Polyurethane/poly(ethyl methacrylate) interpenetrating polymer network organoclay nanocomposites
A number of polyurethane (PU) I poly(ethyl methacrylate) (PEMA) interpenetrating polymer network nanocomposites were investigated with regard to morphology and energy absorbing ability. The nanoclays used were umnodified sodium montmorillonite clay and three different types of organically-modified clays: C15A, C20A and C30B. The nanoclays were incorporated into the IPNs by using an in-situ polymerisation method. The clay dispersions were characterised by wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). The morphologies of the IPNs were determined with dynamic mechanical thermal analysis (DMTA), TEM and modulated-temperature differential scanning calorimetry (M-TDSC), while the mechanical properties were investigated using tensile testing and hardness measurements. Firstly, the original synthesis procedure and formulation was adjusted by varying the nanoclay C20A content, IPN composition ratio, nanoclay mixing time and PU catalyst, including a study of the PU and PEMA homopolymer composites. All IPN composites showed only partially intercalated nanocomposites as revealed by WAXD and TEM results. 70PU/30PEMA (70:30 composition ratio) IPN nanocomposites exhibited potential as materials for damping applications as it had a broad loss factor ≥ 0.3 spanning a wide temperature range. Secondly, the synthesis procedure was modified by changing the order of nanoclay mixing with homopolymer components. All lPN composites were based on a composition ratio of 70PU/30PEMA, 5 wt% C20A content, 1.2 wt% of PU catalyst and 30 min mixing time. High intensity ultrasonic waves were also introduced in the nanoclay mixing step for one hour. However, the ultrasonication showed only a marginal change in damping properties. Finally, a number of other nanoclays were incorporated into the 70PU/30PEMA IPN. All IPN composites achieved only a partial intercalation, except for the C30B-filled lPN where no changes were revealed by W AXD. All nanoclays caused a decrease in the glass transition of both homopolymers. IPN nanocomposites tended to reveal a higher extent of phase separation with increased clay content, but only the Na clay-filled lPN still showed a broad loss factor value, even at higher clay content. Improved modulus of elasticity was shown by all nanoclays, with increased clay loading. Whereas a moderate increase in the tensile strength was only shown at 1 wt% clay content.