Effect of long-term ageing on the tensile properties of a polyamide 12 laser sintering material

The long-term ageing of one of the most widely used commercially available laser sintering materials, Duraform (R) PA, was investigated and compared to an injection moulded polyamide 12 material. Both materials were stored for time periods of up to 52 weeks in three different conditions: "dry", "controlled" (50% relative humidity) and "wet" (totally immersed in water). The effect these storage conditions and the length of time that parts were stored in these conditions had on the tensile properties of produced parts were examined. The absorption of moisture has previously been associated with a reduction in the glass transition temperature, which reduces the operating temperature of the material [1]. For this reason, coupled with the need to establish its suitability and ability to perform in inhospitable climates, testing was also carried out through a temperature range of 40 to 140 degrees C over the three humidity conditions. The laser sintered polyamide material was found to have equivalent, if not better, moisture and water resistance compared to the injection moulded material. Unexpectedly, the strength of the laser sintering parts stored in all conditions increased in the first few weeks of storage. It is proposed that this was due to a physical ageing effect counteracting the normal effect of moisture absorption. The laser sintered samples also appeared to hold their strength at higher temperatures better than injection moulded samples. (C) 2010 Elsevier Ltd. All rights reserved.