Experimental studies on the accuracy of wax patterns used in investment casting

Investment casting is often used to produce fully functional prototype components from sacrificial patterns. These patterns (prototypes) may be made using specialized rapid prototyping techniques such as stereolithography or three-dimensional printing. When multiple functional prototypes are required, interim tools for making wax patterns are employed. The objective of this research work was to determine the precision and accuracy of wax patterns produced using several prototype tools. Linear contraction was used to determine the accuracy as a function of the wax injection parameters used in low-pressure injection moulding. Wax patterns were produced using polyurethane and silicone rubber tools. It has been shown that the accuracy of patterns from both tools is similar. However, silicone tools produce patterns with much higher contraction than those produced by polyurethane tools. Unconstrained patterns dimensions contracted as much as 3.44 +/- 0.40 per cent and 1.70 +/- 0.60 per cent for silicone and polyurethane tools respectively. The constrained dimensions contracted by 2.20 +/- 0.20 per cent in the case of silicone tools and 1.40 +/- 0.20 per cent in the case of polyurethane tools.

Estimating the specific heat capacity of starch-water-glycerol systems as a function of temperature and compositions

Increasing interests in the use of starch as biodegradable plastic materials demand, amongst others, accurate information on thermal properties of starch systems particularly in the processing of thermoplastic starch (TPS), where plasticisers (water and glycerol) are added. The specific heat capacity of starch-water-glycerol mixtures was determined within a temperature range of 40-120degreesC. A modulated temperature differential scanning calorimeter (MTDSC) was employed and regression equations were obtained to predict the specific heat capacity as a function of temperature, water and glycerol content for four maize starches of differing amylose content (0 - 85%). Generally, temperature and water content are directly proportional to the specific heat capacity of the systems, but the influence of glycerol content on the thermal property varied according to the starch type.

Reduction of the in vitro pro-inflammatory response by macrophages to poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

This study evaluates the pro-inflammatory response to the thermoplastic biopolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) through the analysis of cellular responses in vitro. The murine macrophage RAW264.7 cell line was cultured on solvent cast PHBV films, which was found to induce pro-inflammatory activity that required direct contact between the material and the macrophages. The identity of the pro-inflammatory stimulus was determined by culturing bone marrow-derived macrophages from bacterial lipopolysaccharide (LPS) hyporesponsive C3H/HeJ mice and CpG non-responsive TLR9-/- mice on PHBV. The lack of a pro-inflammatory response by the C3H/HeJ cells indicates that the pro-inflammatory agent present within PHBV is predominately LPS while the TLR9-/- macrophages confirmed that CpG-containing bacterial DNA is unlikely to contribute to the activity. A series of purification procedures was evaluated and one procedure was developed that utilized hydrogen peroxide treatment in solution. The optimized purification was found to substantially reduce the pro-inflammatory response to PHBV without adversely affecting either the molecular structure or molecular weight of the material thereby rendering it more amenable for use as a biomaterial in vivo. Crown Copyright (c) 2006 Published by Elsevier Ltd. All rights reserved.