Influence of processing variables on the properties of free films prepared from aqueous polymeric dispersions by a spray technique

Abstract

A novel method for the preparation of free films from aqueous polymeric dispersions by a spray technique is reported. The apparatus included a spray gun, rotary drum and a temperature controlling system. The influence of spray rate and processing temperature on the mechanical properties of free films prepared from aqueous dispersions of Eudragit© L 30D-55, and L 100-55 (methacrylic acid-ethyl acrylate copolymer), Shin-Etsu AQOAT® (hydroxypropyl methylcellulose acetate succinate), Aquateric® (cellulose acetate phthalate) and Aquacoat® (ethyl cellulose), plasticized with triethyl citrate, was investigated. The processing temperature was monitored using a telemetric system. Reproducible free films were obtained from the five polymers using this apparatus. The tensile strength and elongation of films of the two Eudragit® latex dispersions, having a minimum film formation temperature (MFT) less than 20°C, were not influenced by spray rate or processing temperature between 30 and 40°C. The mechanical values of free films from Shin-Etsu AQOAT® were significantly decreased at a slower spray rate, but processing temperature did not affect film properties. This polymeric dispersion contained larger particles than the acrylic dispersions and the free films had a low MFT. The Aquateric® dispersion, having a high MFT, contained larger particles than the acrylic latexes and produced films at high spray rates and slow drying conditions. The drying temperature significantly influenced the elongation properties of the films. The mean tensile strength of free films from Aquacoat®, a high-MFT latex, was slightly higher at higher processing temperature, but this was not significant. The spray rate did not alter the mechanical properties of films prepared from this pseudolatex.