Haile et al. Bioresour. Bioprocess.
(2021) 8:35
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Fig. 13 Dissolving pulp beneficiation: regenerated fibers
biocomposites with a safe environment as a result of pre- ferred disposal and reuse options (Schorr et al. 2014). The fly ash and other mineral-based wastes from pulp and paper mill are underutilized and fully discarded especially in developing countries (Novais et al. 2018). The fly ash is entirely composed of metal oxide minerals. Though it is not a concern of the present review the grits, dregs, and lime muds have also plenty of mineral con- tent for specific biomaterial applications. The biomaterial which can be obtained by a suitable biorefinery technique from fly ash can be used for versatile engineering appli- cations as a biocomposite. The prospective application of fly ash as a biomaterial is by converting the minerals into their polymer counterpart via geo-polymerization which normally are referred to as geopolymers (Mohammadka- zemi 2018; Yoon-moon and Naik 2005). Depending on the end-use the geopolymers can be incorporated in manufacturing composite materials mainly as the reinforcing component of the biocompos- ite. A polymer of fly ash that can be used for biocompos- ite is synthesized using predefined steps. The major step involves treatment with highly alkaline liquors such as using aqueous caustic soda in combination with silicate compounds such as sodium silicate in a process called alkali activation (Saeli et al. 2019; Rajamma et al. 2012). The highly alkaline environment will lead to the break- ing of silica and alumina bonds in the fly ash which pro- vides conditions for the dissolution of free silicon and aluminum ions. The reaction between the free silicon and aluminum ions with active alkali ions leads to the formation of an intermediate precursor which up on
manufacturing of different grades of fibers, especially for high-performance applications. The major challenge in the utilization of pulping waste as a precursor for textile fibers is the limited availability of fiber manufacturing units in areas, where resources are abundant; and associ- ated yield-related problems for producing textile fibers as per the global demand. Biocomposites from pulp and paper mill waste The global concerns for a safe environment and risk min- imized livelihood of society are high. With this regard issues that need immediate intervention are the highest priorities of global nations. As far as feasible interven- tions are concerned focus needs to be given on increas- ing cost of petroleum and the allied depletion and frameworks in line with new environmental regulations. To this end engineering materials which have a vital impact in replacing existing petroleum-based materials and which are capable of addressing the environmental legislations are required. This was the rationale behind seeking eco-friendly green substitutes especially biocom- posites for modern engineering applications (Soucy et al. 2014; Manesh 2012). Renewable lignocellulosic materials are suitable for the reinforcement of polymers and provide biocompos- ites for the relevant industry. Such kinds of production trends provide relief with regards to problems encoun- tered in using petroleum-based composites. These fre- quently available resources provide a remedial solution with regards to the production of attractive, sustain- able, cost-effective, and eco-friendly materials so-called
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