Role of percent grafting and chain length of fully fluorinated pendant units in the grafted acrylic compound on crucial characteristic properties of high density polyethylene

Abstract

This comprehensive study paves way to investigate the effects of not only the extent of grafting but also the chain length of the perfluorinated pendant tail presenting in the three different fluoroalkyl acrylate monomers on the significant characteristic properties; namely the thermal behavior, crystal structure quality, mechanical performance and morphological structure of high density polyethylene (HDPE). The individual graft copolymerizations of the monomer onto HDPE were conducted at the content level from 5 % to 30 % via bulk-melt polymerization. The characterizations of copolymers were performed with differential scanning calorimeter (DSC), powder X-ray diffractometer, universal testing machine and scanning electron microscope (SEM) techniques. As for the results deduced from DSC analysis, both the melting temperatures of HDPE and degree of crystallinity were found to increase systematically with the enhancement in the percent grafting level up to 10 % beyond which the parameters were noted to decrease drastically and reach towards globally minimum values. According to the XRD results, as the percentage of grafting enhanced, the remarkable expansions were observed in unit cell parameters of HDPE crystallized in the orthorhombic symmetry. Moreover, the presence of relatively higher amount of -CF2 groups in the perfluorinated pendant tail caused the formation of three-dimensional lateral repulsions due to its helix structure. Furthermore, there seemed to remarkably improve in the mechanical performance features in case of percent grafting level of 70.6 % where the tensile strength, Modulus and impact strength parameters were measured to be about 42.51 MPa, 539.90 MPa and 41.11 kj/m2, respectively. These reinforcements were found to be explained by the improvement in the regulation, orientations, alignments of HDPE chains. Furthermore, the formation of thick, bulky and long-fibrils were observed at high percent grafting.