Effect Of Formulation Composition On Foam Structure Of Crosslinked PVC Foam

Polymer foam materials are widely used in automotive interior decoration,transportation,aircraft manufacturing,amusement facilities,building,medical treatment,marine products breeding,military and other fields.Rigid foam for sandwich structure has good heat and sound insulation and impact resistance.Crosslinked polyvinyl chloride(PVC)foam has the characteristics of high strength and good mechanical performance and is used in load areas.Rigid crosslinked PVC foam is a polyvinyl chloride foamed material reinforced by cross-linked polyurea network.Currently,80%-85% of the foam is applied to wind turbine blades.In recent years,wind power blades is becoming larger.It resulted that the weight of leaves increased.The absorption amount of adhesive is mainly determined by the diameter of the closed cell foams.The smaller cell size is an effective way to reduce the weight of the blades.Therefore,the PVC foams with smaller cell diameters will become the focus now.In view of the development demand,the influences of the composition of PVC resin,crosslinking network,foaming agent,nucleating agent and other aspects on cell structure were investigated.The reasons for the formation of various structures under different conditions were discussed and the relationship between the properties of the formula embryo and the cell structure was established in this dissertation,which provides guidance for the cell design of PVC structural foam.The more details were introduced in the following.1.The influence of particle size,dosage,molecular weight and preparation process of the PVC paste resin,the PVC blending resin and the PVC suspension resin on the foaming properties and cell structure of PVC foam were studied by replacing the paste resin in the formula.The results showed that the blending resin and the suspension resin could be applied to the PVC structure foam,and the substitution amount could be more than 90%.The foaming process was not affected when the substitution amount of blending resin is less than 90%.The substitution amount of suspension resin is less than 70% without affecting the foaming process.The addition of blending resin or suspension resin with low polymerization degree can control he open porosity of PVC foam.2.The effects of modifiers,such as styrene-maleic anhydride,phthalic anhydride,mixed anhydride,hydroxyl-containing substances(e.g.glycerol,benzyl alcohol,isopropanol),comonomer(e.g.glycidyl methacrylate ether,butyl acrylate,styrene)and other substances on the cell structure of PVC foam crosslinked by isocyanate were investigated.It was found the two groups of cells with excessive amount of maleic anhydride.The structure was due to the decrease of polymer melt strength in the maleic anhydride(MA)enriched region of embryo body.The acidity of phthalic anhydride had more influence on the degradation of PVC than the molding time,and lead to the "scorch" phenomenon in the core.The thermal stability of the system can be improved by adding thermal stabilizer,and the foam with smaller cell was obtained when the inorganic lead salt was used as stabilizer.The organotin and stearate used as foam stabilizer has little influence on the phthalic anhydride system,but they caused a macroporous foam in mixed anhydride system of methyl tetrahydrophthalic anhydride and tetrahydrophthalic anhydride(M/T70).The reason was considered the role of surfactants of two stabilizers.When the PVC foam was modified by vinyl monomers,due to the copolymerization of vinyl monomers and PVC grafting reaction,the decrease of small fractions plasticizing effect on the polymer,and the entanglement between polymer macromolecules strengthens,the foam with a high rate of closed-cell and a good pore structure was prepared.3.The effects of azobisisobutyronitrile(AIBN),azodicarbonamide(AC),modified AC and foaming agent H on the cell structure of PVC foam were studied.It was found that AIBN had a decisive effect on the density of the final foamed body,and the foam density decreased significantly when the amount of AIBN increased.In semi-interpenetrating system,the cell expanded more easily because small molecular components played a role of plasticizer on polymer.AC as "nucleating agent" in the foaming process was conducive to the formation of smaller bubble nuclei.AC modified by Zinc stearate(mAC)showed better dispersion and nucleation in the system.When the dosage changed from 1phr to 8phr,the cell size of the final foam can be adjusted by the dosage.The cell diameter can be reduced with smaller dosage.The mAC has better thermal stability for PVC system.The foaming agent H played the role of "nucleating agent" in the foaming process and could bring the final foam body with two groups of cell.4.The influence of two nucleating agents of precipitated calcium carbonate and ultrafine aluminum silicate on the cell structure was studied.It was found that precipitated calcium carbonate was not a good nucleating agent in the preparation of PVC foam,and the amount of precipitated calcium carbonate had little effect on the pore structure of the foaming body.A small amount of ultra-fine aluminum silicate can reduce the overall bubble size of the foaming body.With the increase of its dosage,the difference of the cell size between the surface and the core increases.there was a great quantity of small cells and a small quantity of bubbles in the surface layer.As the amount of ultrafine aluminum silicate continues to increase,the small cell area of the surface expanded to the core of the foam board.The small cell area became thicker.At last,the three groups of cell appeared after the surface and core fused.This phenomenon was related to the redistribution of ultrafine aluminum silicate caused by temperature.