Fig. 1 shows infrared spectra of the HDPE-g-MA in comparison with the HDPE, which was used as a raw material. The new absorption bands that appeared at 1864 cm−1 (the asymmetric –C O stretching) and 1786 cm−1 (the symmetric –C O stretching) in the spectrum indicate successful grafting of MAH groups onto the HDPE chains. An absorption band at 1710 cm−1 was also observed, which was assigned to the carbonyl groups from the ring-opening reaction of MAH groups on the HDPE chains caused by moisture. According to the quantitative analysis, it was found that the amount of the grafted MAH on the HDPE chains was approximately 0.98 mol%.