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Fabrication and characterization of latex foam shoe insoles made from novel ammonia-free natural rubber latex concentrate

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Abstract

The presence of ammonia as a preservative in natural rubber (NR) latex concentrate induces a variety of problems in the NR latex foam manufacturing process, consequently leading to inconsistency in the quality of the end products. To overcome these issues, a novel ammonia-free NR (AFNR) latex concentrate that uses palm oil-based polymeric surfactants as an alternative preservative has been developed. This study explores the feasibility of using AFNR latex to produce latex foam shoe insoles. In this investigation, the AFNR latex was foamed into extra-high-density (EHD) and high-density (HD) foams using the Dunlop batch foaming process. The study found that HD latex foam is softer than EHD latex foam, with the Shore F hardness of HD latex foam and EHD latex foam being 57 and 77, respectively. The study also discovered that the peak pressure value and rebound resilience properties of HD latex foam shoe insoles, which were fabricated at 7 mm thickness, are 41% and 6% lower than those of EHD latex foam, respectively. Additionally, EHD latex foam and HD latex foam have different morphological characteristics, with EHD latex foam having a thicker cell wall, smaller pore size, and being less porous compared to HD latex foam. Taking these properties into consideration, HD foam could be the ideal choice for shoe insole applications, such as sports shoes.

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Acknowledgements

The authors are grateful for the financial support and facilities provided by the Malaysian Rubber Board (MRB) and The University of Nottingham Malaysia. The authors would also like to thank the Director-General of the MRB for permission to publish this paper. The authors also thank Abdul Yazib Bakar and Mohammad Saiffdin Nordin for their technical assistance during the duration of the study.

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Authors and Affiliations

  1. Technology and Engineering Division, Malaysian Rubber Board, Sungai Buloh, Selangor, Malaysia

    Roslim Ramli, Siang Yin Lee & Asrul Mustafa

  2. Quality and Technical Service Division, Malaysian Rubber Board, Sungai Buloh, Selangor, Malaysia

    Mohd. Aswad Abd. Rahman

  3. Faculty of Science and Engineering, University of Nottingham Malaysia, Semenyih, Selangor, Malaysia

    Ai Bao Chai

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  1. Roslim Ramli
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Contributions

Conceptualization; [RR, SYL, MAAR, ABC, AM]; Methodology: [RR, SYL, MAAR, ABC, AM] Formal analysis and investigation: [RR, SYL, ABC]; Writing—original draft preparation: [RR, ABC]; Writing—review and editing: [RR, SYL, ABC, AM]; Funding acquisition: [RR, SYL]; Resources: [RR, SYL, MAAR]; Supervision: [ABC, AM]. All authors reviewed the results and approved the final version of the manuscript.

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Correspondence to Roslim Ramli.

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Ramli, R., Lee, S.Y., Abd. Rahman, M.A. et al. Fabrication and characterization of latex foam shoe insoles made from novel ammonia-free natural rubber latex concentrate. J Rubber Res 27, 85–101 (2024). https://doi.org/10.1007/s42464-024-00236-8

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