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resins. Due to their relatively high price, isocyanates are mostly used in adhesive systems in combination with tradi- tional formaldehyde-based resins to enhance their perfor- mance. However, pMDI could also be used to bind raw materials that are difficult to glue, such as bagasse, straw, leaves, or straw [27].
properties and can contribute to the particleboard’s mechan- ical strength, biological durability, formation of char, and ul- traviolet degradation [70,71]. Lertwattanaruk and Suntijitto [71] stated that lignin could aid in softening the particles during hot pressing, easing their resination [72].
4.
Particleboard made from agricultural
3.
Agricultural biomass as raw material for
biomass
particleboard manufacturing
4.1.
Straw-based particleboard
3.1.
Classification and availability of agricultural
biomass
In 2020, the production quantity of wheat was 760.93 million tons worldwide, preceded only by sugarcane and maize. With this huge production capacity, finding novel methods to uti- lize the remaining wheat straw in value-added applications effectively is essential. Han et al. [87] created UF-bonded wheat straw particleboard, but its properties were inferior to those of commercial particleboard. A similar finding was made for the reed straw particleboard. However, silane coupling agents were used to improve the particleboard ' s bondability. The treatment was found to enhance the wheat straw and reed straw particleboard performance to varying degrees. Epoxide silane was found to be more effective for reed straw particleboard, while amino silane was found to be more effective for wheat straw particleboard. The surface appearance of straw-based particleboard is shown in Fig. 8. Despite the resultant inferior performance of straw parti- cleboard, some researchers found that straw could serve as a suitable raw material for the surface particleboard layer, provided pMDI resin or a combination of UF and pMDI were employed [88]. Rice straw was successfully used as a partial substitution of wood particles up to 20% without adversely affecting the mechanical properties of the particleboard [89,90]. Li et al. [60] produced rice straw particleboard bonded with pMDI and found that its properties exceeded the M-2 specification of the American National Standard for Wood Particleboard [ANSI A208.1] [91]. However, rice straw is high in ash and silica content, which interferes with its bonding ability and leads to low internal bonding strength. Hence, pre- treatment is necessary to remove the excessive ash and silica content. Rapeseed straw, like wheat and rice straw, has a similar chemical composition to wood, with less cellulose and lignin but more hemicellulose and extractives. Furthermore, rape- seed straw has better gluability than wheat straw because its chemical substances are distributed throughout the entire mass, unlike wheat straw. Rapeseed straw can be easily glued even when conventional wood adhesives was used. Dukarska
According to Alwani et al. [36], agricultural biomass can be classified depending on the part of the plant from which they are extracted. Agricultural biomass can be divided into wood and non-wood biomass. Wood biomass includes hardwood and softwood species. Non-wood biomass can be categorized into leaf, grass, seed, fruit, stem, straw, and stalk [36]. Most non-wood biomass is small in diameter, except for oil palm trunks and bamboo. This characteristic has restricted their practicability to be processed into veneer, lumber, or strips [37]. Therefore, non-wood biomass is suitable to serve as a feedstock for particleboard production where the size and dimensions of the materials are not emphasized. In this study, several non-wood biomasses have been identified as raw materials for particleboard production. For comparison pur- poses, these biomasses, either dicotyledonous or mono- cotyledonous, were classified according to Fig. 7. Common agricultural waste used in particleboard pro- duction is in the forms of straw, stalk, shell, husk, leaves, stem, etc. These post-harvesting and post-production wastes can serve as an alternative source for particleboard manufacturing. The resources of some selected agricultural crops worldwide are displayed in Table 3. Staple food such as rice, maize, wheat, and barley have the highest harvested area (ha), and their corresponding production quantity (tons) is also among the highest. The figures in Table 3 imply the abundance of the biomass generated after harvesting and processing. The respective parts of the crops used in parti- cleboard production are also listed in Table 3.
3.2.
Characteristics of agricultural biomass for
particleboard manufacturing
Summarised information on the chemical composition, i.e. cellulose and lignin content of wood and non-wood biomass as natural feedstocks for particleboard manufacturing, is presented in Table 4. According to Pedzik et al. [4], agricultural waste generally has a slightly lower cellulose content than softwood and hardwood. This might restrict the potential of agricultural biomass in particleboard production as cellulose is responsible for the strength and dimensional stability of the resultant boards. Stalk-based biomass, pineapple leaves, and bamboo have relatively higher cellulose content than the other biomass, which might make them favorable for pro- ducing particleboard with high mechanical strength. On the other hand, lignin is an amorphous, complex three- dimensional aromatic biopolymer with hydrophobic
Table 2 e Cost estimation for particleboard manufacturing based on main cost components [25]. Cost component The portion in production cost
Adhesive
15 e 30% 30 e 40% 15 e 20% 5 e 20% 25 e 30%
Wood raw materials
Energy
Manpower
Processing cost
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