Molecular-scale design of a high performance organic–inorganic hybrid with the help of gamma radiation

Abstract

In the age of green chemistry, gamma-radiation-assisted grafting of polar groups onto polymers in aqueous solution is becoming attractive as it is a rapid, scalable, clean physical process with much less chance of contamination. In this case, a methacrylic acid (MAA) polar group was grafted onto LDPE (low density polyethylene) by gamma radiation to increase the compatibility of LDPE with organically modified clay by reducing the hydrophobicity of LDPE. The clay, cloisite 20A was melt-mixed with g-LDPE (grafted LDPE) to synthesize a nanohybrid and the mixes were subsequently compression-molded to make a sheet, which was used for characterization. Many of the drawbacks of polyolefin based nanohybrid synthesis were overcome by this technique. Wide angle X-ray diffraction (WAXS), transmission electron microscopy (TEM), thermogravemetric analysis (TGA), differential scanning calorimetry (DSC) and tensile testing were conducted to characterize the nanohybrids. The interlayer distance (d values) change in WAXS confirmed nanohybrid formation, which was later directly seen by TEM. TGA revealed that nanohybrids were more thermally stable than pure polymer and this went on increasing with clay loading. From DSC it was noticed that melting temperatures (T_ms) remained unchanged, but the crystallinity of the polymer was increased by more than 5% at higher clay loading (8 wt%), which was useful for barrier properties as well as mechanical property improvement. Young's modulus of nanohybrid was increased considerably by a small mount of clay incorporation (by 50% and 85% for 2 and 8 wt% clay). Uniquely, with increase in modulus toughness was also found to increase by more than 20%, keeping the elongation-at-break unchanged. Thus by this rapid, clean, user friendly and well controlled technique, pure and high-performance nanohybrids were developed successfully.