Coupled thermal stress and moisture absorption in modified a montmorillonite/copolymer nanocomposite: Experimental study

Abstract

N-Dimethylhexadecyclamine (DMHDA+) montmorillonite (Mt) random copolymer polypropylene (CPP-R) nanocomposites (AmK10CPP-R) are increasingly used in industrial applications such as coating subsea pipelines because they have excellent thermomechanical and barrier properties in front of two coupled properties of moisture adsorption and thermal loading. The coupled properties are experimentally investigated at temperature levels of 298 K and 370 K and water content of 0.0% wt. and 100% wt at 1.0 atm. for three different weight fractions (wt. %) of 0.3%, 3%, and 4% of the nanoparticles. X-Ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), static tensile tests, and dynamic material tensile analysis (DMTA) are conducted on the test samples. XRD pattern of nanofiller shows that using loading content less than 1% wt cannot provide a good basal spacing of nano fillers. The nanocomposite sample with major quantity of clay (4%AmK10CPP-R) presented less clusters of clay dispersed by FE-SEM. DSC indicates that glass transition temperature of 3% AmK10CPP-R is the highest value among all samples and melting temperature of all samples does not change. Moreover, it is observed that the diffusion coefficient of the saturated 4% wt. modified clay random copolymer (4AmAMoisK10CPP-R) is decreased almost 79.4% in comparison with 0.3AmMoisK10CPP-R sample at ambient temperature and atmospheric pressure. Furthermore, thermal analysis shows that temperature and loss of the mass at first stage are the lowest values for 4%AmMoisK10CPP-R. However, thermal stability of the saturated sample is increased in the second stage of TGA/DTG. It is seen that the clay nanoparticle can significantly hinder the degradation of mechanical properties of the nanocomposite even when both temperature and water content increase. Stress-strain curve gives that 3% and 4% wt. modified clay in the polymer matrix can significantly increase the mechanical properties of the polymer. Finally, DMTA determines that the 3%AmAMoisK10CPP-R gives the highest elastic modules. This study finds that mechanical, thermal and rheological properties of the polymer nanocomposite improve and the best compatibilising effect is at a content 3 wt% of the modified clay.