Marianne Gilbert

Structure-property relationships of irradiation crosslinked flexible PVC: 1. Structural investigations

Abstract An investigation has been carried out into the effect of irradiation dose and the amount of the unsaturated monomer trimethylolpropane trimethacrylate (TMPTMA) on the irradiation of a di-iso-octyl phthalate (DIOP) plasticized PVC compound. The type of network structure produced and the extent of deterioration of the PVC after crosslinking have been studied. Within the dose range studied, the degradation caused by the electron beam was found to be minimal, but the residual unsaturation in the crosslinked PVC was significant, implying inefficient use of crosslinking agent. Gel yield increased with increased irradiation dose and TMPTMA content, but crosslink density decreased at higher irradiation levels, suggesting the formation of a looser network. The phthalate plasticizer was not involved in gel formation.

Structural order in heat treated vinyl chloride polymers

Abstract Three vinyl chloride polymers were annealed at temperatures in the range 40–160°C for times varying from 0.5 to 5 h. Structural changes occurring in the polymers were examined by density measurement, differential thermal analysis and X-ray diffraction. It was shown that the three polymers varied in their original crystallinity. Attempts to totally remove this crystallinity, were unsuccessful; further crystallinity could be introduced by annealing above Tg Changes induced by annealing below Tg were not due to crystallization. Methods used to measure crystallinity in poly(vinyl chloride) (PVC) were assessed.

Preparation of nickel coated mica as a conductive filler

Electroless plating was used to prepare nickel coated mica fillers. To optimise the conductivity of the filler the nickel coating needed to exceed a certain weight percentage, depending upon the particle size of the mica, and cover the surface of the mica particles. Treatment of the filler in hydrogen improved its conductivity considerably. The fillers were incorporated into an ABS resin to prepare composites as potential electromagnetic interference shielding materials. Increasing the particle size of the mica reduced the critical filler loading required to produce electrically conductive composites. Reducing sample thickness caused a decrease in resistance, due to changes in filler orientation.

Crystallinity in Poly(vinyl Chloride)

Abstract Commercial poly(viny1 chloride) (PVC) contains approximately 10% crystallinity. This relatively low level of order has a surprisingly significant effect on both its processing and properties. In this review, the nature of PVC crystallinity, which is very different from that found in more conventional crystalline polymers, will be discussed. Methods of measuring crystallinity will be considered, and aspects of PVC behavior which are affected by its crystalline nature will be highlighted. The majority of work reported in this area is concerned with bulk and suspension polymerized polymers, so this review will focus on these polymer types.

Structure and properties of talc-filled polypropylene : effect of phosphate coating

Talc surface treatment was carried out using a series of phosphate coating levels. The coated talc was characterized using quantitative diffuse reflectance FTIR analysis, which revealed a saturation of surface coverage at around 6 wt % phosphate. Coated and uncoated talc had a nucleation effect; and the degree of crystallinity of composites increased initially, then gradually decreased with increasing phosphate coating level. The talc dispersion was improved as coating level increased; however, the platelet alignment was reduced. The addition of 0.5 wt % phosphate to talc resulted in a maximum increase in tensile strength and a significant drop in flexural modulus. Improvement of falling weight impact properties of the composites were achieved at high coating levels.

Mechanical properties of HDPE/magnesium hydroxide composites

Fillers incorporated into polymers for flame retardancy can decrease their mechanical strength. Coating of the filler can enhance the properties of polymer composites. A platy magnesium hydroxide, uncoated, or coated with magnesium stearate or stearic was used as filler in high density polyethylene composites. Tensile and flexural properties were measured. Experimental results were compared with various existing models. Experimental data for both tensile and flexural yield strength showed a good fit to the Pukanszky model. Interfacial interaction was also evaluated through this model. Coating modified tensile and flexural yield strength in different ways. Results were explained by the effect of platelet alignment which was measured by X-ray diffraction. Flexural modulus showed a good fit to the Halpin-Tsai equation, but tensile modulus increased less with filler volume fraction, an effect also believed to relate to filler alignment. Elongation at yield decreased with the addition of filler, more so when coatings were present. This property seemed to be controlled mainly by filler dispersion.

Characterization of coated particulate fillers

Stearic acid coated samples of porous and non-porous grades of magnesium hydroxide and calcium carbonate have been characterized using diffuse reflectance infra red (DRIFT), and X-ray photoelectron spectroscopy (XPS). Using DRIFT, the signal due to the reacted coating reached a plateau at a coating level dependent on the filler surface area. XPS showed that coating thickness increased with the amount of coating, slope changes being observed in plots at lower levels of applied coating than those observed by DRIFT. The differences between the measurements for the two techniques is attributed to their different sampling depths. The FTIR having a greater sampling depth probes the internal surface area of the agglomerates present in the porous material, whereas XPS does not. The surface chemistry of the two types of coated filler is compared.

Silane crosslinking of plasticized poly(vinyl chloride)

In this study the use of three different types of aminosilanes for crosslinking plasticized PVC was investigated. The processing techniques used were milling, followed by press molding and extrusion. The processing conditions were carefully adjusted to minimize premature crosslinking. Crosslinking was carried out by immersing the samples in hot water for 4 h. Gel content was determined by Soxhlet extraction in tetrahydrofuran. Tensile properties were measured at room temperature and at 100°C or 130°C. Bis(γ-trimethoxysilylpropyl)amine was found to be the best of the three silanes investigated for crosslinking plasticized PVC, enabling adequate gel content to be obtained to improve the properties at elevated temperature, while avoiding premature crosslinking. Compounds stabilized with either tin or Ba/Zn possessed adequate thermal stability at 190°C. No changes were seen in the tensile properties at room temperature, but significant improvements were obtained at 100°/130°C. Results obtained using thermomechanical analysis showed increased penetration resistance with increase in gel content.

Peroxide crosslinking of plasticized poly(vinyl chloride)

Abstract The peroxide crosslinking of plasticized poly(vinyl chloride), PVC, blended with trimethylolpropane trimethacrylate, TMPTMA, has been studied by following gel formation and changes in mechanical properties. By applying the right preparation conditions and peroxide type, it was possible to avoid crosslinking while dry-blending the materials. During compression moulding, gel yield was found to increase with increased peroxide and TMPTMA concentrations and with curing time and temperature. The crosslinking process was found to be comprised of two primary reaction, a rapid polymerization of TMPTMA followed by grafting of the TMPTMA onto the PVC backbone. In the absence of either peroxide or methacrylate monomer no crosslinking was observed. Crosslinking was found to be independent of the tribasic lead sulfate stabilizer level and contrary to what is expected the crosslinked sheets showed excellent thermal stability. The softening temperature of the cured sheets increased with crosslinking.

Structure-property relationships of irradiation crosslinked flexible PVC: 2. Properties

Abstract Tensile properties at room temperature and at 130°C have been measured for two series of irradiation crosslinked plasticized poly(vinyl chloride) (PVC) samples. The samples have also been examined by thermomechanical analysis. Experimental variables consisted of irradiation does and the amount of the crosslinking agent (trimethylolpropane trimethacrylate (TMPTMA)). Crosslinking caused only minor changes in room temperature properties but a significant change in tensile properties at 130°C and in softening temperature. For this to be observed, a gel content of at least 40% is required. Properties depend on both gel content, and network type, which are in turn controlled by irradiation dose and TMPTMA content.