Design and Fabrication of Cost-Effective Plaster Molds for Natural Rubber Foam

Abstract

Due to the increasing demand for biodegradable cushioning materials, this study develops a low-cost plaster mold for forming natural latex foam and compares molds with edge thicknesses of 5 mm and 10 mm in terms of service life, physical properties, and thermal behavior. Results show that the 10-mm mold is markedly more durable, withstanding 14 cycles before failure, whereas the 5-mm mold endures only 6 cycles. Microstructural analysis indicates that foam produced from the thicker mold features smaller, more uniform cells with higher density, resulting in better compression resistance and recovery. Foam from the 10-mm mold shows an average density of 0.276 g/cm³ and a compression set of 6.43 %, compared with 0.243 g/cm³ and 7.60 % for the 5-mm mold. For thermal performance, the 10-mm mold exhibits higher thermal conductivity (0.6830 W/m·K) than the 5-mm mold (0.4674 W/m·K). The greater thickness slows water evaporation during setting, promoting tighter packing of calcium sulfate dihydrate crystals, improved solid-phase continuity, and reduced porosity, all of which enhance heat-transfer pathways. In contrast, the thinner mold tends to develop air voids from rapid moisture loss, reducing structural continuity and thermal conductivity. The increased thickness also produces a more uniform internal temperature distribution and lowers surface heat loss, allowing measured conductivity to better represent the material’s intrinsic properties.