Effect of increased compacting pressures on the physicomechanical characteristics of metal-filled polyvinyl chloride

Abstract

Based on the principles of linear thermodynamics, molecular physics, and spatial organization of amorphous polymers, the energy of formation of microdefects and the increments in their volumes as functions of the compacting pressure and the content of the filler of polyvinyl chloride systems are calculated.Among promising methods of modifying the physicomechanical properties of polymers is their doping with highly disperse additions and directional control of the technological processes of producing composite materials [1]. Here the question of studying the effect of the T-p compaction mode on their properties remains virtually open [2,3].As the subject of inquiry, we selected industrial polyvinyl chloride (PVC) of the S-65 grade with a molecular weight of 1.4-105 that was produced by suspension polymerization and was purified by reprecipitation from soluton. Cyclohexane of "KhCh" grade (Tboil = 425.5 K, n 29°r = 0.9466) was chosen as the solvent. For more intense dissolution of PVC in cyclohexane, a prepared 3% solution was heated on a water bath with a reflux cooler at a temperature of 310 K. PVC was reprecipitated from the obtained solution with methanol (Tboil = 335 K, n 29°K = 0.7925). The precipitated polymer was washed repeatedly on a filter with methanol and dried in air and then in vacuum at a temperature of 320 K to a constant weight in 10 h. The reprecipitated PVC was a homogeneous powder of white color that was subsequently used for producing composites. As the filler, a highly disperse iron (Fe) powder that was reduced with hydrogen was selected, with a predominant particle size of 15 pro.The specimens were prepared in the T-p mode, which differs from the p-T mode [4] in that the polyvinyl chloride was placed in a mold, which was heated to a temperature of 460 K, and only afterward was a required pressure of 10, 60, 120, 200, and 300 MPa applied, maintaining the temperature mode for another 7 min. Spontaneous cooling during formation of blocks was effected at the corresponding pressure up to T < Tgl. The glass transition temperature (Tgl of the original PVC was 354 K, and the yield temperature (Ty) was 456 K.The density (p) of the PVC systems was studied using the method of hydrostatic weighing [5], and the hardness (Hv) was studied, using the Vickers method, on a PMT-3 microhardness meter with loading for a time of 2 min [6]. With a confidence coefficient of 0.95, the mean relative measurement error for p and Hv, respectively, was 0.2 and 1.3%. Table 1 presents experimental data on the physicomechanical properties of the PVC systems. It follows from the data presented that the density of the original polymer increases_ with the pressure over the entire range considered. However, the density of the PVC compositions increases only at pressures up to 200 MPa. A further increase in it leads to a decrease in the density adequate for the filling (see Table 1).The rise in the density of the PVC systems in the range of 10-200 MPa is caused by "healing" of defects of the material, i.e., a reduction in its fr...

Study of the Effect of Ageing on the Properties of Heterogeneous Systems Based on Flexible-chain Polymers

“…Increase in ρ is due to a change in the proportion of free volume and to ordering of the structure of PVB systems. Reduction in ρ is caused by deformation of the structure of PVB systems to a level where rearrangement of the short-range order no longer occurs, which generates segmental suppression, complications in processes of rearrangement and packing of macrochains, and the formation of microdefects at higher levels of compression moulding and fi lling [6].…”