Crosslinking of Low-Density Polyethylene by Diisocyanates for Superior Barrier Properties

The chemical modification of low-density polyethylene (LDPE) resins with hexamethylene diisocyanate and toluene diisocyanate was achieved. The reaction of LDPE with diisocyanate was monitored by Fourier transform
infrared spectroscopy, wherein the appearance of new
peaks at 3326, 1620, and 1572 cm1 corresponding to
ONOH stretching,O(CAO)ONH2 stretching, and ONOH bending in an amide moiety, respectively, was observed. Modified films of excellent clarity and uniform thickness were obtained by the solution casting of crosslinked polyethylene.
The oxygen transmission rate (OTR), water vapor
transmission rate (WVTR), grease resistance, and thermal
properties of the modified films were studied. The results
clearly indicate that the OTR was improved by 35% and that
grease resistance was improved by 90–125% in the
crosslinked LDPE films with little change in their strengths. The heat seal characteristics, however, showed that relatively higher temperatures were needed to achieve efficient sealing in these films. Differential scanning calorimetry showed a decrease in the melting temperature from 104°C for LDPE to 101°C for both of the crosslinked LDPE films.