Mechanical properties and phase diagrams of alloys of high density polyethylene with some low molecular weight organic compounds

Abstract

This paper reports on measurements of mechanical properties (stress-strain data) of four alloys based on high density polyethylene (PE) in combination with low molecular weight (LMW) organic compounds, together with the corresponding phase diagrams and microstructures. Two of the alloys, 1,2,4,5-tetrachlorobenzene (TCB)/PE and camphor/PE form eutectic structures. The system dimethylterephalate (DMTP)/PE also forms a eutectic but in this case the LMW component has only limited solubility in molten PE. In the thymol/PE system the LMW component acts as a low melting diluent. Apart from some primary grown crystals (camphor, TCB and DMTP), these systems were found to exhibit finely dispersed structures. The LMW additives (TCB and DMTP) with a modulus higher than pure PE impart a higher stiffness to the alloys while the strength and ductility remain approximately unaffected. The softer compounds (camphor and thymol) appear to act as softeners bringing about a decrease in tensile strength and an increase in ductility. The results obtained show that alloying of polymers with suitable LMW substances may represent a novel route to polymer-based composites. The occurrence of maxima in the elastic moduli of such alloys in the vicinity of the eutectic point illustrates the potential of such alloying as a means of modifying the properties of the matrix material.