Development of acyl-bonded aminopropyl silica gel fillers with low interfacial adhesion energy in a polystyrene matrix

Abstract

To develop fillers that adhere closely to a matrix polymer and reduce the glass transition temperature (T g ) of filler/polymer composites, N-acyl-3-aminopropyl silica gel fillers (1) were prepared by the reaction of 3-aminopropyl silica gel (SiO 2 -NH 2 ) and succinimidyl alkanoate (2) by controlling the amount and length of alkyl chains. The surface tension (c) of 1 was measured by the wicking method. The interfacial adhesion energy (W) of composites (1/PS) between 1 and polystyrene (PS) was calculated using the dispersive component (c D ) and the polar component (c P ) of c, according to the Equation) where subscripts m and f indicate matrix and filler, respectively. The W values of 1/PS composites were considerably smaller than those of the SiO 2 -NH 2 /PS composite. A good correlation between W and T g showed that the introduction of acyl groups on SiO 2 was effective for the enhancement of adhesion between 1 and the matrix polymer. Moreover, it was confirmed that the addition of less than 30 wt% of 1 to PS did not affect the tensile strength of composites. Keywords: adhesion energy; aminopropyl silica gel; glass transition temperature; interface energy; surface tension; tensile strength INTRODUCTION Modification of polymers with fillers is widely used to enhance the performance of polymers. 1,2 Inorganic materials such as talc, 3 calcium carbonate, 4,5 glass, 6,7 silica, 8,9 alumina, 10 zeolite 11-13 and wollastonite 14 have been widely used as fillers to improve mechanical performance such as the tensile strength and elongation strength of polymers. To enhance adhesion between inorganic fillers and the polymer matrix, organic additives such as maleic anhydride, carboxylic acids and silane-coupling reagents are mixed with the polymer. 4 However, problems such as the dispersibility of organic additives in the polymer, the increase in glass transition temperatures (T g ) and the elution of organic additives remain in the manufacturing process.Recently, alkyl group-bonded zeolite 12 and wollastonite 14 fillers have been prepared to prevent the elution of organic additives from the polymer and to improve the handling of organic additives in the manufacturing process. 15 Silica gel filler is a stable and safe material that has a wide surface area and the ability to adsorb various materials. 3-Aminopropyl silica gel (SiO 2 -NH 2 ) 16,17 can immobilize functional groups through a covalent bond. To develop a high-performance filler that achieves higher adhesion and a lower T g of filler/polymer composites, the surface tension of the acyl-bonded SiO 2 -NH 2 filler (1) can be modified by controlling the amount and length of alkyl chains (Scheme 1).