Study On Preparation And Properties Of Thermally-Reversible Crosslinked Polyvinyl Chloride Foam

PVC (polyvinyl chloride) resin is one of the five common resins. PVC foam has lots of characters, such as chemical resistance, non-absorbency, self-extinguishment, low density, sound absorption. Due to all such characters, PVC foam is widely used in daily life. For example, rigid PVC foam could be used in sport, boat, aircraft, train; soft PVC foam could be used in shoes, tolls, package and so on.Traditional PVC foam usually is made by chemical foaming agent, AC, which has a problem of residual influencing the properties of foam. Traditional PVC foam is permanent cross-linking, which means PVC losses thermo-plastic ability. In order to settle such problems, thermal reversible cross-linked PVC foam was prepared, and different foaming methods were studied. The effect of substituent and physical form on the temperature of retro Diels-Alder reaction of dicyclopentadiene derivative also was studied.The main work was shown as bellow.Supercritical carbon dioxide was used to prepare thermal reversible cross-linked PVC foam Firstly, the gel content of PVC with different cross-linking agent additive amount was studied and the result showed that the highest cross-linking degree was obtained with 1.5phr cross-linking agent. Secondly, carbon dioxide solubility in PVC was measured under different pressures. Finally, formula and hot press technology was modified according to the properties of PVC foam. The result showed that clay or white carbon black does their work to get a good foaming ratio, cell morphology. The formula with 8phr clay got the highest foaming ratio and better cell morphology and distribution.Crystalline hydrate foaming agent was designed and prepared and then thermal reversible cross-linked PVC foam was obtained with crystalline hydrate foaming agent. Firstly, due to the character of crystalline hydrate salt, the crystalline hydrate foaming agent was designed and prepared.The result showed that the foaming temperature could be adapted to the temperature of PVC processing with the method of crystallization as bentonite or clay being crystallizing carrier. The foaming temperature matched very well with PVC processing as the ratio between alums and bentonite being 15:10 or alums and clay being 5:10. Thermal reversible cross-linked PVC foam was obtained with crystalline hydrate foaming agent.The formula and extrusion process were adjusted according to the properties of PVC foam The result shows that after granulation processing, melt processing, PVC foam could keep its cell structure.The dicyclopentadiene derivative was used as thermal reversal cross-linking agent in PVC progressing. The de-cross-linking temperature is very important in such material. The effect of different substituent on de-dimerization temperature of dicyclopentadiene derivative was studied. The result showed that both electronic and steric effect of substituent could influence the de-dimerization temperature. The rDA reaction temperature of the dimer of substituted cyclopentadiene would increase no matter the substituent is electron-donating or electron-withdrawing. As for the dimer of bi-or multi-substituted cyclopentadiene,the story was different and complex.