- Email: [email protected]
CSM
Composites: Part B 45 (2013) 178–184
Contents lists available at SciVerse ScienceDirect
Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Composites based on waste rubber powder and rubber blends: BR/CSM Gordana Markovic´ a,⇑, Olivera Veljkovic´ a, Milena Marinovic´-Cincovic´ b, Vojislav Jovanovic´ c, Suzana Samarzˇija-Jovanovic´ c, Jaroslava Budinski-Simendic´ d a
Tigar, Nikole Pašic´a 213, 18300 Pirot, Serbia University of Belgrade, Institute of Nuclear Science Vincˇa, Mike Petrovic´a Alasa 12-14, 11000 Belgrade, Serbia c Faculty of Natural Science and Mathematics, University of Priština, Lole Ribara 29, 38220 Kosovska Mitrovica, Serbia d University of Novi Sad, Faculty of Technology, Bulevar cara Lazara 1, 21000 Novi Sad, Serbia b
a r t i c l e
i n f o
Article history: Received 22 January 2012 Received in revised form 8 June 2012 Accepted 25 August 2012 Available online 8 September 2012 Keywords: A. Hybrid D. Thermal analysis D. Mechanical testing E. Strength
a b s t r a c t Blend of polybutadiene (BR) rubber with varying ratios of chlorosulphonated polyethylene rubber (CSM), BR/CSM, keeping the total waste rubber powder (WRP) content constant at 50 phr (parts per 100 rubber) have been prepared on a laboratory-size (300 600 mm) two-roll mixing mill maintained at 40 ± 5 °C. The mechanical properties, namely tensile strength (TS), tensile modulus at 100% elongation (M100), elongation at break (Eb%) and hardness have been followed up as a function of irradiation dose (dose rate of 10 kGy h1 and total absorbed dose of 100, 200, 300 and 400 kGy) as well as blend composition. The results indicated that the addition of CSM has improved the properties of BR/CSM rubber blends waste rubber powder filled composites. The improvement in mechanical properties of the BR/CSM/WRP (50/ 50/50) rubber blends is in correlation with homogenous WRP distribution which has been assigned by scanning electron microscopy. Also BR/CSM rubber blends waste rubber powder filled composites are thermally and irradiation more stable than BR and CSM rubbers alone. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction The production of rubber materials rises every year. Considering the economic and environmental advantages, recycling is one of the best options. A number of possible applications of various forms of waste rubber in broad disciplines have been studied and reported [1]. Recycled rubber can be generalized as any rubber waste that has been converted to an economically useful form, such as reclaimed rubber, ground rubber or reprocessed synthetic rubber. The manufacturing of powdered rubber has obvious economic and social benefits, as it decreases the cost of the product by blending fine powdered rubber with raw rubber [2]. Polymer blends play an important role in the modern polymer industry not only for development of new materials but also for practical recycling purposes. Most polymer blends are incompatible, and a final performance of a polymer blend is determined by the polymer compatibility by and the phase morphology [3,4]. Polybutadiene is an elastomer commonly used in the tire industry [5], passenger and truck tires represent 73% of the U.S. consumption of this synthetic elastomer. Such applications involve large temperature variations, and we can easily conceive situations ⇑ Corresponding author. E-mail addresses: [email protected] (G. Markovic´), olivera. [email protected] (O. Veljkovic´), [email protected] (M. Marinovic´-Cincovic´), [email protected] (V. Jovanovic´), [email protected] (S. SamarzˇijaJovanovic´), [email protected] (J. Budinski-Simendic´). 1359-8368/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compositesb.2012.08.013
were the polymer would be used within its property transition region. Therefore analytically relating the microstructure of the elastomer to the mechanical performance of the system would be a powerful tool for the virtual design of polymer based systems (including composites). Various grades (molecular weights) of polybutadiene are commercially available [6]. The introduction of chlorine and sulfur dioxide onto the polyethylene linking via condenzation or substitution reactions molecule destroys the crystallinity, thereby changing the thermoplastic material into an amorphous polymer, commercially known as chlorosulphonated polyethylene (CSM), which contains 25–43% by weight of chlorine and 1–1.5% by weight of sulfur as SO2Cl units. Thus, CSM rubber is highly reactive, and reactivity is due to the SO2Cl groups [7]. Different types of additives used in processing of rubber into products include a vulcanizing agent’s accelerator, an activator, antidegradants, fillers, a softener, thickeners, a gel sensitizer, a colorant, etc. Fillers modify physical and, to some extent, chemical properties of vulcanizates. Rubber waste is usually generated during the manufacturing process of product of these industries and by disposal of post-consumer (retired) products mainly including scrap tires [8,9]. Thermal stability means the ability of a material to maintain the required properties such as strength, toughness, or elasticity at a given temperature [10]. A detailed understanding of how polymers break down on heating is important in the design of elastomeric materials with improved properties for particular
G. Markovic´ et al. / Composites: Part B 45 (2013) 178–184
application. Markovic et al. [11], made the wood flour filled polyisoprene/chlorosulphonated polyethylene rubber blends. The elastomeric composite has excellent compatibility between two rubbers of different polarity when properly compounded and processed [12]. Maurizio et al. [13] prepared rubber–clay nanocomposites based on nitrile rubber using conventional two-roll mill mixing technique. They found that adding organoclay in NBR elastomer greatly improves material thermal stability and aging performance in different medium at elevated temperature. Pruneda et al. [14] studied the thermal characterization of nitrile butadiene rubber (NBR)/PVC blends. Excellent reports on the ageing characteristics of rubbery systems exist. For example, Sulekha et al. [15] studied the polyisobutylene bound paraphenylene diamine antioxidant in natural rubber. Nair and co-workers studied effects of heat, ozone, gamma radiation and water on ethylene propylene diene monomer rubber/styrene butadiene rubber blends [16]. Thermal, ozone and gamma ageing of styrene butadiene rubber and poly(ethylene-co-vinyl acetate) blends has been studied by Radhakrishnan et al. [17]. The mechanism of characteristic changes in gamma ray irradiated polymers, including degradation and crosslinking has been studied [18]. The aim of the present work is to study the thermal and gamma irradiation resistance of composites based on waste rubber powder filled BR/CSM rubber blends with special reference to the effects of blend ratio. Also, swelling and chemical stability of these composites were investigated.
179
Table 2 Basic formulation used for BR/CSM waste rubber powder filled rubber blends composites.
a b c
Ingredients (phr)
1
2
3
4
5
Polybutadiene rubber (BR) Chlorosulphonated polyethylene rubber (CSM) Stearic acid Zinc oxide Waste rubber powdera Magnesium oxide TMTDb CZc Sulfur
100 / 2.0 5.0 50 2.0 0.8 1.0 2.0
75 25 2.0 5.0 50 2.0 0.8 1.0 2.0
50 50 2.0 5.0 50 2.0 0.8 1.0 2.0
25 75 2.0 5.0 50 2.0 0.8 1.0 2.0
0 100 2.0 5.0 50 2.0 0.8 1.0 2.0
Waste rubber powder (particle size 250–500 lm). Tetramethylthiuram disulfide. N-cyclohexyl-2-benzothiazyl sulphenamide.
The rubber mixes were compression molded at 160 ± 2 °C, using an electrically heated hydraulic press at their optimum cure time derived from rheological measurements. The applied hydraulic force during vulcanization attained 6.7 MPa. Dumbbell shaped tensile strength was punched from the compression molded sheet along the mill grain direction using C-type dumbbell specimens, according to ASTM D-412. The waste rubber powder (WRP) (particle size 250–500 lm) was supplied by Watas holding Sdn Vhd Panang Malaysia). 2.3. Cure characteristics
2. Materials and methods
The cure characteristics of rubber compounds were carried out using an Oscillating Disc Rheometer (ODR) model 4308 from Zwick, Germany.
2.1. Materials
Mc90 ¼ ðM h M l Þ 0:9 þ M l
The basic characteristics of materials used in this work are given in Table 1. The rubber chemicals also used such as plasticizer, sulfur, magnesium oxide, zinc oxide; stearic acid, tetramethylthiuram disulphide TMTD, ethylene thiourea ETU, 2-mercaptobenzthiazol (MBT), dibenzothiazyl disulphide MBTS, N-cyclohexyl-1,2-benzothiazyl sulphenamide (CBS) were of commercial grade.
ð1Þ
The measured parameters are: Ml – minimum torque, Mh – maximum torque, ts2 – time to 2 units of torque increase above minimum, Mc90 – torque at 90% of full torque development. The cure rate is:
CRI ¼
1 100 t c90 t s2
ð2Þ
These measurements were accomplished according to ASTM D2084.
2.2. Mixing procedure The rubber compounds with different blend ratios were prepared on a two roll mixing mill having a friction ratio of 1:1.4. The compounding recipes of the blends are given in Table 2. Mixing of BR with CSM rubber mixtures were carried out on a laboratory open two roll mill (400 mm diameters and 600 mm working length). The gear friction of the mill is 1:1.4. The hollow rolls were cooled by using flushing water in order to regulate the temperature not exceeding 60 °C during the different stages of mixing according to ASTM D-15-627. The rubber mixes obtained were sheeted and left for a period of at least 6 h before testing. The addition of ingredients during mixing was carried following the same order and conditions of mixing.
2.4. Mechanical testing The tensile properties were determined using the tensile testing machine type Zwick 1445 according to ASTM D-412. The average value of the mechanical properties was calculated using at least three samples. A cross head speed of 50 mm/min was used and the tests were performed at 25 °C. 2.5. Hardness measurements Samples of at least 0.12 mm in thickness with flat surface were cut for hardness test. The measurement was carried out according
Table 1 Details of materials. Materials
Characteristics
Polybutadiene rubber (BR), Buna CIS 132,
Mooney viscosity ML1+4 (100 °C) Cis-1,4 content (%) Density (g/cm3) Chloride content (%) Mooney viscosity ML1+4 (100 °C) Density (g/cm3) 250–500 lm
Chlorosulphonated polyethylene rubber CSM Hypalon 40S
Waste rubber powder (WRP)
Source 45 95 0.91
Dow, Germany
Goodrich chemical Co. Du Pont USA 46 ± 5 1.18 Watas holding Sdn Vhd Panang Malaysia
G. Markovic´ et al. / Composites: Part B 45 (2013) 178–184
180
The measurements were made at a heating rate 10 °C min1, at a temperature range 0–800 °C, using Perkin Elmer TGS-2 Thermogravimetric system. The experiments were done in nitrogen atmosphere. About 5–8 mg of the sample was used for the analysis.
and silica. Thus in the presence of WRP the formation of additional crosslinks is possible and consequently an increase in CSM loading will reduce the flow and slightly increase the torque. In BR/CSM rubber blend, cure rate index (CRI) is decrease with CSM content is increase might be due to the lower viscosity of BR compared to CSM. The lower viscosity components lead to form a continuous phase [19] in blends, which is more or less, governs the curing process. However, all blend ratio in the BR/CSM blend exhibits lower curing index according to the activation [20] of the adjacent double bond by the CACl group. It is also evident from the table that the ts2 of BR is longer than for CSM. This is due to the activation of double bond that causes an over all increase in the rate of cross-linking of the blends. More activated precursors to crosslink [21,22] are formed as a result of the activation of double bond. These activated precursors will accelerate the vulcanization between BR and CSM phases that induce faster interphase crosslinking between these molecules. The increased scorch time, indicating higher scorch safety of the rubber blends.
2.8. Swelling measurements
3.2. Mechanical properties
The swelling degree was determined on the basis of equilibrium solvent–swelling measurements in toluene. The samples were submerged in the solvent and after the swelling equilibrium was reached, that means, no change in the weight of the swollen sample was observed, the mass of solvent was determined according to the ASTM D 471. The results were expressed as the mass of solvent absorbed per gram of blend. The solvent used for chemical absorption study included toluene. The percentage of absorption was calculated using the following equation:
In the blends a positive deviation of tensile strength, modulus and hardness is observed, suggesting that synergism has occurs. The maximum of tensile strength, modulus and hardness properties is obtained at 50 phr CSM for BR/CSM/WRP rubber blends. Due to the strain induced crystallization behavior of both rubbers [23], the rubbers reinforced each other when subjected to tensile elongation which is reflected by the higher tensile modulus obtained in the blend. It is generally observed that mechanical properties of blend are closely related to its compatibility and synergistic effect is often obtained with miscible or partially compatible blends [24]. BR/CSM rubber blend were found to be compatible, hence the partial compatibility might be due to the interaction of nonpolar phase of BR and polar phase of CSM phase occurs with the strain induced crystallization of BR rubbers. Gamma irradiation is a powerful means for crosslink elastomers, however, exposure to higher dosage of it degrades the polymer. The extent of crosslinking and degradation undergone by a polymer depends on its structural characteristics and the presence of initiators/sensitizers [25]. The effects of irradiation aging on 50 phr WRP containing BR/CSM rubber blends composites and three different radiation doses of the magnitude 100, 200 and 400 kGy on tensile strength, modulus, hardness and elongation at break are observed. The incorporation of WRP particles in the polymer blend under consideration leads to composites with enhanced properties. This enhancement might be due to the additional effect of unreacted curatives in powdered rubber. These interactions may influence to better physical properties, higher irradiation resistance and low costs of rubber product are obtained. Fig. 1 shows the effect of blend composition and gamma irradiation dosages on tensile strength (TS) values for the BR/CSM waste rubber powder filled rubber blends composites. It can be seen that the TS values for all compositions increase with increasing irradiation dose reaching its maximum value at 200 kGy and then decrease for doses higher than that. As shown, the tensile strength has been found to be increased with increase in CSM content up to 50 phr and after that decrease. It may be observed also that vulcanized BR/CSM/WRP has attained higher TS values over the whole range of irradiation up to 200 kGy, than unirradiated composites. The TS values attained by vulcanized blends lie between these two extremes and decreases after 50 phr of CSM content systematically for blend. On irradiation of polymeric materials such as rubbers for example, radiation induced crosslinking and degradation processes take place simultaneously but with different rates. Accordingly, the data obtained indicate that the crosslinking
to ASTM D 2240 using durometer of model 306L type. The unit of hardness is expressed in (Shore A). 2.6. Gamma irradiation Irradiations have been performed in air in the Co-60 radiation sterilization unit with the dose rate of 10 kGy h1 and total absorbed dose of 100, 200, and 400 kGy. Radiation dose of 400 kGy can be considered as the relatively big dose which many times exceeds the doses for degradation of radiation degradable polymers and is also above the typical doses used in practice for radiation modification of polymer based products. 2.7. Thermo gravimetric analysis
Q¼
mt m0 100 m0
ð3Þ
where mt is the mass of sample at time t and m0 is the dry weight of the sample. 2.9. Scanning electron microscopy The scanning electron microscopy images of the rubber blends fractured surfaces were taken by a JEOL JSM-5400 model of the microscope. The samples were sputter coated with gold for 3 min under high vacuum with image magnifications of 7500. 3. Results and discussion 3.1. Cure characteristics The cure characteristics: the torque evolution, the scorch time ts2, optimum cure time tc90 and the cure rate index (CRI) of waste rubber powder (WRP) filled BR/CSM rubber blends are shown in Table 3. It can be seen that the values for Ml and Mh increases with the CSM loading is increase in the rubber compounds. In general WRP is unreinforcing filler and has a particle size larger than CB
Table 3 The cure characteristics of waste rubber powder (WRP) filled BR/CSM rubber blends. Cure characteristics
1
2
3
4
5
Ml (dNm) Mh (dNm) DM (dNm) ts2 (min) tc90 (min) CRI (min1)
2 36 34 6 28 4.5
2 32 30 2 7 20
2 32 30 2 6 25
3 33 30 5 12 14.3
2 32 30 10 27 5.9
G. Markovic´ et al. / Composites: Part B 45 (2013) 178–184
Fig. 1. Variation of tensile strength as a function of blend compositions and irradiation dose for rubber waste powder filled (WRP) BR/CSM rubber blends composites. The error bars represent one standard deviation.
process was the dominating one for doses up to 200 kGy whereas the degradation process has apparently prevailed for doses higher than 200 kGy. One cannot, however, exclude the impairment of chain orientation of rubber macromolecules due to increased extent of induced crosslinking at a higher dose and hence its eventual contribution in decreasing the TS values for doses higher than 200 kGy. BR in its raw form represents an amorphous and homogenous polymeric material and hence the bulk mechanical properties of the radiation-vulcanized product may be fairly anticipated on the basis of its intrinsic chemical structure and irradiation conditions. Hence, self-reinforcement does not take place at high extensions, as in case of BR and no contribution to its tensile strength would be expected. Based on its chemical structure, the tertiary substituted carbon atom on the main macromolecules chain represents the most susceptible carbon atoms and on irradiation breakage of this bond takes place favorably leading to the formation of the hydrogen atoms and chloride radical. When it happened that such radicals stand favorably to each other then they may react with each other with the result of formation of a covalent bond, i.e., crosslink between two adjacent macromolecules. Under such circumstances a limited crosslinking density would be expected which accounts for the relatively low value of TS attained by vulcanized raw BR/CSMWRP composites. Fig. 2 shows the variation of tensile modulus at 100% elongation (M100) as a function of irradiation dose and blend compositions. It can be seen that the M100 of all samples increases with increasing the irradiation dose, whereby BR/CSM/WRP rubber blends composites has attained higher value than CSM rubber alone. The M100 value increase with content of CSM rubber increase up to 50 phr and it decreases after 50 phr of CSM content in blends. These data indicate that BR vulcanizates have attained the relatively highest retroactive force, i.e., resistance to strain deformation or stretching. Isolated double bonds in BR rubber inhibited the formation of intra-molecular links thus resulting in the increase of the crosslinking rate, which results in a substantial increase in tensile modulus. Variation of elongation at break (Eb%) as a function of blend compositions and irradiation dose for rubber waste powder filled (WRP) BR/CSM rubber blends composites is illustrated in Fig. 3. It can be seen that the value of Eb for all samples decreases with increasing the irradiation dose, but increase with CSM loading. This can be attributed to the amorphous and crystalline nature of BR, respectively and this trend may be attributed to the rigid BR/ CSM interface upon increasing content of CSM.
181
Fig. 2. Variation of modulus at 100% elongation (M100) as a function of blend compositions and irradiation dose for rubber waste powder filled (WRP) BR/CSM rubber blends composites. The error bars represent one standard deviation.
Fig. 3. Variation of elongation at break (Eb%) as a function of blend compositions and irradiation dose for rubber waste powder filled (WRP) BR/CSM rubber blends composites. The error bars represent one standard deviation.
3.3. Hardness Shore A Fig. 4 shows variation of hardness as a function of blend compositions and irradiation dose for waste rubber powder (RWP) BR/ CSM rubber blends composites. The hardness of the rubber blends decrease with increasing the CSM rubber content, but increase with irradiation doses loading. A higher amount CSM would result in an increased hardness of the vulcanizates [26]. It is well known that during irradiation several detrimental processes take place, such as main chain scission, crosslink formation and crosslink breakage. It is also possible that the existing crosslink’s may break and a more stable type of crosslink can be formed. The relative ratios and magnitudes of such reactions will govern to what extent each property is changed. In composites, in addition to the various reactions described above, bonded resin formation also takes place during irradiation. All these reactions influence the changes in the performance of the composites. The increased scorch time, indicating higher scorch safety of the rubber blends. The BR/CSM/WRP rubber blend has attained higher
182
G. Markovic´ et al. / Composites: Part B 45 (2013) 178–184
Fig. 4. Variation of hardness as a function of blend compositions and irradiation dose for rubber waste powder filled (WRP) NR/CSM and BR/CSM rubber blends composites. The error bars represent one standard deviation.
TS values over the whole range of irradiation. Higher scorch safety of the rubber blends results in better mechanical properties. 3.4. Thermo gravimetric analysis The thermal stability of the BR/CSM rubber blend waste rubber powder as a function of blend compositions and irradiation dose was investigated using thermo-gravimetric analysis. Fig. 5a and b shows TG and DTG curve of BR/CSM/WRP rubber blends as a function of blend composition. Fig. 6a and b shows TGA and DTG curve of BR/CSM/WRP (50/50/50) rubber blends as a function of irradiation doses. Table 4 shows detailed summary variation of 0.5% weight loss (T0.5), 10% weight loss (T10) and 30% weight loss (T30) the final decomposition temperature of BR/CSM/WRP (50/50/50) rubber blend composites irradiated at 100, 200 and 400 kGy. Two regions of BR/CSM/WRP rubber blends degradation are observed. The degradation started at 380 °C and was completed at 490 °C. The former stage of degradation is due to the elimination of chlorine from the CSM chain and the later stage is due to the main chain scission. The total mass loss observed at 695 °C was 86.21%. It has been reported that the thermal stability of one type of polymer can be improved by the incorporation of a second polymer. In the case of BR/CSM/WRP rubber blends, the degradation starts at a higher temperature than that for BR and CSM rubber alone. T0.5 indicates the initial thermal stability whereas T10 and T30 show the higher degradation rate of the polymer blends composites. As shown in Fig. 5, the incorporation of the CSM resulted in all samples improvement of thermal stability. Ash residue content increased with higher CSM loading. According to [27], the higher content of ash residue in degradation process depends on the initial CSM plus added experimentally. The thermal stability of polymer composites increase with gamma irradiation increase by up to 200 kGy after that it decreases (Fig. 6 and Table 4). Radiation can produce crosslink like those obtained by sulfur curing, but the net effect is not identical. The crosslink between polymer matrix and WRP is formed and increase as gamma irradiation dose is increase. The above mentioned results could be explained in the scope of the molecular structure of the polymeric matrix, which is directly related to its thermal stability. The decrement in the thermal stability of BR/CSM/WRP (50/50/50) rubber blend composites by
Fig. 5. TG (a) and DTG (b) curve of BR/CSM rubber blend waste rubber composites at different CSM loading.
exposure to irradiation dose at 400 kGy is presumably due to some random degradation of polymer chains, which leads to the reduction of its stability. On the other hand, the increase in the thermal stability of polymer matrix with CSM rubber increase is may be due to the increase in the compatibility between polymer phases due to the increased magnitude of interface linking, which made the composite of higher homogeneity, and as a result its stability increases. The results show positive synergistic effect of radiation and the incorporation of CSM on the thermal stability of its composite, i.e., the incorporation of CSM increases the stability of the composite and the use of gamma radiation up to 200 kGy magnifies such stability. Therefore, the incorporation of CSM into the composite plays an important role for improving its thermal stability. This is because the compatibility between rubbers provides strength to the composites. 3.5. Swelling properties Fig. 7 shows the effect of blend compositions on the swelling degree of BR/CSM/WRP rubber blends composites. CSM rubber has excellent resistance to most chemicals and this explains why percentage of swelling of WRP filled BR/CSM rubber blend matrix is low. When more than 50 phr of CSM was used, the percentage of swelling reduced which might be due to the penetration hindrance of toluene into BR/CSM blends [28,29]. Fig. 8 illustrates the variation of swelling degree as a function of irradiation dose of BR/CSM/WRP (50/50/50) rubber blends composites. The swelling degree values for un-irradiated as well as corresponding irradiated ones are also given in the same figure for sake
G. Markovic´ et al. / Composites: Part B 45 (2013) 178–184
183
Fig. 7. The effect of blend compositions on the swelling degree of BR/CSM/WRP (50/ 50/50) rubber blends composites. The error bars represent one standard deviation.
Fig. 6. TG (a) and DTG (b) curves of BR/CSM (50/50/50) rubber blends waste rubber powder composites at different irradiation dose.
Table 4 The temperature values of BR/CSM (50/50) rubber blends composites containing 50 phr waste rubber powder for selected mass loss (0.5%, 10% and 30%). BR/CSM/WRP (50/50/50) (kGy)
DTG peak (°C)
Mass loss (%)
Total mass loss (%)
T0.5% (°C)
T10% (°C)
T30% (°C)
0 100 200 400
420.1 440.5 470.2 450.3
20.5 29.6 37.2 36.2
65.2 76.8 40.8 45.2
118.4 120.1 129.8 70.7
300.1 310.9 314.8 280.3
400.9 412.5 423.1 395.6
Fig. 8. Variation of swelling degree (%) as a function of irradiation dose for the BR/ CSM/WRP (50/50/50) rubber blends composites. The error bars represent one standard deviation.
of comparison. It can be seen that these un-irradiated composite have attained comparatively high swelling degree values. On the other hand, the swelling degree values attained decreased with irradiation dose at 200 kGy and then they increased over any further increase in dose until 400 kGy. These data indicate clearly that the irradiated composites possess better resistance to be swelled by toluene until reach 200 kGy by means crosslinking occur at low doses then degradation may then predominate with respect to BR/CSM/WRP (50/50/50) rubber blends composite. 3.6. Morphological study In Fig. 9, the SEM micrograph of BR/CSM/WRP (50/50/50) rubber blends composites at 7500 magnification is shown. The micrograph of BR/CSM/WRP (50/50/50) rubber blends composites
Fig. 9. SEM photograph of BR/CSM/WRP (50/50/50) rubber blends composites.
184
G. Markovic´ et al. / Composites: Part B 45 (2013) 178–184
exhibits that the composite’s surface is smooth with homogeneous WRP distribution. This type of failure indicates the higher mechanical properties and a strong interaction between BR and CSM rubbers. 4. Conclusions In this study mechanical, thermal and gamma irradiation resistance of BR/CSM rubber blends waste rubber powder (WRP) composites with special reference to the effects of blend ratio was studied. WRP as alternative filler can be further exploited by controlling the particle size dispersion and also its surface functionality. The values of ts2, tc90 and curing rate of blends increase with increasing CSM content. The torque difference, DM = Mh Ml (max. torque – min. torque), as relate to the cross-link density, is equal in all BR/CSM/WRP rubber blend. The increased scorch time, indicating higher scorch safety of the rubber blends. The BR/CSM/ WRP rubber blend has attained higher TS values over the whole range of irradiation. Higher scorch safety of the rubber blends results in better mechanical properties. The crosslinking process was the dominating one for doses up to 200 kGy whereas the degradation process has apparently prevailed for doses higher than 200 kGy. Positive deviation of tensile strength, modulus at 100% elongation and hardness are indicated that the synergism occurred in BR/CSM blends. The value of elongation at break for all samples decreases with increasing the irradiation dose, but increase with CSM loading. The improvement in mechanical properties of the BR/CSM/WRP (50/50/50) rubber blends is in correlation with homogenous WRP distribution which has been assigned by scanning electron microscopy. The temperature at 0.5% weight loss (T0.5), at 10% weight loss (T10) and at 30% weight loss (T30) obtained from TG curves increase with CSM content increases. Also, thermal stability increases with gamma irradiation dose increase up to 200 kGy, and after that decreases. The quality of waste rubber powder product from the sanding process (polishing) of rubber ball and artificial eggs is variable, i.e., % of filler in WRP is variable. As a result of this, % of final mass loss of BR/CSM/WRP is variable. The swelling and chemical stability of these composites were investigated. When more than 50 phr of CSM was used, the percentage of swelling reduced which might be due to the penetration hindrance of toluene into BR/CSM/WRP rubber blends. Irradiated composites possess better resistance to be swelled by toluene until reach 200 kGy by means crosslinking occur at low doses then degradation. The tendency towards scorchiness in compounds containing powdered rubber waste may be due to additional effect of unreacted curatives in powdered rubber. Also, the source of the waste will affect final compound and vulcanizate properties. It has been suggested that the little interfacial bonding between the powdered rubber waste and the virgin matrix elastomer may be responsible for the reduction of properties when rubber waste was incorporated. Acknowledgement Financial support for this study was granted by the Ministry of Science and Technological Development of the Republic of Serbia (Project Numbers 45022 and 45020). References [1] Baeta DA, Zattera JA, Oliveira MG, Oliveira PJ. The use of styrene–butadiene rubber waste as potential filler in nitrile rubber: order of addition and size of waste particles. Braz J Chem Eng 2009;26(1):23–31.
[2] Sunday D, Ogunniyi S, Mureyani M. Properties of rubber vulcanized containing powdered vulcanized waste. Iran Polym J 2001;10(3):143–7. [3] Laosee T, Phinyocheep P, Axtell FH. Morphlogy and mechanical properties of compatibilised polypropylene/vulcanized rubber blends. J Sci Soc Tailand 1998;24:251–64. [4] Markovic´ G, Jovanovic´ V, Samarzˇija-Jovanovic´ S, Marinovic´-Cincovic´ M, Budinski-Simendic J. Curing and mechanical properties of chlorosulphonated polyethylene rubber blends. Chem Ind Chem Eng Quart 2011;17(3):315–21. [5] Susmita S, Anil KB. Preparation and properties of nanocomposites based on acrylonitrile–butadiene rubber, styrene–butadiene rubber, and polybutadiene rubber. J Polym Sci Part B: Polym Phys 2004;42(9):1573–85. [6] Morrow NL. The industrial production and use of 1,3-butadiene. Environ Health Perspect 1990;86:7–8. [7] Roychoudhura Y, De PP. Studies on chemical interactions between chlorosulphonated polyethylene and carboxylated nitrile rubber. J Appl Polym Sci 1997;63:1761–8. [8] Ismail HS, Yusof AMM. Blend of waste poly(vinylchloride) (PVCw)/acrylonitrile butadiene-rubber (NBR): the effect of maleic anhydride (MAH). Polym Test 2004;23(6):675–83. [9] Bignozzi MC, Sandrolini F. Tyre rubber waste recycling in self-compacting concrete. Research 2006;36(4):735–9. [10] Aji PM, Packirisamy S, Sabu T. Studies on the thermal stability of natural rubber/polystyrene interpenetrating polymer networks: thermogravimetric analysis. Polym Degrad Stabil 2001;72(3):423–39. [11] Markovic´ G, Marinovic´-Cincovic´ M, Radovanovic´ B, Budinski-Simendic´ J. Rheological and mechanical properties of wood flour filled polyisoprene/ chlorosulphonated polyethylene rubber blends. Chem Ind Chem Eng Quart 2007;13(4):186–91. [12] Omran AM, Youssef AM, Ahmed MM, Abdel-Bary EM, Hellipolis RTL. Mechanical and oil resistance characteristics of rubber blends based on nitrile butadiene rubber. Kautsch Gummi Kunstst 2010;5:197–202. [13] Maurizio G, Konstantinos GG, József KK. Rubber–clay nanocomposites based on nitrile rubber. Willey online library; 2011. [14] Pruneda F, Suñol1 JJ, Andreu-Mateu F, Colom X. Thermal characterization of nitrile butadiene rubber (NBR)/PVC blends. J Therm Anal Calorim 2005;80:187–90. [15] Sulekha PB, Joseph R, George KE. Studied on polyisobutylene bound paraphenylene diamine antioxidant in natural rubber. Polym Degrad Stabil 1999;63:225–30. [16] Nair TM, Kumaran MG, Unnikrishnan G, Kunchand S. Ageing studies of ethylene propylene diene monomer rubber/styrene butadiene rubber blends: effects of heat, ozone, gamma radiation and water. Appl Polym Sci 2008;107(5):2923–9. [17] Radhakrishnan CK, Rosamma A, Unnikrishnan G. Thermal, ozone and gamma ageing of styrene butadiene rubber and poly(ethylene-co-vinyl acetate) blends. Polym Degrad Stabil 2006;91:902–10. [18] Markovic´ G, Marinovic´-Cincovic´ M, Jovanovic´ V, Samarzˇija-Jovanovic´ S, Budinski-Simendic´ J. The effect on gamma irradiation on the aging of sulfur cured NR/CSM and NBR/CSM rubber blends reinforced by carbon black. Chem Ind Chem Eng Quart 2009;15(4):291–8. [19] Gisbergen JGM, Meijer HEH, Lemstra PJ. Structured polymer blends: 2. Processing of polypropylene/EDPM blends: controlled rheology and morphology fixation via electron beam irradiation. Polymer 1989;30:2153–7. [20] Ramesana MT, Rosamma A, Khanh NV. Studies on the cure and mechanical properties of blends of natural rubber with dichlorocarbene modified styrene– butadiene rubber and chloroprene rubber. React Funct Polym 2005;62(1):41–50. [21] Markovic´ G, Devic´ S, Budinski-Simendi J. Influence of carbon black on reinforcement and gamma – radiation resistance of EPDM/ CSM CR/CSM rubber blends. Kautsch Gummi Kunstst 2009;6:299–305. [22] Chan Y. Cure characteristics and Dynamic Mechanical properties of acrylic rubber and epoxidized natural rubber blend. J Ind Eng Chem 2001;l7(4):212–7. [23] Abou Zeid MM, Rabie ST, Nada AA, Khalil AM, Hilal RH. Effect of gamma irradiation on ethylene propylene diene terpolymer rubber composites. Nucl Instrum Methods Phys Res B: Beam Interact Mater Atoms 2008;266(1):111–6. [24] Markovic´ G, Marinovic´-Cincovic´ M, Jovanovic´ V, Samarzˇija-Jovanovic´ S, Marinovic´-Cincovic´ M, Budinski-Simendic´ J. Thermal stability of CR/CSM rubber blends filled with nano- and micro-silica particles. J Therm Anal Calorim 2010;100(3):881–8. [25] Chantara TR, Sabariah K, Yaganaidu S, Marina T, Norzawani Y. Radiation crosslinking of rubber phase in poly(vinyl chloride)/epoxidized natural rubber blend: effect on mechanical properties. Polym Test 2006;25(4):75–480. [26] High-hardness and high-modulus rubber composition containing 1,2polybutadiene. United States Patent 4220564. [27] Jyothi TV, Sunny A, Sabu T. Thermal degradation of natural rubber/styrene butadiene rubber latex blends by thermogravimetric method. Polym-Plast Technol Eng 2000;39(3):415–35. [28] Lovely M, Joseph KU, Rani JR. Swelling behaviour of isora/natural rubber composites in oils used in automobiles. Bull Mater Sci 2006;29(1):91–9. [29] Dubey KA, Bhardwaj YK, Chaudhari CV, Sabharwa S. Radiation-processed styrene–butadiene-co-ethylene– propylene diene rubber blends: compatibility and swelling studies. J Appl Polym Sci 2006;99(6):3638–49.
Contents lists available at SciVerse ScienceDirect
Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Composites based on waste rubber powder and rubber blends: BR/CSM Gordana Markovic´ a,⇑, Olivera Veljkovic´ a, Milena Marinovic´-Cincovic´ b, Vojislav Jovanovic´ c, Suzana Samarzˇija-Jovanovic´ c, Jaroslava Budinski-Simendic´ d a
Tigar, Nikole Pašic´a 213, 18300 Pirot, Serbia University of Belgrade, Institute of Nuclear Science Vincˇa, Mike Petrovic´a Alasa 12-14, 11000 Belgrade, Serbia c Faculty of Natural Science and Mathematics, University of Priština, Lole Ribara 29, 38220 Kosovska Mitrovica, Serbia d University of Novi Sad, Faculty of Technology, Bulevar cara Lazara 1, 21000 Novi Sad, Serbia b
a r t i c l e
i n f o
Article history: Received 22 January 2012 Received in revised form 8 June 2012 Accepted 25 August 2012 Available online 8 September 2012 Keywords: A. Hybrid D. Thermal analysis D. Mechanical testing E. Strength
a b s t r a c t Blend of polybutadiene (BR) rubber with varying ratios of chlorosulphonated polyethylene rubber (CSM), BR/CSM, keeping the total waste rubber powder (WRP) content constant at 50 phr (parts per 100 rubber) have been prepared on a laboratory-size (300 600 mm) two-roll mixing mill maintained at 40 ± 5 °C. The mechanical properties, namely tensile strength (TS), tensile modulus at 100% elongation (M100), elongation at break (Eb%) and hardness have been followed up as a function of irradiation dose (dose rate of 10 kGy h1 and total absorbed dose of 100, 200, 300 and 400 kGy) as well as blend composition. The results indicated that the addition of CSM has improved the properties of BR/CSM rubber blends waste rubber powder filled composites. The improvement in mechanical properties of the BR/CSM/WRP (50/ 50/50) rubber blends is in correlation with homogenous WRP distribution which has been assigned by scanning electron microscopy. Also BR/CSM rubber blends waste rubber powder filled composites are thermally and irradiation more stable than BR and CSM rubbers alone. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction The production of rubber materials rises every year. Considering the economic and environmental advantages, recycling is one of the best options. A number of possible applications of various forms of waste rubber in broad disciplines have been studied and reported [1]. Recycled rubber can be generalized as any rubber waste that has been converted to an economically useful form, such as reclaimed rubber, ground rubber or reprocessed synthetic rubber. The manufacturing of powdered rubber has obvious economic and social benefits, as it decreases the cost of the product by blending fine powdered rubber with raw rubber [2]. Polymer blends play an important role in the modern polymer industry not only for development of new materials but also for practical recycling purposes. Most polymer blends are incompatible, and a final performance of a polymer blend is determined by the polymer compatibility by and the phase morphology [3,4]. Polybutadiene is an elastomer commonly used in the tire industry [5], passenger and truck tires represent 73% of the U.S. consumption of this synthetic elastomer. Such applications involve large temperature variations, and we can easily conceive situations ⇑ Corresponding author. E-mail addresses: [email protected] (G. Markovic´), olivera. [email protected] (O. Veljkovic´), [email protected] (M. Marinovic´-Cincovic´), [email protected] (V. Jovanovic´), [email protected] (S. SamarzˇijaJovanovic´), [email protected] (J. Budinski-Simendic´). 1359-8368/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compositesb.2012.08.013
were the polymer would be used within its property transition region. Therefore analytically relating the microstructure of the elastomer to the mechanical performance of the system would be a powerful tool for the virtual design of polymer based systems (including composites). Various grades (molecular weights) of polybutadiene are commercially available [6]. The introduction of chlorine and sulfur dioxide onto the polyethylene linking via condenzation or substitution reactions molecule destroys the crystallinity, thereby changing the thermoplastic material into an amorphous polymer, commercially known as chlorosulphonated polyethylene (CSM), which contains 25–43% by weight of chlorine and 1–1.5% by weight of sulfur as SO2Cl units. Thus, CSM rubber is highly reactive, and reactivity is due to the SO2Cl groups [7]. Different types of additives used in processing of rubber into products include a vulcanizing agent’s accelerator, an activator, antidegradants, fillers, a softener, thickeners, a gel sensitizer, a colorant, etc. Fillers modify physical and, to some extent, chemical properties of vulcanizates. Rubber waste is usually generated during the manufacturing process of product of these industries and by disposal of post-consumer (retired) products mainly including scrap tires [8,9]. Thermal stability means the ability of a material to maintain the required properties such as strength, toughness, or elasticity at a given temperature [10]. A detailed understanding of how polymers break down on heating is important in the design of elastomeric materials with improved properties for particular
G. Markovic´ et al. / Composites: Part B 45 (2013) 178–184
application. Markovic et al. [11], made the wood flour filled polyisoprene/chlorosulphonated polyethylene rubber blends. The elastomeric composite has excellent compatibility between two rubbers of different polarity when properly compounded and processed [12]. Maurizio et al. [13] prepared rubber–clay nanocomposites based on nitrile rubber using conventional two-roll mill mixing technique. They found that adding organoclay in NBR elastomer greatly improves material thermal stability and aging performance in different medium at elevated temperature. Pruneda et al. [14] studied the thermal characterization of nitrile butadiene rubber (NBR)/PVC blends. Excellent reports on the ageing characteristics of rubbery systems exist. For example, Sulekha et al. [15] studied the polyisobutylene bound paraphenylene diamine antioxidant in natural rubber. Nair and co-workers studied effects of heat, ozone, gamma radiation and water on ethylene propylene diene monomer rubber/styrene butadiene rubber blends [16]. Thermal, ozone and gamma ageing of styrene butadiene rubber and poly(ethylene-co-vinyl acetate) blends has been studied by Radhakrishnan et al. [17]. The mechanism of characteristic changes in gamma ray irradiated polymers, including degradation and crosslinking has been studied [18]. The aim of the present work is to study the thermal and gamma irradiation resistance of composites based on waste rubber powder filled BR/CSM rubber blends with special reference to the effects of blend ratio. Also, swelling and chemical stability of these composites were investigated.
179
Table 2 Basic formulation used for BR/CSM waste rubber powder filled rubber blends composites.
a b c
Ingredients (phr)
1
2
3
4
5
Polybutadiene rubber (BR) Chlorosulphonated polyethylene rubber (CSM) Stearic acid Zinc oxide Waste rubber powdera Magnesium oxide TMTDb CZc Sulfur
100 / 2.0 5.0 50 2.0 0.8 1.0 2.0
75 25 2.0 5.0 50 2.0 0.8 1.0 2.0
50 50 2.0 5.0 50 2.0 0.8 1.0 2.0
25 75 2.0 5.0 50 2.0 0.8 1.0 2.0
0 100 2.0 5.0 50 2.0 0.8 1.0 2.0
Waste rubber powder (particle size 250–500 lm). Tetramethylthiuram disulfide. N-cyclohexyl-2-benzothiazyl sulphenamide.
The rubber mixes were compression molded at 160 ± 2 °C, using an electrically heated hydraulic press at their optimum cure time derived from rheological measurements. The applied hydraulic force during vulcanization attained 6.7 MPa. Dumbbell shaped tensile strength was punched from the compression molded sheet along the mill grain direction using C-type dumbbell specimens, according to ASTM D-412. The waste rubber powder (WRP) (particle size 250–500 lm) was supplied by Watas holding Sdn Vhd Panang Malaysia). 2.3. Cure characteristics
2. Materials and methods
The cure characteristics of rubber compounds were carried out using an Oscillating Disc Rheometer (ODR) model 4308 from Zwick, Germany.
2.1. Materials
Mc90 ¼ ðM h M l Þ 0:9 þ M l
The basic characteristics of materials used in this work are given in Table 1. The rubber chemicals also used such as plasticizer, sulfur, magnesium oxide, zinc oxide; stearic acid, tetramethylthiuram disulphide TMTD, ethylene thiourea ETU, 2-mercaptobenzthiazol (MBT), dibenzothiazyl disulphide MBTS, N-cyclohexyl-1,2-benzothiazyl sulphenamide (CBS) were of commercial grade.
ð1Þ
The measured parameters are: Ml – minimum torque, Mh – maximum torque, ts2 – time to 2 units of torque increase above minimum, Mc90 – torque at 90% of full torque development. The cure rate is:
CRI ¼
1 100 t c90 t s2
ð2Þ
These measurements were accomplished according to ASTM D2084.
2.2. Mixing procedure The rubber compounds with different blend ratios were prepared on a two roll mixing mill having a friction ratio of 1:1.4. The compounding recipes of the blends are given in Table 2. Mixing of BR with CSM rubber mixtures were carried out on a laboratory open two roll mill (400 mm diameters and 600 mm working length). The gear friction of the mill is 1:1.4. The hollow rolls were cooled by using flushing water in order to regulate the temperature not exceeding 60 °C during the different stages of mixing according to ASTM D-15-627. The rubber mixes obtained were sheeted and left for a period of at least 6 h before testing. The addition of ingredients during mixing was carried following the same order and conditions of mixing.
2.4. Mechanical testing The tensile properties were determined using the tensile testing machine type Zwick 1445 according to ASTM D-412. The average value of the mechanical properties was calculated using at least three samples. A cross head speed of 50 mm/min was used and the tests were performed at 25 °C. 2.5. Hardness measurements Samples of at least 0.12 mm in thickness with flat surface were cut for hardness test. The measurement was carried out according
Table 1 Details of materials. Materials
Characteristics
Polybutadiene rubber (BR), Buna CIS 132,
Mooney viscosity ML1+4 (100 °C) Cis-1,4 content (%) Density (g/cm3) Chloride content (%) Mooney viscosity ML1+4 (100 °C) Density (g/cm3) 250–500 lm
Chlorosulphonated polyethylene rubber CSM Hypalon 40S
Waste rubber powder (WRP)
Source 45 95 0.91
Dow, Germany
Goodrich chemical Co. Du Pont USA 46 ± 5 1.18 Watas holding Sdn Vhd Panang Malaysia
G. Markovic´ et al. / Composites: Part B 45 (2013) 178–184
180
The measurements were made at a heating rate 10 °C min1, at a temperature range 0–800 °C, using Perkin Elmer TGS-2 Thermogravimetric system. The experiments were done in nitrogen atmosphere. About 5–8 mg of the sample was used for the analysis.
and silica. Thus in the presence of WRP the formation of additional crosslinks is possible and consequently an increase in CSM loading will reduce the flow and slightly increase the torque. In BR/CSM rubber blend, cure rate index (CRI) is decrease with CSM content is increase might be due to the lower viscosity of BR compared to CSM. The lower viscosity components lead to form a continuous phase [19] in blends, which is more or less, governs the curing process. However, all blend ratio in the BR/CSM blend exhibits lower curing index according to the activation [20] of the adjacent double bond by the CACl group. It is also evident from the table that the ts2 of BR is longer than for CSM. This is due to the activation of double bond that causes an over all increase in the rate of cross-linking of the blends. More activated precursors to crosslink [21,22] are formed as a result of the activation of double bond. These activated precursors will accelerate the vulcanization between BR and CSM phases that induce faster interphase crosslinking between these molecules. The increased scorch time, indicating higher scorch safety of the rubber blends.
2.8. Swelling measurements
3.2. Mechanical properties
The swelling degree was determined on the basis of equilibrium solvent–swelling measurements in toluene. The samples were submerged in the solvent and after the swelling equilibrium was reached, that means, no change in the weight of the swollen sample was observed, the mass of solvent was determined according to the ASTM D 471. The results were expressed as the mass of solvent absorbed per gram of blend. The solvent used for chemical absorption study included toluene. The percentage of absorption was calculated using the following equation:
In the blends a positive deviation of tensile strength, modulus and hardness is observed, suggesting that synergism has occurs. The maximum of tensile strength, modulus and hardness properties is obtained at 50 phr CSM for BR/CSM/WRP rubber blends. Due to the strain induced crystallization behavior of both rubbers [23], the rubbers reinforced each other when subjected to tensile elongation which is reflected by the higher tensile modulus obtained in the blend. It is generally observed that mechanical properties of blend are closely related to its compatibility and synergistic effect is often obtained with miscible or partially compatible blends [24]. BR/CSM rubber blend were found to be compatible, hence the partial compatibility might be due to the interaction of nonpolar phase of BR and polar phase of CSM phase occurs with the strain induced crystallization of BR rubbers. Gamma irradiation is a powerful means for crosslink elastomers, however, exposure to higher dosage of it degrades the polymer. The extent of crosslinking and degradation undergone by a polymer depends on its structural characteristics and the presence of initiators/sensitizers [25]. The effects of irradiation aging on 50 phr WRP containing BR/CSM rubber blends composites and three different radiation doses of the magnitude 100, 200 and 400 kGy on tensile strength, modulus, hardness and elongation at break are observed. The incorporation of WRP particles in the polymer blend under consideration leads to composites with enhanced properties. This enhancement might be due to the additional effect of unreacted curatives in powdered rubber. These interactions may influence to better physical properties, higher irradiation resistance and low costs of rubber product are obtained. Fig. 1 shows the effect of blend composition and gamma irradiation dosages on tensile strength (TS) values for the BR/CSM waste rubber powder filled rubber blends composites. It can be seen that the TS values for all compositions increase with increasing irradiation dose reaching its maximum value at 200 kGy and then decrease for doses higher than that. As shown, the tensile strength has been found to be increased with increase in CSM content up to 50 phr and after that decrease. It may be observed also that vulcanized BR/CSM/WRP has attained higher TS values over the whole range of irradiation up to 200 kGy, than unirradiated composites. The TS values attained by vulcanized blends lie between these two extremes and decreases after 50 phr of CSM content systematically for blend. On irradiation of polymeric materials such as rubbers for example, radiation induced crosslinking and degradation processes take place simultaneously but with different rates. Accordingly, the data obtained indicate that the crosslinking
to ASTM D 2240 using durometer of model 306L type. The unit of hardness is expressed in (Shore A). 2.6. Gamma irradiation Irradiations have been performed in air in the Co-60 radiation sterilization unit with the dose rate of 10 kGy h1 and total absorbed dose of 100, 200, and 400 kGy. Radiation dose of 400 kGy can be considered as the relatively big dose which many times exceeds the doses for degradation of radiation degradable polymers and is also above the typical doses used in practice for radiation modification of polymer based products. 2.7. Thermo gravimetric analysis
Q¼
mt m0 100 m0
ð3Þ
where mt is the mass of sample at time t and m0 is the dry weight of the sample. 2.9. Scanning electron microscopy The scanning electron microscopy images of the rubber blends fractured surfaces were taken by a JEOL JSM-5400 model of the microscope. The samples were sputter coated with gold for 3 min under high vacuum with image magnifications of 7500. 3. Results and discussion 3.1. Cure characteristics The cure characteristics: the torque evolution, the scorch time ts2, optimum cure time tc90 and the cure rate index (CRI) of waste rubber powder (WRP) filled BR/CSM rubber blends are shown in Table 3. It can be seen that the values for Ml and Mh increases with the CSM loading is increase in the rubber compounds. In general WRP is unreinforcing filler and has a particle size larger than CB
Table 3 The cure characteristics of waste rubber powder (WRP) filled BR/CSM rubber blends. Cure characteristics
1
2
3
4
5
Ml (dNm) Mh (dNm) DM (dNm) ts2 (min) tc90 (min) CRI (min1)
2 36 34 6 28 4.5
2 32 30 2 7 20
2 32 30 2 6 25
3 33 30 5 12 14.3
2 32 30 10 27 5.9
G. Markovic´ et al. / Composites: Part B 45 (2013) 178–184
Fig. 1. Variation of tensile strength as a function of blend compositions and irradiation dose for rubber waste powder filled (WRP) BR/CSM rubber blends composites. The error bars represent one standard deviation.
process was the dominating one for doses up to 200 kGy whereas the degradation process has apparently prevailed for doses higher than 200 kGy. One cannot, however, exclude the impairment of chain orientation of rubber macromolecules due to increased extent of induced crosslinking at a higher dose and hence its eventual contribution in decreasing the TS values for doses higher than 200 kGy. BR in its raw form represents an amorphous and homogenous polymeric material and hence the bulk mechanical properties of the radiation-vulcanized product may be fairly anticipated on the basis of its intrinsic chemical structure and irradiation conditions. Hence, self-reinforcement does not take place at high extensions, as in case of BR and no contribution to its tensile strength would be expected. Based on its chemical structure, the tertiary substituted carbon atom on the main macromolecules chain represents the most susceptible carbon atoms and on irradiation breakage of this bond takes place favorably leading to the formation of the hydrogen atoms and chloride radical. When it happened that such radicals stand favorably to each other then they may react with each other with the result of formation of a covalent bond, i.e., crosslink between two adjacent macromolecules. Under such circumstances a limited crosslinking density would be expected which accounts for the relatively low value of TS attained by vulcanized raw BR/CSMWRP composites. Fig. 2 shows the variation of tensile modulus at 100% elongation (M100) as a function of irradiation dose and blend compositions. It can be seen that the M100 of all samples increases with increasing the irradiation dose, whereby BR/CSM/WRP rubber blends composites has attained higher value than CSM rubber alone. The M100 value increase with content of CSM rubber increase up to 50 phr and it decreases after 50 phr of CSM content in blends. These data indicate that BR vulcanizates have attained the relatively highest retroactive force, i.e., resistance to strain deformation or stretching. Isolated double bonds in BR rubber inhibited the formation of intra-molecular links thus resulting in the increase of the crosslinking rate, which results in a substantial increase in tensile modulus. Variation of elongation at break (Eb%) as a function of blend compositions and irradiation dose for rubber waste powder filled (WRP) BR/CSM rubber blends composites is illustrated in Fig. 3. It can be seen that the value of Eb for all samples decreases with increasing the irradiation dose, but increase with CSM loading. This can be attributed to the amorphous and crystalline nature of BR, respectively and this trend may be attributed to the rigid BR/ CSM interface upon increasing content of CSM.
181
Fig. 2. Variation of modulus at 100% elongation (M100) as a function of blend compositions and irradiation dose for rubber waste powder filled (WRP) BR/CSM rubber blends composites. The error bars represent one standard deviation.
Fig. 3. Variation of elongation at break (Eb%) as a function of blend compositions and irradiation dose for rubber waste powder filled (WRP) BR/CSM rubber blends composites. The error bars represent one standard deviation.
3.3. Hardness Shore A Fig. 4 shows variation of hardness as a function of blend compositions and irradiation dose for waste rubber powder (RWP) BR/ CSM rubber blends composites. The hardness of the rubber blends decrease with increasing the CSM rubber content, but increase with irradiation doses loading. A higher amount CSM would result in an increased hardness of the vulcanizates [26]. It is well known that during irradiation several detrimental processes take place, such as main chain scission, crosslink formation and crosslink breakage. It is also possible that the existing crosslink’s may break and a more stable type of crosslink can be formed. The relative ratios and magnitudes of such reactions will govern to what extent each property is changed. In composites, in addition to the various reactions described above, bonded resin formation also takes place during irradiation. All these reactions influence the changes in the performance of the composites. The increased scorch time, indicating higher scorch safety of the rubber blends. The BR/CSM/WRP rubber blend has attained higher
182
G. Markovic´ et al. / Composites: Part B 45 (2013) 178–184
Fig. 4. Variation of hardness as a function of blend compositions and irradiation dose for rubber waste powder filled (WRP) NR/CSM and BR/CSM rubber blends composites. The error bars represent one standard deviation.
TS values over the whole range of irradiation. Higher scorch safety of the rubber blends results in better mechanical properties. 3.4. Thermo gravimetric analysis The thermal stability of the BR/CSM rubber blend waste rubber powder as a function of blend compositions and irradiation dose was investigated using thermo-gravimetric analysis. Fig. 5a and b shows TG and DTG curve of BR/CSM/WRP rubber blends as a function of blend composition. Fig. 6a and b shows TGA and DTG curve of BR/CSM/WRP (50/50/50) rubber blends as a function of irradiation doses. Table 4 shows detailed summary variation of 0.5% weight loss (T0.5), 10% weight loss (T10) and 30% weight loss (T30) the final decomposition temperature of BR/CSM/WRP (50/50/50) rubber blend composites irradiated at 100, 200 and 400 kGy. Two regions of BR/CSM/WRP rubber blends degradation are observed. The degradation started at 380 °C and was completed at 490 °C. The former stage of degradation is due to the elimination of chlorine from the CSM chain and the later stage is due to the main chain scission. The total mass loss observed at 695 °C was 86.21%. It has been reported that the thermal stability of one type of polymer can be improved by the incorporation of a second polymer. In the case of BR/CSM/WRP rubber blends, the degradation starts at a higher temperature than that for BR and CSM rubber alone. T0.5 indicates the initial thermal stability whereas T10 and T30 show the higher degradation rate of the polymer blends composites. As shown in Fig. 5, the incorporation of the CSM resulted in all samples improvement of thermal stability. Ash residue content increased with higher CSM loading. According to [27], the higher content of ash residue in degradation process depends on the initial CSM plus added experimentally. The thermal stability of polymer composites increase with gamma irradiation increase by up to 200 kGy after that it decreases (Fig. 6 and Table 4). Radiation can produce crosslink like those obtained by sulfur curing, but the net effect is not identical. The crosslink between polymer matrix and WRP is formed and increase as gamma irradiation dose is increase. The above mentioned results could be explained in the scope of the molecular structure of the polymeric matrix, which is directly related to its thermal stability. The decrement in the thermal stability of BR/CSM/WRP (50/50/50) rubber blend composites by
Fig. 5. TG (a) and DTG (b) curve of BR/CSM rubber blend waste rubber composites at different CSM loading.
exposure to irradiation dose at 400 kGy is presumably due to some random degradation of polymer chains, which leads to the reduction of its stability. On the other hand, the increase in the thermal stability of polymer matrix with CSM rubber increase is may be due to the increase in the compatibility between polymer phases due to the increased magnitude of interface linking, which made the composite of higher homogeneity, and as a result its stability increases. The results show positive synergistic effect of radiation and the incorporation of CSM on the thermal stability of its composite, i.e., the incorporation of CSM increases the stability of the composite and the use of gamma radiation up to 200 kGy magnifies such stability. Therefore, the incorporation of CSM into the composite plays an important role for improving its thermal stability. This is because the compatibility between rubbers provides strength to the composites. 3.5. Swelling properties Fig. 7 shows the effect of blend compositions on the swelling degree of BR/CSM/WRP rubber blends composites. CSM rubber has excellent resistance to most chemicals and this explains why percentage of swelling of WRP filled BR/CSM rubber blend matrix is low. When more than 50 phr of CSM was used, the percentage of swelling reduced which might be due to the penetration hindrance of toluene into BR/CSM blends [28,29]. Fig. 8 illustrates the variation of swelling degree as a function of irradiation dose of BR/CSM/WRP (50/50/50) rubber blends composites. The swelling degree values for un-irradiated as well as corresponding irradiated ones are also given in the same figure for sake
G. Markovic´ et al. / Composites: Part B 45 (2013) 178–184
183
Fig. 7. The effect of blend compositions on the swelling degree of BR/CSM/WRP (50/ 50/50) rubber blends composites. The error bars represent one standard deviation.
Fig. 6. TG (a) and DTG (b) curves of BR/CSM (50/50/50) rubber blends waste rubber powder composites at different irradiation dose.
Table 4 The temperature values of BR/CSM (50/50) rubber blends composites containing 50 phr waste rubber powder for selected mass loss (0.5%, 10% and 30%). BR/CSM/WRP (50/50/50) (kGy)
DTG peak (°C)
Mass loss (%)
Total mass loss (%)
T0.5% (°C)
T10% (°C)
T30% (°C)
0 100 200 400
420.1 440.5 470.2 450.3
20.5 29.6 37.2 36.2
65.2 76.8 40.8 45.2
118.4 120.1 129.8 70.7
300.1 310.9 314.8 280.3
400.9 412.5 423.1 395.6
Fig. 8. Variation of swelling degree (%) as a function of irradiation dose for the BR/ CSM/WRP (50/50/50) rubber blends composites. The error bars represent one standard deviation.
of comparison. It can be seen that these un-irradiated composite have attained comparatively high swelling degree values. On the other hand, the swelling degree values attained decreased with irradiation dose at 200 kGy and then they increased over any further increase in dose until 400 kGy. These data indicate clearly that the irradiated composites possess better resistance to be swelled by toluene until reach 200 kGy by means crosslinking occur at low doses then degradation may then predominate with respect to BR/CSM/WRP (50/50/50) rubber blends composite. 3.6. Morphological study In Fig. 9, the SEM micrograph of BR/CSM/WRP (50/50/50) rubber blends composites at 7500 magnification is shown. The micrograph of BR/CSM/WRP (50/50/50) rubber blends composites
Fig. 9. SEM photograph of BR/CSM/WRP (50/50/50) rubber blends composites.
184
G. Markovic´ et al. / Composites: Part B 45 (2013) 178–184
exhibits that the composite’s surface is smooth with homogeneous WRP distribution. This type of failure indicates the higher mechanical properties and a strong interaction between BR and CSM rubbers. 4. Conclusions In this study mechanical, thermal and gamma irradiation resistance of BR/CSM rubber blends waste rubber powder (WRP) composites with special reference to the effects of blend ratio was studied. WRP as alternative filler can be further exploited by controlling the particle size dispersion and also its surface functionality. The values of ts2, tc90 and curing rate of blends increase with increasing CSM content. The torque difference, DM = Mh Ml (max. torque – min. torque), as relate to the cross-link density, is equal in all BR/CSM/WRP rubber blend. The increased scorch time, indicating higher scorch safety of the rubber blends. The BR/CSM/ WRP rubber blend has attained higher TS values over the whole range of irradiation. Higher scorch safety of the rubber blends results in better mechanical properties. The crosslinking process was the dominating one for doses up to 200 kGy whereas the degradation process has apparently prevailed for doses higher than 200 kGy. Positive deviation of tensile strength, modulus at 100% elongation and hardness are indicated that the synergism occurred in BR/CSM blends. The value of elongation at break for all samples decreases with increasing the irradiation dose, but increase with CSM loading. The improvement in mechanical properties of the BR/CSM/WRP (50/50/50) rubber blends is in correlation with homogenous WRP distribution which has been assigned by scanning electron microscopy. The temperature at 0.5% weight loss (T0.5), at 10% weight loss (T10) and at 30% weight loss (T30) obtained from TG curves increase with CSM content increases. Also, thermal stability increases with gamma irradiation dose increase up to 200 kGy, and after that decreases. The quality of waste rubber powder product from the sanding process (polishing) of rubber ball and artificial eggs is variable, i.e., % of filler in WRP is variable. As a result of this, % of final mass loss of BR/CSM/WRP is variable. The swelling and chemical stability of these composites were investigated. When more than 50 phr of CSM was used, the percentage of swelling reduced which might be due to the penetration hindrance of toluene into BR/CSM/WRP rubber blends. Irradiated composites possess better resistance to be swelled by toluene until reach 200 kGy by means crosslinking occur at low doses then degradation. The tendency towards scorchiness in compounds containing powdered rubber waste may be due to additional effect of unreacted curatives in powdered rubber. Also, the source of the waste will affect final compound and vulcanizate properties. It has been suggested that the little interfacial bonding between the powdered rubber waste and the virgin matrix elastomer may be responsible for the reduction of properties when rubber waste was incorporated. Acknowledgement Financial support for this study was granted by the Ministry of Science and Technological Development of the Republic of Serbia (Project Numbers 45022 and 45020). References [1] Baeta DA, Zattera JA, Oliveira MG, Oliveira PJ. The use of styrene–butadiene rubber waste as potential filler in nitrile rubber: order of addition and size of waste particles. Braz J Chem Eng 2009;26(1):23–31.
[2] Sunday D, Ogunniyi S, Mureyani M. Properties of rubber vulcanized containing powdered vulcanized waste. Iran Polym J 2001;10(3):143–7. [3] Laosee T, Phinyocheep P, Axtell FH. Morphlogy and mechanical properties of compatibilised polypropylene/vulcanized rubber blends. J Sci Soc Tailand 1998;24:251–64. [4] Markovic´ G, Jovanovic´ V, Samarzˇija-Jovanovic´ S, Marinovic´-Cincovic´ M, Budinski-Simendic J. Curing and mechanical properties of chlorosulphonated polyethylene rubber blends. Chem Ind Chem Eng Quart 2011;17(3):315–21. [5] Susmita S, Anil KB. Preparation and properties of nanocomposites based on acrylonitrile–butadiene rubber, styrene–butadiene rubber, and polybutadiene rubber. J Polym Sci Part B: Polym Phys 2004;42(9):1573–85. [6] Morrow NL. The industrial production and use of 1,3-butadiene. Environ Health Perspect 1990;86:7–8. [7] Roychoudhura Y, De PP. Studies on chemical interactions between chlorosulphonated polyethylene and carboxylated nitrile rubber. J Appl Polym Sci 1997;63:1761–8. [8] Ismail HS, Yusof AMM. Blend of waste poly(vinylchloride) (PVCw)/acrylonitrile butadiene-rubber (NBR): the effect of maleic anhydride (MAH). Polym Test 2004;23(6):675–83. [9] Bignozzi MC, Sandrolini F. Tyre rubber waste recycling in self-compacting concrete. Research 2006;36(4):735–9. [10] Aji PM, Packirisamy S, Sabu T. Studies on the thermal stability of natural rubber/polystyrene interpenetrating polymer networks: thermogravimetric analysis. Polym Degrad Stabil 2001;72(3):423–39. [11] Markovic´ G, Marinovic´-Cincovic´ M, Radovanovic´ B, Budinski-Simendic´ J. Rheological and mechanical properties of wood flour filled polyisoprene/ chlorosulphonated polyethylene rubber blends. Chem Ind Chem Eng Quart 2007;13(4):186–91. [12] Omran AM, Youssef AM, Ahmed MM, Abdel-Bary EM, Hellipolis RTL. Mechanical and oil resistance characteristics of rubber blends based on nitrile butadiene rubber. Kautsch Gummi Kunstst 2010;5:197–202. [13] Maurizio G, Konstantinos GG, József KK. Rubber–clay nanocomposites based on nitrile rubber. Willey online library; 2011. [14] Pruneda F, Suñol1 JJ, Andreu-Mateu F, Colom X. Thermal characterization of nitrile butadiene rubber (NBR)/PVC blends. J Therm Anal Calorim 2005;80:187–90. [15] Sulekha PB, Joseph R, George KE. Studied on polyisobutylene bound paraphenylene diamine antioxidant in natural rubber. Polym Degrad Stabil 1999;63:225–30. [16] Nair TM, Kumaran MG, Unnikrishnan G, Kunchand S. Ageing studies of ethylene propylene diene monomer rubber/styrene butadiene rubber blends: effects of heat, ozone, gamma radiation and water. Appl Polym Sci 2008;107(5):2923–9. [17] Radhakrishnan CK, Rosamma A, Unnikrishnan G. Thermal, ozone and gamma ageing of styrene butadiene rubber and poly(ethylene-co-vinyl acetate) blends. Polym Degrad Stabil 2006;91:902–10. [18] Markovic´ G, Marinovic´-Cincovic´ M, Jovanovic´ V, Samarzˇija-Jovanovic´ S, Budinski-Simendic´ J. The effect on gamma irradiation on the aging of sulfur cured NR/CSM and NBR/CSM rubber blends reinforced by carbon black. Chem Ind Chem Eng Quart 2009;15(4):291–8. [19] Gisbergen JGM, Meijer HEH, Lemstra PJ. Structured polymer blends: 2. Processing of polypropylene/EDPM blends: controlled rheology and morphology fixation via electron beam irradiation. Polymer 1989;30:2153–7. [20] Ramesana MT, Rosamma A, Khanh NV. Studies on the cure and mechanical properties of blends of natural rubber with dichlorocarbene modified styrene– butadiene rubber and chloroprene rubber. React Funct Polym 2005;62(1):41–50. [21] Markovic´ G, Devic´ S, Budinski-Simendi J. Influence of carbon black on reinforcement and gamma – radiation resistance of EPDM/ CSM CR/CSM rubber blends. Kautsch Gummi Kunstst 2009;6:299–305. [22] Chan Y. Cure characteristics and Dynamic Mechanical properties of acrylic rubber and epoxidized natural rubber blend. J Ind Eng Chem 2001;l7(4):212–7. [23] Abou Zeid MM, Rabie ST, Nada AA, Khalil AM, Hilal RH. Effect of gamma irradiation on ethylene propylene diene terpolymer rubber composites. Nucl Instrum Methods Phys Res B: Beam Interact Mater Atoms 2008;266(1):111–6. [24] Markovic´ G, Marinovic´-Cincovic´ M, Jovanovic´ V, Samarzˇija-Jovanovic´ S, Marinovic´-Cincovic´ M, Budinski-Simendic´ J. Thermal stability of CR/CSM rubber blends filled with nano- and micro-silica particles. J Therm Anal Calorim 2010;100(3):881–8. [25] Chantara TR, Sabariah K, Yaganaidu S, Marina T, Norzawani Y. Radiation crosslinking of rubber phase in poly(vinyl chloride)/epoxidized natural rubber blend: effect on mechanical properties. Polym Test 2006;25(4):75–480. [26] High-hardness and high-modulus rubber composition containing 1,2polybutadiene. United States Patent 4220564. [27] Jyothi TV, Sunny A, Sabu T. Thermal degradation of natural rubber/styrene butadiene rubber latex blends by thermogravimetric method. Polym-Plast Technol Eng 2000;39(3):415–35. [28] Lovely M, Joseph KU, Rani JR. Swelling behaviour of isora/natural rubber composites in oils used in automobiles. Bull Mater Sci 2006;29(1):91–9. [29] Dubey KA, Bhardwaj YK, Chaudhari CV, Sabharwa S. Radiation-processed styrene–butadiene-co-ethylene– propylene diene rubber blends: compatibility and swelling studies. J Appl Polym Sci 2006;99(6):3638–49.