Synthesis, mechanical, thermal and chemical properties of polyurethanes based on

Bull. Mater. Sci., Vol. 27, No. 3, June 2004, pp. 235–241. ? Indian Academy of Sciences.

Synthesis, mechanical, thermal and chemical properties of polyurethanes based on cardanol

C V MYTHILI, A MALAR RETNA and S GOPALAKRISHNAN*

Department of Chemistry, Manonmaniam Sundaranar University, Abishekapatti, Tirunelveli 627 012, India

MS received 28 August 2003; revised 19 February 2004

Abstract. Cardanol, an excellent monomer for polymer production, has been isolated from CNSL and allowed to react with formaldehyde in a particular mole ratio in the presence of glutaric acid catalyst to give high-ortho novolac resin. Such characterized polyol has been condensed with diphenylmethane diisocyanate to produce rigid polyurethane. A commercially available polyol, polypropylene glycol-2000 (PPG-2000), has also been condensed with diphenylmethane diisocyanate and polyol to produce tough polyurethane. These polyure-thanes were characterized with respect to their resistance to chemical reagents and mechanical properties such as tensile strength, percentage elongation, tear strength and hardness. Differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) were undertaken for thermal characterization.

Keywords. Cardanol; polyurethane; diphenylmethane diisocyanate; polypropylene glycol-2000.

1. Introduction

In the last 20 years, considerable attention has been paid to the synthesis of polymers based on cardanol (Patel et al 1989; Pillot et al 1989; Manjula et al 1991, 1992), a natural meta-substituted phenol from cashew nut shell liquid. There have been a large number of publications on modification of cardanol using the reactivity of hydroxy phenyl group (Ghatge and Vailva 1975; Ghatge and Shinde 1979; Balakrishna et al 1990; Manjula et al 1990; John and Pillai 1992; Madhusudhan and Murthy 1992; Antony 1993). However, reports concerning the cardanol formaldehyde resins leading to novel polyurethanes are very limited. In the present study, cardanol formaldehyde resin has been prepared and it is made to react with di-phenylmethane diisocyanate to form rigid polyurethane. Tough polyurethane has also been prepared using the com-mercially available polypropylene glycol–2000 (PPG-2000) along with the cardanol formaldehyde resin and the diiso-cyanate in a particular mole ratio. 2. Experimental

2.1 Materials and methods

2.1a Materials: Cardanol was obtained from M/s Rishabh Resins & Chemicals Ltd., Hyderabad. Formaldehyde (40% solution) and methanol were received from M/s BDH (India) Ltd., glutaric acid and diphenylmethane diisocy-anate were received from E. Merck (Germany), PPG-2000

*Author for correspondence was received from Aldrich Chemicals (USA), and dibutyl tindilaurate was received from Fluka Chemie (Germany). The chemicals were used as received.

2.1b Methods: Ultraviolet spectral analysis was carried out in a Shimadzu UV 2100 UV-visible spectrophotome-ter. Infrared spectra were taken in a JASCO FT–IR spec-trophotometer by KBr pellet method. 1H–NMR spectra was recorded using an R 248?H?Hitachi 300 MHz NMR spectrophotometer. Thin layer chromatographic separa-tion was carried out in three different solvent systems. Specific gravity, iodine value, hydroxyl value and intrin-sic viscosity of the resin were determined according to the IS standard 840-1964. Molecular weight of the resin was determined by gel permeation chromatography using μ-styragel columns, 100 ? and 500 ?, UV detector and 280 nm filter. The tear strength of the polyurethanes was determined using a Zwick Universal testing machine (UTM) as per ASTM standard D624. Indentation hard-ness (shore A) was determined as per ASTM standard D2240. Hardness tester durometer was used. Tensile strength of the polyurethanes was determined as per ASTM standard D412. The polyurethanes were subjected to dif-ferential thermal analysis (DTA)/thermogravimetric ana-lysis (TGA) studies at a rate of 10 K/min in air/nitrogen using Rheometric scientific STA1500 + machine. Acid, alkali and solvent resistance were estimated according to ASTM standard D3137, C267. Polyurethane samples (3 × 1 × 0?1 cm) were immersed in the medium (100 ml) for a total duration of 60 days under ambient conditions. The medium was changed and fresh medium was added at an interval of one week. The loss of weight was deter-mined using an electronic weighing balance.

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