Research On Self-nucleation Of Copolymer Polypropylene And The Crystallization Kinetics And Morphology Of High Impact Polypropylene Copolymer

Since the polypropylene (PP) becomes commercially available in 1958, itis widely used in many domains, and become one of the four currency materialsincluding PE, PVC, PS and PP rapidly. Up to the present, the annual consumequantum is increased at an approximate 10% speed. The application foregroundis still optimism with all kinds of high performance PP. because PP ishalf-crystalline polymer with complex crystallization behavior, herewith, sinceit was manufactured, theory research on the crystallization structure andcrystallization behavior etc. was widely developed. The basic research providesthe guidance and basis for the PP's commerce application. So, the PP researchhas important significance not only on commerce application but also on theoryresearch.In addition, PP is limited in many applications, especially at lowtemperatures,HIPP becomes the research emphasis due to its low impacttoughenss. Presently HIPP is manufactured and applied successfully, but as acomplicated macromolecule system, it still need be researched to control andoptimize it's performance. Presently many international companies have turnedto the research of the convention macromolecule system. That indicatessufficiently the convention polyolefin system contains the magnitude researchvalue.iPP is a half-crystalline polymer and has α-form, β-from and γ-fromcrystalline forms.The overall crystallization in polymers is a combination of the nucleationand growth. Nucleation increases the number of crystal growth sites in apolymer. There are three kinds of nucleation: homogeneous nucleation,heterogeneous nucleation, and self-nucleation. Homogeneous nucleation is theprocess of the birth of small regions of crystalline phase in the superhood melt.Self-nucleation is now used as the general term describing nucleation of amacromolecular melt or solution by its own crystals grown previously.HIPP is prepared by sequential homopolymerization of propylene in thefirst reactor, followed by ethylene/propylene copolymerization in a secondreactor. The composing of high impact copolymer lies in the copolymerdirection, copolymer technics, catalyst and so on.The composing and structure of HIPP is more complex than that of iPP andpropylene random copolymer's. It has not only structure problem of iPP anddisturbing problem of copolymer monomer, but also phase structure,morphology and interface problem with phase's separation. To improve PP'simpact toughness, especially impact toughness at low temperature, HIPP ismanufactured. Under normal conditions, toughness, rigidity, intensity and hotdistortion of HIPP may decrease, so it is important to balance rigidity andtoughness. To achieve rigidity-toughness balance, we must control thecomposing, structure of every ingredient and morphology disturbing of EPRphase well.This thesis concerns with crystallization kinetics and morphology of iPP,cPP and HIPP and discusses the differences among them.First, the effects of self-nucleation on the crystallization behavior and thecrystalline morphology of cPP were studied. The increase of crystallizationactive energy and chain folding work indicate that the self-nucleation cangreatly weaken the overall crystallization of cPP because it is crystallized at thehigher temperature. The results of the morphological observations show that thespheruleite size decreased significantly.Second, Crystallization kinetics and morphology of HIPP and iPP arestudied comparatively by differential scanning calorimetry (DSC) and polarizedoptical microscopy (PLM). The crystallization and melting temperatures ofHIPP are lower than those of iPP. Isothermal crystallization kinetics studyindicates that the crystallization half-time (t1/2) of HIPP is slightly longer, whileits activation energy (?E) and chain folding surface free energy (σe) are higher,compared with those of iPP. These results indicate the partial compatibilitybetween the copolymeric components and the matrix in HIPP, which hinders thecrystallization of the matrix. The PLM images of HIPP show that there are lotsof rubbery particles (ca.1-2 μm in diameter) dispersed uniformly in the matrixof HIPP. The uniform dispersion and strong interfacial adhesion of the rubberyphase with the polypropylene matrix are key factors for the toughness-rigiditybalance of this material.