Enhancement of the gas barrier property of polypropylene by introducing plasma-treated silane coating with SiOx-modified top-surface

K. Tsuji, M. Nakaya, A. Uedono, A. Hotta

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


Polypropylene (PP) is a widely used packaging polymer due to its high transparency and high thermal durability. It is, however, also known to possess a relatively low gas barrier property. To solve the gas barrier problem of PP, a surface modification method by a silane coating was introduced: 3-aminopropyltrimethoxysilane (APTMS) was coated onto PP substrate (APTMS/PP) and treated by oxygen plasma. It was found that, after 60s of the oxygen plasma treatment, the oxygen transmission rate (OTR) of the APTMS/PP was reduced by a factor of 15 as compared with that of pure PP. The free volume size analyzed by the monoenergetic positron beam significantly decreased at the surface of APTMS observed through the plasma-treatment time. The results indicated that the amount of the free volume of APTMS, through which the gas molecules permeated, was significantly decreased, eventually causing a considerable reduction in the OTR of the APTMS/PP. From the X-ray photoelectron spectroscopy (XPS), it was found that the plasma treatment of APTMS notably reduced both the carbon and the nitrogen atom fractions, simultaneously generating additional Si-O bonding to generate SiOx-like structures at the surface. The formation of the SiOx-like structure at the top surface of the APTMS/PP was considered as the major reason for the enhancement of the oxygen barrier property. In fact, the drastic decrease in the OTR was actually observed at a certain ratio of C/Si. The time of flight secondary ion mass spectroscopy (ToF-SIMS) also revealed that the side-chain scission from the APTMS molecules could generate amine and amide fragments, which could hinder the polymerization of the SiOx. Thus the removal of the fragments would promote the efficient formation of SiOx networks at the top surface of APTMS. Additional plasma treatment could introduce more polymerized SiOx networks in APTMS, resulting in the smaller size of the free volume and hence the higher gas barrier property of APTMS/PP.

Original languageEnglish
Pages (from-to)377-383
Number of pages7
JournalSurface and Coatings Technology
Publication statusPublished - 2015 Dec 25


  • Coating
  • Gas barrier
  • Plasma treatment
  • Polypropylene
  • SiO
  • Silane coupling

ASJC Scopus subject areas

  • General Chemistry
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry


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