The team said that surface-coating is considered to be one of the most efficient ways to improve gas barrier property.
Some DLC-coated polypropylene (PP) films pretreated with certain types of organosilane interlayers showed marked improvement in the gas barrier property and low oxygen transmission rates.
300 times greater
The barrier improvement factor (BIF) of DLC-coated PP by the amino-organosilane interlayer became 300 times higher than that of the untreated neat PP.
By observing the DLC surface, it was found that gas barrier improvement occurred due to the establishment of flawless DLC on PP with few cracks.
Most polymeric materials, including PP, have low gas barrier properties which allow oxygen molecules to easily penetrate the polymeric package potentially leading to damage on the quality of food products.
To address this issue they introduced an organosilane interlayer between DLC and PP, producing flawless DLC and to fabricate the organosilane interlayer, a silane-coupling agent was used as a precursor.
“DLC-coated polymers with the organosilane interlayer possessing 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,” said Tashiro et al.
OTR rate differences
The untreated PP shows a very high oxygen transmission rate (OTR) of 800 cc/m2/day/atm.
The researchers said that the OTR differs to a large extent if treated by different types of silane-coupling agents (ranging from 2.5 cc/m2/day/atm to 591.1 cc/m2/day/atm)
The samples with the organosilane interlayer fabricated by the silane-coupling agents with amino groups showed very low OTR.
The researchers identified KBM-903 and KBM-803 amino groups as presenting the most significant improvement in gas barrier property.
The surface-treatment method for DLC was found to be applicable to other types of polymers including polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS) and polylactide (PLA).
“The new surface modification method by organosilane interlayer on polymers before DLC coating is expected to be one of the greatest methods to produce a high-barrier DLC on polymers, which would certainly contribute to expand the industrial applications of the DLC-coated polymeric materials,” the researchers concluded.
Source: Diamond and Related Materials, volume 35, May 2013, pages 7-13
Online ahead of print, DOI: 10.1016/j.diamond.2013.03.001
“Enhancement of the gas barrier property of polymers by DLC coating with organosilane interlayer”
Authors: Hiroki Tashiro, Masaki Nakaya, Atsushi Hotta