Effects of scrap addition on the physico-chemical properties of rigid polyvinyl chloride products

Abstract

Raw material powder mixtures have been prepared with polyvinylchloride (PVC) resin, unplasticized polyvinylchloride (uPVC) scraps and additives by melt mixing method. A twin screw extruder has been used to make pipe for sample preparation from the mixture. Domestic and external uPVC scraps were formulated and blended with PVC resin to form melt compound. Domestic samples designated as DS-10, DS-20, DS-30, DS-40, DS-50 and DS-100 have been prepared by blending 10, 20, 30, 40, and 50phr and 100% uPVC domestic scrap with PVC resin and various additives followed by extrusion, flattening and machining. Following the similar procedure, external samples such as ES-10, ES-20, ES-30, ES-40, ES-50 and ES-100 have been prepared using external uPVC scraps. Effects of the proportions of uPVC scraps in the raw material mix on the properties of the recycled uPVC products have been investigated. The specific properties under studies include the (i) physical (ii) mechanical properties, (iii) chemical (iv) thermal properties, (v) surface morphology and (vi) structural properties of the recycled uPVC products. All the samples prepared have successfully satisfied the requirements of acetone test. Density of samples containing domestic scraps shows the minimum value of 0.64% for DS-50 and the maximum value of 1.91% for DS-20. On the other hand, in samples containing 10 and 40 phr external scraps the density increases by 0.64% while in sample containing 30 phr external scraps the density decreases by 4.46%. Mechanical properties, such as break stress and % elongation-at-break, impact strength, flexural strength and harness values vary with proportions of scraps in the samples. The maximum decrease in break stress is 11.40% for 20 phr domestic scraps, while in samples containing external scraps this decrease is 15.71% for 40 phr scraps. The decrease in break stress for sample containing 100% external scraps is 38.95%. The minimum decrease (9.48%) in viscosity number is found in sample containing 30 phr domestic scraps, while in sample containing external scraps the maximum decrease is 42.24% in sample containing 30 phr scraps. Fourier transform infrared (FTIR) spectroscopic investigation has been followed to detect new functional groups with the addition of different proportions of domestic and external scraps. Only a variation in IR light intensity has been observed. X-ray fluorescence investigation shows a decrease in the percentage of carbon revealing the maximum decrease of 15.53% in sample containing 50 phr domestic scraps. The amount of lead added to samples as a stabilizer from lead sulphate, increases with the amount of scraps in the sample. The maximum increase is 18.52% in sample containing 40 phr domestic scraps and 37.04% in sample containing 40 phr external scraps. Scanning electron microscopy together with energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD) analysis show the same phases in all samples. However, variation in shape and distribution of the phases and interfaces has been observed in different samples. EDS spot analysis shows a variation in elemental composition. XRD analysis shows an amorphous polymer and crystalline calcium carbonate (CaCO3) phases. The relative intensities of the different peaks were different and these results can be attributed to the presence of different amount of CaCO3 in the different samples. Results of thermogravimetric analysis(TGA) and EDS are in good agreement with the observation suggesting that no new phases are formed due to the addition of different proportions of scraps. Differential scanning caloriemetry indicates two glass transition temperatures indicating a immiscibility of two components. In different samples, differences in thermal expansion or contraction have been detected by thermo-mechanical analysis (TMA). The observed values by TMA have been attributed to the difference in coefficient of thermal expansion of the different phases. TGA thermograms show that degradation temperature (around 300oC) is much higher than the processing temperatures used (around 200oC). Thermal analysis results have shown that the residue content left at 1000oC is in general higher in the samples containing external scraps. Vicat softening temperature values show that the resistance to heat increases with an increase in the amount of scraps in the samples, wherein the effect of external scraps is more pronounced. This has been attributed to the increased amount of CaCO3 in the sample containing external scraps.