Wood is one of the most important biomass resources on the earth. Pine trees can grow in a variety of locations, and it has the potential to serve as a commodity wood material. Wood industries use Pinewood as raw material, and sawmill residue considers industrial waste. Considering the environmental issues and growing desire to use bio-based materials, using sawmill residue as industrial waste is a step forward for waste management and developing technologies to produce bio-based materials which are worth studying. 

The wood is mainly composed of cellulose, but lignin and hemicelluloses are also present in significant amounts. Biomass can be converted into value-added bio-based materials by hydrolyzing cellulose and hemicellulose into monomer sugars, which can then be used as a feedstock for bacterial fermentation. The high lignin content makes the lignocellulose structure stiffer, which results in diminishing the fermentable sugar (glucose, xylose) production. The pretreatment of lignocellulosic biomass could be a beneficial method for producing fermentable sugars and can be used to produce higher content of fermentable sugar for use in various applications. Nonetheless, repolymerization of lignin may occur and decrease hydrolysis efficiency. Therefore, it should be studied.  In the present study, the effect of delignification on sugar production is studied. Sawdust of sapwood and heartwood of pine tree was used as the raw material, and acid-chlorite delignification was used as a pretreatment method. In the delignification process, heartwood and sapwood are delignified in a shaking water bath at 70°C. The samples were cooled and were filtered by a vacuum filter and were dried in an oven at 105°C overnight. The experiments were run 20 times, and the average lignin content was calculated. Hemicellulose and cellulose can be hydrolyzed chemically or enzymatically after pretreatment. The most common chemicals applied in chemical hydrolysis are H2SO4 and NaOH, and enzymes use for enzymatic hydrolysis. The enzymatic hydrolysis is an environmentally friendly process since it operates at mild temperature, pH, and pressure conditions. In this project commercial enzymes (Trichoderma reesei) were used to perform enzymatic hydrolysis. The enzyme was diluted with citrate buffer solution with pH 5.0. The enzyme solutions concentrations were prepared at 0.5, 1, 5, and 7 mg/ml. The biomass-to-enzyme solution ratio was set at 10:1 (w/v). Samples were placed in a shaker water bath for 72 h, the temperature was set at 50°C, and the speed at 150 rpm. The experiment was repeated five times.  

The results showed that heartwood has a higher lignin content, and the acid-chlorite delignification method is a proper method to remove lignin from pinewood sawdust. The FTIR results of sapwood and heartwood before and after the delignification pretreatment showed an increase in the cellulose percentage and significant changes in the crystalline structure of cellulose after delignification. In addition, the changes in cellulose percentage and crystallinity were higher in heartwood rather than sapwood. The lignin index (LI) calculations based on the FTIR results, illustrated that LI in delignified heartwood is lower than LI in delignified sapwood. 

FTIR results after enzymatic hydrolysis showed a peak that attests the monosaccharide production, and the fermentable sugar production was higher in the heartwood. The higher enzyme loading up to 7 mg/ml, the higher fermentable sugar production. The XPS results between delignified heartwood hydrolysate at 7 mg/ml and control heartwood hydrolysate at 7 mg/ml were performed. The results showed lower surface lignin coverage and a higher O/C ratio which in delignified wood hydrolysate that results in an increase in fermentable sugar production due to the delignification process.