Study On The Crystallization Behavior Of Isotactic Polypropylene(iPP)/Poly(Ethylene Terephthalate)(PET) Fibre Composite

The work of this paper is mainly to study the crystallization behavior of isotactic polypropylene (iPP)/poly(ethylene terephthalate)(PET) fibre composite. It contains two parts as follows:first, non-isothermal crystallization behavior of the iPP/PET fi-bre was carried on a differential scanning calorimeter (DSC). It primarily studys the influence of different cooling rates and introduced PET fibres on the crystallization rate, crystallization temperature, crystallinity of iPP matrix. Second, the iPP/PET fi-bre composite was moulded by a mintype mixing-injection moulding machine devel-oped in our group. And the samples were characterized by a series of experimental instrument. It researches the effect of injection moulding process and the introduced PET fibres on the interfacial crystallization of iPP.In this paper, the main conclusions drawn are as follows:1. The PET fibres sandwiched between two iPP films were prepared by com-pression moulding and then the films were characterized by DSC to research the im-pact of introduced PET fibres and different cooling rates on the non-isothermal crys-tallization kinetics of iPP/PET fibre composite. It turns out that, with the increase of the cooling rate, the crystallization peaks of neat iPP and iPP/PET fibre composite shift from high to low temperature, and peak shapes become wide. This mainly be-cause faster cooling rate can degrade the ordered arrangement of molecular chain in crystallization process, which makes nucleation lag behind and makes initial crystal-lization delay. At last, crystallization peaks move from high to low temperature. Meanwhile, faster cooling rate also leads to worse mobility of molecular chain. Then the imperfect crystals form, which results in more range of crystallization temperature and wider crystallization peaks. The introduced PET fibres promote the formation and growth of crystal nucleus as well as the whole crystallization process. For iPP based composites, PET fibres introduced can act as a nucleating agent and have the poten-tial to induce iPP to form transcrystallization. Finally, crystals grow along the direc-tion of orientation.2. The iPP/PET fibre composite was moulded by a minitype mixing-injection moulding machine developed in our group. The result of WAXD discovers that, β-crystal can be found in the whole part (including the skin, intermediate, core re-gion). Unexpectedly, there is a remarkably increasing Xβ from skin to core region. The result of SEM indicates that, in skin region, there are well parallel lamellar structures. Combined with the corresponding2D-SAXS patterns, it can be safely de-duced that these aligned lamellae are actually shish-kebab structure. Oriented shish-kebab structure also presents in intermediate region. In core region, bright and dim spherulitic crystals can be observed in the matrix. Meanwhile, brighter crystals can be observed in the vicinity of PET fibres parallel to flow direction. Moreover, such brighter crystals surrounding the PET fibre perpendicular to flow direction are discernable. The presence of PET fibre in iPP melt during injection moulding pro-motes the development of β-crystal especially in core region. This primarily attributes to local shear caused by different flow rates of molten iPP and solid PET fibre, which leads to a-row nuclei and subsequently β-crystal. On the other hand, pre-shear brought by the rotating screw of the MIM machine gives rise to smectic ordering during plasticization and melt mixing. Once the melt containing smectic ordering was injected into the mould cavity, survived smectic orderings provide nucleating sites for the growth of β-crystal.