Polymers 2023 , 15 , 1393
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2.1.2. Sisal ( Agave sisalana ) Sisal is one of the most commonly used natural fibres grown in tropical and subtropical regions of North and South America, Africa, the West Indies and the Far East. Moreover, the hydroalcoholic extract obtained from sisal leaves possesses significant antimicrobial activity against Aspergillus niger and Candida albicans [68,69]. Pulikkalparambil et al. [70] examined the reuse of discarded polypropylene (PP)-based disposable face masks with sisal and hemp fibre mats. They used hot compression moulding to sandwich the PP masks and natural fibres. The resulting composites showed excellent mechanical properties with antimicrobial activities against S. aureus . 2.1.3. Kenaf ( Hibiscus cannabinus L.) Kenaf is a member of the Malvaceae family and herbaceous fibre crops. Kenaf plants are grown throughout the year with a short harvest time in West Africa, India and China [71]. They can grow up to 2.5–4.5 m tall with stems up to 1–2 m in length. Kenaf seeds and leaves are used in food products as they are rich in nutritional and phytochemical compounds [72]. 2.1.4. Bamboo ( Bambusa vulgaris ) Bamboo ( Bambusa vulgaris ) grows in Asia-Pacific, African, European and North and South American regions. Bamboo reaches maturity in 3 years when its tensile strength is effectively comparable to mild steel. Moso bamboo has a growth rate of 2 inches per hour. Some bamboo species reach a height of 60 feet in 3 months. Therefore, cutting down this wood does not affect the ecological and natural balance much [73]. Bamboo is considered the most under-utilised natural fibre and is abundantly available in Southeast Asian countries. The annual global availability of bamboo fibres is 30 million tonnes with a maturity cycle of only 3–4 years. Bamboo fibres have excellent mechanical strength. The specific stiffness and strength is comparable to glass fibres [74]. Afrin et al. [75] reported strong antibacterial properties of bamboo fibres against E. coli and S. aureus due to retained lignin. Another possible reason was the presence of H 2 O 2 that damaged the DNA sequencing of E. coli . However, they believed that this was not possible as H 2 O 2 was thermally decomposed during the extraction process. 2.1.5. Jute Jute is often neglected but considered as one of the most important fibres. Jute is in the Tiliaceae family with the scientific name Corchorus capsularis because it is extracted from Corchorus plants. Jute fibres are mostly found in the Mediterranean but recently the finest growth fibres come from Bangladesh, India, China, Nepal, Thailand, Indonesia and Brazil. Jute fibres are brittle and can grow 2–3.5 m in height. They possess very high lignin content (12–16%) and thus have low elongation at break. Jute fibres possess unique properties which, if utilised effectively, can solve problems in the textile and food packaging fields. The incorporation of jute fibres in PLA matrices improved both oxygen and water vapour barrier properties. 2.1.6. Flax ( Linum usitatissimum ) Flax is commonly grown in moderate climatic regions such as India, Argentina, South- ern Europe, China and Canada [28]. Flax plants can grow to heights of 80 to 150 cm in less than 110 days. Fibres from flax bast grow between 60 and 140 cm long with diameters ranging from 40 to 80 μ m. They are members of the bast family. The bast fibres are collected from the fibrous bundles located in the inner bark of a plant stem. The major components of flax fibres are pectin, hemicellulose, cellulose, and lignin. There are also small amounts of wax, oil and water. The incorporation of flax fibres increases strength and stiffness, which can be further improved by modification with a malleated coupling agent [76].
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