Influence Of The Additives On The Crystallization Behavior, Microscopic Morphology And Properties Of Polyvinyl Chloride

In this paper,acetanilide,adipic acid and potassium hydrogen phthalate were chosen as additives to advance polyvinyl chloride (PVC) to crystallize. The effects of compress mold,annealing temperature and time,additive property and loading on the crystallization,microscopicmorphology and mechanical properties of PVC were studied by means of wide angle X-ray diffraction(WAXD),differential scanning calorimetry(DSC),fourier transform infrared spectrophotometer(FT-IR),scanning electron microscope(SEM)and tensile test.The analysis results indicated that there are two kinds of crystal in PVC. One is chain-folded crystal N,the other is micelle crystal M.They are different in the way of molecule chain array, herefore the way in which they grow and develop is also different.Peak B on the DSC melting curve was caused by the melting of chain-folded crystal. Its melting temperature was above 180℃.Peak A was caused by the melting of micelle crystal. Its melting temperature was below 180℃.The growth of chain-folded crystal was affected by the fundus substance,additive property and the mobility of chain segment. Adipic acid could advance PVC to form TTTT sequence,and can provide base of the array of fold chains,so it promoted the development of chain-folded crystal. Potassium hydrogen phthalate could also provide base for the array of fold chains,so it promoted the development of chain-folded crystal as well. But following the rise of its loading, potassium hydrogen phthalate aggregated in grain,as decreased the interface with PVC and reduced the proportion of chain-folded crystal. While adipic acid formed large lamellar,which increased the interface with PVC,so following the rise of the content of adipic acid,the proportion of chain-folded crystal was lifted. Acetanilide could promoted the growth of micelle crystal . During compress mold,the chains were easy to form extended chain conformation,and if there was additive to advance the mobility of chain segment at the moment, the chain-folded crystal would be accelerated to grow,otherwise the micelle crystal woule be benefited to develop. There was no enough time for some chain segments to array regularly during compress mold,they arraied regularly to enter in crystal lattice during annealing. When annealed at 110℃,the mobility of chain segments was low, they arraied parallelly to form micelle crystal,while annealed at 130℃,the mobility of chain segments was raised, they formed chain-folded crystal.The X-ray diffraction peaks of PVC were caused by chain-folded crystal and micelle crystal together.The diffraction peaks between20°and 26°were mainly caused by chain-folded crystal,and the diffraction peaks between 16°and 20°were primarily caused by micelle crystal.The crystallite growth was the competitive result of two opposite processes:one was chain segment shift to nucleus,which made crystal grow,the other was chain segment left nucleus through thermal motion.When the rate of the two process was equal,the equilibrium was reached,and the degree of crystallinity reached the maximum,afterwords,the crystallites melted and the crystallinity was reduced.How long would it reach the balance? It was dependent on the annealing temperature and the content of acetanilide. When PVC with 1w.t.% acetanilide was annealed at 130℃,it is about 45minutes,while annealed at 110℃,it was not reached within 120min.When PVC with 3w.t.% acetanilide was annealed at 130℃,it was reached at about 30min.The mechanical property of PVC was affected by crystallinity,crystallite size,the proportion of chain-folded crystal,and the microscopic morphology as well.When the crystallinity and the crystallite size were enlarged,or the proportion of chain-folded crystal was lifted,the tensile strength and the elastic modulus were increased.Adipic acid and potassium hydrogen phthalate could induce PVC to form a regular and rigid network on the microscopic scale,as lifted the mechanical properties of PVC.While acetanilide could induce PVC to form a soft network,as made the elongation at break be 11 times of pure PVC.