Structure And Properties Of Isocyanurate-modified Crosslinked PVC Foam

Rigid cross-linked polyvinyl chloride(PVC)foams are important polymer foam material with a low moisture absorption,heat insulation effect,small density,high strength and good processing performance,and so on,which is widely used in automobile turbines,transportation,aerospace,wall insulation,leaf materials,etc.However,PVC foams can not be applied in high temperature environment due to the poor heat resistance.In this paper,a series of isocyanurate-modified rigid cross-linked PVC foams were prepared by using PVC as matrix resin,toluene diisocyanate(TDI)as crosslinking agent,azodicarbonamide(AC),azobisisobutyronitrile(AIBN)as blowing agent,phthalic anhydride(PA)as cross-linked regulator,and isocyanurate(t-TDI)as heat-resistant component.The chemical properties of the rigid cross-linked PVC foam were characterized by Fourier transform infrared spectroscopy(FT-IR)and solid-state nuclear magnetic resonance(CP/MAS 13C NMR).The chemical bonds of the crosslinked network were discussed.The relationship between isocyanurate content and glass transition temperature(Tg)was studied by dynamic thermomechanical analysis(DMA).A series of the cross-linked PVC foams modified by isocyanurate were obtained by changing the ratio of isocyanurate and TDI.The chemical structures of rigid cross-linked PVC foams modified by isocyanurate were analyzed.The effect of isocyanurate content on the glass transition temperature of PVC foams was studied.It was found that the cross-linked network did not form by comparison to FT-IR spectra of the pre-foam,cross-linked foam,and gel.The result of solid-NMR spectra showed that a polyurea network formed by the reaction of TDI and isocyanurate with water.The Tg value increased 4.5 ℃,when the mass fraction of isocyanurate attained 10%.By means of adding of PA to the system,the imide produced by the reaction of PA and isocyanurate blocked the extension of polyurea chains.The content of gel decreased.The Tg value increased 5 ℃,where the mass fraction of isocyanurate was 30%.The cross-linked PVC foams modified by isocyanurate were prepared by using 1,3,5-Tris[3-(dimethylamino)propyl]hexahydro-1,3,5-triazine as catalyst.The result suggested that content of isocyanurate had little effect on the flame retardancy of foams.When the mass fraction of catalyst was 0.3%,the Tg was increased by 5.5 ℃.Furthermore,the imide blocked the formation of cross-linked network.But the gel content increased with the increase of the catalyst mass fraction.When the mass fraction of catalyst was 0.8%,the Tg was increased by 4.16 ℃.Then,the mechanical properties of PVC foam were characterized by universal testing machine.It was found that the foam density decreased with the increase of the opening temperature,and the mechanical properties,including tensile,compression,shear properties,of the foam decreased with the decrease of the density.