Improvement of surface properties of natural rubber latex films with a novel plasticizer

Abstract

Softeners and plasticisers are used in latex compounding to reduce toughness and increase flexibility of articles such as gloves, balloons, etc. Petroleum based mineral oils and vegetable oils are the conventional plasticisers used in the industry. The main aim of this research was to improve surface properties of natural rubber latex films by replacement of paraffinic oil also known as white oil with an environmentally friendly plasticiser. Linseed oil obtained from the flax plant is a drying oil commonly used in oil paints to make paints more fluid, transparent and glossy. Commercially available linseed oil was selected as the novel plasticiser for this study. Linseed oil contains 52-55% of triply unsaturated α-linolenic acid and the ratio of unsaturated to saturated fatty acids in linseed oil is greater than that of vegetable oils and paraffinic oil. A series of natural rubber (NR) latex based compounds was prepared with 4, 6, 8 and 10 phr using a 50% emulsion of the linseed oil together with the other compounding ingredients. Two control NR latex compounds were also prepared; one with 6 phr using a 50% emulsion of white oil and the other without any plasticiser. Subsequently, cast films were prepared after curing at 100oC. Surface properties and physico-mechanical properties of these films were evaluated and compared with those of the two controls.Cast films prepared with linseed oil exhibited a smooth, glossy surface in comparison to those of the two controls indicating easy removal of articles from moulds and formers. Physico-mechanical property results showed that the tensile strength of the cast film prepared with 6 phr linseed oil is 39% and 77% higher than that of the films prepared with 6 phr white oil and without any plasticiser, respectively. Film prepared with 4 phr linseed oil showed the highest tensile strength.  Increasing the oil loading upto 10 phr at 2 phr intervals resulted in a decrease in tensile strength. The tear strength of the cast film prepared with linseed oil was three times that of the film prepared with white oil. Improvement of properties of the film prepared with linseed oil over those of the film prepared with white oil could be attributed to increased interaction between unsaturated NR chains and highly unsaturated linseed oil. Results in overall indicated that petroleum based white oil could be replaced by plant based, and hence environmentally friendly, linseed oil in latex products manufacture with improvements in surface and strength properties.