Study On The Preparation And Properties Of PET/POSS Composites

Poly(ethylene terephthalate)(PET) is widely used in the fields of the fiber, film andengineering plastics because of its excellent rigid, heat and chemical resistance properties.Nevertheless, with the developmed requirements of products, the study focusing on PET resin hasbeen paid attention. The cage-structured Polyhedral Oligomeric Silsesquioxane (POSS) is a newtype of organic-inorganic hybrid materials with merits like: intra-molecular hetero structure, nano-size effect, high heat resistance, improved mechanical properties of polymers, etc. Combiningorganic phase and inorganic phase with covalent bonds at the molecular level may result inmaterials with significantly improved performance. Compared with the conventional nanoparticles,polyhedral oligomeric silsesquioxane (POSS) with formula of (RSiO1.5)n, is a componentbetween silica (SiO2) and polysiloxane (R2SiO)n. When R groups are reactive, POSS can beintroduced to side group or end of the polymer chains by copolymerization, graft or blendingIn this article,1,2-propanediollsobutyl POSS was used as an additive to PET to preparePOSS/PET composites. The POSS/PET composites were prepared by in-situ polymerization andmelting blending with1.5-5.0wt%loading of POSS. The composites were charactered by SEM,NMR, XPS, DSC, etc, it showed good dispersion with the content of1.5and2.5wt%of POSS.The composites showed good processabilities when being casting into films and spinning intofibers with1.5and2.5wt%loading of POSS. The main research contents and conclusions are asfollows:(1) Firstly, the POSS/PET copolymer was prepared by in-situ polymerization. GPCtesting showed that the products possessed relatively high molecular weight, the number averagemolecular weight of the POSS/PET copolymer ranged from23000-27000g/mol and the intrinsic viscosity from0.649-0.673dL/g. The dispersion of POSS in PET matrix was deserved byscanning electron microscope (SEM). The results showed that the aggregate extent of POSS in thepolymer matrix increased as the POSS contents increased. But the particles disperse evenly innanosize (80-100nm) in PET matrix with the content of2.5wt%. The interaction between POSSand PET chains was studied by nuclear magnetic resonance (NMR) and X-ray photoelectronspectroscopy (XPS), there was a covalent linkage present between POSS and PET chains. Thecrystallization and thermal behavior of PET/POSS composites were investigated by DSC and TG.It was indicated that when POSS exists, the crystallization temperature of PET during coolingfrom melt moves to higher temperature as POSS had played a role of heterogeneous nucleation.The rheology behavior of the POSS/PET copolymer was measured using rotational rheometer(ARES-RFS) in a dynamic mode. It was found that the storage modulus(G’) and the lossmodulus(G’’) of the copolymer increased with introduction of POSS. This indicated that therewere some interactions between POSS and PET.(2) POSS/PET copolymer composites were synthesized by20L reaction kettle with1.5and2.5wt%loading of POSS. The copolymer was extruded into thick film, and the thick film wasprepared by biaxial stretching machine with the stretching ratio of3.5*3.5. We studied on theinfluence of POSS content on the optical properties and mechanical properties of the films. Themechanical properties of the film were measured by Instron5969. The addition of POSS wasbeneficial to improve the mechanical properties of the films, and the tensile strength and breakelongation increased as the content of POSS increased. The optical performances such astransmittance, haze of the film were measured using Lambda950spectrophotometer and Haze-Gard Plus C haze meter. The results indicated that the transparency of PET film increased and theoptical properties of materials were improved with the addition of POSS particles, but the hazevalue increased as the content of POSS increased. The POSS/PET fibers were prepared by meltspinning. And we investigated the influence of POSS content on the mechanical andcrystallization properties of the fibers. The mechanical properties of the POSS/PET fibers werebetter than the PET fiber. The tensile strength increased as the content of POSS increased. Thecrystallinity and average size of [010] plane from the XRD curves decreased with the increasingPOSS content.(3) POSS/PET blending composites were prepared by the melt compounding apparatus.The molecular structures of the composites were characterized by XPS, and the results showedthat there was no chemical bond between PET and POSS. Nonisothermal crystallization behaviorof POSS/PET composites was studied by differential scanning calorimetry (DSC), and itindicated that when POSS existed, the crystallization temperature of PET during cooling frommelt moveed to higher temperature and its crystallization rate increased, thus POSS played a role of heterogeneous nucleation. There were two melting peak during the melting process of, as thePET had two crystal forms: extended chain crystals and folded chain crystals. The POSS/PETblending fibers were prepared by melt spinning. The mechanical properties of the fibers decreasedwith the increasing of POSS.