K. T. Varughese

Miscible blends from rigid poly(vinyl chloride) and epoxidized natural rubber: Part 1 Phase morphology

Miscible blends of rigid poly(vinyl chloride), PVC, and epoxidized natural rubber (ENR) having 50 mol % epoxidation level, are prepared in a Brabender Plasticorder by the melt-mixing technique. Changes in Brabender torque and temperature, density, dynamic mechanical properties and DSC thermograms of the samples are studied as a function of blend composition. The PVC-ENR blends behave as a compatible system as is evident from the singleTg observed both in dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The moderate level broadening of theTg zone in blends is due to microinhomogeneity, which may arise from the particle structures of PVC perturbing the molecular level mixing of PVC and ENR. Scanning electron microscopic studies were conducted on nitric acid-etched samples and the results showed continuous structures of blend components as well as the occurrence of solvent-induced cracks in high PVC blends.

Miscible blends from rigid poly(vinyl chloride) and epoxidized natural rubber: Part 2 Studies on mechanical properties and SEM fractographs

Mechanical properties and fracture of melt-blended poly(vinyl chloride) (PVC) and epoxidized natural rubber (ENR) having 50 mol % epoxidation level are studied at different compositions. The effect of blend ratio on tensile strength, tear strength, elongation at break, tension set after failure, and hardness are determined. The stress-strain behaviour of low ENR blends exhibits yielding and necking, whereas that of high ENR blends exhibits soft elastomeric deformation. At higher compositions of ENR, plots of tensile strength, tear strength, and hardness against blend composition are concave in nature; and plots of the elongation at break deviate markedly from the additive value with a pronounced maximum occurring at the 70wt% composition of ENR. The scanning electron microscopic examination of fracture surfaces of blends does not show any features of phase separation of ENR or PVC. The tensile fracture surface of rigid PVC exhibits partially fused particle structures of PVC and that of blends exhibits features of shearing and horizontal discontinuous striations. The torn surface of rigid PVC shows evidence of intrinsic crazing and that of blends shows features of shear fibrils, vertically changed discontinuous striations, steps, and unstable and stable tear fronts.

Tensile and tear failure of plasticized poly (vinyl chloride)/epoxidized natural rubber miscible blends

A study on the tensile and tear failure of miscible blends of plasticized poly (vinyl chloride), PVC, and epoxidized natural rubber (ENR) was carried out. Fractographs were taken in a scanning electron microscope in order to obtain an insight into the failure mechanism of the samples. It was found that low ENR blends failed by shearing in tensile testing, and they exhibited irregular stick-slip deformation and characteristics like vulcanizates in tear testing. Blends of plasticized PVC and ENR were more flexible than the individual components. As a result of the geometrical effect the tear fracture surface has rougher features than the tensile fracture surface. Sinusoidal wavy tear patterns in the form of a typical sine wave and rectified half sine wave of the fracture surface are characteristic features of tear resistant non-vulcanizates of rubber-like materials. Moreover, the study revealed that there were no features of phase separation of PVC and ENR due to incompatibility at any of the fracture surfaces examined.

Contact angle behaviour of poly(vinyl chloride)/ epoxidized natural rubber miscible blends

—Contact angle studies of miscible poly(vinyl chloride)/epoxidized natural rubber (PVC/ ENR) blends were carried out in air using water and methylene iodide. The solid surface free energy was calculated from harmonic mean equations. Blending of PVC and ENR decreased their contact angle or increased their solid surface free energy due to the improved chain mobility, and the accumulation of excess polar sites at the surface through conformational alterations resulting from the specific interaction of PVC and ENR. The work of adhesion, interfacial free energy, spreading coefficient, and Girifalco-Goods interaction parameter changed markedly with the blend composition. In blends, PVC and ENR improved hydrophilicity, and wettability with polar and non-polar liquids. The presence of a plasticizer in PVC, in general, further improved the wettability and hydrophilicity in blends.

Flame Retardant Effects in PVC-Epoxidised Natural Rubber Miscible Blends: Halogen and Non-Halogen Based Additives

Effects of four flame retardant additives, (1) antimony trioxide, (2) zinc borate, (3) chlorinated paraffin wax and (4) decabromodiphenyl ether in a PVC-epoxidised natural rubber miscible composition in the presence of a phthalate plasticizer and a phosphate plasticizer were studied. Mixing was done in a Brabender plasticorder at 180 °C. Incorporation of additives did not affect the miscibility of the blend components, and the strength property re tained between 83% and 91%. The processibility of the blend was improved due to chlorinated paraffin wax and slightly impaired due to zinc borate. Antimony trioxide and decabromodiphenyl ether had little influence on the processibility. The flame retardant additives were more effective in a phthalate plasticizer medium than in a phosphate plasticizer medium. The thermal stability of com ponents was mutually influenced by the additive and the matrix. The vapor phase flame inhibiting action of antimony trioxide in PVC compositions was more pronounced in a phthalate plasticizer medium than in a phosphate plas ticizer medium. Phosphate plasticizer in general induced a condensed phase mechanism in the presence of a flame retardant additive.

The Effects of Flame Retardant Combinations in PVC-Epoxidised Natural Rubber Miscible Blends: Antimony Trioxide in Combination with Halogen and Non-Halogen Based Additives

Effects of antimony trioxide in combination with halogen and non-halogen based additives in a matrix of PVC/ENR miscible blends were studied for processibility, miscibility of blend components, strength properties, thermal stability, and flammability. Flammability measurements were carried out by limiting oxygen index measurement. The impairments in processibility and strength properties were within tolerable limits. Additive combinations did not alter the miscibility of blend components. Thermal stability was greatly influenced. Synergistic flame retardation of zinc borate with Sb2O3 with and without decabromodiphenyl ether was explained by a vapor phase- condensed phase flame retardation mechanism. The antagonistic effect of phosphorus/antimony was greatly deactivated by a halogen additive and/or zinc borate.