- Email: [email protected]
Modification of Waste Polypropylene with Waste Rubber Dust from Textile Cot Industry and its Characterization
MODIFICATION OF WASTE POLYPROPYLENE WITH WASTE RUBBER DUST FROM TEXTILE COT INDUSTRY AND ITS CHARACTERIZATION J. Jose1, S. Satapathy2, A. Nag1 and G. B. Nando2, 1
Department of Chemistry, Indian Institute of Technology, Kharagpur, India. Rubber Technology Center, Indian Institute of Technology, Kharagpur, India.
2
Abstract: Waste plastics collected from municipality solid waste (MSW), were segregated, washed and dried. The fractions consisting predominantly of polypropylene were further segregated from the lot, cleaned and dried. These were chopped into pieces and then mixed in a Brabender Plasticoder with rubber dust from rubber textile cot industry at various proportions, till homogeneity is achieved. The tensile strength, impact strength and flexural strength of the blends were measured and observed that these properties increasing with increase in loading of rubber dust, reach a maximum at 10 wt% and then decreases. The dynamic mechanical properties of blends such as storage modulus, loss modulus and tan d measured by DMA-2980 shows an increase in damping characteristics with an increase in the proportion of rubber dust. The rubber dust consists of blends of NBR and PVC used in making textile cots in the textile industry after vulcanization. It is observed that 10% of rubber dust imparts better strength properties with waste PP. The dispersion of the scrap rubber dust in PP has been analysed under SEM and its compatibility has been studied. Keywords: recycling; polypropylene; rubber dust; composites; impact strength.
INTRODUCTION
Correspondence to: Professor G.B. Nando, Rubber Technology Center, Indian Institute of Technology, Kharagpur721302, India. E-mail: [email protected]. ernet.in
DOI: 10.1205/psep06045 0957–5820/07/ $30.00 þ 0.00 Process Safety and Environmental Protection Trans IChemE, Part B, July 2007 # 2007 Institution of Chemical Engineers
day. From the statistical point of view, the amount of polymer waste has been increased by about 30 times in the last 20 years (Garforth et al., 2004). The main problem due to polymer disposal comes in two broad categories; one from the packaging industry where thermoplastic materials are predominantly being used and vulcanized rubber scrap from tyre and other non-tyre rubber industries. Among thermoplastics, the main commodity plastics like PE, PP, PET and PS along with PVC are creating the major problem because they are very stable in nature and hardly attacked by the environmental effects and degrade (Awaja and Pavel, 2005; Samsudin et al., 2005; Najafi et al., 2006). The process of polymer recycling would be of much advantage from processing and economic point of view as it diverts the polymer waste into a useful product avoiding the problem of landfill and incineration (Abraham et al., 2005). The ideal solution to polymer waste disposal is recycling which shall be both environmentally acceptable and economically viable similar to that is being practiced with aluminium or iron (Choudhury et al., 2005). However, the nature of macromolecular materials present special
Polymer industries have grown substantially over the last 50 years. Thermoplastics play a major role today encompassing wide range of engineering products and involving a large spectrum of different polymers. The intended life-span of plastic products varies from several months, for example packaging materials, to over 50 years for building/ construction industry components. The world’s annual consumption of thermoplastics has increased from around 5 million tonnes in 1950s to nearly 100 million tonnes today. Packaging industry represents the largest single sector in the consumption of plastic today. In India the estimated production of polymers is 4.7 million metric tons annually. Of this, 60 –70% accounts for the production of polyethylene (PE) and polypropylene (PP) only (Satapathy et al., 2006; Stein, 1992; Santana and Manrich, 2003). Solid waste disposal is a growing world wide problem. Earlier most of them were buried in the landfill. But in the case of polymer material, it leads to serious after effects on environment as most of the polymers are not biodegradable and the space needed to fill those material are being reduced day by 318
Vol 85 (B4) 318–326
MODIFICATION OF WASTE POLYPROPYLENE WITH WASTE RUBBER DUST challenges to effective recycling, and at this point of time, the door remains open to advanced recycling techniques. Material recycling is the processes in which the macromolecular structure is kept basically intact, and the material is reformed into a new product. Some alteration of the molecular structure and/or morphology of the material may be brought about for the purpose of enhancing performance properties. This is the most desirable approach, as it may lead to conservation of energy and expense of minimum energy. It however, may pose technologically the most difficult task. Lots of work has already been carried out as blends, composites and additives involving thermoplastics, elastomers and thermoplastic elastomers by incorporating different additives such as cross-linking agents, surfactants, reinforcing fillers, and so on for improving the end-use properties and making value added products (Satapathy et al., 2006; Stein, 1992; Santana and Manrich, 2003; Garforth et al., 2004; Awaja and Pavel, 2005; Samsudin et al., 2005; Bengtsson et al., 2005; Wang and Sheng, 2005; Liu et al., 2005). Recently a large number of products from recycled polymer materials have been found their way in applications at various levels such as floor parquets, flower vases, waste paper baskets, park benches, picnic tables, plastic lumbers and so on. Quite often the recycled plastics compete with the virgin materials, in the market. Similarly accumulation of rubber waste particularly from tyre industries and tyre users has caused great concern among environmentalists about its proper utilization. These polymers are crosslinked rubbers having three-dimensional network structure, which render them non-biodegradable. They are utilized as grounded scrap rubber and are combined with various thermoplastic and rubbery materials to provide reduced-cost and better processing characteristics. Ground rubber particles of various mesh sizes are being used to modify materials such as linear low-density polyethylene (LLDPE), polypropylene (PP), polyurethane (PU) and polyvinyl chloride (PVC), apart from being used in rubber industries itself (Phinyocheep et al., 1993; Sasee and Emig, 1998; Shanmugharaj et al., 2005). Typically the rubber particles are blended at levels from 5 to 70% into the thermoplastic and elastomeric matrix using a batch mixer or melt extrusion system (twin-screw preferred) and chopped or cut into pellets suitable for further melt processing of the compounded material. In the present study attempts have been made to investigate the effect of rubber dust from textile cot industry in waste polypropylene. PP and rubber dust were melt-mixed in a Brabender Plasticoder and their physico-mechanical properties, fractured surface analysis and thermal properties have been reported.
EXPERIMENTAL Materials Used Waste polypropylene (WPP) collected from municipal solid waste was segregated on the basis of melting temperature (Tm), density and FTIR Spectroscopy. The waste rubber powder (rubber dust/RD) was supplied by INARCO, Gujarat, India. Rubber dust consists of PVC/NBR blend, Carboxylated NBR, animal glue, barium stabilizer, epoxidized soyabean oil, Carbon-black, silica, rutile grade TiO2, zinc oxide, apart from sulphur and accelerators. Rubber dust was sieved to remove coarse particles and the foreign materials.
319
Polypropylene pouches purchased from the market were used as recycled PP for comparison. The virgin polypropylene (Koylene HP) obtained from IPCL, Vadodara, India also used as reference.
Determination of Physical Properties Density Uniform square shapes (20 mm 20 mm2) of solid samples were prepared and the density was measured according to ASTM D 792. Butyl acetate (density ¼ 0.876 g cc21) has been used as the reference liquid (Table 1).
Heat distortion temperature HDT was measured using HDT/VSP Apparatus (Model CA-100 255701) according to ASTM D 648 (Table 1).
Melt flow index MFI of virgin and recycled polypropylene were measured using Melt Flow Tester (CEAST, Italy) at a temperature of 2308C. The virgin polypropylene (Koylene HP) has a melt flow index of 10.154 g/10 min and the recycled PP has an MFI of 12.707 g/10 min.
Preparation of Samples The waste plastic pouches were segregated from the municipal solid waste, cleaned, washed with detergent powder mechanically and dried. This waste is segregated in such a way that it consists of mostly PP with minor proportions of HDPE, LDPE, LLDPE, PET and PS. They are chopped into formidable sizes for further processing in a Brabender Plasticorder. The rubber dust also sieved through a 500 microns mesh and the coarse particle were removed. Melt blending of waste PP, recycled PP and virgin PP rubber dust was carried out in a Brabender Plasticorder (Model PLE 651). The processing conditions were optimized by using Taguchi method with waste PP. The conditions are; a temperature of 1908C, rotor speed of 60 rpm and residential time of 8 min. The proportions of rubber dust varied from 10 and 30 to 50 wt% of the total polymer. The molten mass was immediately sheeted into thin sheets of 3 mm thick on an open mixing mill (Schwabenthan, Berlin) at room temperature. The sheets were compression molded between Teflon sheets at a temperature of 1908C and at a pressure of 106 MPa in an electrically heated compression molding hydraulic Press (Moore make, UK) for 2 min and cooled
Table 1. Physical properties of PP materials and rubber dust. Material code Virgin polypropylene (VPP) Virgin polypropylene with 10% rubber dust composite (VPP10RD) Recycled polypropylene (RPP) Recycled polypropylene with 10% rubber dust composite (RPP10RD) Waste polypropylene (WPP) Waste polypropylene with 10% rubber dust composite (WPP10RD) Rubber dust
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318 –326
Density (g cc21) HDT (8C) 0.916 0.929
94 92
0.919 0.921
81 94
0.889 0.897
80 84
0.920
—
320
JOSE et al.
down to room temperature by passing cold water through the platens to obtain tensile sheets of dimension 15 cm 15 cm.
FTIR Studies Thin films of different waste plastics were cleaned thoroughly, dried and prepared in a compression molding press between two Teflon sheets at 1908C under 10 MPa pressure. Similarly, thin films of virgin polymers (LDPE, LLDPE, HDPE, PP, PS and PVC) and recycled PP were also prepared. FTIR studies on the thin films were performed using the Perkin Elmer Spectrum GX spectrometer in the range of 4000–400 cm21. Results of waste and virgin plastics were compared and used in the segregation of waste PP from the lot.
Dynamic Mechanical Analysis Elastic and viscous response of the polymers and its composites with rubber dust were determined by using a DMA Model 2980 (TA make) in the temperature range of 2508C to þ1208C in presence of liquid nitrogen medium at a frequency of 1 Hz. The heating rate was maintained at 58C min21.
SEM Analysis A JEOL-JSM-5800 scanning electron microscope was used to study the topography of the tensile fracture surfaces of the specimens after testing in order to understand the failure mechanism. Before examination, the fracture surfaces were sputter-coated with a thin layer of gold in a vacuum chamber.
Physico-Mechanical Property Determination Dumbbell specimens were punched out from the tensile sheets using ASTM cutting Die-C. The tensile property measurement was performed in an universal testing machine (Model No. H25KS of Hounsfield, UK) at a cross head speed of 10 mm min21 at 258C as per the ASTM D 638. The average values of five test results are reported. Flexural test specimens were also punched out from the tensile sheets and the flexural modulus was determined as per ASTM D 790 in a universal testing machine (Model No. H25KS of Hounsfield, UK). The testing speed was kept constant at 1 mm/min for all samples. Tensile impact specimens were punched out from the tensile sheet and the tests were performed as per DIN 53448 in an Impact Tester (Model No. 6545/000 of Ceast make). Izod and Charpy Impact property measurements were performed on Digital Pendulum Impact Tester (CEAST, Italy; model-P/N 6963.000) according to ASTM D 256 A & B. Notching of 2.54 mm depth on the sample has been done by using notching apparatus Notch Vis—CEAST, Italy. The Shore D hardness measurement was performed according to ASTM D 1132 by a Shore-D Hardness Tester (STD-D). Each specimen was tested thrice at three spots which were at a distance of at least 5 mm from each other and 13 mm from any edge of the test piece.
RESULTS AND DISCUSSION FTIR Studies The plastic wastes after segregating for PP and other thermoplastics, were extensively studied by taking four different samples through visual inspection. These samples coded as P1, P2, P3 and P4 were analysed by FTIR and the band widths were presented as follows (Table 2). By comparing the FTIR peaks of different waste plastics with the peaks of virgin materials, the waste plastics have been further categorized into P1 as low density polyethylene (WLDPE), P2 as polypropylene (WPP), P3 as linear low density polyethylene (WLLDPE) and P4 as high density polyethylene with impurities (WHDPE). The portion designated as WPP has been taken for further study (Figure 1). Similarly the rubber dust, a waste from rubber cots and apron industry was analysed by FTIR spectroscopy and the band widths with peaks are shown in Figure 2. The peaks obtained confirm the presence of following groups in the material (Table 3).
Table 2. Peaks position of different waste plastics analysed. Sample code P1 (WLDPE)
2921, 2846, 1471, 1377, 729 2921, 2846, 1464, 720 2921, 1464, 729, 720
P2 (WPP)
1458, 1375, 1167
DSC Analysis The waste PP and rubber dust were subjected to differential scanning chromatography (DSC) study using DSC Q100 model in the temperature range from room temperature to 4008C at a heating rate of 108C min21 in N2 atmosphere. The peaks of melting temperature were used to categorize the waste PP from the lot.
P3 (WLLDPE)
Thermo Gravimetric Analysis Thermal degradation studies of the waste polypropylene and its composites with rubber dust were carried out using a Thermo Gravimetric Analyzer, TA instruments (Model TG Q50) at a heating rate of 208C min21 in an atmosphere of nitrogen, from room temperature to a temperature of 6008C.
Peaks position (cm21)
2951, 2877, 1458, 1375 2951, 1458, 1375, 1167, 973 2905, 1714, 1464, 1377, 729, 720 2905, 1464, 720
P4 (WHDPE)
2922, 2850, 1462, 876, 719 1018
Assignment of peak Aliphatic hydrocarbon with long chain Alkyl group—long chain compound Aliphatic hydrocarbon— possibly long chain crystalline Aliphatic hydrocarbon with branched chain Alkyl group—methyl substituent Aliphatic hydrocarbon with highly branched chain Aliphatic hydrocarbon— possibly long chain crystalline Long chain compound with alkyl group Long chain crystalline compound Aryl ether group
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318– 326
MODIFICATION OF WASTE POLYPROPYLENE WITH WASTE RUBBER DUST
321
Physico-Mechanical Properties The physico-mechanical properties such as tensile strength, elongation at break, flexural strength, breaking energy impact strength studies by tensile impact, Izod impact and Charpy impact test as well as hardness properties of virgin PP and waste plastics as well as their composites with rubber dust at different proportions have been studied and shown in Figures 3–8. The virgin PP has higher mechanical strength properties such as tensile strength impact strength, but with degradation it loses the properties rapidly to an extent of nearly 50% of its original strength. In the case of waste PP, it exhibits lower mechanical
Figure 1. FTIR spectra of major thermoplastic wastes.
Figure 3. Tensile strength of different PP-rubber dust systems.
Figure 2. FTIR spectrum of rubber dust.
Table 3. FTIR peaks of rubber dust. Sample code Rubber dust
Peaks position (cm21)
Assignment of peak
3152
2 2OH group
2927, 2856, 1457 2927, 2237, 1725, 1457
Alkyl groups Nitrile type substituent in the aliphatic chain Aromatic compound—mono or possibly distributed Aromatic compound—possibly phenoxy or amino substituent Carbonyl compound—possibly ester or ketone
3042, 1592, 1488, 754, 688 1592, 1488, 1297, 754 1725, 1297, 1189, 1162
Figure 4. Elongation at break comparison of different PP-rubber dust systems.
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318 –326
322
JOSE et al.
Figure 5. Flexural strength properties of different PP-rubber dust systems.
Figure 7. Izod impact strength of different PP-rubber dust systems.
properties initially after reprocessing. This is because during long term exposure to sunlight, humidity, air and other environmental conditions, the saturated polymer chains undergoes chain scission particularly at tertiary C-atoms forming C2 2OH or C5 5O groups. This leads to the reduction in molecular weight. It has been observed that the mechanical properties of the waste PP containing 10 parts by weight (pbw) of rubber dust is almost equal to those of virgin PP. The tensile strength of WPP containing 10 wt% of rubber dust is enhanced by 100% as compared to that of reprocessed WPP. Similarly the impact strength of WPP improves on incorporation of rubber dust to the extent of 10 pbw as compared to that of virgin PP which shows a decline in the impact strength on incorporating rubber dust. Thus the enhancement in mechanical properties of waste
PP may be attributed to the following reasons: The C–OH or C5 5O groups generated during the degradation process are more polar as compared to the saturated C–C and C –H bonds present in the virgin polymers. Since rubber dust contains NBR-PVC blends as well as carboxylated NBR which are polar in nature helps in compatibility due to dipole –dipole interactions. Also the devulcanized component of the rubber dust may contribute to the formation of additional crosslinks during molding resulting in enhanced properties. On the other hand as the percentage of the rubber dust increases further, the vulcanized rubber forms a separate phase and causing phase separation resulting in reduction of properties. The virgin thermoplastic due to its long chain molecule are very flexible and is having low hardness value. The polymer can become harder when the crystallinity is increased or hard
Figure 6. Tensile impact strength of different PP-rubber dust systems.
Figure 8. Charpy impact strength of different PP-rubber dust systems.
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318– 326
MODIFICATION OF WASTE POLYPROPYLENE WITH WASTE RUBBER DUST
323
Table 4. Hardness value of different PP materials and its composites. Sample code
Hardness (shore D)
VPP0RD VPP10RD WPP0RD WPP10RD WPP30RD WPP50RD RPP0RD RPP10RD RPP30RD RPP50RD
45 + 1 46 + 1 62 + 1 61 + 1 50 + 2 38 + 2 43 + 1 42 + 1 39 + 2 39 + 2
segments are introduced to the long chain. But in the case of waste plastic the degradation make them very hard. The vulcanized rubber part is having less effect on the hardness of virgin PP because its hardness value is very less compared to that of waste PP. But the presence of rubber dust in the waste PP significantly reduces the hardness of waste PP (Table 4).
Figure 10. TGA curves for rubber dust and PP materials.
The segregated waste PP were subjected to differential scanning calorimetry (DSC) study using DSC Q100 model in the temperature range from room temperature to 4008C. The DSC thermogram [Figure 9(a)] showed two endothermic peaks; one at 1658C corresponds to PP and the other at 2358C corresponds to polyethylene terephthalate (PET), respectively. Thus it has been inferred that the sample may be primarily PP and may contain small amount of PET. The DSC thermogram of the rubber dust has been shown in Figure 9(b). The thermogram shows a large number of peaks indicating that the material is a mixture of different polymers and additives; as expected.
two stage degradation one at around 3508C and the other at 450 –4708C. Where as virgin PP shows a clearly simple degradation temperature at 5008C considered to be the most stable material. (In the case of rubber dust, the degradation temperatures are 2908C and 4468C and the residue remained is 29 wt%. The degradation temperatures of WPP-rubber dust composite were 3198C and 4658C.) It seems the presence of rubber dust reduces the thermal stability of WPP to a great extent. It may be attributed to the presence of large quantities of volatile materials in the rubber dust as well as due to the presence of various metallic salts which might activate the degradation process in PP. The catalytic degradation of PP polymer occurs at much lower temperature compared to the thermal degradation (Bajsic et al., 2005; Aguado et al., 2000; Filho et al., 2005).
TG Analysis
Dynamic Mechanical Analysis
TGA thermograms of waste PP, virgin PP, rubber dust and rubber dust-PP composite are shown in Figures 10 and 11. The WPP looses nearly 10% of it weight at 3008C due to devolatilization of volatile matters as well as plasticizers in the compound/product mix. Thereafter it sharply degrades at 460 –4708C considered to be the degradation temperature of WPP. Residual weight is nearly 12%. On the other hand, the rubber dust and the PP-rubber dust composites exhibit
The DMA analysis of the waste PP and the thermoplastic vulcanizates containing 10 wt% and 50 wt% of rubber dust has been carried out. As expected the storage modulus increases with increased proportion of rubber dust (Figure 12). The loss modulus (E00 ) versus temperature plots of the TPVs are shown in Figure 13. A sharp increase in E00 value at around 108C in the case of WPP containing 10 wt% of rubber dust implies that the crystallinity of PP
DSC Analysis
Figure 9. DSC thermogram of (a) waste PP (WPP) and (b) rubber dust. Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318 –326
324
JOSE et al.
Figure 11. Derivative peaks for rubber dust and PP materials.
matrix has been disturbed and the system is able to dissipate more energy in the form of heat. Also, there is no any characteristic shift in the tan d peak towards higher temperature when rubber dust is added to WPP as is evident from Figure 14. This may be attributed to reduction in the crystallinity of WPP on the addition of rubber dust and also no significant crosslink formation. Thus the damping characteristic of the material has increased to a greater extent due to the introduction of rubber dust (vulcanized particles) which shows better elasticity in the composite along with good mechanical properties. This can be very useful in applications where high load transfer is required for products which are subjected to high static and cycling loading. Dynamic mechanical analyses of WPP, RPP and VPP containing 10 wt% of rubber dust have been shown in Figure 12 –14. Figure 12 shows the storage modulus (E0 ) versus temperature in the temperature range from 2608C to þ1408C. The E0 value reduces from 2250 MPa to below 1000 MPa at influx temperature of 08C for WPP containing 10 wt% of rubber dust. Where as for RPP10RD the influx temperature is increased to nearly 208C and the storage modulus reduced marginally to 1500 MPa. For virgin PP (VPP) initial storage modulus is around 1800 MPa at 2608C which just lowered onto 1300 MPa at 308C. Loss modulus (E00 ) versus temperature plots for the PP (WPP, RPP and VPP) containing 10 wt% of rubber dust is shown in Figure 13. WPP10RD shows the maximum loss modulus of 220 MPa at 08C where as RPP10RD and VPP10RD shows the maximum loss modulus of 175 and 160 MPa at 158C. This exhibits that WPP with rubber dust (10 wt%) always has a higher loss, thus maximum damping characteristics. The above findings are further supported from the damping peaks of the samples shown in Figure 14. WPP10RD shows maximum damping. WPP has the advantage of higher energy dissipation at a temperature of 08C. This is quite significant from the application point of view.
SEM ANALYSIS Figure 12. Storage modulus of PP composites.
The SEM photographs of fractured surface of waste PP is shown in Figure 15 which shows a fibrillar structure. The fibrils are generated due to extensive stretching leading to order
Figure 13. Loss modulus for PP composites.
Figure 14. Tan d curves for PP composites.
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318– 326
MODIFICATION OF WASTE POLYPROPYLENE WITH WASTE RUBBER DUST
325
crystallinity developement. The surface is found to be very rough and mutilated. The surface morphology of waste polymer composites with rubber dust (Figure 16) shows a smoother surface topography because of better particles stress distribution at the interfaces and easier stress distribution by the crosslinked rubber dust particles. It also exhibits better PP-rubber dust interaction. This is in agreement with tensile property results which exhibit higher strength properties. Further the smaller particle size of the rubber dust which is already crosslinked acts as reinforcing fillers in the PP matrix which enhances the tensile as well as impact strength properties. Figure 17 shows the SEM photomicrograph of the rubber dust with an average particle size of 5 mm.
CONCLUSION Figure 15. SEM of waste PP.
Waste polypropylene has been segregated from municipal solid waste by visual means and FTIR is used as basic tool for characterization. The addition of rubber dust as waste from the textile cot industry into virgin PP, results in a reduction in the mechanical properties because of poor interaction between the two phases where as incorporation of the same rubber dust onto waste PP improve the properties significantly. However, the thermal stability is reduced marginally. Impact properties improve on the addition of rubber dust with WPP, where as that with virgin PP and recycled PP this property reduces. The SEM photomicrographs support greater interaction of the waste PP with the crosslinked rubber dust. The damping characteristics of WPP with 10 pbw of rubber dust improve remarkably most of the properties implying that this composite may be made use of various damping applications.
Future Scope
Figure 16. SEM of WPP-rubber dust composite.
Recycling of plastics and rubber waste is a major environmental issue and a task for the society and technologist. Research is in progress in this field for utilization of waste rubber and plastic in making different value added products.
Figure 17. SEM of rubber dust particles.
Abraham, T.N., George, K.E. and Peijs, T., 2005, Progress in Rubber, Plastics and Recycling Technology, 21: 73–83. Aguado, P.J., Serrano, D., Escola, J.M., Garagorri, E. and Ferna´ndez, J.A., 2000, Polym Degradation Stability, 69: 11 –16. Awaja, F. and Pavel, D., 2005, European Polymer Journal, 41: 1453–1477. Bajsic, E.G., Rek, V., Leskova, M. and Smit, I., 2005, Proceedings of the 8th Polymers for Advanced Technologies International Symposium, Hungary. Bengtsson, M., Gatenholm, P. and Oksman, K., 2005, Composites Science and Technology, 65: 1468– 1479. Choudhury, A., Mukherjee, M. and Adhikari, B., 2005, Progress in Rubber, Plastics and Recycling Technology, 21: 117– 137. Filho, P., Graciliano, E.C., Silva, A.O.S., Souza, M.J.B. and Araujo, A.S., 2005, Catalyst Today, 107– 108: 507–512. Garforth, A.A., Ali, S., Herna´ndez-Martı´nez, J. and Akah, A., 2004, Current Opinion in Solid State and Materials Science, 8: 419– 425. Liu, W., Misra, M., Askeland, P., Drzal, L.T. and Mohanty, A.K., 2005, Polymer, 46: 2710– 2721. Najafi, S.K., Elham, H. and Tajvidi, M., 2006, J of Applied Polymer Science, 100: 3641–3645. Phinyocheep, P. and Axtell, F.H., 1993, ACS Rubber Division 144th Meeting, Conference Proceedings, 26– 29 October, Paper No. 40.
REFERENCES
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318 –326
326
JOSE et al.
Samsudin, S.A., Hassan, A., Mokhtar, M. and Jamaluddin, S.M.S., 2005, Progress in Rubber, Plastics and Recycling Technology, 21: 261–276. Santana, R.M.C. and Manrich, S., 2003, J of Applied Polymer Science, 88: 2861–2867. Sasee, F. and Emig, G., 1998, Review paper, Chem Eng Tech, 21: 777– 789. Satapathy, S., Chattopadhyay, S., Chakrabarty, K.K., Nag, A., Thiwari, K.N., Tikku, V.K. and Nando, G.B., 2006, Studies on the effect of electron beam irradiation on waste polyethylene and its
blends with virgin polyethylene, J of Applied Polymer Science, 101: 715– 726. Shanmugharaj, A.M., Kim, J.K. and Ryu, S.H., 2005, Polymer Testing, 24: 739– 745. Stein, R.S., 1992, Colloquium Paper, Proc Nati Acad Sci, 89: 835– 838. Wang, L. and Sheng, J., 2005, Polymer, 46: 6243–6249. The manuscript was received 28 July 2006 and accepted for publication after revision 12 December 2006.
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318– 326
Department of Chemistry, Indian Institute of Technology, Kharagpur, India. Rubber Technology Center, Indian Institute of Technology, Kharagpur, India.
2
Abstract: Waste plastics collected from municipality solid waste (MSW), were segregated, washed and dried. The fractions consisting predominantly of polypropylene were further segregated from the lot, cleaned and dried. These were chopped into pieces and then mixed in a Brabender Plasticoder with rubber dust from rubber textile cot industry at various proportions, till homogeneity is achieved. The tensile strength, impact strength and flexural strength of the blends were measured and observed that these properties increasing with increase in loading of rubber dust, reach a maximum at 10 wt% and then decreases. The dynamic mechanical properties of blends such as storage modulus, loss modulus and tan d measured by DMA-2980 shows an increase in damping characteristics with an increase in the proportion of rubber dust. The rubber dust consists of blends of NBR and PVC used in making textile cots in the textile industry after vulcanization. It is observed that 10% of rubber dust imparts better strength properties with waste PP. The dispersion of the scrap rubber dust in PP has been analysed under SEM and its compatibility has been studied. Keywords: recycling; polypropylene; rubber dust; composites; impact strength.
INTRODUCTION
Correspondence to: Professor G.B. Nando, Rubber Technology Center, Indian Institute of Technology, Kharagpur721302, India. E-mail: [email protected]. ernet.in
DOI: 10.1205/psep06045 0957–5820/07/ $30.00 þ 0.00 Process Safety and Environmental Protection Trans IChemE, Part B, July 2007 # 2007 Institution of Chemical Engineers
day. From the statistical point of view, the amount of polymer waste has been increased by about 30 times in the last 20 years (Garforth et al., 2004). The main problem due to polymer disposal comes in two broad categories; one from the packaging industry where thermoplastic materials are predominantly being used and vulcanized rubber scrap from tyre and other non-tyre rubber industries. Among thermoplastics, the main commodity plastics like PE, PP, PET and PS along with PVC are creating the major problem because they are very stable in nature and hardly attacked by the environmental effects and degrade (Awaja and Pavel, 2005; Samsudin et al., 2005; Najafi et al., 2006). The process of polymer recycling would be of much advantage from processing and economic point of view as it diverts the polymer waste into a useful product avoiding the problem of landfill and incineration (Abraham et al., 2005). The ideal solution to polymer waste disposal is recycling which shall be both environmentally acceptable and economically viable similar to that is being practiced with aluminium or iron (Choudhury et al., 2005). However, the nature of macromolecular materials present special
Polymer industries have grown substantially over the last 50 years. Thermoplastics play a major role today encompassing wide range of engineering products and involving a large spectrum of different polymers. The intended life-span of plastic products varies from several months, for example packaging materials, to over 50 years for building/ construction industry components. The world’s annual consumption of thermoplastics has increased from around 5 million tonnes in 1950s to nearly 100 million tonnes today. Packaging industry represents the largest single sector in the consumption of plastic today. In India the estimated production of polymers is 4.7 million metric tons annually. Of this, 60 –70% accounts for the production of polyethylene (PE) and polypropylene (PP) only (Satapathy et al., 2006; Stein, 1992; Santana and Manrich, 2003). Solid waste disposal is a growing world wide problem. Earlier most of them were buried in the landfill. But in the case of polymer material, it leads to serious after effects on environment as most of the polymers are not biodegradable and the space needed to fill those material are being reduced day by 318
Vol 85 (B4) 318–326
MODIFICATION OF WASTE POLYPROPYLENE WITH WASTE RUBBER DUST challenges to effective recycling, and at this point of time, the door remains open to advanced recycling techniques. Material recycling is the processes in which the macromolecular structure is kept basically intact, and the material is reformed into a new product. Some alteration of the molecular structure and/or morphology of the material may be brought about for the purpose of enhancing performance properties. This is the most desirable approach, as it may lead to conservation of energy and expense of minimum energy. It however, may pose technologically the most difficult task. Lots of work has already been carried out as blends, composites and additives involving thermoplastics, elastomers and thermoplastic elastomers by incorporating different additives such as cross-linking agents, surfactants, reinforcing fillers, and so on for improving the end-use properties and making value added products (Satapathy et al., 2006; Stein, 1992; Santana and Manrich, 2003; Garforth et al., 2004; Awaja and Pavel, 2005; Samsudin et al., 2005; Bengtsson et al., 2005; Wang and Sheng, 2005; Liu et al., 2005). Recently a large number of products from recycled polymer materials have been found their way in applications at various levels such as floor parquets, flower vases, waste paper baskets, park benches, picnic tables, plastic lumbers and so on. Quite often the recycled plastics compete with the virgin materials, in the market. Similarly accumulation of rubber waste particularly from tyre industries and tyre users has caused great concern among environmentalists about its proper utilization. These polymers are crosslinked rubbers having three-dimensional network structure, which render them non-biodegradable. They are utilized as grounded scrap rubber and are combined with various thermoplastic and rubbery materials to provide reduced-cost and better processing characteristics. Ground rubber particles of various mesh sizes are being used to modify materials such as linear low-density polyethylene (LLDPE), polypropylene (PP), polyurethane (PU) and polyvinyl chloride (PVC), apart from being used in rubber industries itself (Phinyocheep et al., 1993; Sasee and Emig, 1998; Shanmugharaj et al., 2005). Typically the rubber particles are blended at levels from 5 to 70% into the thermoplastic and elastomeric matrix using a batch mixer or melt extrusion system (twin-screw preferred) and chopped or cut into pellets suitable for further melt processing of the compounded material. In the present study attempts have been made to investigate the effect of rubber dust from textile cot industry in waste polypropylene. PP and rubber dust were melt-mixed in a Brabender Plasticoder and their physico-mechanical properties, fractured surface analysis and thermal properties have been reported.
EXPERIMENTAL Materials Used Waste polypropylene (WPP) collected from municipal solid waste was segregated on the basis of melting temperature (Tm), density and FTIR Spectroscopy. The waste rubber powder (rubber dust/RD) was supplied by INARCO, Gujarat, India. Rubber dust consists of PVC/NBR blend, Carboxylated NBR, animal glue, barium stabilizer, epoxidized soyabean oil, Carbon-black, silica, rutile grade TiO2, zinc oxide, apart from sulphur and accelerators. Rubber dust was sieved to remove coarse particles and the foreign materials.
319
Polypropylene pouches purchased from the market were used as recycled PP for comparison. The virgin polypropylene (Koylene HP) obtained from IPCL, Vadodara, India also used as reference.
Determination of Physical Properties Density Uniform square shapes (20 mm 20 mm2) of solid samples were prepared and the density was measured according to ASTM D 792. Butyl acetate (density ¼ 0.876 g cc21) has been used as the reference liquid (Table 1).
Heat distortion temperature HDT was measured using HDT/VSP Apparatus (Model CA-100 255701) according to ASTM D 648 (Table 1).
Melt flow index MFI of virgin and recycled polypropylene were measured using Melt Flow Tester (CEAST, Italy) at a temperature of 2308C. The virgin polypropylene (Koylene HP) has a melt flow index of 10.154 g/10 min and the recycled PP has an MFI of 12.707 g/10 min.
Preparation of Samples The waste plastic pouches were segregated from the municipal solid waste, cleaned, washed with detergent powder mechanically and dried. This waste is segregated in such a way that it consists of mostly PP with minor proportions of HDPE, LDPE, LLDPE, PET and PS. They are chopped into formidable sizes for further processing in a Brabender Plasticorder. The rubber dust also sieved through a 500 microns mesh and the coarse particle were removed. Melt blending of waste PP, recycled PP and virgin PP rubber dust was carried out in a Brabender Plasticorder (Model PLE 651). The processing conditions were optimized by using Taguchi method with waste PP. The conditions are; a temperature of 1908C, rotor speed of 60 rpm and residential time of 8 min. The proportions of rubber dust varied from 10 and 30 to 50 wt% of the total polymer. The molten mass was immediately sheeted into thin sheets of 3 mm thick on an open mixing mill (Schwabenthan, Berlin) at room temperature. The sheets were compression molded between Teflon sheets at a temperature of 1908C and at a pressure of 106 MPa in an electrically heated compression molding hydraulic Press (Moore make, UK) for 2 min and cooled
Table 1. Physical properties of PP materials and rubber dust. Material code Virgin polypropylene (VPP) Virgin polypropylene with 10% rubber dust composite (VPP10RD) Recycled polypropylene (RPP) Recycled polypropylene with 10% rubber dust composite (RPP10RD) Waste polypropylene (WPP) Waste polypropylene with 10% rubber dust composite (WPP10RD) Rubber dust
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318 –326
Density (g cc21) HDT (8C) 0.916 0.929
94 92
0.919 0.921
81 94
0.889 0.897
80 84
0.920
—
320
JOSE et al.
down to room temperature by passing cold water through the platens to obtain tensile sheets of dimension 15 cm 15 cm.
FTIR Studies Thin films of different waste plastics were cleaned thoroughly, dried and prepared in a compression molding press between two Teflon sheets at 1908C under 10 MPa pressure. Similarly, thin films of virgin polymers (LDPE, LLDPE, HDPE, PP, PS and PVC) and recycled PP were also prepared. FTIR studies on the thin films were performed using the Perkin Elmer Spectrum GX spectrometer in the range of 4000–400 cm21. Results of waste and virgin plastics were compared and used in the segregation of waste PP from the lot.
Dynamic Mechanical Analysis Elastic and viscous response of the polymers and its composites with rubber dust were determined by using a DMA Model 2980 (TA make) in the temperature range of 2508C to þ1208C in presence of liquid nitrogen medium at a frequency of 1 Hz. The heating rate was maintained at 58C min21.
SEM Analysis A JEOL-JSM-5800 scanning electron microscope was used to study the topography of the tensile fracture surfaces of the specimens after testing in order to understand the failure mechanism. Before examination, the fracture surfaces were sputter-coated with a thin layer of gold in a vacuum chamber.
Physico-Mechanical Property Determination Dumbbell specimens were punched out from the tensile sheets using ASTM cutting Die-C. The tensile property measurement was performed in an universal testing machine (Model No. H25KS of Hounsfield, UK) at a cross head speed of 10 mm min21 at 258C as per the ASTM D 638. The average values of five test results are reported. Flexural test specimens were also punched out from the tensile sheets and the flexural modulus was determined as per ASTM D 790 in a universal testing machine (Model No. H25KS of Hounsfield, UK). The testing speed was kept constant at 1 mm/min for all samples. Tensile impact specimens were punched out from the tensile sheet and the tests were performed as per DIN 53448 in an Impact Tester (Model No. 6545/000 of Ceast make). Izod and Charpy Impact property measurements were performed on Digital Pendulum Impact Tester (CEAST, Italy; model-P/N 6963.000) according to ASTM D 256 A & B. Notching of 2.54 mm depth on the sample has been done by using notching apparatus Notch Vis—CEAST, Italy. The Shore D hardness measurement was performed according to ASTM D 1132 by a Shore-D Hardness Tester (STD-D). Each specimen was tested thrice at three spots which were at a distance of at least 5 mm from each other and 13 mm from any edge of the test piece.
RESULTS AND DISCUSSION FTIR Studies The plastic wastes after segregating for PP and other thermoplastics, were extensively studied by taking four different samples through visual inspection. These samples coded as P1, P2, P3 and P4 were analysed by FTIR and the band widths were presented as follows (Table 2). By comparing the FTIR peaks of different waste plastics with the peaks of virgin materials, the waste plastics have been further categorized into P1 as low density polyethylene (WLDPE), P2 as polypropylene (WPP), P3 as linear low density polyethylene (WLLDPE) and P4 as high density polyethylene with impurities (WHDPE). The portion designated as WPP has been taken for further study (Figure 1). Similarly the rubber dust, a waste from rubber cots and apron industry was analysed by FTIR spectroscopy and the band widths with peaks are shown in Figure 2. The peaks obtained confirm the presence of following groups in the material (Table 3).
Table 2. Peaks position of different waste plastics analysed. Sample code P1 (WLDPE)
2921, 2846, 1471, 1377, 729 2921, 2846, 1464, 720 2921, 1464, 729, 720
P2 (WPP)
1458, 1375, 1167
DSC Analysis The waste PP and rubber dust were subjected to differential scanning chromatography (DSC) study using DSC Q100 model in the temperature range from room temperature to 4008C at a heating rate of 108C min21 in N2 atmosphere. The peaks of melting temperature were used to categorize the waste PP from the lot.
P3 (WLLDPE)
Thermo Gravimetric Analysis Thermal degradation studies of the waste polypropylene and its composites with rubber dust were carried out using a Thermo Gravimetric Analyzer, TA instruments (Model TG Q50) at a heating rate of 208C min21 in an atmosphere of nitrogen, from room temperature to a temperature of 6008C.
Peaks position (cm21)
2951, 2877, 1458, 1375 2951, 1458, 1375, 1167, 973 2905, 1714, 1464, 1377, 729, 720 2905, 1464, 720
P4 (WHDPE)
2922, 2850, 1462, 876, 719 1018
Assignment of peak Aliphatic hydrocarbon with long chain Alkyl group—long chain compound Aliphatic hydrocarbon— possibly long chain crystalline Aliphatic hydrocarbon with branched chain Alkyl group—methyl substituent Aliphatic hydrocarbon with highly branched chain Aliphatic hydrocarbon— possibly long chain crystalline Long chain compound with alkyl group Long chain crystalline compound Aryl ether group
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318– 326
MODIFICATION OF WASTE POLYPROPYLENE WITH WASTE RUBBER DUST
321
Physico-Mechanical Properties The physico-mechanical properties such as tensile strength, elongation at break, flexural strength, breaking energy impact strength studies by tensile impact, Izod impact and Charpy impact test as well as hardness properties of virgin PP and waste plastics as well as their composites with rubber dust at different proportions have been studied and shown in Figures 3–8. The virgin PP has higher mechanical strength properties such as tensile strength impact strength, but with degradation it loses the properties rapidly to an extent of nearly 50% of its original strength. In the case of waste PP, it exhibits lower mechanical
Figure 1. FTIR spectra of major thermoplastic wastes.
Figure 3. Tensile strength of different PP-rubber dust systems.
Figure 2. FTIR spectrum of rubber dust.
Table 3. FTIR peaks of rubber dust. Sample code Rubber dust
Peaks position (cm21)
Assignment of peak
3152
2 2OH group
2927, 2856, 1457 2927, 2237, 1725, 1457
Alkyl groups Nitrile type substituent in the aliphatic chain Aromatic compound—mono or possibly distributed Aromatic compound—possibly phenoxy or amino substituent Carbonyl compound—possibly ester or ketone
3042, 1592, 1488, 754, 688 1592, 1488, 1297, 754 1725, 1297, 1189, 1162
Figure 4. Elongation at break comparison of different PP-rubber dust systems.
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318 –326
322
JOSE et al.
Figure 5. Flexural strength properties of different PP-rubber dust systems.
Figure 7. Izod impact strength of different PP-rubber dust systems.
properties initially after reprocessing. This is because during long term exposure to sunlight, humidity, air and other environmental conditions, the saturated polymer chains undergoes chain scission particularly at tertiary C-atoms forming C2 2OH or C5 5O groups. This leads to the reduction in molecular weight. It has been observed that the mechanical properties of the waste PP containing 10 parts by weight (pbw) of rubber dust is almost equal to those of virgin PP. The tensile strength of WPP containing 10 wt% of rubber dust is enhanced by 100% as compared to that of reprocessed WPP. Similarly the impact strength of WPP improves on incorporation of rubber dust to the extent of 10 pbw as compared to that of virgin PP which shows a decline in the impact strength on incorporating rubber dust. Thus the enhancement in mechanical properties of waste
PP may be attributed to the following reasons: The C–OH or C5 5O groups generated during the degradation process are more polar as compared to the saturated C–C and C –H bonds present in the virgin polymers. Since rubber dust contains NBR-PVC blends as well as carboxylated NBR which are polar in nature helps in compatibility due to dipole –dipole interactions. Also the devulcanized component of the rubber dust may contribute to the formation of additional crosslinks during molding resulting in enhanced properties. On the other hand as the percentage of the rubber dust increases further, the vulcanized rubber forms a separate phase and causing phase separation resulting in reduction of properties. The virgin thermoplastic due to its long chain molecule are very flexible and is having low hardness value. The polymer can become harder when the crystallinity is increased or hard
Figure 6. Tensile impact strength of different PP-rubber dust systems.
Figure 8. Charpy impact strength of different PP-rubber dust systems.
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318– 326
MODIFICATION OF WASTE POLYPROPYLENE WITH WASTE RUBBER DUST
323
Table 4. Hardness value of different PP materials and its composites. Sample code
Hardness (shore D)
VPP0RD VPP10RD WPP0RD WPP10RD WPP30RD WPP50RD RPP0RD RPP10RD RPP30RD RPP50RD
45 + 1 46 + 1 62 + 1 61 + 1 50 + 2 38 + 2 43 + 1 42 + 1 39 + 2 39 + 2
segments are introduced to the long chain. But in the case of waste plastic the degradation make them very hard. The vulcanized rubber part is having less effect on the hardness of virgin PP because its hardness value is very less compared to that of waste PP. But the presence of rubber dust in the waste PP significantly reduces the hardness of waste PP (Table 4).
Figure 10. TGA curves for rubber dust and PP materials.
The segregated waste PP were subjected to differential scanning calorimetry (DSC) study using DSC Q100 model in the temperature range from room temperature to 4008C. The DSC thermogram [Figure 9(a)] showed two endothermic peaks; one at 1658C corresponds to PP and the other at 2358C corresponds to polyethylene terephthalate (PET), respectively. Thus it has been inferred that the sample may be primarily PP and may contain small amount of PET. The DSC thermogram of the rubber dust has been shown in Figure 9(b). The thermogram shows a large number of peaks indicating that the material is a mixture of different polymers and additives; as expected.
two stage degradation one at around 3508C and the other at 450 –4708C. Where as virgin PP shows a clearly simple degradation temperature at 5008C considered to be the most stable material. (In the case of rubber dust, the degradation temperatures are 2908C and 4468C and the residue remained is 29 wt%. The degradation temperatures of WPP-rubber dust composite were 3198C and 4658C.) It seems the presence of rubber dust reduces the thermal stability of WPP to a great extent. It may be attributed to the presence of large quantities of volatile materials in the rubber dust as well as due to the presence of various metallic salts which might activate the degradation process in PP. The catalytic degradation of PP polymer occurs at much lower temperature compared to the thermal degradation (Bajsic et al., 2005; Aguado et al., 2000; Filho et al., 2005).
TG Analysis
Dynamic Mechanical Analysis
TGA thermograms of waste PP, virgin PP, rubber dust and rubber dust-PP composite are shown in Figures 10 and 11. The WPP looses nearly 10% of it weight at 3008C due to devolatilization of volatile matters as well as plasticizers in the compound/product mix. Thereafter it sharply degrades at 460 –4708C considered to be the degradation temperature of WPP. Residual weight is nearly 12%. On the other hand, the rubber dust and the PP-rubber dust composites exhibit
The DMA analysis of the waste PP and the thermoplastic vulcanizates containing 10 wt% and 50 wt% of rubber dust has been carried out. As expected the storage modulus increases with increased proportion of rubber dust (Figure 12). The loss modulus (E00 ) versus temperature plots of the TPVs are shown in Figure 13. A sharp increase in E00 value at around 108C in the case of WPP containing 10 wt% of rubber dust implies that the crystallinity of PP
DSC Analysis
Figure 9. DSC thermogram of (a) waste PP (WPP) and (b) rubber dust. Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318 –326
324
JOSE et al.
Figure 11. Derivative peaks for rubber dust and PP materials.
matrix has been disturbed and the system is able to dissipate more energy in the form of heat. Also, there is no any characteristic shift in the tan d peak towards higher temperature when rubber dust is added to WPP as is evident from Figure 14. This may be attributed to reduction in the crystallinity of WPP on the addition of rubber dust and also no significant crosslink formation. Thus the damping characteristic of the material has increased to a greater extent due to the introduction of rubber dust (vulcanized particles) which shows better elasticity in the composite along with good mechanical properties. This can be very useful in applications where high load transfer is required for products which are subjected to high static and cycling loading. Dynamic mechanical analyses of WPP, RPP and VPP containing 10 wt% of rubber dust have been shown in Figure 12 –14. Figure 12 shows the storage modulus (E0 ) versus temperature in the temperature range from 2608C to þ1408C. The E0 value reduces from 2250 MPa to below 1000 MPa at influx temperature of 08C for WPP containing 10 wt% of rubber dust. Where as for RPP10RD the influx temperature is increased to nearly 208C and the storage modulus reduced marginally to 1500 MPa. For virgin PP (VPP) initial storage modulus is around 1800 MPa at 2608C which just lowered onto 1300 MPa at 308C. Loss modulus (E00 ) versus temperature plots for the PP (WPP, RPP and VPP) containing 10 wt% of rubber dust is shown in Figure 13. WPP10RD shows the maximum loss modulus of 220 MPa at 08C where as RPP10RD and VPP10RD shows the maximum loss modulus of 175 and 160 MPa at 158C. This exhibits that WPP with rubber dust (10 wt%) always has a higher loss, thus maximum damping characteristics. The above findings are further supported from the damping peaks of the samples shown in Figure 14. WPP10RD shows maximum damping. WPP has the advantage of higher energy dissipation at a temperature of 08C. This is quite significant from the application point of view.
SEM ANALYSIS Figure 12. Storage modulus of PP composites.
The SEM photographs of fractured surface of waste PP is shown in Figure 15 which shows a fibrillar structure. The fibrils are generated due to extensive stretching leading to order
Figure 13. Loss modulus for PP composites.
Figure 14. Tan d curves for PP composites.
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318– 326
MODIFICATION OF WASTE POLYPROPYLENE WITH WASTE RUBBER DUST
325
crystallinity developement. The surface is found to be very rough and mutilated. The surface morphology of waste polymer composites with rubber dust (Figure 16) shows a smoother surface topography because of better particles stress distribution at the interfaces and easier stress distribution by the crosslinked rubber dust particles. It also exhibits better PP-rubber dust interaction. This is in agreement with tensile property results which exhibit higher strength properties. Further the smaller particle size of the rubber dust which is already crosslinked acts as reinforcing fillers in the PP matrix which enhances the tensile as well as impact strength properties. Figure 17 shows the SEM photomicrograph of the rubber dust with an average particle size of 5 mm.
CONCLUSION Figure 15. SEM of waste PP.
Waste polypropylene has been segregated from municipal solid waste by visual means and FTIR is used as basic tool for characterization. The addition of rubber dust as waste from the textile cot industry into virgin PP, results in a reduction in the mechanical properties because of poor interaction between the two phases where as incorporation of the same rubber dust onto waste PP improve the properties significantly. However, the thermal stability is reduced marginally. Impact properties improve on the addition of rubber dust with WPP, where as that with virgin PP and recycled PP this property reduces. The SEM photomicrographs support greater interaction of the waste PP with the crosslinked rubber dust. The damping characteristics of WPP with 10 pbw of rubber dust improve remarkably most of the properties implying that this composite may be made use of various damping applications.
Future Scope
Figure 16. SEM of WPP-rubber dust composite.
Recycling of plastics and rubber waste is a major environmental issue and a task for the society and technologist. Research is in progress in this field for utilization of waste rubber and plastic in making different value added products.
Figure 17. SEM of rubber dust particles.
Abraham, T.N., George, K.E. and Peijs, T., 2005, Progress in Rubber, Plastics and Recycling Technology, 21: 73–83. Aguado, P.J., Serrano, D., Escola, J.M., Garagorri, E. and Ferna´ndez, J.A., 2000, Polym Degradation Stability, 69: 11 –16. Awaja, F. and Pavel, D., 2005, European Polymer Journal, 41: 1453–1477. Bajsic, E.G., Rek, V., Leskova, M. and Smit, I., 2005, Proceedings of the 8th Polymers for Advanced Technologies International Symposium, Hungary. Bengtsson, M., Gatenholm, P. and Oksman, K., 2005, Composites Science and Technology, 65: 1468– 1479. Choudhury, A., Mukherjee, M. and Adhikari, B., 2005, Progress in Rubber, Plastics and Recycling Technology, 21: 117– 137. Filho, P., Graciliano, E.C., Silva, A.O.S., Souza, M.J.B. and Araujo, A.S., 2005, Catalyst Today, 107– 108: 507–512. Garforth, A.A., Ali, S., Herna´ndez-Martı´nez, J. and Akah, A., 2004, Current Opinion in Solid State and Materials Science, 8: 419– 425. Liu, W., Misra, M., Askeland, P., Drzal, L.T. and Mohanty, A.K., 2005, Polymer, 46: 2710– 2721. Najafi, S.K., Elham, H. and Tajvidi, M., 2006, J of Applied Polymer Science, 100: 3641–3645. Phinyocheep, P. and Axtell, F.H., 1993, ACS Rubber Division 144th Meeting, Conference Proceedings, 26– 29 October, Paper No. 40.
REFERENCES
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318 –326
326
JOSE et al.
Samsudin, S.A., Hassan, A., Mokhtar, M. and Jamaluddin, S.M.S., 2005, Progress in Rubber, Plastics and Recycling Technology, 21: 261–276. Santana, R.M.C. and Manrich, S., 2003, J of Applied Polymer Science, 88: 2861–2867. Sasee, F. and Emig, G., 1998, Review paper, Chem Eng Tech, 21: 777– 789. Satapathy, S., Chattopadhyay, S., Chakrabarty, K.K., Nag, A., Thiwari, K.N., Tikku, V.K. and Nando, G.B., 2006, Studies on the effect of electron beam irradiation on waste polyethylene and its
blends with virgin polyethylene, J of Applied Polymer Science, 101: 715– 726. Shanmugharaj, A.M., Kim, J.K. and Ryu, S.H., 2005, Polymer Testing, 24: 739– 745. Stein, R.S., 1992, Colloquium Paper, Proc Nati Acad Sci, 89: 835– 838. Wang, L. and Sheng, J., 2005, Polymer, 46: 6243–6249. The manuscript was received 28 July 2006 and accepted for publication after revision 12 December 2006.
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B4): 318– 326