Regulation of Phase Separation in PP/EPR In-Reactor Alloy and Its Effect on Crystallization Kinetics

Abstract

The low molecular weight ethylene−propylene random copolymer (LEPR) in a polypropylene (PP)/EPR inreactor alloy is replaced by high molecular weight EPR (HEPR). It is found that the phase separation rate of PP/HEPR alloy is much slower than that of PP/LEPR alloy. The effect of phase separation on the crystallization kinetics of PP/HEPR alloy is studied and compared with that of PP/LEPR alloy. The pre-phase-separated PP/HEPR alloy exhibits a faster spherulitic growth rate and overall crystallization rate, as compared with the directly quenched one. This is contrary to the PP/LEPR alloy and is interpreted in terms of the relative rate of crystallization and phase separation based on phase diagram. It is also observed that directly quenched PP/HEPR alloy has a larger long period after crystallization. This can be attributed to more inclusion of EPRrich phase into inter-lamellae, which is advantageous to the mechanical properties. INTRODUCTIONPolypropylene/ethylene-propylene random copolymer (PP/ EPR) in-reactor alloys have excellent balance in tensile and impact strengths, thus there are many reports on structureproperties of PP/EPR in-reactor alloys, including structural characterization, 1−21 polymerization process, 22−25 crystallization, 26−36 phase morphology 37−48 and mechanical properties. 49,50 PP/EPR in-reactor alloys are usually prepared by a two-stage or multistage polymerization process, 51−53 and contain different components, such as propylene homopolymer, ethylene-propylene random copolymer (EPR), ethylenepropylene multiblocky copolymer and even minor polyethylene. 54−56 The PP/EPR in-reactor alloy is typically a multicomponent system containing crystalline components. In such a system, phase separation may occur in its melt and plays an important role on its crystallization, morphology and thus the final mechanical properties. 57−64 As a result, it is of great importance to study the effect of phase separation on crystallization and morphology of PP/EPR in-reactor alloy. However, although many researches have been conducted on PP/EPR in-reactor alloys, the effect of phase separation on crystallization and morphology is rarely reported, as compared with the blends containing a crystalline component.In our previous work we reported the effect of phase separation on morphology, linear spherulitic growth rate and overall crystallization kinetics of PP/EPR in-reactor alloys prepared by two-stage and multistage polymerization processes. 65−67 It was found that prior phase separation in the melt could retard crystallization rate and lead to more amorphous components included into the spherulites. These results were ascribed to the smaller PP content in the concentrated phase (PP-rich phase) formed by phase separation than that in the PP-rich phase of the directly quenched sample, as shown in Figure 1. However, in this situation, the PP/EPR in-reactor alloy directly quenched from the homogeneous melt is believed to have a faster phase separation rate and forms to two phases prior to crystallization (route a ...

Effect of annealing‐induced interfacial demixing on crystallization of PEO confined in coaxial electrospun nanofibers

“…The effect of annealing temperature on crystallization behavior of PEO/PAN coaxial electrospun fibers can be interpreted in terms of the composition of the PEO‐rich phase formed in demixing process. It is clearly that the PEO/PAN mixture exhibits an upper critical solution temperature‐type phase diagram, since demixing occurs while lowering the temperature . Figure shows the schematic phase diagram at the PEO/PAN interface in the coaxial electrospun fibers.…”

Influence of Chain Microstructure on Liquid–Liquid Phase Structure and Crystallization of Dual Reactor Ziegler–Natta Made Impact Propylene–Ethylene Copolymers

“…Xu and co-workers have carried out studies of melt annealing for different lengths of time inside the binodal using impact propylene copolymers synthesized by a multistage sequential polymerization process. − These authors observed that by increasing annealing time at melt temperatures between 160 and 180 °C, the isothermal crystallization rate at temperatures >120 °C decreases, and dispersed domains trapped within the growing spherulites grow with time. Comparatively, minor differences were observed in linear growth rates with time .…”

Time-Resolved SAXS/WAXD under Tensile Deformation: Role of Segmental Ethylene–Propylene Copolymers in Impact-Resistant Polypropylene Copolymers

“…It has been shown that sEP chains could also affect the phase separation in IPCs during cooling. , However, bEP chains with long block segments are rarely observed in commercial IPCs. Recently, several studies have indicated that, instead of bEP chains, it could be a mixture of sEP/bEP chains with varieties of ethylene (E) and propylene (P) segmental lengths. ,− Some sEP chains have either E or P segmental lengths long enough to crystallize individually; these materials are referred to as “crystalline ethylene–propylene (cEP) copolymers”.…”

“…21 It has been shown that sEP chains could also affect the phase separation in IPCs during cooling. 22,23 However, bEP chains with long block segments are rarely observed in commercial IPCs. Recently, several studies have indicated that, instead of bEP chains, it could be a mixture of sEP/bEP chains with varieties of ethylene (E) and propylene (P) segmental lengths.…”