Free-Radical Photopolymerization of Acrylonitrile Grafted onto Epoxidized Natural Rubber.

Rawdah Whba,Azizan Ahmad,Lee Tian Khoon,Mohd Sukor Su’ait,Nor Sabirin Mohamed,Salmiah Ibrahim

doi:10.3390/polym13040660

Rawdah Whba, Azizan Ahmad + Show 4 more

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https://doi.org/10.3390/polym13040660

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Abstract

The exploitation of epoxidized natural rubber (ENR) in electrochemical applications is approaching its limits because of its poor thermo-mechanical properties. These properties could be improved by chemical and/or physical modification, including grafting and/or crosslinking techniques. In this work, acrylonitrile (ACN) has been successfully grafted onto ENR- 25 by a radical photopolymerization technique. The effect of (ACN to ENR) mole ratios on chemical structure and interaction, thermo-mechanical behaviour and that related to the viscoelastic properties of the polymer was investigated. The existence of the –C≡N functional group at the end-product of ACN-g-ENR is confirmed by infrared (FT-IR) and nuclear magnetic resonance (NMR) analyses. An enhanced grafting efficiency (~57%) was obtained after ACN was grafted onto the isoprene unit of ENR- 25 and showing a significant improvement in thermal stability and dielectric properties. The viscoelastic behaviour of the sample analysis showed an increase of storage modulus up to 150 × 103 MPa and the temperature of glass transition (Tg) was between −40 and 10 °C. The loss modulus, relaxation process, and tan delta were also described. Overall, the ACN-g-ENR shows a distinctive improvement in characteristics compared to ENR and can be widely used in many applications where natural rubber is used but improved thermal and mechanical properties are required. Likewise, it may also be used in electronic applications, for example, as a polymer electrolyte in batteries or supercapacitor.

Highlights

Natural rubber (NR) is an essential raw material and accounts for over 50,000 various rubber and latex-related products
The peak in the –C≡N stretching was of medium intensity and observed at 2230 cm−1 for ACN corroborates with the grafted epoxidized natural rubber (ENR)-25 samples at 2242 cm−1
Compared with ENR- 25, the existence of this peak proves that the grafting of ACN occurred successfully onto the ENR- 25 backbone

Summary

Introduction

Natural rubber (NR) is an essential raw material and accounts for over 50,000 various rubber and latex-related products. Under Statistics Malaysia (2020), NR crop production in January 2020 has increased by 13.3% to 66,232 tonnes compared with previous months [1]. This value is expected to extend beyond the 2nd quarter of 2020 because of the high demand for medical gloves to fight the global pandemic, COVID-19. The existence of epoxide groups in the ENR structure has enhanced the originality of NR properties This is clear through its improved polarity, good strength, excellent adhesion, high hardness, compatibility blend with other polymers, and good oil and temperature resistance, as well as its low air permeability [5]. This is attributed to the oxygen atom, which promotes the dissociation of salt, and provides conductivity while maintaining the adhesion property that can promote good contact between the electrolyte layer and electrode for electronic devices [6,7]

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