Katherine Dean

Curing behaviour of IPNs formed from model VERs and epoxy systems I amine cured epoxy

Abstract The curing behaviour for an Interpenetrating Polymer Network (IPN) formed from a model Vinyl ester resin (VER) and an amine cured epoxy resin has been studied by scanning DSC and isothermal mid-FTIR. The interactions between the VER initiating system (azobisisobutyronitrile or cumene hydroperoxide, benzoyl peroxide or methyl ethyl ketone peroxide/cobalt octoate) and the epoxy curative (aniline, diaminodiphenyl methane, butylamine or diamino-octane) have been examined. For most of the IPNs, there was evidence for a reduction in reaction rate due to the dilution of each reacting system by the other resin components. When cumene hydroperoxide, benzoyl peroxide or methyl ethyl ketone peroxide (with or without cobalt octoate) were used as the radical initiating systems, there was strong redox interaction between the peroxide and the amine, which caused acceleration of the peroxide decomposition in the early stages of reaction and also resulted in premature depletion of the initiator system. Evidence for a grafting reaction between the amines and the methacrylate groups by Michael addition was also found. In some systems cured isothermally at 70°C, the slow cure of the epoxy component allowed the unreacted DGEBA to plasticise the system and enhance the extent of cure of the VER components prior to vitrification of the IPN. As a consequence of the additional crosslinks introduced by the VER component, premature vitrification occurred during the slower cure of the DGEBA component, thus reducing the extent of cure of the epoxy groups in the IPN. Near full cure could be obtained for most of the IPN systems when post-cured at elevated temperature, indicating that the presence of each network imposed minimal topological restrictions on cure.

Control of gel time and exotherm behaviour during cure of unsaturated polyester resins

The curing behaviour of an unsaturated polyester resin has been studied by gel time and pseudo-adiabatic exotherm measurements. The gel time corresponded closely with the initial rise in exotherm temperature. Incorporation of tert-butyl catechol inhibitor increased the gel time in a linear fashion and the exotherm was similarly delayed. An increase in the concentrations of initiator (either methyl ethyl ketone peroxide or acetyl acetone peroxide) or cobalt octoate accelerator decreased the gel time in a reciprocal fashion and increased the rate of polymerization. These results are fitted to a theoretical model for inhibition and initiation. n n n n© 2001 Society of Chemical Industry

Natural Fibre Bio-Composites Incorporating Poly(Lactic Acid)

In recent years increasing awareness in relation to the worlds petrochemical resources no longer being finite, the rising cost of oil and concerns surrounding climate change and the necessity for reducing our carbon footprint, are resulting in a renewed demand and expe‐ diation of development of polymeric materials that are produced from sustainable and eco‐ logically sound raw material feedstocks that are not petrochemically derived and are generally more abundant. Poly(lactic acid) (PLA), being a compostable synthetic polymer produced using monomer feedstock derived from corn starch, satisfies many of the environ‐ mental impact criteria required for an acceptable replacement for oil-derived plastics [1]. PLA exhibits mechanical properties that make it useful for a wide range of applications, but mainly in applications that do not require high performance including plastic bags, packag‐ ing for food, disposable cutlery and cups, slow release membranes for drug delivery and liq‐ uid barrier layers in disposable nappies [2]. However, the wider uptake of PLA is restricted by performance deficiencies, such as its relatively poor impact properties which arise from its inherent brittleness, but also the limited supply and higher cost of PLA compared with commodity polymers such as polyethylene and polypropylene [3].