Evolution of double crystal melting peak in polypropylene foam assisted by β‐nucleating agent and supercritical CO 2

Self Cite

It is of great interest and importance to design and fabricate the double crystal melting peak (DCMP) structure for the expanded polypropylene (EPP) bead foams during sintering. Two kinds of methods with different mechanisms were proposed to prepare long-chainbranched polypropylene (LCBPP) samples with a DCMP structure: One was that the DCMP structure was prepared by generating crystals of different perfection degrees and the other one was that the DCMP structure was prepared by adding β-NA to produce various crystal forms. In addition, zeolite molecular sieve (ZMS) as the synergist was introduced into LCBPP/β-NA system to increase the efficiency of β-NA. The crystallization behaviors of various PP and their foams were tested by differential scanning calorimetry and wide-angle X-ray diffraction, as well as the cellular morphologies of various LCBPP foams were observed by scanning electron microscope. The results showed that a DCMP structure was formed in pure LCBPP in the presence of CO 2 at 168-172 C. The content of β-crystal in LCBPP/β-NA system was the highest when the content of β-NA optimized as 1.5 phr. The percentage of β-crystal in LCBPP/β-NA system was further increased when a small content (0.045 phr) of ZMS was added. Compared with that in unfoamed LCBPP, the percentage of β-crystal in LCBPP foams was obviously enhanced, due to the coupling effect of crystal nucleation and cell nucleation. In the LCBPP foams, the cell size became smaller and the cell density became larger, owing to the addition of ZMS.

Section: Resultsmentioning

confidence: 99%

Φ = \frac{X_{normalβ}}{X_{α} + X_{β}} \times 100 %,

where X α and X β are the crystallinity of the α‐crystal and β‐crystal. The crystallinity was evaluated by the following equation:

X_{i} = \frac{Δ H_{i}}{Δ H_{i}^{0}} \times 100 %,

…”

Section: Methodsmentioning

confidence: 99%

“…The melting enthalpies of α‐crystal and β‐crystal were individually based on eqs.

A = {[1 - (\frac{h_{2}}{h_{1}})]}^{0.6}

Δ H_{β} = A \times Δ H_{β}^{*}

Δ H_{α} = ΔH - Δ H_{β} .

…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Jiang

et al. 2019

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A novel combination of sandwich and co‐continuous structure based on polypropylene and styrene‐butadiene‐styrene block copolymer formed with wide range of polypropylene content

Wang

Zhang

2018

The styrene-butadiene-styrene block copolymer (SBS)/polypropylene (PP) blends with a unique sandwich layered cocontinuous structure were prepared by melt compounding. Differing from single conventional co-continuous and sandwich structure, this structure was formed, where pure PP and co-continuous SBS/PP phase acting as the face sheets and core. Even though the volume content was 20 or 10 vol %, PP always amazingly formed a continuous phase in SBS/PP blends, whereas the morphology of SBS phase relatively changed from dispersed particles to continuous network as its content increased to 50 vol %. For immiscible SBS/PP blends, due to the huge difference of complex viscosity and surface tension between SBS and PP, a pure PP layer existed on the surface of blends which can be ascribed to the PP enrichment. Herein, the structure of blends with more than 50 vol % SBS was presented as sandwich layered co-continuous structure by combining the pure PP layer and co-continuous structure. V C 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46580.

Influence of crystallization on microcellular foaming behavior of polyamide 6 in a supercritical CO₂‐assisted route

Han

Jiang

et al. 2020

Supercritical CO2 as a blowing agent has attracted increasing interest in the preparation of microcellular polyamide 6 (PA6) foams. In this work, we developed the supercritical CO2‐assisted method to prepare a series of different microcellular PA6 foams by controlling its crystallization properties in two steps and carefully investigated the corresponding crystallization properties of modified PA6 and foams using various techniques. Initially, a multifunctional epoxy‐based chain extender (CE) was used to produce high‐melt strength‐modified PA6 with improved foaming ability; then, the resulting PA6 was foamed to prepare the microcellular foams of PA6 using supercritical CO2 as a blowing agent in a batch foaming route. The CE effectively enhanced the melt strength of PA6, and CE usage was optimized to obtain a threshold of high branching without crosslinking. The number of crystals was also adjusted by the saturation temperature. Furthermore, these crystals that formed during the saturation process served as high‐efficiency bubble nucleating agents and then limited the growth of bubbles at the same time. The microcellular foams of PA6 were successfully obtained with a cell size of 10.0 μm, and cell density of 2.0 × 109 cells/cm3 at the saturation temperature of 225°C.