Synthesis of linear poly-cardanol and its application in rubber materials

Abstract

People have been trying to find natural products that can replace rubber due to the land occupied by rubber planting and the environmental pollution caused by waste rubber. Herein, the linear poly-cardanol (LPCA) is obtained by undergoing a Friedel-Crafts alkylation reaction at 100 °C for 2 h at the catalyst of 5% of p-toluene sulfonate. The Mw of LPCA is about 4·104, and its polymeric degree is about 133. The weakening of 3009, 1263, and 1154 cm–1 in IR spectrum, the blue shift of UV absorption, the new chemical shifts of protons in 1H-NMR spectrum all certify the formation of LPCA. LPCA has obvious characteristics of elastomer. Its glass transition temperature (Tg) is –20.7 °C on the DSC curve. During the cocrosslinking of LPCA and liquid polyisoprene rubber (LIR), LPCA induces the crystallization of long LIR chain segments, which is confirmed by the transition peaks of the DSC curve in 40°C. This partial crystal structure is beneficial for LPCA/LIR blends to possess high strength. The tensile strength and the elongation at break of LPCA/LIR blend with 20% of LIR are about 2.04 MPa and 92%, respectively. LPCA possesses flexible alkyl chains and hydrophilic phenolic hydroxyl groups, so it can be used as a plasticizer just like LIR and compatibilizer at the same time. This study affords a possible way for renewable cardanol to replace rubber partially or completely.

Keywords

• polymer blends and alloys
• cardanol
• friedel-crafts reaction
• rubber
• crystallization