Utilization of date palm tree fibres as biomass resources for developing sustainable composites for industrial applications

Abstract

Petroleum based fibres are dominating our everyday usage of fibres, textiles, and composite development reaching an annual consumption of more than 50 million tons in 2020. Over the years, there has been a desperate need for sustainable alternatives; but unfortunately, the global production of natural fibres (NF) has reached a plateau due to the reliance on very few natural sources and lack of biodiversity. With the growing concern on climate change due to the pollution emitted from petroleum-based manufacturing products and their end life disposal, sustainable manufacturing of sustainable materials represents a primary concern for the construction industry. New technologies and materials are extensively investigated and proposed to meet sustainability guidelines imposed by governments and specifically the United Nations (UN). NF represent one of the most investigated renewable and sustainable materials. The date palm tree (DPT), Phoenix Dactylifera L., produces globally an approximate of 4.8 million tons (dry weight) where 3.6 million tons are produced in the MENA region only as by-products of pruning, regarded as agricultural waste, which are either landfilled or incinerated. This research investigates and develops novel methodologies to overcome the drawbacks of utilizing DPT by-products where DPT fibre (DPF) can be extracted from and utilized as a reinforcement in developing sustainable composites for industrial applications. An intensive literature review database was developed to highlight previous research work and investigations carried out to date on the utilization of DPF and their effect in developing sustainable composites and the drawbacks limiting their feasibility for upscaling and industrialization. This identified the problem statement in current research that must be addressed to distinguish the potential of DPF utilization and industrialization. Various surface modification treatments as well as their conditions (soaking time and duration) effect on the characteristics of DPF (surface morphology, chemical composition, chemical structure, and crystallinity) was investigated and evaluated to develop a more hydrophobic fibre that enhances the interfacial bonding when used as a reinforcement with various matrix systems (i.e., polymers and cementitious). DPF treated with sodium hydroxide (NaOH) solution, 6%, for 3 hours showed optimal results where an increase in tensile strength of the fibre by 147%. Scanning electron microscopy (SEM) images demonstrated the effectiveness of the surface treatment showing a more porous surface where the impurities and waxes were successfully removed. Furthermore, investigations, evaluation and prediction on the effect of DPF particle size distribution, density, diameter size (unsieved, ≥1,000 μm, 500 – 1,000 μm, 250 – 500 μm, 125 – 250 μm, and ≤125 μm) and loading content (10, 20, 30, 40 wt.% of matrix) on both the mechanical, physical, fungal resistance and disintegration properties of recycled thermoplastic, recycled polyvinyl chloride (RPVC), and biodegradable thermoplastic, polylactic acid (PLA), were evaluated. The hydrophilic nature of DPF contributed to an increase in thickness swelling (TS), moisture content (MC) and water absorption (WA) for both RPVC and PLA reinforced composites. TS, WA and MC increased by 1.57%, 1.76%, and 10.80%, respectively at 40 wt.% DPF loading content when reinforced with RPVC. Moreover, the flexural strength, tensile strength and impact strength decreased as the loading content increased showing maximum reduction at 40 wt.% loading, varying depending on DPF geometry. Furthermore, micromechanics modelling scenarios to predict the fibre orientation was investigated. To determine the effectiveness of DPF orientations in the PLA and RPVC, the rule of mixtures (ROM), modified ROM, inverse rule of mixture (IROM), modified IROM and Halpin-Tsai were applied with three possible fibre orientations in the composites. The modified ROM and modified IROM closely matches the experimental results with the DPF oriented between 0° to 45° in the direction of compression force of the DPF/PLA and DPF/RPVC composites. Also, Composites where exposed to the brown-rot fungus Irpex lacteus and white rot fungus Tyromyces palustris to evaluate its resistance to biodegradation. To evaluate their feasibility to be utilized in the construction sector as a cladding and decking composite which can act as a substitute to wood in developing wood plastic composites (WPC). Composites developed using PLA had higher weight loss (%) when compared to the same samples but reinforced with RPVC. Composites with higher DPF content showed high rates of decay when used with different polymer matrix. Also, DPF length had a significant effect on the disintegration of the composites. DPF/PLA composites did not demonstrate significant weight loss under fungal decay in 8 weeks where the composites with 40 wt.% DPF showed the highest WL% reaching 5.61% and 5.46% when exposed to Tyromyces palustris and Irpex lacteus respectively. Furthermore, a novel investigation on the biodegradation of the samples showed that DPF reinforced PLA can be implemented and developed within a circular economy scheme in which the composite was fully decomposed by earth worm within 6 weeks, developing vermicompost as manure that may be utilized as a nutrient for plants. Furthermore, an investigation of the processing parameters effect (processing time, temperature, and pressure) on the physical and mechanical properties of DPF reinforced polyester (PES) composite is evaluated. For that, two different temperatures (90 and 110 oC) and three different pressures (1.0, 1.65, and 2.18) MPa which was achieved by varying the load applied (10, 15, and 20) ton and keeping the sample size constant are examined for three different processing durations (3, 6, and 9 min). Results showed that every processing parameter had different effects on the mechanical and physical properties of the composites developed. Moreover, investigations on the effect of varying DPF loading content (1, 2, and 3 wt.% of matrix), and length (10, 20, 30, and 40 mm) of untreated and alkali treated DPF on the mechanical properties of DPF reinforced Ordinary Portland cement (OPC) and DPF reinforced OPC/ground-granulated blast furnace slag (GGBS) were evaluated. Two different curing conditions, water and air, effect on the mechanical strength and physical properties of the composites developed were explored. Results showed that the inclusion of 20 mm treated DPF at a loading content of 1 wt.% with OPC/GGBS as a matrix showed the greatest enhancement in strength by 57.12% and 30.97% of flexural and compressive strength respectively at 28 days of ageing in a water bath. Alkali treatment of DPF demonstrated higher mechanical properties enhancing the optimal mix designs’ mechanical strength by 10% and at 28 days of water curing when compared to the untreated. Moreover, OPC as a pure matrix system had lower mechanical properties where the optimal mix design had an increase in 37.48% and 19.36% on flexural and compressive strength respectively at 28 days of curing in a water bath when compared to OPC/GGBS reinforced composites. Overall, this thesis paves the way for developing a comprehensive foundation for utilizing DPT by-products by optimizing the parameters of surface modification, fibre geometry, fibre loading, and processing parameters for developing sustainable composites that can be industrialised for various non-structural industrial applications (i.e., construction and automotive industries).