Effect of Maillard reaction in ammonia preserved natural rubber latex using reducing sugars
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ORIGINAL PAPER
Effect of Maillard reaction in ammonia preserved natural rubber latex using reducing sugars Manroshan Singh1,3 · Azhar Mat Easa2 · Baharin Azahari2 Received: 16 June 2020 / Accepted: 29 September 2020 © The Malaysian Rubber Board 2020
Abstract Investigation of Maillard reaction in natural rubber (NR) latex was carried out using two reducing sugars, glucose and ribose. Both reducing sugars together with a 1:1 mixture were added as 5 wt% solution to concentrated NR latex preserved with ammonia in a 1:1 ratio and preheated at 27, 70 and 90 °C for 2 h. The changes in the latex due to the reaction were characterised using pH and L values for 216 h (9 days). Cast latex films were then prepared and investigated for their swelling index (SI), gel content and tensile properties. Results obtained showed reduction in both pH and L values with time for the latexes with reducing sugars indicating progress of the Maillard reaction. For the Maillard reacted films, SI reduced whereas gel content, tensile stress and tensile strength increased. However, no significant changes were observed for the elongation at break of the reacted samples compared to the unreacted samples. Increasing the preheating temperature of the latex and reducing sugar mixtures to 70 and 90 °C from 27 °C increased the Maillard reaction which further improved the film properties. Although both reducing sugars improved the film properties, the improvements brought by reacting NR latex with ribose were more significant compared to reacting NR latex with glucose. From the current findings, it is evident that reducing sugars could be used to enhance the physical properties of natural rubber latex films. This technique will benefit the latex industry as it is environmentally friendly, easily applicable and cheaper compared to currently available techniques. Keywords Natural rubber latex · Non-rubbers · Maillard reaction · Tensile properties
Introduction There are approximately 12,500 species of laticiferous plants, but only 7000 of these produce polyisoprene [1]. However, most of these plants do not produce the highmolecular-weight polymers required for high-performance commercial products [2]. To date, natural rubber (NR) latex possessing a cis-1,4-polyisoprene structure obtained from the Hevea brasiliensis species tree of the Enphorbiaceae famili found in the tropical regions in Amazon, South America has been the choice of the industry. Furthermore, due to * Manroshan Singh [email protected] 1
School of Materials and Mineral Resource Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau Pinang, Malaysia
2
School of Industrial Technology, Universiti Sains Malaysia, 11800 Nibong Tebal, Pulau Pinang, Malaysia
3
Rubber Research Institute of Malaysia, Malaysian Rubber Board, 47000 Sungai Buloh, Selangor, Malaysia
its molecular structure and high molecular weight (Mr > 106 Dalton (Da)) [3], NR latex has the required properties that remain unmatched by synthetic latexes. Freshly tapped NR latex is co
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