# Lignocellulosic Composites from Acetylated Sunflower Stalks
## 1 Introduction  
Worldwide economic development has caused increased needs for converted wood products [1; 2; 3; 4; 5; 6]. A big challenge in the composites industry is the availability of cheaper materials in order to minimize the production cost. The implementation of agricultural residues as an option is growing and has come to the minds of many researchers in laboratories worldwide [7; 8; 9; 10; 11]. The use of such materials may benefit both socioeconomic and environmental development since they are normally burnt in the field or plugued into the soil.  
Therefore, looking for potential replacements for slow-growing trees is of great importance, and available agricultural plants might be good alternatives [12; 13]. A variety of plants have been studied for use in composites manufacturing, including vine stalks [14], topinambour stalks [12; 15], cotton stalks [16; 17], coconut chips [18], bamboo chips [19; 20; 21], flax chips [22], and banana chips [23]. Other agriculture residues also include rice and wheat straw [24; 25], canola straws [26], reed stem [27], date palms [28], oil palms and poppy husks [29], and stalks from cotton [30].  
Sunflower (_Helianthus annuus_ L.), from the Asteraceae family, is another annual plant. It is an annual forb which is grown as a crop for its edible oil and edible fruits. Sunflower grows in biomass at 4 t/ha and is widely cultivated all over the world [31]. The harvested area in Europe is 368 \(\times\) 10\({}^{6}\) ha, which represents the 16% of the harvested area worldwide [13].  
Several research studies have been performed so far focusing on the utilization of sunflower stalks in particleboard manufacturing. Panels from sunflower stalks were successfully produced for the first time at the University of Minnesota [32; 33]. Another study used sunflower stalks to reduce the cost of the final product [34]. Other researchers attempted to use sunflower stalks in combination with pine particles. They reported improved physico-mechanical properties; inaddition, the boards met the requirements for general-grade particleboards [35]. The same conclusion was drawn in a study which used sunflower stalks in combination with poplar chips [36]. Other researchers suggested that sunflower stalk may be incorporated as a cheap raw material to produce particleboard with acceptable properties [37]. The feasibility of agricultural crop residues, such as cup plant, topinambour, and sunflower, used as an alternative raw material for particleboards was investigated [15]. The findings revealed that particleboards can be successfully produced from agricultural residues, especially when isocyanate is used as a binder. In all the abovementioned studies, particleboard composites met the British P2 general use and P3 interior fitment board criteria, as far as the thickness swelling value is concerned. However, the P4 load-bearing panel, which requires a thickness swelling value of 14%, has not been satisfied. A value of 16%, close to the critical 14%, was reported when 8% of titanium dioxide nanoparticles was incorporated during board production [37]. Therefore, reaching this value can be considered a challenge and may be achieved by applying the chemical modification technique [38].  
As a consequence, the objective of this communication was to investigate the technical feasibility of manufacturing particleboards from chemically modified sunflower stalks. The most studied type of chemical modification is the reaction with acetic anhydride, known as acetylation, which is depicted in Figure 1a [38] and schematically illustrated in Figure 1b. Acetic anhydride replaces the abundant hydrophilic hydroxyl groups which are present in the lignocellulosic material with hydrophobic acetyl groups. Thus, the material remains permanently in a swollen condition due to the bulking action of the hydrophobic acetyl groups.