Sustainability 2023 , 15 , 6915
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and have shifted to alternative options such as bamboo, wheat straw, and rice straw [63]. The production of paper from non-wood sources has several advantages, such as ease of pulping and the high quality of the fibers, which can be used for the production of special types of paper [64]. Rice straw has a high cellulose content making it an excellent resource for paper production. Rice straw combined with wastepaper can produce paper that can be used as wrapping paper, art paper, and writing paper [65]. Moreover, non-wood fibers obtained from agricultural residues can solve the problem of agricultural waste disposal as it is commonly incinerated. Non-wood fibers also vary in length, which can be used to produce several types of paper [66]. Tea waste from the incorrect harvesting of black tea leaves, which is disposed of by landfilling, can also be used for papermaking [67]. Pineapple leaves and banana plant fibers are also good alternative raw materials for paper production as they both have high cellulose content [68]. 3. Paper Waste and Rejects and Their Recycling Paper can be virgin paper, which is produced from virgin pulp, or recycled paper, produced from recycled wastepaper or reprocessed pulp [3]. Paper recycling reduces the burden on the environment by minimizing natural resource consumption and reducing the amount of toxic chemicals released into the environment [59]. Paper recycling also plays a major role in decreasing greenhouse gas emissions since fewer trees are cut down, leading to more CO 2 captured through photosynthesis; paper manufacturing costs are also reduced because fewer processes are required [69,70]. A study conducted using material flow analysis and life cycle assessment on waste paper recycling in Spain showed that each ton of virgin paper emits around 530 kg CO 2 − eq while a ton of recycled paper emits only around 210 kg CO 2 − eq , reducing CO 2 emission by 320 kg CO 2 − eq per ton of paper [71]. Recycling reduces pollution in water bodies by 35% and air pollution by 74%. Moreover, it reduces land space usage and conserves natural resources [72]. The main sources of paper waste for recycled papermaking are industries, households, and small businesses. Globally, approximately half of the paper waste is recycled, whereas half is incinerated or landfilled [73]. Households generally are a good source of mixed and graphic papers, whereas trade and industries provide corrugated paper used for packaging. Offices, along with printing and conversion operations, are a source of high-grade paper [74,75]. There are around 50 identified grades of wastepaper, and the quality of wastepaper is a determinant of the end quality of the recycled paper. However, purity and quality are negatively affected if different types of wastepaper are mixed together [72]. Wastepaper often contains substances introduced in the collection and handling processes known as non-paper components, such as laminated covers, staples, cosmetic samples, and plastic wrapping. These components can be removed in limited amounts during recycling, but cost increases if they are present in high amounts. This highlights the importance of an efficient waste collection and handling stage [74]. The paper recycling process involves several steps, including repulping, deinking, and refining. Repulping involves separating the fibers of the wastepaper using water and chemicals. Deinking and refining are not absolutely necessary steps for paper recycling, but they greatly increase the strength and appearance of the final product [74]. Deinking improves the visual quality of the recycled paper but does not whiten unbleached fibers. Therefore, bleaching may be needed. Several methods of deinking are used, with the floatation method being the most common [74]. The quality of deinked pulp is determined by several factors, including the printing method, composition of the ink, and recycling method. Paper printed using xerographic and inkjet technology with water- and toner- based inks further increase the issues in recycling systems. Paper printed by flexographic and offset methods should not be treated together as both require different deinking mediums [76]. Finally, the deinked pulp is refined to prepare it for the papermaking process [77]. Cellulosic fibers undergo different changes when recycled. After several recycling processes, they have a significantly low bonding potential compared to virgin fibers. This loss of bonding can be mostly restored by refining, but eventually, the fiber
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