR: 30 g/ 10 min (190 °C, 2.16 kg), density: 0.954 g/cm3, from Sabic Poland Sp. z o.o.; Waxy Maize Starch from Cargill Poland Sp. z o.o.; Polycaprolactone (PCL) CAPAÒ 6800, MFR: 7.29 g/10 min (190 °C, 2.16 kg) MW 80,000 from Perstorp, Polyethylene-Grafted Maleic Anhydride (PE-g-MA), PolybondÒ 3029 MFR: 4 g/10 min, (190 °C, 2.16 kg), density: 0.960 g/cm3, from Chemtura. The materials for research were prepared in a few stages: preparation of starch to extrusion, extrusion of native starch, extrusion of TPS/PE and TPS/PE/PCL, injection molding of tests samples. 2.2. Native starch modification The first step to prepare starch for extrusion was to modify starch by glycerin. For this purpose Intensive Mixer manufactured by Maschinenfabrik Gustav Eirich (Germany) was used (Fig. 1). In the Eirich intensive mixers 90% of the energy is used for mixing the mass in the range of the high-speed agitator, which rotates
Fig. 1. Principle of operation of the intensive mixer (A), Intensive Mixer Erich R 02 (B) [13].
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SKW
350 300
Counts Co nts
250 200 150 100 50 0
5
12
19
26
33
2Θ
40
47
54
47
54
Fig. 3. XRD curves of native starch.
TPSWK SWK
450 400 350
Fig. 2. Granulated glycerine modified native starch.
in the opposite direction to the direction in which the mixer pan rotates. The movement of the material in the device also runs at the level parallel to the axis of the rotor. Components of any consistence can be mixed in the device. The intensive mixer enables to realize the mixture homogenization and granulation process during one technological operation. Such a granulation procedure is an innovative method for preparation of powders for further processing. The way in which the material moves in the mixer and the mixer’s construction enable homogenous distribution of the additives in the whole volume of the mixed material. Granulation in the intensive mixer is a process which gives the mass the form of dense and stable granules, as the result, a dense and at the same time granulated material with required shape and size and good stability parameters is obtained. The homogeneity degree of the mixture decides about the level of quality and influences the repeatability and the properties of the respective material batches. Homogeneity is of a particular significance in case when small amounts of the introduced additives (i.e. binding substances – in this case glycerine) are used, which have to be homogenously distributed in the total material volume in order to efficiently influence the composition properties. High mixing degree also means higher stability of the granulates at a given content of the binder. Granulation in the intensive mixer enables to control the grain size distribution, ensures their high density and gives the granulate surface properties which are beneficial for the rheological properties.
Counts Co nts
300 250 200 150 100 50 0
5
12
19
26
2Θ
33
Fig. 4. XRD curves of starch after modification by extrusion.
The mechanical granulation eliminates the typical granulate defects such as, for example, nutshell structure. The ability to granulate follows from the way in which the material moves which is similar to the material stream in the disc pelletizer, the difference lies in the fact that in the intensive mixer the granulation is much faster and facilitated by the mechanical impact of the mixer and the movement of the pan correlated with the direction of the material stream formed by the high-speed rotor. In comparison to the disc or drum pelletizer, granulation in the intensive mixer runs in the whole volume of the processed material and does not require such a complex control [13]. During the tests, starch and glycerin were mixed and granulated in Intensive Mixer Eirich R02 (Fig. 1). Starch and glycerin were mixed in ratio 75 wt.% and 25 wt.%. Mixing parameters: agitator rotations 3000 rpm, pan rotations 120 rpm, mixing time 60 s. Granulation
Table 1 Composition of the analyzed composites and MFR value. Specimens
B1 B2 B3 B4 B5 B6 B7 B8 B9 a b
40
Weight content (%) HDPE
Polybond 3029
TPS
PCL
65 47.5 30 60 42.5 25 55 37.7 20
5 7.5 10 5 7.5 10 5 7.5 10
30 45 60 30 45 60 30 45 60
– – – 5 5 5 10 10 10
Theoretical values for neat thermoplastic matrix without TPS. Experimental values for obtained composition.
Theoreticala MFR190°C/2.16 g/10 min 19.7 14.6 9.4 18.4 13.2 8.1 17.4 12.3 7.1
kg,
Experimentalb MFR190°C/2.16 kg, g/10 min 1.06 1.13 1.20 1.08 1.14 1.22 1.08 1.13 1.21
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2.3. Composites preparation All composites were prepared using a twin screw extruder Leistritz ZSE model 27 HP (Germany). The screw diameter was 27 mm, and a length to diameter ratio was 44 (L/D = 44). Constructions of used plasticizing systems and detailed description of screws are shown in details in [14,15]. The extruder had ten heating and cooling zones. All materials were dosed by Brabender gravimetric screw feeders (Germany) with a constant flow rate. The mass ratio of the components is presented in Table 1. Temperature profile of the extruder was as follows (from feeding section) 110/120/130/140/150/160/160//160/160/160 °C. The screw rotation during the extrusion processes (shear forces acting on the material) was 300 rpm. The obtained thermoplastic composition was injection molded using Arburg type Allrounder 270-210-500 injection-molding
70
PCL
HDPE
PB
60
Heat Flux (mW)
HDPE
50
1st Cooling
40 30
PB PCL
20 10 0 20
40
60
80
100 120 140 160 180
0
Heat Flux (mW)
parameters: first stage of granulation – to build granules: agitator rotations 2100 rpm, pan rotations 120 rpm for 180 s, second stage of granulation – to make granules smooth: agitator rotations 900 rpm, pan rotations 120 rpm for 60 s. During the granulation process, glycerin and the moisture of the starch (8 wt.%) act as binder for starch grains. Additional water was not used. Granulated, glycerine modified native starch is presented on Fig. 2. Obtained granules were extruded with the use of enhanced technological installation based on the (L/D = 44) Leistritz ZSE model 27 HP twin screw extruder equipped with a die with three orifices of circle diameter of 3 mm, BRABENDER gravimetric screw feeders ensuring proportion accuracy of 0.1 by weight% as well as CF SCHEER and CIE SGS 50E granulator. The process parameters for all the mixtures were the same: feeding section – 90 °C, plasticizing section – 140 °C, metering section – 120 °C, screw rotations 200 rpm, output – 18 kg/h.
-10
PCL -20
PB
-30 HDPE
1st Heating 20
40
60
80
100 120 140 160 180
Temperature ( 0 C) Fig. 5. DSC curves of PCL, HDPE, Polybond.
Table 2 Mechanical properties of composite (average ± standard deviation). Specimens Tensile strength (MPa) B1 B2 B3 B4 B5 B6 B7 B8 B9 Modulus of elasticity (MPa) B1 B2 B3 B4 B5 B6 B7 B8 B9 Elongation at break (%) B1 B2 B3 B4 B5 B6 B7 B8 B9
Dry 23.0 ± 0.2 24.9 ± 0.5 27.8 ± 0.2 22.7 ± 0.1 24.3 ± 0.1 27.0 ± 0.5 21.6 ± 0.2 23.9 ± 0.2 24.8 ± 0.5 1181 ± 48 1321 ± 79 1641 ± 119 1114 ± 47 1266 ± 49 1547 ± 38 1065 ± 34 1260 ± 91 1525 ± 56 10.7 ± 2.7 9.4 ± 1.5 8.4 ± 1.9 10.2 ± 1.2 9.5 ± 0.7 4.5 ± 0.5 6.7 ± 0.8 7.2 ± 1.0 3.5 ± 0.2
1 day in water
14 days in water
28 days in water
22.5 ± 0.2 19.5 ± 0.2 12.2 ± 0.2 20.5 ± 0.4 20.4 ± 0.2 9.3 ± 1.4 20.8 ± 0.3 17.2 ± 0.7 8.7 ± 0.2
21.4 ± 0.2 11.4 ± 0.2 8.8 ± 0.3 18.6 ± 0.1 10.7 ± 0.1 7.2 ± 0.2 17.3 ± 0.2 10.2 ± 0.4 6.3 ± 0.4
19.5 ± 0.2 10.6 ± 0.1 8.3 ± 0.1 15.9 ± 0.5 9.9 ± 0.1 6.7 ± 0.2 15.1 ± 0.2 9.1 ± 0.4 6.0 ± 0.4
1113 ± 70 976 ± 32 640 ± 42 1007 ± 52 1085 ± 59 533 ± 53 1071 ± 62 935 ± 73 500 ± 15
1048 ± 42 406 ± 20 299 ± 34 938 ± 15 363 ± 21 245 ± 32 886 ± 43 324 ± 12 205 ± 21
975 ± 44 350 ± 14 257 ± 20 753 ± 42 335 ± 18 193 ± 12 700 ± 29 324 ± 17 176 ± 12
9.8 ± 1.2 7.8 ± 1.6 8.2 ± 1.8 9.8 ± 0.7 7.9 ± 0.6 4.7 ± 1.7 6.2 ± 0.7 5.7 ± 0.8 3.7 ± 0.2
9.1 ± 2.2 13.9 ± 1.5 23.6 ± 12.2 8.5 ± 1.1 29.4 ± 5.8 10.9 ± 2.1 6.7 ± 0.3 19.6 ± 3.3 9.2 ± 1.9
10.8 ± 1.3 22.0 ± 3.1 36.1 ± 14.3 7.8 ± 1.4 40.9 ± 6.8 18.4 ± 2.9 6.1 ± 0.6 10.3 ± 2.1 11.1 ± 2.5
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machine into standard so called dog-bone specimens (ASTM 527) with the cross section of the measurement part equal 40 mm2. The machine is equipped with Priamus (Switzerland) injection process controller. ARBURG Allrounder characteristics: screw diameter: 25 mm, injection pressure – max 1400 bar, clamping force – 500 kN. Sample injection parameters: temperature of the polymer melt – 160 °C ± 2 °C, form temperature – 30 °C ± 1 °C, injection speed – 190 mm/s, cycle period – 60 s, injection pressure – 500 bar, clamping pressure – 350 bar.
Dry B122_0 B122_28 28 days in water
20
10
2nd Cooling
2.4. Composite testing
0 XRD tests of starches were performed by JEOL JDX-7S diffractometer (Japan). The tensile properties have been estimated by determining the elastic modulus, tensile strength and elongation at break. The tests were conducted according to the PN-EN ISO 527 standard, using the Instron tensile testing machine with elongation head and extensometer. The elongation velocity: 1 mm/min (elastic modulus), 50 mm/min (tensile strength and elongation at break). Number of samples: 5 per test. Blue Hill software was used for evaluation of the test results. To estimate the influence of hydrolytic degradation process on the properties of materials, the specimens were placed in water for 1, 14 and 28 days. Thermal characteristics of the blends were determined using a differential scanning calorimeter Mettler-Toledo TGA/DSC 1 (Switzerland). The images of structure were taken from samples after a tensile test using the scanning electron microscope under low vacuum SEM Hitachi 3400 N (Japan).
The increase in the weight content of TPS in the composites caused the slight increase in the MFR. Composition of analyzed composites is presented in Table 1. To better understanding of this pheDry B122_0 28 days in B122_28 water
2nd Heating
-10
-20 20 40 60 80 100 120 140 160 180 200 220 0
Temperature ( C)
Table 3 Melting characteristics and degree of crystallinity of selected samples. Specimens
HDPE Polybond 3029 B1 B2 B3
10
1st Cooling
0 20 40 60 80 100 120 140 160 180 200 220 5 0
0
Fig. 7. DSC curves of specimen B9, after immersion in water for 28 days.
3. Results and discussion
20
20 40 60 80 100 120 140 160 180 200 220
1st Heating
-5 -10 -15 -20 20 40 60 80 100 120 140 160 180 200 220 0
Temperature ( C) Fig. 6. DSC curves of specimen B9.
Melting
Xc (%)
To, (°C)
Tm, (°C)
DHm, (J/g)
123.1 120.7 123.0 122.0 121.3
130.1 128.7 129.2 129.5 128.5
158.8 122.1 99.2 80.0 61.8
54.1 41.6 33.8 27.6 21.1
To – onset temperature of melting, Tm – melting temperature, DHm – melting enthalpy, Xc – degree of crystallinity.
nomenon theoretical values of MFR for neat thermoplastic matrix (without TPS) were determined. Theoretical MFR of thermoplastic matrix were calculated basing on additivity principle and the MFR characteristics of neat substrate (presented in material section). For example, the formula for calculation of MFR of thermoplastic matrix in sample B1 was: 0.65 30 g/10 min (HDPE) + 0.05 4 g/ 10 min (Polybond 3029), resulting 19.7 g/10 min. It was noticed that partial substitution of HDPE by using Polybond 3029 or PCL caused decrease of mass flow rate, due to increasing molecular weight of thermoplastic matrix. As we can see the addition of TPS to thermoplastic matrix influences on significant decrease of its mass flow rate. On the other hand, the increase of TPS content slightly affected the mass flow rate of obtained compositions. This phenomenon may be due to three main factors. Firstly, granulation and extrusion of native starch have an influence on formation of thermoplastic starch (TPS) with amorphous structure, which allows better dispersion of TPS in polyethylene matrix. Secondly, the low value of glass transition temperature of used thermoplastic polymers (HDPE Tg around 120 °C, PCL Tg around 60 °C) caused decrease of glass transition temperature of TPS. This plastification effect of native starch contributes to easier processing of obtained
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TPS
Fig. 8. SEM image of fracture of specimen B3.
composite. Moreover, different viscosity of used substrate affected on its mixing efficiency, which has significant influence on thermo-mechanical degradation of materials obtained during processing in co-rotating twin screw extruder. To estimate the rate of native starch modification during extrusion with glycerin the XRD analysis was done (Figs. 3 and 4).
315
The analysis of diffraction patterns of starch used in the studies revealed that, during the extrusion process in the presence of glycerine and water as plasticizers, native starches have been deprived of a part of the crystal structure and the obtained thermoplastic starch (TPS) has amorphous structure. Peaks of semi crystalline phase of native starch (Fig. 3) after extrusion disappeared, (Fig. 4) and we can observe wide, fuzzy curves typical for amorphous material. The changes of basic mechanical properties of dry specimens and after immersion in water are presented In Table 2. In case of dry composites an increase in TPS content caused an increase in tensile strength and modulus of elasticity similar like in case of use of other natural filler like for example natural fibers [1,16–20]. Tensile strength and modulus of elasticity of specimens decreased for those with 5 and 10 wt.% PCL content, respectively. In the literature the tensile strength of PE/TPS/PCL films increased with PCL content, for injection molded specimens tensile strength increases also with PCL content but starts to increase from 50 wt.% of PCL in PE/TPS/PCL [6]. Adding of TPS and PCL caused decrease of the elongation at break. The effect of polycaprolactone addition in amount of 5 and 10 wt.% on the mechanical properties of PE/TPS/ PCL materials was not satisfied. Mechanical properties of specimens with 30 wt.% of TPS changed insignificantly after immersion in water. Mechanical properties of biopolymers filled with 45 and 60 wt.% of TPS decreased under influence of water, and this effect is stronger with time of incubation in water. Water acted as a plasticizer especially for biopolymers
Fig. 9. Schematic reaction between HDPE, PE-g-MA and TPS [24].
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filled with 45 and 60 wt.% of TPS where the value of elongation at break increased after immersion in water. Thermal analysis results of PCL, HDPE, Polybond (Fig. 5) and specimen B9 are presented on Fig. 6 and specimen B9, after immersion in water for 28 days (Fig. 7). DSC curves are presented only for samples with the highest content of TPS and PCL. For all DSC curves of PE/TPS/PCL an endothermic peak is observed around 60 °C and 135–140 °C. The enthalpy associated with those peaks depends on the PCL and HDPE content and allows us to attribute this to the melting of PCL and HDPE. The melt temperature and enthalpy of PCL and HDPE in the blends change with increased amount of TPS, due to increased level of amorphous phase in blend. Similar situation is also on the exothermic curves of crystallization. For test samples part of the crystalline phase was calculated with use of following equation [21]:
v¼
DH m 100% DH c
where: v – degree of crystallinity, %; DHm – melting enthalpy, J/g; DHc – melting enthalpy at 100% crystallinity, J/g. For calculation heat of fusion of PE at 100% crystallinity, 293.6 J/ g [22], was used. In Table 3 the melting characteristics and the degree of crystallinity of selected samples are presented. HDPE has higher degree of crystallinity than Polybond 3029, possessing grafted maleic anhydride groups on polyethylene chains. Similar observation was described in work [23]. Lowering of HDPE content in the blend by using higher amount of Polybond 3029 and TPS caused decrease of onset temperature of melting, enthalpy and degree of crystallinity. Fig. 8 shows the morphology of specimen B3. On the fractured surface, after the elongation test, we can observe TPS in the droplet-like form. TPS particles are very well dispersed in the compatibilized HDPE matrix. We can observe that some particles of TPS are pulled out from the matrix, but most of them are still tightly linked to the matrix. It is an effect of developed surface of TPS and good adhesion caused by use of PE-g-MA as a compatibilizer. Fig. 9 shows schematic reaction during the reactive blending of HDPE, PE-g-MA and TPS. Also homogeneous distribution of TPS is a reason for increased strength of material with TPS content. Obtained results confirm that native starch after modification in continuous process has amorphous structure and can be successfully used as renewable bio-filler for thermoplastic matrix. Tensile properties of obtained partially biodegradable composites are dependent mainly on TPS and PCL content. Increased amount of TPS causes improvement of mechanical properties of TPS/PE blends. On the other hand, addition of PCL to TPS/PE blends influences on deterioration of their mechanical properties. The values of mechanical properties after hydrolytic degradation confirm that biodegradability of obtained blends is strongly connected with TPS content. 4. Conclusion This study shows that native starch can be easily granulated with the use of an intensive mixer. During the granulation process, added glycerin and water (present in starch) act as a binder, then during extrusion of starch glycerin and water act as plastifying agents. Granulated starch has a higher bulk density compared to powder. Dense granules are easier for the storage and dosage compared to powders, which is important from a technological point of view. Increase of flowability properties of granulated starch (compare to non-granulated powder) and elimination of dust was very helpful during dosing into extruder feed zone. Reactive extrusion of native starch with the presence of a plastifying agent is the only way to obtain amorphous homogeneous
material in continuous process. The fine and uniform dispersion of the TPS in the PE matrix is not only the result of the use of a co-rotating twin screw extruder (intensive mixing) but also the result of using the PE-g-MA copolymer as a compatibilizer. Depending on the amount of starch we can obtain the nonbiodegradable material or partially biodegradable material. Thanks to the use of starch we can reduce the use of crude oil and increase the use of renewable resources for polymer composite production. Further investigations on that field should be focused on optimization of granulation process, starch modification with use of other plastifying agents, modification of obtained blends by filling with natural fillers like wood flour or natural fibers, searching for new methods of compatibilization. Acknowledgment This work was supported by the POIG Project No. 01.01.02-10123/09-00. References [1] Korol J. Polyethylene matrix composites reinforced with keratin fibers obtained from waste chicken feathers. J Biobased Mater Bioenergy 2012;6(4):355–60. [2] Gasper M, Benko Z, Dogossy G, Reczey K, Czigany T. Reducing water absorption in compostable starch-based plastics. Polym Degrad Stab 2005;90(3):563–9. [3] Czaplicka-Kolarz K, Burchart-Korol D, Korol J. Environmental assessment of biocomposites based on LCA. Polimery 2013;58(6):476–81. [4] Czaplicka-Kolarz K, Burchart-Korol D, Korol J. Application of life cycle assessment and exergy to environmental evaluation of selected polymers. Polimery 2013;58(7–8):605–9. [5] Bajer K, Richert A, Bajer D, Korol J. Biodegradation of plastified starch obtained by corotation twin screw extrusion. Polym Eng Sci 2012;52(12):2537–42. [6] Matzinos P, Tserki V, Gianikouris C, Pavlidou E, Panayiotou C. Processing and characterization of LDPE/starch/PCL blends. Eur Polym J 2002;38(9):1713–20. [7] Koenig MF, Huang SJ. Biodegradable blends and composites of polycaprolactone and starch derivatives. Polymer 1995;36(9):1877–82. [8] Mahieu A, Terrié C, Agoulon A, Leblanc N, Youssef B. Thermoplastic starch and poly(e-caprolactone) blends: morphology and mechanical properties as a function of relative humidity. J Polym Res 2013;20(229):1–13. [9] Liua Hongsheng, Xiea Fengwei, Yua Long, Chena Ling, Lia Lin. Thermal processing of starch-based polymers. Prog Polym Sci 2009;34(12):1348–68. [10] Xiea Fengwei, Yua Long, Sua Bing, Liua Peng, Wanga Jun, Liua Hongshen, et al. Rheological properties of starches with different amylose/amylopectin ratios. J Cereal Sci 2009;49(3):371–7. [11] Bajer K, Kaczmarek H. Methods of biodegradation study of polymeric materials. Polimery 2007;52(1):13–8. [12] Averous L, Moroa L, Doleb P, Fringantcet C. Properties of thermoplastic blends: starch–polycaprolactone. Polymer 2000;41:4157–67. [13] Burchart-Korol D, Korol J, Francik P. Application of the new mixing and granulation technology of raw materials for iron ore sintering process. Metalurgija 2012;51(2):187–90. [14] Korol J, Lenza J, Burchart-Korol D, Bajer K. Extrusion and testing the changes of recyclate LDPE properties. Przem Chem 2012;91(11):2196–201. [15] Formela K, Korol J, Cysewska M, Haponiuk JT. Przem Chem 2013;92(4):512–7. [16] Koziol M, Bogdan-Wlodek A, Myalski J, Wieczorek J. Influence of wet chemistry treatment on the mechanical performance of natural fibres. Pol J Chem Technol 2011;13(40):21–7. [17] Koziol M, Wieczorek J, Bogdan-Włodek A, Myalski J. Evaluation of jute fiber preforms absorbability using optical profilographometer. J Compos Mater 2013;47(19):2309–19. [18] Zimniewska M, Myalski J, Kozioł M, Man´kowski J, Bogacz E. Natural fiber textile structures suitable for composite materials. J Nat Fibers 2012;9(4):229–39. [19] Kozłowski R, Władyka-Przybylak M, Bujnowicz K, Latest achievements in the area of composites reinforced with natural fiber. In: Proceedings of fiber reinforced composites 2007, 9–12 December, Port Elizabeth; 2007. [20] Kuciel S, Liber-Knec´ A, Zajchowski S. Biocomposites based on thermoplastic starch or polylactide/starch blends as the matrices filled with natural fibers. Polimery 2009;54(10):667–73. [21] Przygocki W. Metody fizyczne badan´ polimerów. Warszawa: Polish Scientific Publishers PWN; 1990. [22] Wunderlich B, Dole M. Specific heat of synthetic high polymers. VIII. Low pressure polyethylenes. J Polym Sci 1957;24(106):201–13. [23] Roy D, Simon GP, Forsyth M. Blends of maleic-anhydride-grafted polyethylene with polyethylene for improved cathodic disbondment performance. Polym Int 2001;50(10):1115–23. [24] Kahar AWM, Ismail H, Othman N. Effects of polyethylene-grafted maleic anhydride as a compatibilizer on the morphology and tensile properties of (thermoplastic tapioca starch)/(high-density polyethylene)/(natural rubber) blends. J Vinyl Addit Technol 2012;18(1):65–70.
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Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Manufacture and research of TPS/PE biocomposites properties q _ a, Krzysztof Formela b Jerzy Korol a,⇑, Joanna Lenza a b
Central Mining Institute, Department of Material Engineering, Pl. Gwarkow 1, 40-166 Katowice, Poland Gdansk University of Technology, Faculty of Chemistry, Department of Polymer Technology, ul. Narutowicza 11/12, 80-233 Gdansk, Poland
a r t i c l e
i n f o
Article history: Received 22 February 2014 Received in revised form 15 July 2014 Accepted 25 August 2014 Available online 6 September 2014 Keywords: E. Extrusion B. Environmental degradation D. Mechanical testing E. Thermal analysis
a b s t r a c t In this paper the process of native starch preparing for modification by extrusion and manufacture of biocomposites is presented. The first aim of this study was to determine the mixing and granulating condition of native starch to obtain granulated native starch. For mixing and granulation of native starch Intensive Mixer manufactured by Maschinenfabrik Gustav Eirich was used. Mixing and granulation in a single process is a new method of preparation of powders for other processing. The main task of granulation is the elimination of dust emissions and the increase in density of powders. Granules are easy for dosage and more handy for transport and storage than powders, which is important from a technological point of view. The second aim of this study was to manufacture TPS/PE biocomposites. At first thermal modification of waxy maize starch was carried out with the use of a co-rotating twin screw extruder. During extrusion native starches have been deprived of their crystallinity and the obtained starch (TPS) has fully amorphous structure. XRD analysis revealed that semi crystalline phase of native starch after extrusion disappeared. During extrusion crystal structure of native starch is transformed into amorphous structure of thermoplastic starch (TPS), which was confirmed by XRD analysis. Reactive extrusion of obtained thermoplastic starch and high density polyethylene (HDPE) in the presence of polyethylene-grafted maleic anhydride (PE-g-MA) was done. To modify properties of TPS/PE blend polycaprolactone (PCL) was added in amount of 5 and 10 wt.%. The mass flow rate, static mechanical properties, thermal properties and morphology of obtained biocomposites were examined. The results show that the increased amount of TPS caused an increase in tensile strength and modulus of elasticity of prepared biocomposites. Addition of PCL to TPS/PE blends decreased tensile strength and modulus of elasticity. Moreover, higher amount of TPS and PCL in TPS/PE blends caused decrease of the elongation at break. On the other hand, using of PE-g-MA in TPS/PE blends cause increasing phase compatibility, which was confirmed by mechanical properties and morphology measurements. Biocomposites filled with higher TPS content (45 and 60 wt.%) possess lower resistance to hydrolytic degradation, which cause decrease of mechanical properties. It was found that higher amount of TPS in TPS/PE blends have small effect on mass flow rate and thermal properties estimated by differential scanning calorimetry (i.e. melting temperature, degree of crystallinity, melting enthalpy). This phenomenon have significant influence on processing of obtained biocomposites. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction The development of environmentally friendly materials has attracted extensive interest because of environmental pollution problems caused by using crude oil for synthetic polymers q The results of this work have been presented at the 4th Conference of Natural Fibre Composites, Rome 17–18 October 2013. ⇑ Corresponding author. _ E-mail addresses: [email protected] (J. Korol), [email protected] (J. Lenza), kformela. [email protected] (K. Formela).
http://dx.doi.org/10.1016/j.compositesb.2014.08.045 1359-8368/Ó 2014 Elsevier Ltd. All rights reserved.
production [1–4]. Recently the development of partially or totally biodegradable materials based on starch, in combination with synthetic thermoplastic polymers has been the subject of considerable research effort [5]. Starch, owing to its reproducibility, availability, and relatively low price, becomes a key raw material for the production of biopolymers and biocomposites. Native starch should be modified by plasticization to improve its processability. Common way of plastification is extrusion of native starch in presence of plasticizers, mostly glycerine and water [7–9]. Use of plasticizers decreases the glass transition
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temperature (Tg) of native starch improving its polymer chain mobility. It is necessary during processing, because Tg of native starch is higher than its decomposition temperature. However, starch-based plastics have some drawbacks, including limited long-term stability caused by water absorption, ageing caused by retrogradation, poor mechanical properties and bad processability. To overcome these weaknesses, the association of plasticized starch with another biodegradable polymer is a way to obtain compostable material. For example TPS is widely used in blends with other polymers, such as polycaprolactone. Also blending TPS with synthetic polymers such as polyethylene has been commonly used, leading to non fully biodegradable materials. [10–12]. In this paper native starch before extrusion was mixed with glycerine and granulated with use of Intensive Mixer manufactured by Maschinenfabrik Gustav Eirich (Germany). With use of intensive mixer we can carry out the two process steps: mixing and granulation. Obtained granules are dense and more useful for further technological operation (transport, storage, dosage) than powders, which is important from a technological point of view. Thermoplastic starch (TPS) (obtained in own way from disposal starch with expiry date of use as a food product) is introduced into HDPE at a variable weight percentage up to 60 wt.%. To modify some properties (i.e. processing) of TPS/PE blends, polycaprolactone (PCL) was added in an amount 5 wt.% and 10 wt.%. PCL was chosen for this purpose because of its good mechanical properties, biodegradability and compatibility with many types of polymers [7]. The use of disposal starch (expired date of use expired date of use as a food product), can reduce environmental impact of obtained material by using renewable resources and also increase eco-efficiency of polymer composites. As a result, the consumption of non-renewable fossil materials is reduced.
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2. Experimental The first aim of this study was to determine the mixing and granulating condition of native starch to obtain granulated native starch before extrusion. The second aim of this study was to manufacture TPS/PE biocomposites based on TPS, obtained during twin screw extrusion and on PE with addition of PCL, to modify properties of TPS/PE. The static tensile mechanical properties, structure and thermal properties of obtained biocomposites were examined. Also the effect of hydrolytic degradation on structure, mechanical and thermal properties of biocomposites was examined. 2.1. Materials used in the research Basic materials for research were: HDPE M300054, MFR: 30 g/ 10 min (190 °C, 2.16 kg), density: 0.954 g/cm3, from Sabic Poland Sp. z o.o.; Waxy Maize Starch from Cargill Poland Sp. z o.o.; Polycaprolactone (PCL) CAPAÒ 6800, MFR: 7.29 g/10 min (190 °C, 2.16 kg) MW 80,000 from Perstorp, Polyethylene-Grafted Maleic Anhydride (PE-g-MA), PolybondÒ 3029 MFR: 4 g/10 min, (190 °C, 2.16 kg), density: 0.960 g/cm3, from Chemtura. The materials for research were prepared in a few stages: preparation of starch to extrusion, extrusion of native starch, extrusion of TPS/PE and TPS/PE/PCL, injection molding of tests samples. 2.2. Native starch modification The first step to prepare starch for extrusion was to modify starch by glycerin. For this purpose Intensive Mixer manufactured by Maschinenfabrik Gustav Eirich (Germany) was used (Fig. 1). In the Eirich intensive mixers 90% of the energy is used for mixing the mass in the range of the high-speed agitator, which rotates
Fig. 1. Principle of operation of the intensive mixer (A), Intensive Mixer Erich R 02 (B) [13].
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SKW
350 300
Counts Co nts
250 200 150 100 50 0
5
12
19
26
33
2Θ
40
47
54
47
54
Fig. 3. XRD curves of native starch.
TPSWK SWK
450 400 350
Fig. 2. Granulated glycerine modified native starch.
in the opposite direction to the direction in which the mixer pan rotates. The movement of the material in the device also runs at the level parallel to the axis of the rotor. Components of any consistence can be mixed in the device. The intensive mixer enables to realize the mixture homogenization and granulation process during one technological operation. Such a granulation procedure is an innovative method for preparation of powders for further processing. The way in which the material moves in the mixer and the mixer’s construction enable homogenous distribution of the additives in the whole volume of the mixed material. Granulation in the intensive mixer is a process which gives the mass the form of dense and stable granules, as the result, a dense and at the same time granulated material with required shape and size and good stability parameters is obtained. The homogeneity degree of the mixture decides about the level of quality and influences the repeatability and the properties of the respective material batches. Homogeneity is of a particular significance in case when small amounts of the introduced additives (i.e. binding substances – in this case glycerine) are used, which have to be homogenously distributed in the total material volume in order to efficiently influence the composition properties. High mixing degree also means higher stability of the granulates at a given content of the binder. Granulation in the intensive mixer enables to control the grain size distribution, ensures their high density and gives the granulate surface properties which are beneficial for the rheological properties.
Counts Co nts
300 250 200 150 100 50 0
5
12
19
26
2Θ
33
Fig. 4. XRD curves of starch after modification by extrusion.
The mechanical granulation eliminates the typical granulate defects such as, for example, nutshell structure. The ability to granulate follows from the way in which the material moves which is similar to the material stream in the disc pelletizer, the difference lies in the fact that in the intensive mixer the granulation is much faster and facilitated by the mechanical impact of the mixer and the movement of the pan correlated with the direction of the material stream formed by the high-speed rotor. In comparison to the disc or drum pelletizer, granulation in the intensive mixer runs in the whole volume of the processed material and does not require such a complex control [13]. During the tests, starch and glycerin were mixed and granulated in Intensive Mixer Eirich R02 (Fig. 1). Starch and glycerin were mixed in ratio 75 wt.% and 25 wt.%. Mixing parameters: agitator rotations 3000 rpm, pan rotations 120 rpm, mixing time 60 s. Granulation
Table 1 Composition of the analyzed composites and MFR value. Specimens
B1 B2 B3 B4 B5 B6 B7 B8 B9 a b
40
Weight content (%) HDPE
Polybond 3029
TPS
PCL
65 47.5 30 60 42.5 25 55 37.7 20
5 7.5 10 5 7.5 10 5 7.5 10
30 45 60 30 45 60 30 45 60
– – – 5 5 5 10 10 10
Theoretical values for neat thermoplastic matrix without TPS. Experimental values for obtained composition.
Theoreticala MFR190°C/2.16 g/10 min 19.7 14.6 9.4 18.4 13.2 8.1 17.4 12.3 7.1
kg,
Experimentalb MFR190°C/2.16 kg, g/10 min 1.06 1.13 1.20 1.08 1.14 1.22 1.08 1.13 1.21
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2.3. Composites preparation All composites were prepared using a twin screw extruder Leistritz ZSE model 27 HP (Germany). The screw diameter was 27 mm, and a length to diameter ratio was 44 (L/D = 44). Constructions of used plasticizing systems and detailed description of screws are shown in details in [14,15]. The extruder had ten heating and cooling zones. All materials were dosed by Brabender gravimetric screw feeders (Germany) with a constant flow rate. The mass ratio of the components is presented in Table 1. Temperature profile of the extruder was as follows (from feeding section) 110/120/130/140/150/160/160//160/160/160 °C. The screw rotation during the extrusion processes (shear forces acting on the material) was 300 rpm. The obtained thermoplastic composition was injection molded using Arburg type Allrounder 270-210-500 injection-molding
70
PCL
HDPE
PB
60
Heat Flux (mW)
HDPE
50
1st Cooling
40 30
PB PCL
20 10 0 20
40
60
80
100 120 140 160 180
0
Heat Flux (mW)
parameters: first stage of granulation – to build granules: agitator rotations 2100 rpm, pan rotations 120 rpm for 180 s, second stage of granulation – to make granules smooth: agitator rotations 900 rpm, pan rotations 120 rpm for 60 s. During the granulation process, glycerin and the moisture of the starch (8 wt.%) act as binder for starch grains. Additional water was not used. Granulated, glycerine modified native starch is presented on Fig. 2. Obtained granules were extruded with the use of enhanced technological installation based on the (L/D = 44) Leistritz ZSE model 27 HP twin screw extruder equipped with a die with three orifices of circle diameter of 3 mm, BRABENDER gravimetric screw feeders ensuring proportion accuracy of 0.1 by weight% as well as CF SCHEER and CIE SGS 50E granulator. The process parameters for all the mixtures were the same: feeding section – 90 °C, plasticizing section – 140 °C, metering section – 120 °C, screw rotations 200 rpm, output – 18 kg/h.
-10
PCL -20
PB
-30 HDPE
1st Heating 20
40
60
80
100 120 140 160 180
Temperature ( 0 C) Fig. 5. DSC curves of PCL, HDPE, Polybond.
Table 2 Mechanical properties of composite (average ± standard deviation). Specimens Tensile strength (MPa) B1 B2 B3 B4 B5 B6 B7 B8 B9 Modulus of elasticity (MPa) B1 B2 B3 B4 B5 B6 B7 B8 B9 Elongation at break (%) B1 B2 B3 B4 B5 B6 B7 B8 B9
Dry 23.0 ± 0.2 24.9 ± 0.5 27.8 ± 0.2 22.7 ± 0.1 24.3 ± 0.1 27.0 ± 0.5 21.6 ± 0.2 23.9 ± 0.2 24.8 ± 0.5 1181 ± 48 1321 ± 79 1641 ± 119 1114 ± 47 1266 ± 49 1547 ± 38 1065 ± 34 1260 ± 91 1525 ± 56 10.7 ± 2.7 9.4 ± 1.5 8.4 ± 1.9 10.2 ± 1.2 9.5 ± 0.7 4.5 ± 0.5 6.7 ± 0.8 7.2 ± 1.0 3.5 ± 0.2
1 day in water
14 days in water
28 days in water
22.5 ± 0.2 19.5 ± 0.2 12.2 ± 0.2 20.5 ± 0.4 20.4 ± 0.2 9.3 ± 1.4 20.8 ± 0.3 17.2 ± 0.7 8.7 ± 0.2
21.4 ± 0.2 11.4 ± 0.2 8.8 ± 0.3 18.6 ± 0.1 10.7 ± 0.1 7.2 ± 0.2 17.3 ± 0.2 10.2 ± 0.4 6.3 ± 0.4
19.5 ± 0.2 10.6 ± 0.1 8.3 ± 0.1 15.9 ± 0.5 9.9 ± 0.1 6.7 ± 0.2 15.1 ± 0.2 9.1 ± 0.4 6.0 ± 0.4
1113 ± 70 976 ± 32 640 ± 42 1007 ± 52 1085 ± 59 533 ± 53 1071 ± 62 935 ± 73 500 ± 15
1048 ± 42 406 ± 20 299 ± 34 938 ± 15 363 ± 21 245 ± 32 886 ± 43 324 ± 12 205 ± 21
975 ± 44 350 ± 14 257 ± 20 753 ± 42 335 ± 18 193 ± 12 700 ± 29 324 ± 17 176 ± 12
9.8 ± 1.2 7.8 ± 1.6 8.2 ± 1.8 9.8 ± 0.7 7.9 ± 0.6 4.7 ± 1.7 6.2 ± 0.7 5.7 ± 0.8 3.7 ± 0.2
9.1 ± 2.2 13.9 ± 1.5 23.6 ± 12.2 8.5 ± 1.1 29.4 ± 5.8 10.9 ± 2.1 6.7 ± 0.3 19.6 ± 3.3 9.2 ± 1.9
10.8 ± 1.3 22.0 ± 3.1 36.1 ± 14.3 7.8 ± 1.4 40.9 ± 6.8 18.4 ± 2.9 6.1 ± 0.6 10.3 ± 2.1 11.1 ± 2.5
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machine into standard so called dog-bone specimens (ASTM 527) with the cross section of the measurement part equal 40 mm2. The machine is equipped with Priamus (Switzerland) injection process controller. ARBURG Allrounder characteristics: screw diameter: 25 mm, injection pressure – max 1400 bar, clamping force – 500 kN. Sample injection parameters: temperature of the polymer melt – 160 °C ± 2 °C, form temperature – 30 °C ± 1 °C, injection speed – 190 mm/s, cycle period – 60 s, injection pressure – 500 bar, clamping pressure – 350 bar.
Dry B122_0 B122_28 28 days in water
20
10
2nd Cooling
2.4. Composite testing
0 XRD tests of starches were performed by JEOL JDX-7S diffractometer (Japan). The tensile properties have been estimated by determining the elastic modulus, tensile strength and elongation at break. The tests were conducted according to the PN-EN ISO 527 standard, using the Instron tensile testing machine with elongation head and extensometer. The elongation velocity: 1 mm/min (elastic modulus), 50 mm/min (tensile strength and elongation at break). Number of samples: 5 per test. Blue Hill software was used for evaluation of the test results. To estimate the influence of hydrolytic degradation process on the properties of materials, the specimens were placed in water for 1, 14 and 28 days. Thermal characteristics of the blends were determined using a differential scanning calorimeter Mettler-Toledo TGA/DSC 1 (Switzerland). The images of structure were taken from samples after a tensile test using the scanning electron microscope under low vacuum SEM Hitachi 3400 N (Japan).
The increase in the weight content of TPS in the composites caused the slight increase in the MFR. Composition of analyzed composites is presented in Table 1. To better understanding of this pheDry B122_0 28 days in B122_28 water
2nd Heating
-10
-20 20 40 60 80 100 120 140 160 180 200 220 0
Temperature ( C)
Table 3 Melting characteristics and degree of crystallinity of selected samples. Specimens
HDPE Polybond 3029 B1 B2 B3
10
1st Cooling
0 20 40 60 80 100 120 140 160 180 200 220 5 0
0
Fig. 7. DSC curves of specimen B9, after immersion in water for 28 days.
3. Results and discussion
20
20 40 60 80 100 120 140 160 180 200 220
1st Heating
-5 -10 -15 -20 20 40 60 80 100 120 140 160 180 200 220 0
Temperature ( C) Fig. 6. DSC curves of specimen B9.
Melting
Xc (%)
To, (°C)
Tm, (°C)
DHm, (J/g)
123.1 120.7 123.0 122.0 121.3
130.1 128.7 129.2 129.5 128.5
158.8 122.1 99.2 80.0 61.8
54.1 41.6 33.8 27.6 21.1
To – onset temperature of melting, Tm – melting temperature, DHm – melting enthalpy, Xc – degree of crystallinity.
nomenon theoretical values of MFR for neat thermoplastic matrix (without TPS) were determined. Theoretical MFR of thermoplastic matrix were calculated basing on additivity principle and the MFR characteristics of neat substrate (presented in material section). For example, the formula for calculation of MFR of thermoplastic matrix in sample B1 was: 0.65 30 g/10 min (HDPE) + 0.05 4 g/ 10 min (Polybond 3029), resulting 19.7 g/10 min. It was noticed that partial substitution of HDPE by using Polybond 3029 or PCL caused decrease of mass flow rate, due to increasing molecular weight of thermoplastic matrix. As we can see the addition of TPS to thermoplastic matrix influences on significant decrease of its mass flow rate. On the other hand, the increase of TPS content slightly affected the mass flow rate of obtained compositions. This phenomenon may be due to three main factors. Firstly, granulation and extrusion of native starch have an influence on formation of thermoplastic starch (TPS) with amorphous structure, which allows better dispersion of TPS in polyethylene matrix. Secondly, the low value of glass transition temperature of used thermoplastic polymers (HDPE Tg around 120 °C, PCL Tg around 60 °C) caused decrease of glass transition temperature of TPS. This plastification effect of native starch contributes to easier processing of obtained
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TPS
Fig. 8. SEM image of fracture of specimen B3.
composite. Moreover, different viscosity of used substrate affected on its mixing efficiency, which has significant influence on thermo-mechanical degradation of materials obtained during processing in co-rotating twin screw extruder. To estimate the rate of native starch modification during extrusion with glycerin the XRD analysis was done (Figs. 3 and 4).
315
The analysis of diffraction patterns of starch used in the studies revealed that, during the extrusion process in the presence of glycerine and water as plasticizers, native starches have been deprived of a part of the crystal structure and the obtained thermoplastic starch (TPS) has amorphous structure. Peaks of semi crystalline phase of native starch (Fig. 3) after extrusion disappeared, (Fig. 4) and we can observe wide, fuzzy curves typical for amorphous material. The changes of basic mechanical properties of dry specimens and after immersion in water are presented In Table 2. In case of dry composites an increase in TPS content caused an increase in tensile strength and modulus of elasticity similar like in case of use of other natural filler like for example natural fibers [1,16–20]. Tensile strength and modulus of elasticity of specimens decreased for those with 5 and 10 wt.% PCL content, respectively. In the literature the tensile strength of PE/TPS/PCL films increased with PCL content, for injection molded specimens tensile strength increases also with PCL content but starts to increase from 50 wt.% of PCL in PE/TPS/PCL [6]. Adding of TPS and PCL caused decrease of the elongation at break. The effect of polycaprolactone addition in amount of 5 and 10 wt.% on the mechanical properties of PE/TPS/ PCL materials was not satisfied. Mechanical properties of specimens with 30 wt.% of TPS changed insignificantly after immersion in water. Mechanical properties of biopolymers filled with 45 and 60 wt.% of TPS decreased under influence of water, and this effect is stronger with time of incubation in water. Water acted as a plasticizer especially for biopolymers
Fig. 9. Schematic reaction between HDPE, PE-g-MA and TPS [24].
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filled with 45 and 60 wt.% of TPS where the value of elongation at break increased after immersion in water. Thermal analysis results of PCL, HDPE, Polybond (Fig. 5) and specimen B9 are presented on Fig. 6 and specimen B9, after immersion in water for 28 days (Fig. 7). DSC curves are presented only for samples with the highest content of TPS and PCL. For all DSC curves of PE/TPS/PCL an endothermic peak is observed around 60 °C and 135–140 °C. The enthalpy associated with those peaks depends on the PCL and HDPE content and allows us to attribute this to the melting of PCL and HDPE. The melt temperature and enthalpy of PCL and HDPE in the blends change with increased amount of TPS, due to increased level of amorphous phase in blend. Similar situation is also on the exothermic curves of crystallization. For test samples part of the crystalline phase was calculated with use of following equation [21]:
v¼
DH m 100% DH c
where: v – degree of crystallinity, %; DHm – melting enthalpy, J/g; DHc – melting enthalpy at 100% crystallinity, J/g. For calculation heat of fusion of PE at 100% crystallinity, 293.6 J/ g [22], was used. In Table 3 the melting characteristics and the degree of crystallinity of selected samples are presented. HDPE has higher degree of crystallinity than Polybond 3029, possessing grafted maleic anhydride groups on polyethylene chains. Similar observation was described in work [23]. Lowering of HDPE content in the blend by using higher amount of Polybond 3029 and TPS caused decrease of onset temperature of melting, enthalpy and degree of crystallinity. Fig. 8 shows the morphology of specimen B3. On the fractured surface, after the elongation test, we can observe TPS in the droplet-like form. TPS particles are very well dispersed in the compatibilized HDPE matrix. We can observe that some particles of TPS are pulled out from the matrix, but most of them are still tightly linked to the matrix. It is an effect of developed surface of TPS and good adhesion caused by use of PE-g-MA as a compatibilizer. Fig. 9 shows schematic reaction during the reactive blending of HDPE, PE-g-MA and TPS. Also homogeneous distribution of TPS is a reason for increased strength of material with TPS content. Obtained results confirm that native starch after modification in continuous process has amorphous structure and can be successfully used as renewable bio-filler for thermoplastic matrix. Tensile properties of obtained partially biodegradable composites are dependent mainly on TPS and PCL content. Increased amount of TPS causes improvement of mechanical properties of TPS/PE blends. On the other hand, addition of PCL to TPS/PE blends influences on deterioration of their mechanical properties. The values of mechanical properties after hydrolytic degradation confirm that biodegradability of obtained blends is strongly connected with TPS content. 4. Conclusion This study shows that native starch can be easily granulated with the use of an intensive mixer. During the granulation process, added glycerin and water (present in starch) act as a binder, then during extrusion of starch glycerin and water act as plastifying agents. Granulated starch has a higher bulk density compared to powder. Dense granules are easier for the storage and dosage compared to powders, which is important from a technological point of view. Increase of flowability properties of granulated starch (compare to non-granulated powder) and elimination of dust was very helpful during dosing into extruder feed zone. Reactive extrusion of native starch with the presence of a plastifying agent is the only way to obtain amorphous homogeneous
material in continuous process. The fine and uniform dispersion of the TPS in the PE matrix is not only the result of the use of a co-rotating twin screw extruder (intensive mixing) but also the result of using the PE-g-MA copolymer as a compatibilizer. Depending on the amount of starch we can obtain the nonbiodegradable material or partially biodegradable material. Thanks to the use of starch we can reduce the use of crude oil and increase the use of renewable resources for polymer composite production. Further investigations on that field should be focused on optimization of granulation process, starch modification with use of other plastifying agents, modification of obtained blends by filling with natural fillers like wood flour or natural fibers, searching for new methods of compatibilization. Acknowledgment This work was supported by the POIG Project No. 01.01.02-10123/09-00. References [1] Korol J. Polyethylene matrix composites reinforced with keratin fibers obtained from waste chicken feathers. J Biobased Mater Bioenergy 2012;6(4):355–60. [2] Gasper M, Benko Z, Dogossy G, Reczey K, Czigany T. Reducing water absorption in compostable starch-based plastics. Polym Degrad Stab 2005;90(3):563–9. [3] Czaplicka-Kolarz K, Burchart-Korol D, Korol J. Environmental assessment of biocomposites based on LCA. Polimery 2013;58(6):476–81. [4] Czaplicka-Kolarz K, Burchart-Korol D, Korol J. Application of life cycle assessment and exergy to environmental evaluation of selected polymers. Polimery 2013;58(7–8):605–9. [5] Bajer K, Richert A, Bajer D, Korol J. Biodegradation of plastified starch obtained by corotation twin screw extrusion. Polym Eng Sci 2012;52(12):2537–42. [6] Matzinos P, Tserki V, Gianikouris C, Pavlidou E, Panayiotou C. Processing and characterization of LDPE/starch/PCL blends. Eur Polym J 2002;38(9):1713–20. [7] Koenig MF, Huang SJ. Biodegradable blends and composites of polycaprolactone and starch derivatives. Polymer 1995;36(9):1877–82. [8] Mahieu A, Terrié C, Agoulon A, Leblanc N, Youssef B. Thermoplastic starch and poly(e-caprolactone) blends: morphology and mechanical properties as a function of relative humidity. J Polym Res 2013;20(229):1–13. [9] Liua Hongsheng, Xiea Fengwei, Yua Long, Chena Ling, Lia Lin. Thermal processing of starch-based polymers. Prog Polym Sci 2009;34(12):1348–68. [10] Xiea Fengwei, Yua Long, Sua Bing, Liua Peng, Wanga Jun, Liua Hongshen, et al. Rheological properties of starches with different amylose/amylopectin ratios. J Cereal Sci 2009;49(3):371–7. [11] Bajer K, Kaczmarek H. Methods of biodegradation study of polymeric materials. Polimery 2007;52(1):13–8. [12] Averous L, Moroa L, Doleb P, Fringantcet C. Properties of thermoplastic blends: starch–polycaprolactone. Polymer 2000;41:4157–67. [13] Burchart-Korol D, Korol J, Francik P. Application of the new mixing and granulation technology of raw materials for iron ore sintering process. Metalurgija 2012;51(2):187–90. [14] Korol J, Lenza J, Burchart-Korol D, Bajer K. Extrusion and testing the changes of recyclate LDPE properties. Przem Chem 2012;91(11):2196–201. [15] Formela K, Korol J, Cysewska M, Haponiuk JT. Przem Chem 2013;92(4):512–7. [16] Koziol M, Bogdan-Wlodek A, Myalski J, Wieczorek J. Influence of wet chemistry treatment on the mechanical performance of natural fibres. Pol J Chem Technol 2011;13(40):21–7. [17] Koziol M, Wieczorek J, Bogdan-Włodek A, Myalski J. Evaluation of jute fiber preforms absorbability using optical profilographometer. J Compos Mater 2013;47(19):2309–19. [18] Zimniewska M, Myalski J, Kozioł M, Man´kowski J, Bogacz E. Natural fiber textile structures suitable for composite materials. J Nat Fibers 2012;9(4):229–39. [19] Kozłowski R, Władyka-Przybylak M, Bujnowicz K, Latest achievements in the area of composites reinforced with natural fiber. In: Proceedings of fiber reinforced composites 2007, 9–12 December, Port Elizabeth; 2007. [20] Kuciel S, Liber-Knec´ A, Zajchowski S. Biocomposites based on thermoplastic starch or polylactide/starch blends as the matrices filled with natural fibers. Polimery 2009;54(10):667–73. [21] Przygocki W. Metody fizyczne badan´ polimerów. Warszawa: Polish Scientific Publishers PWN; 1990. [22] Wunderlich B, Dole M. Specific heat of synthetic high polymers. VIII. Low pressure polyethylenes. J Polym Sci 1957;24(106):201–13. [23] Roy D, Simon GP, Forsyth M. Blends of maleic-anhydride-grafted polyethylene with polyethylene for improved cathodic disbondment performance. Polym Int 2001;50(10):1115–23. [24] Kahar AWM, Ismail H, Othman N. Effects of polyethylene-grafted maleic anhydride as a compatibilizer on the morphology and tensile properties of (thermoplastic tapioca starch)/(high-density polyethylene)/(natural rubber) blends. J Vinyl Addit Technol 2012;18(1):65–70.