Swelling parameters of industrial polymers used in the whiteware industry

Abstract

Solubility parameters are useful in determining the ability of a material to withstand particular environments, particularly in respect to their industrial and domestic applications [1, 2]. Part I of this series [3] dealt with the solubility parameters of nylon 6,6 which is a common material used in applications such as rollers in dishwashers. The work reported here concentrates on another engineering polymer, acetal. Acetal homopolymer (polyoxymethylene, POM, or polyformaldehyde) is a highly crystalline thermoplastic. Its good lubricity properties allow the material to be used for bearing and gear applications. It has been used in water contact applications, including dishwashers, because of its hydrolytic resistance [4]. Previous studies on polypropylene [5, 6] have shown that solubility maps can be constructed, and have been used to look at how the material behaves in commercial solvents, such as dishwasher detergents, which have unknown solubility parameters, by investigating the solubility of the material in a number of known solvents. By knowing the solubility parameter and hydrogen bonding parameter of the known solvents, and that of acetal, solubility maps can be constructed for the material. The reported solubility parameter value for acetal is 24.7 MPa 1/2 [7]. Hoeschst Celcon M90 (melt temperature 165 °C, melt index 9.0) was used in this investigation. As discussed in Part I, rectangular pieces (10 m m x 1 mm, and approximately 2 g) were injection moulded, but for acetal at a melt temperature of 190-200°C and injection pressure of 1100psi (7584 kPa). Ten samples were submerged in each solvent and ten were kept as controls. All of the numbered samples were placed in a dark area at room temperature, in a controlled atmosphere, and periodically dried and weighed, using a Mettler balance accurate to 4 decimal places. Twenty-four solvents were used in this study. Detailed information regarding their Hildebrand solubility parameters 6, (~d and 6p, where 6d a n d 6p are the dipolar and dispersion components of the solubility parameter, respectively, is given in Part I [3]. The hydrogen bonding parameter, go, and the hydrogen bonding component of the solubility parameter are also shown in [3]. In this study, the volume dependent component of the Hildebrand parameter, 6v, was calculated from the following relationship: