Study On Preparation And Properties Of PET/PBT Alloys

Polyethylene terephthalate(PET), a low-cost polymer with excellentcomprehensive performance, has been widely used in fiber, film and hollowcontainer, etc. However, due to its slow crystallization rate, imperfect anduneven crystallization, PET has some disadvantages such as long moldingcycle, easy to warp and low notched impact strength, which strongly restrictsthe industrial application of PET as an engineering plastic. At present, thepreparation of polymer alloy by simple and practical method of extrusionblending has become a trend on modification of PET. Nevertheless, PET cannot be well compatible with majority of polymers during the process ofextrusion blending. Under this background, polybutylene terephthalate(PBT)has become a very good choice. The chemical structure of PBT is similar tothat of PET, so they have excellent blending condition in theory. Moreover,owing to its high degree of crystallinity and rapid molding, PBT is very suitableto tune the crystalline behavior of PET.In this dissertation, we first studied the PET/PBT blend system and foundthat the introduction of PBT enhance the movement of polymer molecules. Thestudy shows that when the contents of PET and PBT get close, the twocomponents present an incompatible tendency. The results demonstrate that themass content of PBT should be below30%for ensuring the stability andcompatibility of PET/PBT alloy. When the mass content of PBT arrives at10%,the PET/PBT alloy exhibited the relatively best in crystallization performanceand the mechanical property of PET/PBT alloy also improves in a certaindegree. In the meantime, the demanded crystallization temperature and thecrystallinity are slightly down.After confirming the right mass proportion for PET and PBT is9:1, fourdifferent nucleating agents with adding amount of0.5%were introduced intothe PET/PBT alloy. The effect of nucleation for inorganic nucleating agent,JC-C503, is inferior to the other three different nucleating agents as it is easy toreunite in the resin matrix. Additionally, the organic nucleating agent NaV101can reduce the crystallization activation energy of the system, which isattributed to the homogeneous nucleation mechanism for NaV101. However,NaV101can cause excessive rupture of molecular chain for PET and PBT, as a result, the alloy system can’t form effective nucleation center. The results alsoshow that PET-103, a hybrid nucleating agent with organic intercalation, hasboth heterogeneous and homogeneous nucleations in the composite.Successively, the competition of nucleation types delays the process ofmacromolecular arranging regularity, leading to decrease the crystallizationrate.By contrast, the nucleation effect of macromolecular nucleating agentSurlyn8920is relatively the best. Surlyn8920can react with PET and PBTchains at high temperature, its heterogeneous nucleation effect not only reducesthe crystallization activation energy, but also increases the crystallization rate ofthe alloy. When the content of surlyn8920gradually increases, theself-aggregation ability of ion clusters which form in the reaction weakens andthe effective nucleation center gradually tends to saturate. And then, thecrystallization rate no longer speeds up, instead slows down. The introdcutionof Surlyn8920can make up for the defect of PBT in modification on PET.When the content of Surlyn8920is3wt%, its nucleation effect is optimal, butthe mechanical property of PET/PBT alloy improves inconspicuously.After confirming the kind and content of nucleating agent, glass fiber wasintroduced into PET/PBT/Surlyn8920alloy. With the increase of glass fibercontent, the mechanical properties of the composite has significantimprovement, merely after the content of glass fiber is more than40wt%, thiseffect is restrained under the influence of compatibility between glass fiber andthe resin. The crystallization properties of the alloy are inversely proportionalto the content of glass fiber, the higher the content of glass fiber, the worse thecrystallization properties. When the content of glass fiber is10wt%, itsheterogeneous nucleation effect is relatively the best. Compared with pure alloy,the crystallization temperature of the system rises, the crystallization rateincreases, and the crystallization activation energy reduces. Although thecrystallization properties of PET/PBT alloy are not as good as PBT, but the heatresistant performance is better than the latter.