Enhancement of the gas barrier property of polymers by DLC coating with organosilane interlayer

• Amino organosilane interlayer on polymers before DLC coating was proposed.
• Gas barrier of DLC-coated polymers with interlayer was enhanced by 300 times.
• Barrier effect was investigated by surface observation and structural analysis.
• The number of cracks on DLC decreased after the silane pretreatment.
• The sp3-rich DLC was synthesized on the organosilane interlayer.

A new surface modification method by DLC coating with organosilane interlayer was introduced. Some DLC-coated polypropylene (PP) films pretreated with certain types of organosilane interlayers showed marked improvement in the gas barrier property. Among the DLC-coated PP, the PP films modified by organosilane interlayers with an amino group presented an extremely low oxygen transmission rate, which was even comparable to the existing low oxygen transmission rate of commercial DLC-coated PET with very high gas-barrier property. The barrier improvement factor (BIF) of DLC-coated PP by the amino-organosilane interlayer became approximately 300 times higher than that of the untreated neat PP. By observing the DLC surface, it was considered that such gas barrier improvement occurred due to the establishment of flawless DLC on PP with few cracks. In addition, DLC which was deposited onto the organosilane interlayer showed higher sp3/sp2 ratio than an ordinary DLC, indicating a fairly dense DLC structure synthesized on PP with the organosilane interlayer, which was revealed by XPS. Furthermore, the new surface-treatment method for DLC was extensively found to be applicable to several other types of polymers including polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS), and polylactide (PLA) which are all important polymeric materials for industry.

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