Thermoplastic elastomers from waste polyethylene and reclaim rubber blends and their composites with fly ash

Thermoplastic elastomers from waste polyethylene and reclaim rubber blends and their composites with fly ash

Process Safety and Environmental Protection 8 8 ( 2 0 1 0 ) 131–141 Contents lists available at ScienceDirect Process Safety and Environmental Prote...

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Process Safety and Environmental Protection 8 8 ( 2 0 1 0 ) 131–141

Contents lists available at ScienceDirect

Process Safety and Environmental Protection journal homepage: www.elsevier.com/locate/psep

Thermoplastic elastomers from waste polyethylene and reclaim rubber blends and their composites with fly ash Sukanya Satapathy a , A. Nag b , Golok Bihari Nando a,∗ a b

Rubber Technology Center, Indian Institute of Technology, Kharagpur, Kharagpur-721302, West Bengal, India Department of Chemistry, Indian Institute of Technology, Kharagpur-721302, West Bengal, India

a b s t r a c t Waste polyethylene (WPE) collected from the municipality solid waste (MSW) was melt blended with reclaim rubber (RR) in different proportions and composites with fly ash (FA) were prepared and characterized. Mechanical and dynamic mechanical properties of the blends and composites were studied in presence as well as in absence of a silane-coupling agent (Si-69). Tensile strength, flexural strength, flexural modulus, impact strength and hardness properties of the FA composites was found to improve in presence of Si-69. Phase morphology of the blends has been reported. Crown Copyright © 2010 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers. All rights reserved. Keywords: Waste polyethylene; Reclaim rubber; Fly ash composites; Impact strength; Blend phase morphology; Dynamic mechanical properties

1.

Introduction

Management of municipality solid waste (MSW) has become the biggest problem in recent years. In India, out of the total MSW generated everyday; nearly 12–15% consists of polymer wastes. Efforts are being made constantly to find out newer avenues for the disposal of this huge waste. Since methods like incineration and land filling have become impracticable posing a threat to the environment and biodegradation of the polymer waste is far from achieved, the only alternative left for easy disposal of this huge polymer waste is ‘Recycling’ and ‘Reuse’ to obtain value added products (Molgaard, 1995; Shent et al., 1999; Eriksson et al., 2005; Satapathy et al., 2006; Mutha et al., 2006). The polymer waste in the municipality solid waste stream consists of polyolefin’s as its major proportion. In this paper attempts are made to segregate the polyethylenes such as LDPE, HDPE, LLDPE from the rest of the polymers such as PP, PS and PVC, which have been processed separately (Jose et al., 2007). Whole tire reclaim derived from scrap tires and butyl reclaim derived from scrap tubes are the two major streams of RR produced worldwide. Disposal of these used tires and tubes also pose a serious problem to the environment as they



are also non-biodegradable because of high recovery as well as disposal costs. Several studies on the reclamation and recycling of waste tire rubber have been carried out by various researchers earlier (Adhikari et al., 2000; De et al., 2000). It has also been reported that RR is used to blend with styrene butadiene rubber (SBR) and natural rubber (NR) to produce cheaper articles (Sreeja and Kutty, 2003; Yehia et al., 2004). The tensile strength and elongation at break of the NR/RR and SBR/RR blends decrease with the increasing RR proportion in the blends as reported earlier (Yehia et al., 2004). The mechanical behavior of RR/SBR and RR/NBR blends studied reveal that an increase in the tensile strength, tear strength, elongation at break occurs with a decrease in the resilience (Sreeja and Kutty, 2002). The mechanical properties of maleic anhydride grafted RR and SBR blends have also been reported (Nelson and Kutty, 2004). Thermoplastic elastomers from linear low-density polyethylene and latex product waste based on NR latex have been studied for various uses (Rajalekshmi and Joseph, 2005). Thermoplastic elastomers derived from polyethylene and maleic anhydride grafted ground rubber tire have been reported to be re-processable (Naskar et al., 2002). The mechanical properties of the blends of reclaimed tire rubber and high-density polyethylene have been studied before

Corresponding author. Tel.: +91 3222283194. E-mail address: [email protected] (G.B. Nando). Received 29 September 2008; Received in revised form 6 December 2009; Accepted 9 December 2009

0957-5820/$ – see front matter Crown Copyright © 2010 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers. All rights reserved.

doi:10.1016/j.psep.2009.12.001

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Nomenclature DMA DSA DTA E E0 E∞ Ei Ef E EDX FA HDPE LDPE LLDPE MPW MSW NR NBR PP PS PVC RR SBR SEM Si-69 TGA TPE tan ı WPE

dynamic mechanical analysis double strain amplitude derivative thermogram storage modulus storage modulus at zero strain storage modulus at infinite strain storage modulus at 1% strain storage modulus at 100% strain difference in storage modulus energy dispersed X-ray analysis fly ash high-density polyethylene low-density polyethylene linear low-density polyethylene municipality polymer waste municipality solid waste Natural Rubber nitrile rubber polypropylene polystyrene polyvinyl chloride reclaim rubber styrene butadiene rubber scanning electron microscopy silane-coupling agent thermogravimetric analysis thermoplastic elastomer damping factor waste polyethylene

and after dynamic vulcanization (Punnarak et al., 2006). When the RR is blended with thermoplastics it is expected to give rise to thermoplastic elastomers (more specifically TPEs) and similar studies on scrap rubber powder/LLDPE blends have been reported earlier (Guo et al., 2004). The effect of various treatments on to the blends of HDPE-reused tires has been studied (Colom et al., 2006, 2007). Literature reports various methods of compatibility of polyethylene as well as polypropylene with ground tire rubber (Wagenknecht et al., 2006; Sonnier et al., 2006, 2007, 2008). Fly ash is an inorganic waste from thermal power stations produced by combustion of coal and is considered as a waste. Non-disposal of this waste is a natural threat to the society because of environmental pollution. More than 84 thermal power stations (both public and private sector) are located in various parts of the country that produce huge quantity of FA as waste, the generation per annum being nearly 130 million tons. Utilization of this waste is only 47% of the total waste generated in various sectors. Thus there is enormous scope for utilization of the FA in non-conventional areas such as polymer and rubber industries. Earlier, authors have demonstrated that the mechanical properties of NR filled with fresh FA exhibited marginal increase in tensile strength, modulus at various elongations and hardness establishing that FA utilization makes the products economical in addition to reducing environmental pollution (Hundiwale et al., 2002). The utilization of FA as filler in polybutyleneterepthalate-toughened epoxy resin was studied and significant improvement in the mechanical properties were obtained (Ramakrishna et al., 2006). Results of the partial replacement of carbon black by

fresh FA in SBR are reported and it was found that FA can be used as a potential replacement to the conventional nonreinforcing fillers (Bidkar et al., 2006). In order to increase the filler–rubber interaction, adhesion, dispersion and mechanical properties of FA filled rubber vulcanizates, attempts have been made to utilize different coupling agents in varied proportions into the rubber. The effect of titanate coupling agent on the mechanical properties of fresh FA filled polybutadiene rubber as well as polycholoroprene rubbers were studied and an enhancement was observed in their mechanical properties (Alkadasi et al., 2004, 2006). The effect of Si-69 on the properties of FA/NR blends was studied and improvement in the tensile modulus and tear strength was observed with no change in tensile strength with only 2 and 4% of Si-69 (Thongsang and Sombatsompop, 2005). Rubber/plastic blends based on waste plastics have found potential applications in highway products. LDPE can be used as functional filler in modifying bitumen for road applications (Nag et al., 2006). Increased process ability, ultimate elongation and set properties of thermoplastic elastomers derived from RR and waste plastic (LDPE) have already been reported (Nevatia et al., 2002). The thermal analysis of thermoplastic elastomer compositions prepared from recycled polyethylene and ground tire rubber, along with its mechanical and rheological properties were studied (Grigoryeva et al., 2006; Scaffaro et al., 2005). It was observed that RR enhanced the impact strength of PP (Tantayanon and Juikham, 2004). Investigations to produce a new building material from FA and WPE were conducted (Alkan et al., 1995). Similarly, materials from FA and post-consumer PET present in MSW were produced for improvement in mechanical properties (Li et al., 1998). The effect of treatment of FA with Si-69 and loading of FA on mechanical and morphological properties of recycled high-density polyethylene was studied. The authors observed that Si-69 treatment imparted significant improvement in the mechanical properties of the HDPE-FA composites (Atikler et al., 2006). In the present study attempts have been made to resolve the problem of solid waste disposal such as WPE, RR and FA in making value added products from the blends and composites of these materials to achieve economic advantage. Since all these materials are derived from waste streams, their use would help ease the solid waste management problem and help prevention of environment pollution. Thermoplastic elastomers derived from WPE and RR and their composites with fresh and Si-69 treated FA have been studied for its mechanical, dynamic mechanical as well as morphological characteristics; with an objective to use these composites for making value added products such as vibration dampers in automobile industry, bumpers, traffic signal posts, floor tiles and so on.

2.

Experimental

2.1.

Materials

Post-consumer carry bags and pouches were collected manually from the downstream of MSW of Indian Institute of Technology, Kharagpur campus, India. It is termed as municipality polymer waste (MPW). From this MPW, the WPE was segregated and its specifications are given in Table 1. The WPE consists mostly of high-density polyethylene (HDPE) and small quantities of low-density polyethylene (LDPE) with

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Table 1 – Properties of waste polyethylene. Typical data ◦

MFI 5 kg/190 C Density Tensile strength

Unit

Value

g/10 min g/cm3 MPa

1.876 0.95 21.2 ± 0.2

Table 3 – Properties of reclaimed rubber. Test method

Typical data

ASTM D 1238 ASTM D792 ASTM D 638

Mooney viscosity Density Tensile strength

Unit ◦

ML (1 + 4) @ 100 C g/cm3 MPa

Value

Test method

53 1.2 5.5 ± 0.3

ASTM D 1646 ASTM D792 ASTM D 638

Table 4 – Composition of the fresh fly ash (Class F). % Elemental composition Component Aluminium Silicon Calcium Iron Titanium

Content (%)

% Oxide composition Component

33.71 54.84 1.41 6.97 3.07

Al2 O3 SiO2 CaO Fe2 O3 TiO2

Content (%) 32.16 59.23 0.99 5.03 2.59

Table 5 – Formulation of the blends. Sample code

Fig. 1 – FTIR curves for different waste plastics. minor proportions of polypropylene (PP) and polystyrene (PS) as characterized from infra-red spectroscopy data given in Fig. 1. The peak positions assigned have been characterized in comparison with virgin polymers. The peak positions and the corresponding group frequencies are given in Table 2. RR (65% rubber, 28% carbon black and 7% residue) specifications as given in Table 3 were procured from Gujarat Reclaim and Rubber Products Limited, India. FA (class F type) having a density of 2.33 g/cm3 and total evaporable moisture content of 1.54% was procured from Kolaghat Thermal Power Station, West Bengal, India. It was sieved using ASTM meshes ranging in size from 72 to 350 and then dried at 100 ◦ C for 24 h. The particle size of FA falls in the range of 60–100 ␮m. The chemical composition of the FA (used in this work) was characterized by Energy dispersed X-ray analysis (EDX) as shown in Table 4 (Paul et al., 2007). Bis (3-triethoxy silyl) propyl tetra sulphide (Si-69) procured from M/S Birla Tyres Limited; Balasore, India was used as the coupling agent.

2.2.

Preparation of blends and test samples

The carry bags and pouches (WPE) in the thickness range of 10–20 ␮m were collected, segregated, cleaned and washed with detergent in a washing machine and dried in air in absence of sunlight. It was then chopped into formidable square shaped sizes of approximately 4 × 6 cm2 for further processing in a plastics processing equipment. RR was melt mixed with WPE in a Brabender Plasticorder (Model PLE 651) at the optimized processing conditions of 180 ◦ C, rotor speed

Waste polyethylene (W)

Whole tire reclaimed rubber content (R)

100 95 90 85 80 70 60 50 40 30

0 5 10 15 20 30 40 50 60 70

WR0 WR5 WR10 WR15 WR20 WR30 WR40 WR50 WR60 WR70

of 80 rpm and mixing time of 5 min. WPE was melted first for 2 min before the addition of RR. The blend ratio between WPE and RR has been shown in Table 5. After melt blending, the molten mass was immediately sheeted out to thin sheets of 3 mm thick on a two roll cold open mixing mill (size 152 × 330 mm2 ). It was then compression molded in an electrically heated hydraulic press for 2 min at 180 ◦ C and 5 MPa to 2.5 mm sheets and subsequently cooled under pressure by water circulation through the platens.

2.3.

Surface treatment of FA

The fresh FA was treated with Si-69 at concentrations varying from 1 to 5 percent by weight (% wt). First the S-i69 was made into a solution in ethanol. About 1% by wt i.e. 1 g of the Si-69 was dissolved in 100 ml of ethanol, and stirred for 30 min. 100 g of FA was then added into the solution while stirring for a further period of 15 min, in order to ensure a uniform distribution of the coupling agent on the FA surface. The surface treated FA was then dried at 100 ◦ C for 12 h in an oven till constant weight. Similarly, 3 and 5% solutions of Si-69 were prepared and treated with FA for modifying the surface of the FA.

Table 2 – Peak position of different waste plastics analyzed. Sample name

Peaks position (cm−1 )

Assignment of peaks

WHDPE

2922, 2850, 1462, 876, 720 1018

Long chain crystalline compound Aryl ether group

WLDPE

2921, 2846, 1471, 729

Aliphatic hydrocarbon with long chain, alkyl group-long chain compound

WPP

1458, 1375, 1167 2951, 2877, 1458, 1375 2951, 1458, 1375, 1167, 973

Aliphatic hydrocarbon with branched chain Alkyl group-methyl substituent Aliphatic hydrocarbon with highly branched chain

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Table 6 – Formulation of the composites. Sample code

WPE:RR blend

WR1510FA WR1520FA WR1530FA WR1540FA WR1550FA WR1560FA WR1550FA1CA WR1550FA3CA WR1550FA5CA

85:15 85:15 85:15 85:15 85:15 85:15 85:15 85:15 85:15

2.4.

Fly ash content (FA) 10 20 30 40 50 60 50 50 50

Si-69 content (CA) – – – – – – 1 3 5

Preparation of composites

FA in the proportion of 10–60% (w/w) was melt mixed with WR15 blend in the Brabender Plasticorder (PLE-651) under the optimum processing conditions as described in our earlier section. In another set FA was surface treated with Si-69 at three different concentrations (1, 3 and 5%) and then the treated FA was mixed with WR15 blend at 50 phr loading. The sample codes are given in Table 6.

2.5.

Physicomechanical properties

Tensile properties of the blends and the composites were determined in accordance with ASTM D638 method using dumbbell shaped specimens, of type IV in an Universal Testing Machine of Hounsfield make (H25 KS). Crosshead speed of the UTM was maintained at 50 mm/min. Flexural tests were conducted as per ASTM D790 at a crosshead speed of 1.2 mm/min. Dimensions of specimens for the test was 65 × 12.7 × 3 mm3 . Tension set at 100% elongation was determined using dumbbell test specimens as per ASTM D638. The dumbbell with a gauge length of 25 mm was elongated up to 100% and kept under strained condition for 10 min. Then the stress was released to allow the sample to retract at the same rate of extension. The sample was kept for 10 min for recovery at room temperature. The difference in gauge length expressed as the percentage of initial gauge length was taken as the set. Five replicates were run for each composition. All tests were performed on a Universal Testing Machine (Hounsfield, Model H25 KS) at room temperature. The tensile impact energy of the blends was measured using an Impact Tester (6545/000) as per DIN 53448. The Shore D hardness measurement was performed according to ASTM D 1132 by a Shore-D Durometer (STD-D).

2.6.

Thermogravimetric analysis

Thermal stability of the WPE:RR blends and WR15-FA filled composites was studied by using a thermogravimetric analyzer (TG-Q50) of TA Instruments, USA under nitrogen atmosphere at a heating rate of 20 ◦ C/min.

2.7.

Dynamic mechanical analysis

2.7.1.

Temperature sweep measurement

Dynamic mechanical analysis (DMA) measurements were performed with the help of a Dynamic Mechanical Analyzer, 2980 V1.7B of TA instruments, USA. The experiments were carried out using the dual cantilever mode over the temperature range from −50 to +120 ◦ C, at a rate of 5 ◦ C/min in an atmosphere of nitrogen. The samples were scanned at a frequency of 1 Hz,

and a strain level of 20 ␮m was applied which was well within the linear viscoelastic region. The storage (E ) modulus, loss (E ) modulus and the loss tangent (tan ı) were recorded as a function of temperature. The test was performed using rectangular samples of dimensions 35 × 12.79 × 3.17 mm. The exact dimensions of each sample were measured before the scan.

2.7.2.

Double strain amplitude (DSA) study

To study the degree of inter-aggregate interaction due to the modifications; the dynamic mechanical behavior of the blends and composites were studied in strain sweep mode. The tests were carried out in a dynamic mechanical analyzer, model 2980 DMA V1.7B of TA instruments make in multi-strain dual cantilever mode at 1 Hz frequency.

2.8.

SEM study

For studying the phase morphology of the WPE:RR blends, the blends were etched in concentrated nitric acid at room temperature for 72 h to remove the rubber phase. The samples were then washed thoroughly with water and dried. Then the samples were sputter coated with gold and scanned under the SEM with the help of a JEOL (Model JSM-5800) scanning electron microscope, at zero degree tilt angle. Also failure analysis of the tensile fracture surface of the WR15-FA filled composites was carried out using SEM. The fractured surfaces were sputter coated with a thin layer of gold to avoid electrostatic charging during examination, and were examined under the SEM at zero degree tilt angle.

3.

Results and discussion

3.1.

Mechanical properties of WPE:RR blends

The formulations and coding of the blends are given in Tables 5 and 6, respectively. The WPE: RR blend ratio was varied from 95:5 to 30:70. The mechanical properties of the blends such as tensile strength, elongation at break, flexural strength and modulus, tensile impact strength, hardness and tension set are shown in Table 7. From Table 7, it is observed that the tensile strength decreases and the elongation at break increases with the increase in the RR proportion in the blend. WPE has a tensile strength of 21.2 MPa, which reduces to 9.8 MPa on incorporation of about 70 wt.% proportion of RR (WR70). This is expected as RR is a partially degraded rubber and contains carbon black as well as other additives in addition to the unperturbed sulfur crosslinks. Also RR is a mixture of partially degraded vulcanized NR and SBR, containing conventional tire additives and carbon black. However, the elongation at break increases from 101% for WPE to 789% for the WR70 blend. This trend has also been reflected in the flexural strength and flexural modulus of the WPE:RR blends, which decreases with an increase in RR content. Interestingly, the tensile impact strength increases with the increase in RR content in the blend up to 20 wt.% of RR. Thereafter it becomes difficult to determine the tensile impact strength of the blends, as the samples do not break with further addition of RR due to higher elongation. The blends exhibit more rubbery characteristics. The Shore D hardness of the blends increase with addition of RR onto WPE and this increase is distinct up to 20 wt.% of RR, thereafter it levels off, or even decreases marginally at higher proportions of 50 to 70 wt.% RR content. The tension set value of the blends goes on decreasing steadily as the RR content increases up to 70 wt.% implying

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Table 7 – Mechanical properties of WPE:RR blends. Sample

Tensile strength (MPa)

WR0 WR5 WR10 WR15 WR20 WR30 WR40 WR50 WR60 WR70 a

21.2 18.6 18.3 18.2 16.3 15.8 13.6 12.1 11.9 9.8

± ± ± ± ± ± ± ± ± ±

Elongation at break (%)

0.2 0.4 0.2 0.3 0.4 0.5 0.3 0.9 0.4 0.1

101 390 384 383 420 456 524 630 659 789

± ± ± ± ± ± ± ± ± ±

Flexural strength (MPa)

3 7 4 12 4 8 10 6 10 5

25.4 13.9 14.1 14.0 12.8 12.3 11.8 10.7 10.2 9.7

± ± ± ± ± ± ± ± ± ±

0.5 0 0 0.6 0.3 0.2 0.4 0.1 0.3 0.2

Flexural modulus (MPa) 1154 334 412 418 320 311 302 304 290 278

± ± ± ± ± ± ± ± ± ±

10 4 18 8 3 5 8 11 13 17

Tensile impact strength (kJ/m2 )

Hardness (Shore D)

Tension set (%)

± ± ± ± ± ± ± ± ± ±

28 41 43 45 47 47 45 44 43 42

100 80 76 74 72 68 64 60 56 52

144 311 382 451 461 462 463 466 525 577

57 14 5 25 17 16a 13a 5a 16a 19a

No break.

increased elasticity of the blends. WPE has almost 100% set value whereas WR70 has a set of 52%. The reduction in the mechanical strength properties of the blends on increasing RR content owes to the presence of over limited amount of carbon black along with low level of homogeneity in the blends. The similar observation has been reported earlier in the blend of RR and HDPE (Punnarak et al., 2006).

3.2. Effect of untreated FA on the mechanical properties of WPE:RR (WR15) blends The mechanical properties of WPE:RR blends as a whole decreases in comparison with WPE (from Table 7). However, of all the proportions WR15 was taken as the optimum and FA was added to it at various loadings (Table 6). The mechanical properties of FA filled WR15 matrix were determined and the results are corroborated in Table 8. It can be clearly seen from Table 8 that as the filler content increases, the tensile and flexural strength of the blend composites increases up to 50 wt.% of the FA, thereafter it decreases on increasing the FA content in the WR15 blend matrix. The increase in the tensile and flexural strength of the composites can be attributed to the inter-diffusion between the matrix and filler. The elongation at break of the WR15 blend decrease drastically on incorporation of FA filler onto it. The decrease is steady with increase in FA content. The decrease in percentage elongation is assumed to be due to the restriction imposed on it to stretch because of packed FA particles. This results in de wetting or de bonding of the FA particle from the matrix causing cavitations. At lower filler concentrations, the matrix predominates with the filler particles completely and filler–filler interaction is relatively less causing higher elongation on stretching. At higher filler loadings, polymer–filler interaction reduces and filler–filler interaction takes a major

role, causing de bonding of the filler from the polymer matrix. The tensile impact strength of the WR15-FA decreases with increase in FA concentrations. This decrement in impact strength is obviously due to decrease in elasticity of the matrix and increase in brittleness due to higher dose of rigid FA particles. The hardness of FA filled WR15 composites are shown in Table 8. It is observed that the hardness of the blend increase from 45 to 55 Shore D as the FA filler loading increases to 50 wt.%. This is because FA consists of a mixture of inorganic metal oxides such as SiO2 , Al2 O3 and Fe2 O3 , which are rigid in nature. Similar increase in the hardness value was observed earlier in case of FA filled NR composites (Hundiwale et al., 2002).

3.3. Effect of treated FA on the mechanical properties of WR15 blend Table 8 shows the mechanical properties of treated and untreated FA filled WR15 composites. It can be clearly seen that the tensile strength increases with surface treatment of FA with Si-69 varying from 1 to 3% by wt. On increasing the concentration of Si-69 to 5% by wt. there is a decrease in the tensile strength of the composite. This may be due to the plasticizing effect of Si-69 between the FA and the blend matrix at higher concentrations of the coupling agent. Similarly the flexural strength and modulus of the composites increase with the increase in Si-69 up to 3 wt.% on the FA. This increase in the properties has been attributed to the better bonding of the treated FA particles with the WR15 thermoplastic elastomer matrix due to interaction of the silica component of FA with the Si-69 and the blend matrix consisting of diene rubbers in the RR. Thus 3% concentration of the Si-69 is considered to be optimum for surface treatment of FA

Table 8 – Variation in mechanical properties of WR15 blend with addition of treated and untreated FA. Sample WR15 WR1510FA WR1520FA WR1530FA WR1540FA WR1550FA WR1560FA WR1550FA1CA WR1550FA3CA WR1550FA5CA

Fly ash Si-69 Tensile Elongation at Flexural Flexural Tensile impact Hardness content content strength (MPa) break (%) strength (MPa) modulus (MPa) strength (kJ/m2 ) (Shore D) 0 10 20 30 40 50 60 50 50 50

0 0 0 0 0 0 0 1 3 5

18.2 ± 18.7 ± 18.9 ± 19.2 ± 19.6 ± 21.8 ± – 23.1 ± 24.8 ± 21.6 ±

0.3 0.1 0.0 0.3 0.1 0.2 0.4 0.5 0.1

383 ± 40.2 ± 31.2 ± 26.0 ± 20.2 ± 14.0 ± – 13.2 ± 13.5 ± 17.7 ±

12 3.6 2.4 1.2 2.2 1.3 1.2 0.7 2.1

14.0 16.3 18.5 18.7 18.7 19.0 20.0 19.6 23.9 18.0

± ± ± ± ± ± ± ± ± ±

0.6 0.5 1.4 1.2 0.2 1.9 0.2 0.9 0.3 0.3

418 423 612 614 620 698 1087 700 712 665

± ± ± ± ± ± ± ± ± ±

8 10 50 45 30 60 199 57 26 22

451 ± 156 ± 130 ± 130 ± 128 ± 127 ± – 138 ± 166 ± 142 ±

25 16 18 18 10 10 10 5 8

45 46 49 50 52 55 57 56 58 60

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for achieving best balance in physicomechanical properties. At this optimum level of coupling agent the tensile strength reaches a value of 24.8 MPa, the flexural strength of 23.9 MPa and the flexural modulus of 712 MPa as compared to absence of coupling agent. It is also observed that the tensile impact strength increases to166 kJ/m2 from 127 kJ/m2 with the incorporation of 3% Si-69. However the elongation at break decreases down to 13.5%, as expected with coupling agent treated FA incorporation. On the other hand hardness increases with the Si-69 treatment onto the FA filler. The increase is linear with an increase in treatment level of FA. This is obviously due to increase in modulus values because of increased filler–polymer interaction and rigidity of the matrix.

3.4.

Thermal stability

The TGA/DTA curves for the WPE, RR and their blends are given in Fig. 2(a). It can be observed that in the thermograms of WPE:RR blends there is only one slope which implies there is single stage decomposition for both the blend constituents. The WPE shows a residual weight of nearly 4.5% and has a maximum degradation temperature of nearly 466 ◦ C and the RR has a residual weight of 39.3% and a two-stage degradation temperature of 344 and 468 ◦ C, respectively. With the incorporation of RR into the WPE matrix the maximum degradation temperature is 483 ◦ C for WR15 blend and 486 ◦ C for WR70 blend. The residual weight is found to be 9.6 and 27.3% for WR15 and WR70 blend, respectively. Thus by adding RR to the WPE matrix a synergistic effect in thermal stability is observed. The TGA/DTA curves for the WR15-FA (treated and untreated) filled composite are given in Fig. 2(b). With the addition of FA onto the WR15 blend matrix the degradation temperature increases to 484 ◦ C for untreated and 486 ◦ C for treated composite implying again an increase in thermal stability with filler incorporation. The residual weight for untreated composite is 40.3% and it is 37.2% for the treated composite. From the TGA/DTA curves it can be confirmed that the thermal stability of the blends increases in comparison with the individual blend constituents and that of the treated and untreated WR15FA filled composite also increases in comparison with WR15 blend implying good indication of these being used for various applications.

3.5.

Dynamic mechanical analysis

3.5.1. Temperature dependence of storage modulus and loss tangent on WPE:RR blends Fig. 3(a) and (b) shows the storage modulus (E ) and damping factor (tan ı) versus temperature plots for the WPE and its blend with reclaimed rubber (values at different temperature are depicted in Table 9). The storage modulus of WPE:RR blend decreases with increasing temperature because of decrease in material stiffness. The storage modulus value increases with the increase in the proportion of RR at various temperatures as depicted in Table 9. In case of WR70, due to higher proportion of RR an inversion in the storage modulus is observed owing to the material becoming soft because of the plasticizing effect of RR. Hence RR acts as a plasticizer in the WPE matrix at higher proportion. In the WPE:RR blends, the low temperature transition due to WPE is not so prominent. It was also reported earlier that in RR-PE blends the glass transition temperature

Fig. 2 – TGA/DTA curves for (a) WPE:RR blends and (b) WR15-FA filled composite. of PE is masked by its crystallinity, and suppression of the secondary relaxation occurs due to the interaction of the blend components (Nevatia et al., 2002). In comparing the various proportions of WPE:RR blends, they do not show any prominent transitions due to PE at very low temperatures. At higher temperatures also no prominent transition is observed in the case of the blends. The peak tan ı value of the same system is higher as a result (Table 9).

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Table 9 – Storage modulus and loss tangent of the WPE:RR blend system. E (MPa)

Sample code

WR0 WR15 WR70

tan ı

−50 ◦ C

0 ◦C

25 ◦ C

75 ◦ C

−50 ◦ C

0 ◦C

25 ◦ C

75 ◦ C

1146 1344 1940

1035 1179 1382

870 953 953

342 375 299

0.046 0.074 0.091

0.078 0.078 0.087

0.104 0.100 0.104

0.206 0.208 0.214

clear from the table that in the WPE:RR blends the E value increases with the increase in RR content. With the addition of FA to this blend matrix the E value increases further showing increase in the Payne effect. But with the incorporation of Si-69 the E value decreases slightly. So this decrease may be explained due to higher filler–filler interaction by incorporating Si-69 coupling agent. Strain sweep tests are performed in order to investigate the effect of treated and fresh FA on the WR15 matrix. The E’ of the WR15 blend increases with incorporation of RR and FA which improves the properties further.

Fig. 3 – Plots of (a) storage modulus and (b) loss tangent versus temperature for the WPE:RR blends.

3.5.2. Strain amplitude dependence of storage modulus, loss modulus and tan ı An investigation of the strain dependence on the dynamic properties of the WPE, WPE:RR and treated and untreated WR15-FA composite were carried out at room temperature at a constant frequency of 1 Hz. The plots of storage modulus, loss modulus and tan ı with respect to double strain amplitude are presented in Fig. 4. In all the cases as seen in Fig. 4(a), storage modulus is found to be highly strain dependent, as it decreases with increasing strain. Literature report shows that this dependence of storage modulus on the strain level under dynamic deformation is referred to as the Payne effect (Payne, 1962; Payne and Whittaker, 1971). The difference in storage modulus at very low and high strains (E0 − E∞ ) as considered being the structure contribution to the storage modulus. E0 and E∞ are characterized by storage modulus at zero and infinite strain respectively and in this case due to the machine constraints are measured at 1% initial (Ei ) and final (Ef ) 100%. These results are tabulated in Table 10. It is

Fig. 4 – Effect of addition of FA and Si-69 onto the WR15 blend matrix on the strain dependence of storage modulus, loss modulus and tan ı.

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Table 10 – Effect of FA and Si-69 treatment on the strain dependence of storage modulus. Ei (MPa) (at 1% strain)

Sample WR0 WR15 WR70 WR1550FA WR1550FA3CA

3.024 2.867 2.768 3.106 3.070

The strain dependence of the loss modulus of the samples is also presented in Fig. 4(b). It is found that in contrast to storage modulus in the WPE:RR blends and WR15-FA composite, which decreases continuously with increasing strain, the loss modulus property shows a gradual increase with increasing strain for these particular samples and test conditions. This also shows increased filler aggregation in the composites. From Fig. 4(c), it can be observed that the tan ı, which is the ratio of the loss modulus to the storage modulus, is high for WPE (WR0) in comparison with WR15 and WR70 blends. Also the tan ı is high for the untreated filler loaded WR15 composite (WR1550FA) compared to the treated filler loaded WR15 composite (WR1550FA3CA). This lower tan ı can be attributed to a greater bonding between the polymer and the filler that withstands the dynamic deformation.

3.6.

Morphological properties

The phase morphology of the WPE:RR blend was studied. The blend morphology of WR0, WR15 and WR70 are shown in Fig. 5. The SEM study was carried out by removing the RR phase by concentrated nitric acid (etching) as explained in the experimental section. Fig. 5(a) shows the SEM photomicrographs of WPE after etching in conc. nitric acid. It shows only flowers of crystalline matrix shown by white domains and flow lines. Fig. 5(b) shows the SEM photomicrographs of WR15 blend after etching. It clearly shows a two-phase structure where the RR

Ef (MPa) (at 100% strain) 2.957 2.781 2.657 2.976 2.957

E = Ei − Ef 0.067 0.086 0.111 0.13 0.113

phase has been removed by etching. The white portions in Fig. 5(b) represent semi-crystalline WPE and the dark cavities are the areas where the rubber dwelt prior to extraction by conc. nitric acid. It also shows good dispersion of the rubber in the continuous thermoplastic matrix (WPE). Fig. 5(c) shows the SEM photomicrographs of WR70 blend after etching in conc. nitric acid. The figure shows large numbers of voids indicated by dark cavities and less crystal flows due to semi-crystalline WPE. Incompatibility between WPE and RR is quite evident in this case. Information about the nature of adhesion, failure and the relationship between structures and mechanical properties may be obtained by examining the tensile fracture surfaces by scanning electron microscopy of the composites. Fig. 6(a) shows tensile fractograph of WR15 at a lower magnification. The micrograph shows a very interesting mode of failure where the matrix is almost drawn to form fibrous structure of WPE in presence of the RR, simulating ‘noodle’ like structure. This is a clear indication of matrix flow and ductile failure. Whereas in the fracture surface of WR15-untreated/treated FA filled composite [WR1550FA (Fig. 6(b) and WR1550FA3CA [Fig. 6(c)] at a lower magnification the failure pattern changes significantly. In WR15 without FA [Fig. 6(a)] ductile failure is observed due to the presence of the soft RR matrix. However the thick fibrillar structure formation may be due to flow of the WPE matrix along with the RR during pull out in the applied stress direction. As soon as FA is incorporated into the WR15

Fig. 5 – Scanning electron micrographs of (a) WR0, (b) WR15 and (c) WR70 with rubber phase etched out.

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Fig. 6 – Scanning electron micrographs of tensile fractured samples of (a) WR15, (b) WR1550FA and (c) WR1550FA3CA (at lower magnification). matrix [Fig. 6(b)], the fibrillar structure is no more formed, but irregular particulate type structures appear. The influence of Si-69 can be clearly seen in Fig. 6(c), which shows greater adhesion of filler to the blend matrix and in turn supports the mechanical properties.

Fig. 7(a)–(c) shows the fracture surfaces of WR15 and untreated/treated FA filled WR15 (WR1550FA and WR1550FA3CA) composite at a higher magnification. Fig. 7(a) shows a fibrillar structure owing to higher proportion of WPE in the WR15 blend and the mode of failure is ductile. Fig. 7(b)

Fig. 7 – Scanning electron micrographs of tensile fractured samples of (a) WR15, (b) WR1550FA and (c) WR1550FA3CA (at higher magnification).

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illustrates that the filler is well dispersed in the matrix without agglomeration and exhibits no fibrillar structure. It is because the fibril formation due to orientation is hampered by the introduction of FA particles resulting in a rigid matrix. The effect of Si-69 treatment on the interfacial adhesion between FA and WR15 matrix (WR1550FA3CA) is shown in Fig. 7(c). This indicates greater embedment of the treated FA in the matrix. The treated FA particles are surrounded completely by the blend matrix resulting in better adhesion between the two and improved mechanical properties.

4.

Conclusion

Thermoplastic elastomers from WPE and RR were prepared and their properties were studied in detail. The tensile impact strength of all the blends showed a marked improvement with increase in RR proportion. WR15 blend was found to give the best balance in mechanical properties. Further the effect of FA filler on the properties of WR15 blend was evaluated. Tensile and flexural strength of the blend was increased to 21.8 and 19 MPa from 18.2 and 14 MPa on incorporation of 50 wt.% FA. With Si-69 treatment the tensile and flexural strength increased further to 24.8 and 23.9 MPa, respectively. Thermal stability of the WR15-FA filled composite improved significantly in comparison with that of the blend. Combining post-consumer WPE and RR with FA introduces a potentially useful composite material with improved technical properties.

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