Specialty natural rubber latex and latex foam products made therefrom

Ramli, Roslim (2023) Specialty natural rubber latex and latex foam products made therefrom. PhD thesis, University of Nottingham.

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Specialty natural rubber (SpNR) latex is a modified form of natural rubber (NR) latex, a colloidal natural polymer harvested from rubber trees known as Hevea brasiliensis. To date, there is limited information on the use of SpNR latex in latex foam products, possibly due to low total solid content (TSC), of which, for the production of latex foam products, the minimum TSC of the latex should be at least 60 %. In this study, a new generation of SpNR latex has been developed. Unlike the traditional method, which requires a processed latex known as low-ammonia NR (LATZ) latex as the starting material, SpNR latex in this study is produced directly from freshly tapped NR latex. Two varieties of SpNR latex: deproteinized natural rubber (DPNR) latex and epoxidized natural rubber (ENR) latex were produced. DPNR latex is prepared via a heat enzymatic hydrolysis process, whilst ENR latex is prepared via an in-situ epoxidation chemical modification process. Afterward, both DPNR and ENR latex were concentrated to a TSC of 60% via ultrafiltration process using membrane separation technology. The physicochemical properties of the SpNR latex were determined, and found to be slightly different to the commercial LATZ latex. Nevertheless, the availability of SpNR latex at 60% TSC, allows SpNR latex to be used to produce latex foam. In this study, the foamability and subsequent stability of the SpNR latex were evaluated, and hence the compounding, foaming, and gelling formulations to produce latex foam were developed. Additionally, this study found that DPNR latex can be used to produce latex foams in the three intended densities of high, medium, and low-density. However, for ENR latex, only high- and medium-density latex foams have been successfully produced. The lower the density the softer the material. Therefore, these findings suggest that DPNR latex foam is a better choice compared to ENR latex foam for certain latex foam products, especially when the latex foam products require light-weight and soft properties.

Suitable latex foam products made from SpNR latex were identified. The first product developed is latex foam pillows from DPNR latex. Unlike conventional pillows, the DPNR latex foam pillows were produced in a cervical shape with a unique dual density. The purpose of producing pillows with such structures is to improve pressure-relief performance, which is an important feature for therapeutic pillows application to improve sleep quality. The extraordinary properties of DPNR latex foam, such as good support properties, pressure-relief are also beneficial for other cushioning product applications. Thus, seat cushions have been produced with aims to substitute the conventional seat cushions made from polyurethane used in the transportation industry. The developed DPNR latex foam shows good vibration isolation performance, suitable for seat cushions intended for the transportation industry that require the isolation of higher frequency vibrations such as high-speed crafts, trains, and trucks. Apart from cushioning products, the porous structure of SpNR latex foam is also useful for noise and vibration control applications such as acoustic foam materials in buildings and the transportation industry. The results show that the acoustic properties of SpNR latex foam are comparable with those of commercial grade synthetic foam. Nevertheless, in order to utilize SpNR latex foam for buildings and the transportation industry, the thermal stability of SpNR latex foam must be improved to meet fire safety criteria. Oil palm fiber trunk biochar (OPTB) was incorporated as a flame-retardant agent into SpNR latex foam. The addition of OPTB to SpNR latex foam up to 24 phr improved the thermal stability of the material, but was not sufficient to meet fire rating requirements for building applications. However, the study found that the addition of OPTB to SpNR latex foam increased the dimensional stability, elongation at break and hardness of the SpNR latex foam. In addition to that, the OPTB/SpNR latex foam composite also has a high-damping property, making it appropriate for applications that require impact absorption, for example, in transportation industry, where a high level of crashworthiness is a key aspect to improve the safety of the transport vehicle.

It can be concluded that SpNR latex foam produced in this study is suitable to manufacture latex foam products. Cushioning products such as pillows and seat cushions have been successfully produced. The SpNR latex foam is also beneficial for sound and vibration control applications in the building and transportation industry, thus indicating that the application of latex foam can be broadened beyond its traditional bedding applications.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Chai, Ai-Bao
Ho, Jee-Hou
Kamaruddin, Shamsul
De Focatiis, Davide
Keywords: specialty natural latex; latex foam; rubber; heat enzymatic hydrolysis; physicochemical
Subjects: T Technology > TJ Mechanical engineering and machinery
Faculties/Schools: University of Nottingham, Malaysia > Faculty of Science and Engineering — Engineering > Department of Mechanical, Materials and Manufacturing Engineering
Item ID: 72892
Depositing User: Ramli @ Lim Chai, Roslim
Date Deposited: 22 Jul 2023 04:40
Last Modified: 01 Jan 2024 04:30
URI: https://eprints.nottingham.ac.uk/id/eprint/72892

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