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Studies On Preparation And Properties Of Ploy(ethylene Trephthalte)/Barite Nanocomposites

Posted on:2011-04-03Degree:DoctorType:Dissertation
Country:ChinaCandidate:C H GeFull Text:PDF
GTID:1101360308476476Subject:Materials science
Abstract/Summary:PDF Full Text Request
Current domestic production of fiber-forming polyester is overcapacity, while the production status of poly(ethylene terephthalate) (PET) engineering plastics just the reverse. Used a novel functional nanoparticle—nano-barite as filler, PET/Barite nanocomposites were prepared by direct melt compounding. The effects of surface nature and contents of barite nanoparticles on the crystallization, dynamic mechanical and mechanical properties were investigated systematically. In order to improve the mechanical properties and flammability of PET/Barite nanocomposites, maleic anhydride grafted polyethylene octane copolymer (POE-g-MA), ethylene-ethylacrylate-glycidylmethacrylate copolymer (E-EA-GMA) and microencapsulated red phosphorus (MRP) were employed to modify them, and to prepare PET engineering plastics with high performance. Furthermore, the modification mechanism was also discussed. The main content and results were as follows:1. The effects of surface nature and contents of barite nanoparticles on the crystallization behaviors and mechanical properties of PET were studied. The results showed that a small amount of UNBarite or SABarite added into PET matrix can act as efficient nucleating agents and improve the crystallization rate of PET but SABarite shows higher efficiency. SABarite nanoparticles induce preferential lamellae orientation because of the strong interfacial interaction between PET chains and SABarite nanoparticles, which is not the case in UNBarite filled PET as determined by WAXD. The rigid inorganic nanoparticles possess high rigidity and induce an increase in the interfacial stiffness, thus PET/Barite nanocomposites have the higher value of storage modulus (E') and glass transition temperature (Tg) than pure PET, which would increase with increasing SABarite content. SABarite nanoparticles have excellent interfacial interaction with PET through physical entanglement of alkyl chains at the interface. The increased interfacial interaction constrains motion of PET molecular chain segments, leading to an increase of Tg·Surprisingly, both E' and Tg of PET nanocomposites filled with SABarite were a little lower than that of unmodified UNBarite at the same concentration, which could be attributed to the higher heterogeneous nucleating activity of SABarite than that of UNBarite, therefore resulting in an increase of crystallization rate, i.e. polymer molecular chains in amorphous region exhibit higher mobility and thus reduce the E' and Tg·Barite nanoparticles can facilitate the crystallization process and thus clearly reinforce the PET matrix. Compared with pure PET, the maximum tensile strength and flexural modulus of PET/SABarite nanocomposites increase by 18.5 and 21.7 at 0.5 and 3.0 wt% and that of PET/UNBarite nanocomposites increase by 9.4 and 21.9 both at 3.0 wt%, respectively. The thermal stability of the nanocomposites is enhanced by addition of barite nanoparticles. The incorporation of organic small molecule group on the surface of modified nanoparticles reduce the thermal stability of the nanocomposites, but still higher than that of pure PET.2. Isothermal crystallization process of pure PET and PET/Barite nanocomposites were analyzed. In the isothermal crystallization process, pure PET demonstrate stronger secondary crystallization process than that of PET nanocomposites, in which more homogeneously sized spherulites formed from barite nucleation. The crystalline phase in PET/Barite nanocomposites is more perfect than that of pure PET. The strong nucleation activity of the SABarite nanoparticles could further increase the crystal perfection. The Avrami exponent n for pure PET is more than 4 by and large. For PET nanocomposites, the n ranges between 2 and 4, the spherulites are thought to be grown in a 3D morphology from heterogeneous nuclei, accompanied by the change in nucleation mechanism from instantaneous nucleation to sporadic nucleation. The addition of barite nanoparticles decreases the isothermal crystallization activation energy. The enhanced interfacial interaction reduces the crystallization free energy barrier for nucleus formation.3. The nonisothermal melt crystallization kinetics of pure PET and PET/Barite nanocomposites was also studied, where a kinetic analysis was made by Jeziorny, Ozawa and Mo methods. The results demonstrated that Mo method is successful in describing the nonisothermal crystallization kinetics of pure PET and its nanocomposites. Analysis of the crystallization process shows that the crystallization rate increases with adding barite nanoparticles. UNBarite nanoparticles promote the overall crystallization process of PET matrix by improving the nucleation process, so the occurrence of crystallization is more easily than that of pure PET due to the lower△E. However, SABarite nanoparticles retard the rearrangement of PET chain segments to some extent due to the strong interfacial interaction between two phases, thereby decreasing the crystallization ability, but the nucleation effect is still dominant role on the crystallization of PET matrix.4. Two types of functional polyolefin elastomers were employed to toughen the PET/SABarite nanocomposites. At the appropriate elastomer content, brittle-to-ductile transition of ternary compositions takes place, indicating that both elastomers have a significant toughening effect on PET. Found that, at the same content, E-EA-GMA is more effective in toughening PET/SABarite nanocomposites than POE-g-MA, which resulted from its better compatibility with PET. Differential scanning calorimetry analysis showed that the addition of elastomers restrict the mobility of PET molecular segments, lower the crystallization rate and reduce the crystal perfection of PET/SABarite nanocomposites.5. The flame retardancy, mechanical and thermal behaviors of PET filled with complex flame retardant composed of SABarite and MRP have been studied. Combination of MRP and SABarite shows effective synergistic effect. Limited oxygen index (LOI) value decreases and subsequently increases with the addition of nanoparticles as the content of MRP is designated at 5 wt%. When the mass proportion of PET, MRP and SABarite is 100/5/10, the LOI is 32.7%, UL94 rating is V-0. Meanwhile, flame-retardant nanocomposites exhibit good mechanical properties and antidropping behavior. TGA analysis shows that the introduction of nanoparticles can greatly enhance the thermal stabilities and charring abilities of PET. Glass fiber reinforced and/or halogen-free flame-retardant PET engineering plastics prepared in present thesis can be used as a substitute for similar products provided by Dupont.
Keywords/Search Tags:poly(ethylene terephthalate), barite, nanocomposites, crystallization, toughen, flame retardant
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