Mechanical Property of Polypropylene Gels Associated with That of Molten Polypropylenes.

Tetsu Ouchi,Atsushi Hotta,Misuzu Yamazaki,Tomoki Maeda

doi:10.3390/gels7030099

Abstract

This study aims to understand the fundamental mechanical relationship between polypropylene (PP)-gels and solid PPs without solvent through mechanical and thermal analyses, by which the mechanical similarities between molten PPs and PP gels were found, leading to the reliable estimate of the mechanical properties of semi-crystalline gels. The gelation of syndiotactic and isotactic polypropylenes (sPP and iPP) was found when PPs were dissolved in 1,2,3,4-tetrahydronaphthalene (tetralin). Interestingly, it was found that the storage modulus of sPP-gel became higher than that of iPP-gel at low PP concentration (<~40 wt%). The result was distinctly different from the result of neat solid PPs (without solvent), where the modulus of solid sPP is generally significantly lower than that of solid iPP. Such inversion behavior in the mechanical property of semi-crystalline gels had not been reported and discussed before. By further investigation of the storage moduli of neat sPP and iPP, it was found that the storage modulus of sPP became higher than that of iPP above the melting points of PP, which was similar to the behavior of the storage moduli observed in the diluted PP-gels. Such similarity between PP-gels and PP melts was also observed within iPP samples with different molecular weights.

Highlights

Polymeric gels are widely used materials for practical applications such as sensors, dampers, and contact lenses [1,2,3,4,5]
The results indicate that the amorphous region of the PP-gels brought about a decisive effect on the mechanical properties of PP-gels at low PP concentration (
Dynamic mechanical analyses (DMA) of isotactic polypropylene (iPP) and syndiotactic polypropylene (sPP) were performed to study the difference in the mechanical properties between iPP and sPP

Summary

Introduction

Polymeric gels are widely used materials for practical applications such as sensors, dampers, and contact lenses [1,2,3,4,5]. Physical gels have recently gained attention since they have the potential to be effectively used as e.g., eco-materials by remoulding and reusing the gels. Such thermal reversibility of the physical gels can be largely attributed to their relatively low intermolecular forces including van der Waals force and hydrogen bonding. Semi-crystalline polymers can form efficient molecular crosslinks that can lead to the construction of physical gels [6,7,8,9,10,11,12,13]. It was concluded that syndiotactic polystyrene (sPS) in naphthalene formed a gel that transformed into sol by heating, which was thermoreversible (i.e., the sol transformed into gel by cooling) [6]

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