Biaxial orientation of poly(vinyl chloride) compounds Part 2 –Structure–property relationships and their time dependency

X-ray diffraction and thermomechanical analysis have been used, respectively, to examine structural order and shrinkage behaviour for oriented samples of rigid and flexible poly(vinyl chloride) (PVC). Results were compared with previously measured tensile properties and structure–property relationships explored. X-ray diffraction showed that drawing produces planar crystallite orientation in PVC sheets. If drawing and subsequent annealing conditions are held constant, but draw ratio is varied, there is good correlation between structural order measured by X-ray diffraction and tensile strength. Increased annealing time and temperature improve crystallite order and dimensional stability, while tensile strength is unchanged. The greatest enhancement in tensile strength is achieved by stretching PVC towards its maximum draw ratio at 90°C, but optimum thermal stability of the oriented structure is achieved when higher annealing temperatures are used. Room temperature recovery is observed for flexible PVC when the material has a glass transition temperature below ambient. This can be delayed by increased annealing time and temperature, and by increased draw ratio

Crosslinking of rigid poly(vinyl chloride)

Various formulations for the crosslinking of rigid poly(vinyl chloride) have been investigated including three different thermal stabilisers: a tin maleate; an octyl thio tin stabiliser; and a tribasic lead sulphate. The possibility of using aminosilanes and peroxides as crosslinking agents was considered and the additives used in the formulations were bis(-trimethoxysilylpropyl)amine, a blend of trimethylol propane trimethacrylate and amorphous silica, and 1,1-di-t-butylperoxy-3,3,5-trimethyl cyclohexane incorporating 40% peroxide. It was shown that rigid poly(vinyl chloride) can be crosslinked using both aminosilane and peroxide systems and the optimum level of the aminosilane was found to be 2 phr while significant property improvements were achieved with only 0·5 phr peroxide. The effects of the various thermal stabilisers and crosslinking additives are presented and discussed

Peroxide crosslinking of rigid poly(vinyl chloride)

Peroxide crosslinking of unplasticised poly(vinyl chloride), PVC with trimethylolpropane trimethacrylate (TMPTMA) has been investigated. Formulations used in this work contained a nontoxic lead free stabiliser and showed good colour and heat stability. The samples have been examined by differential scanning calorimeter(DSC) and tensile properties at room temperature and at 130oC were measured. Gel content or tetrahydrofuran (THF) insoluble material was measured as an indication of crosslinking. It is shown that premature crosslinking can be avoided during processing. It was found that 190oC was the optimum processing temperature for maximum gel content. The residual unsaturation was monitored using FTIR

Characterisation of stearatestearic acid coated fillers

Selected magnesium hydroxide and calcium carbonate fillers were dry coated with stearic acid and calcium, magnesium, and zinc stearates. The course of the coating reaction was monitored using a quantitative diffuse reflectance Fourier transform infrared spectroscopy method and by thermal analysis. The coated fillers were also examined by wide angle X-ray diffraction and by X-ray photoelectron spectroscopy. These techniques were shown to produce complementary information. When the dry coating process was useded, complex reactions occurred. Stearic acid reacted to produce stearate, while the stearates melted and formed coatings, but in some cases they also appeared to form polymorphic metal stearates. Stearic acid produced the best coverage on calcium carbonate, but the poorest on magnesium hydroxide. Of the metal stearates, the best filler coverage was produced when zinc stearate was used, while calcium stearate was the least effective coating

Cross-linking of unplasticised poly(vinyl chloride) with peroxide

The peroxide cross-linking of poly(vinyl chloride) (PVC) with trimethylolpropane trimethacrylate (TMPTMA) has been investigated. The degree of cross-linking was measured in terms of the gel content of the material, i.e. the insoluble residue remaining after soxhlet extraction in tetrahydrofuran. Cross-linking gave rise to significant improvements in high temperature tensile strength, but at higher levels of peroxide, dehydrochlorination of PVC was found to compete with grafting and cross-linking reactions. The results have been analysed to predict the optimum amount of TMPTMA and peroxide to maximise gel content and strength while maintaining thermal stability

FTIR analysis of silane grafted high density polyethylene

Vinyltrimethoxysilane (VTMOS) monomer was grafted onto high density polyethylene by reactive processing in a twin screw extruder in the temperature range of 180-240°C. The effect of VTMOS and 1,3-bis (tert-butylperoxyisopropyl) benzene peroxide (BTBB) on the extent of grafting was studied using qualitative and quantitative Fourier transform infrared spectroscopy. The grafting reactions were confirmed via infrared absorption bands present in the 800 cm-1 region which are characteristic wavenumbers for the vibration modes of the Si-CH group from VTMOS (CH2=CH-Si-(OCH3)3). The percentage of reacted and unreacted VTMOS was calculated by a novel Fourier transform infrared spectroscopy quantitative method developed through measurements of infrared absorbance bands at peaks 795 and 814 cm-1 that are influenced by both reacted and unreacted silane. The effect of silane and peroxide concentrations on the concentration of reacted and unreacted silane present in the material was determined. The change in unsaturation content measured at absorbance 1009 cm-1 supported these findings

Plate-out in PVC extrusion. I. Analysis of plate-out

Samples of extruder plate-out from industrial rigid PVC production lines have been investigated using a number of analytical techniques. The combined use of SEM-EDX (scanning electron microscopy – energy dispersive x-ray analysis), thermal analysis, FTIR (Fourier Transform infra Red spectrophotometry) and LIMA (laser induced mass analysis) has enabled most plate-out components to be identified, and linked to likely formulation ingredients. FTIR and thermal analysis were used to identify organic components. FTIR was also useful for identifying some inorganic compounds present in sufficient quantities, while EDX detected elements present. LIMA was the most sensitive technique, detecting trace quantities of both cations and anions. Calcium carbonate, titanium dioxide and lead stabilizers were found in all die plate-out samples studied, together with small amounts of lubricants

Suspension polymerisation of vinyl chloride in presence of ultra fine filler particles

Polymer composites, filled with ultra fine particulate fillers, are alternatives to the conventional filled polymers. The reinforcement of the mechanical properties occurs to a greater extent when ultra fine particulate fillers are used in comparison with the conventional microdimensional fillers. To achieve all the benefits that the ultra fine fillers can provide, optimal dispersion as primary particles is essential. To achieve better dispersion of the inorganic particles in a polymer matrix, the ultra fine particles (UFP) are added to the polymerisation reactor so that they are dispersed in the monomer before polymerisation. Hence, the monomer is polymerised in the presence of the UFP (in situ). In this paper the effects of the UFP on the initial monomer dispersion are examined. The presence of the inorganic UFP in the polymerisation reactor influences the properties of the monomer phase and affects the drop size distribution. This in turn influences the grain sizes as well as their distribution, which influence the processability of the resin

Hybridization of Nafion membranes by the infusion of functionalized siloxane precursors

Polysiloxane modified hybrid membranes were prepared by introducing pre-swelled commercial Nafion membrane into a sol-gel precursor solution, consisting of a pre-hydrolyzed mixture of tetraethoxysilane (TEOS) and a mercaptan functionalized organoalkoxysilane. The structure of the polysiloxane network was changed by altering the ratio of the two silane components within the precursor solution. The mercaptosilane modifier was used to provide an additional source of acidic Bronsted sites through the oxidisation of the mercaptan groups to sulfonic acid groups. The physical and chemical properties of the hybrid membranes were examined by TGA, FTIR and SEM analysis. The water vapour sorption and proton conductivity characteristics were evaluated at temperatures up to 70°C and with water activity in the region of 0.4 to 1. It was found that the polysiloxane network alters the water vapour sorption mechanism of the Nafion membrane, resulting in an increase in the equilibrium amount of water absorbed in the middle range of water activity (0.4-0.6). At the same time, the increased water absorption capability produced a concomitant increase in ionic conductivity at low water activities

Inorganic impact modifier and processing aid for PVC

An amorphous silica, SIDISTAR has been investigated as an impact modifier for rigid PVC. Optimal dispersion of the silica as primary particles is essential and this can be achieved by incorporating it at an early stage of the mixing process before other fillers are added. This ensures that the PVC grains are coated with SIDISTAR. This material is able to function as an impact modifier via the cavitation mechanism and it will also improve the dispersion of the other ingredients in the compound. It was found that SIDISTAR delayed gelation of the PVC compound, but this could be avoided by minor changes in formulation and processing conditions. Reduction in gelation time resulted in improved impact performance. Furthermore, compounds containing SIDISTAR possessed a wide processing window