Avoiding Moisture Damage

T he demands of the automotive industry on components are increasing continuously and thus time and again raise new challenges for the materials used. That means that plugs, plug connectors and housings for electronic components (Title picture) as well as overmolded sensors for under the hood applications which are often made from polybutylene terephthalate (PBT) have to pass even harder tests. Moisture – particularly at higher temperatures – damages PBTs and therefore alters their material properties. Processors of PBT know only too well that moisture and temperature can be critical since without adequate predrying of the pellet, components fresh out of the injection molding tool can be brittle and unusable. However, at temperatures under 100°C the damaging effect of moisture only makes itself noticeable later on. Under typical terrestrial climatic conditions even PBTs without any special modification can retain practically constant properties over many years. However, in automobiles at least sometimes temperature and moisture conditions that are much more demanding than natural weathering can be found. For this reason many specifications require testing at 85°C and 85 % relative humidity. For applications with high demands on moisture resistance BASF SE, Ludwigshafen, Germany, has developed special grades of PBT which allow components with many times the service life of those made from conventional grades to be produced. These materials are available with 30 % glass fiber reinforcement under the brand name of Ultradur B4330 G6 HR and with 15 % glass fiber reinforcement as Ultradur B4330 G3 HR. The suffix HR stands for hydrolysis resistant. Hydrolysis is the chemical term for the reaction between water and polyester that damages the material.