Shear-induced β -form polypropylene in long chain branching isotactic polypropylene

Abstract

Long chain branching polypropylene (LCBPP) with different long chain branching (LCB) contents were prepared by reactive extrusion in the presence of styrene and benzoyl peroxide, and their shear-induced crystallization behaviors were investigated. The results indicated that the LCB structure extended the relaxation time of LCBPP in the molten state, which led to the formation of b-form polypropylene under shear and high cooling rate. The content of b-form (K b ) increased with the increase of LCB content, shearing rate and cooling rate. The K b value of LCBPP3 whose weight average molecular weight was 920,000 g mol 21 could be up to 52.0% with a shear rate of 60 s 21 associated with a cooling rate of 2808C min 21 . This study is expected not only to have a deeper understanding of the shearinduced crystallization behavior of LCBPP, but also provide a new strategy to obtain high level b-form polypropylene. POLYM. ENG. SCI., 56:240-247, 2016.

Relationship between molecular structure, crystallization behavior, and mechanical properties of long chain branching polypropylene

“…The k b value of HMSPP1, HMSPP2, and HMSPP3 was 4.8, 17.9 and 36.8 %, respectively. The reason that LCBPP samples formed b-crystal under injection molding condition was the combined effects of shear, rapid cooling, and LCB structures, which has been demonstrated in our previous study [41]. Generally, b-crystal can improve the impact strength of PP, but decrease the flexural modulus and the tensile strength of PP [42,43].…”

Effect of β‐nucleating agent and zeolite molecular sieves on supercritical CO2‐assisted cell and crystal nucleation during the long‐chain‐branched polypropylene foaming

“…There are some methods for forming β‐crystal in PP such as shearing or elongation deformation, directed crystallization in a temperature gradient field or adding β‐nucleating agent (β‐NA) into PP . The introduction of β‐NA into PP could generate β‐crystal, which has a lower T m than α‐crystal …”

Isothermal crystallization kinetics and subsequent melting behavior of β‐nucleated isotactic polypropylene/graphene oxide composites with different ordered structure

“…As is well known, iPP is a kind of semi‐crystalline resin with five crystalline structures: α ‐form, β ‐form, γ ‐form, δ ‐form and smectic phase . Among them, β ‐form, as a metastable phase, can only form under special conditions as follows: crystallization after quenching to a certain temperature range, directional crystallization in a specific temperature gradient, crystallization of melt subject to shear or elongation, or crystallization in the presence of a β ‐nucleating agent ( β ‐NA) .…”