Effect of Alkali Treatment on the Flexural Properties of Hildegardia Fabric Composites B. R. Guduri, 1 A. V. Rajulu, 2 A. S. Luyt 1 1 Department of Chemistry, University of the Free State (Qwaqwa Campus), Private Bag X13, Phuthaditjhaba, 9866, South Africa 2 Department of Polymer Science & Technology, Sri Krishnadevaraya University, Anantapur-515 003. (A.P), India Received 24 March 2005; accepted 15 August 2005 DOI 10.1002/app.23522 Publication online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: A uniaxial natural fabric of Hildegardia popu- lifolia was treated with 5% sodium hydroxide solution for 1 h, and the resulting changes were analyzed by polarized and scanning electron microscopic techniques. The un- treated and treated H. populifolia fabric was reinforced in epoxy and toughened with 10% polycarbonate. The varia- tion of the flexural strength and flexural modulus with different fabric contents and fiber orienrations was studied. The effect of sodium hydroxide and a silane coupling agent on the flexural properties of the composite was also studied. It was observed that the flexural properties increased on alkali treatment and when the coupling agent was used. The morphology of the cryogenically fractured surfaces indi- cated good bonding between the matrix and the reinforce- ment when a coupling agent was used. © 2006 Wiley Period- icals, Inc. J Appl Polym Sci 102: 1297–1302, 2006 Key words: natural fabric; epoxy resin; polycarbonate; blend matrix; flexural properties; morphology; alkali treatment INTRODUCTION Natural fibers as reinforcement have advantages such as low cost, high strength, environmentally friendly nature, and easy dispersion in polymer composites. They are also biodegradable. In the last decade there has been a renewed interest in natural fibers as a substitute for glass, carbon, and synthetic fibers, be- cause natural fibers are less dense and cheaper than conventional fibers, and may be easily recycled. At present, the trend is slowly changing towards using natural fibers as reinforcements. Composites made with natural fiber reinforcements, known as “green composites,” were developed by several workers 1–10 using sisal, banana, bamboo, coir, pineapple leaf fiber, and so forth. However, being hydrophilic, natural fi- bers need to be treated first to make them more com- patible with hydrophobic thermosets and thermoplas- tics. Several researchers reported improvement in me- chanical properties of cellulose fibers when alkalized at different NaOH concentrations. Bisanda and Ansell 11 applied an aqueous 0.5N NaOH solution on sisal fiber, while Sreekala and coworkers 12 and Geethamma and coworkers 13 used 5% NaOH to re- move surface impurities on oil palm fibers and short coir fibers, respectively. Mwaikambo and Ansell 14 treated hemp, jute, sisal, and kapok fibers with various concentrations of NaOH. Varada Rajulu et al. 15,16 studied the properties and effect of alkali treatment of the lignocellulosic natural fabric Hildegardia populifolia. Recently, Babu Rao 17 developed H. populifolia fabric/ polycarbonate-toughened epoxy composites and stud- ied their performance. He reported that the mechani- cal properties of the matrix improved substantially on reinforcing it with this natural fabric. Roy and Sarkar 18 studied the physical and mechanical properties of jute fibers after alkali treatment. They reported improve- ment in these properties after alkali treatment. Hill and Abdul Khalil 19 studied the effect of acetylation on the mechanical properties of coir and oil palm fiber- reinforced polyester composites. They reported an in- crease in interfacial shear strength between the fiber and the matrix after acetylation of coir. Mannan and Munir 20 characterized jute fibers treated with soap– glycerol micelles. They reported improvement of the mechanical properties after treatment. In the present work, we studied the effect of alkali treatment, cou- pling agent, fiber content, and orientation of the fabric on the flexural properties of the natural fabric H. popu- lifolia-reinforced polycarbonate-toughened epoxy composites. EXPERIMENTAL Materials The epoxy resin Araldite LY-556 and hardener HY-951 (M/s Hindustan Ciba-Geigy) and polycarbonate (Cal- Correspondence to: B. R. Guduri (bguduri@csir.co.za). Journal of Applied Polymer Science, Vol. 102, 1297–1302 (2006) © 2006 Wiley Periodicals, Inc.