Study On Intrinsic Viscosity, Crystallization And Mechanical Properties Of R-PET /Inorganic Powder Composite

Poly(ethylene terephthalate)(PET) was synthetized by ethylene glycol(EG) and terephthalic acid(TPA) through polycondensation. Since it owns superior mechanical properties and easily changeable crystallinity, most of the PET is processed into film, container and fibre for package, food and clothing industry. At present, the demand for PET is still growing.Due to the numerous consumption of PET, making effective use of waste PET(r-PET)can produce giant benefits economically and environmentally. Nowadays, the most used recycle process for r-PET is melting extrusion. However, this simple processing method usually cause the breaking and degradation of PET molecule chains followed by a decrease of intrinsic viscosity(IV). This will surely deteriorate the properties of PET, reduce its practical value and shrink its application range. Therefore the research of r-PET chain extension and modification of its properties is of great significance in theory and in practice. Among many modification methods, adding different kinds of chemical chain extender to enhance its IV is one of the research directions. Nevertheless some problems may occur, such as residue of chemical chain extender, which is strictly forbidden in food industry. Therefore, the thesis uses many kinds of inorganic powder to increase IV of r-PET and to modify r-PET.The thesis firstly investigated the influence of different kinds of inorganic powder and their content on the IV of r-PET and then systematically study the their effect on the mechanical properties, crystallization properties, thermal stability and Vicat softening point of r-PET. The result showed that proper content of nano-silica could raise the IV and the hydrophobic kind silica HB630 displayed the best performance. The appropriate amount of nano-silica can promote the tensile strength, bending strength and bending modulus of r-PET and nanosilica-HB630 showed best effect in promoting the general mechanical properties of r-PET.Sodium montmorillonite(Na-MMT), kaolin, talcum powder and two kinds of wollastonite can all increase the tensile strength, bending strength and bending modulus of r-PET, among which talcum powder can also increase the notched impact strength of r-PET. In those inorganic powder used, nanosilica-HB630 and Na-MMT can better promote the mechanical properties of r-PET at low content.All the kinds of inorganic powder used in r-PET can elevate the Vicat softening point, among which Na-MMT and talcum powder demonstrated the best effect. 3phr of Na-MMT and 6phr of talcum powder elevated the r-PET Vicat softening point to 162.2℃ and164.5℃ respectively.Nanosilica-HB630, Na-MMT, kaolin, talcum powder and wollastonite all promoted the crystallization process of r-PET, raised the crystallization peak temperature, narrowed the half width of crystallization peak and reduced the degree of subcooling to some extent. Nanosilica-HB630 could also increase the crystallization degree, reduce the size of crystal and increase the density of crystalline grain.To better disperse the nano inorganic powder( nanosilica-HB630 and Na-MMT), the thesis also used two processing methods to prepare the composites by masterbatch. The result showed that proper content of nanosilica-HB630 could still raise the IV of r-PET. Compared to masterbatch-one-step method, the masterbatch-two-step method had better effect in dispersing the nanosilica particles in r-PET. Those processed by masterbatch-two-step method had better mechanical performance. Especially the notched impact strength is superior to those prepared by masterbatch-one-step and nonmasteratch method. The notched impact strength was raised from 2.95KJ/m2 to 4.57 KJ/m2 with 0.4phr HB630, which increased by 54.9%.Via the masterbatch-two-step processing method, nanosilica-HB630 could better promote the crystallization process of r-PET, increase the crystallization peak temperature and reduce the half width of crystallization peak as well as the degree of subcooling. Besides, it could also raise the crystallization degree at proper content and decrease the size of crystalline grain. The study of non-isothermal crystallization showed that nanosilica can shrink the crystallization time and increase the crystallization rate and constant.Compared to nanosilica-HB630, Na-MMT didn’t show any sign of increasing the IV of r-PET and even slightly decreased the IV at high content. R-PET/Na-MMT composite prepared by masterbatch-two-step method had more stable mechanical properties. Moreover, the r-PET/Na-MMT composite prepared by masterbatch-two-step method had better performance in tensile strength than those prepared by masterbatch-one-step method.Through masterbatch-two-step method, Na-MMT reduced the time for r-PET to reach the same crystallinity, shrank the time for primary stage at crystallization and raised the crystalline rate and constant. At last, Na-MMT was still effective in elevating the thermal stability and Vicat softening point of r-PET through masterbatch-two-step method.