Preparation Of Nano Cellulose From Corncob And Its Application In Insulated Polyurethane Foam Material

Nanocellulose as a kind of biopolymer material is extracted from renewable natural cellulose.Cellulose feedstock has advantages of abundance,low-cost,and renewability,correspondingly nanocellulose has attracted great attention due to its excellent properties,such as high Young's modulus,high tensile strength and unique optical properties.In the research field of nanocellulose,an efficient preparation technique is always the key aspect to achieve these potentials.In this study,the efficient methods for nanocellulose preparation using corncob as feedstock were investigated.The prepared nanocellulose also was used as filler for polyurethane foamed plastic.The main results are as follows:Firstly,we developed a new pretreatment strategy for corncob using formic acid/hydrochloric acid.Effects of pretreament parameters on the compositions and structure of corncob were investigated.Removal ratios of cellulose,hemicellulose and lignin under the optimal pretreatment conditions(formic acid concentration 80w%,temperature 90 ~oC,time 3h)were 8.76%,83.98%and 63.29%,respectivley.This pretreatment method caused slight degradation of cellulose(less than 9%)and was believed as an efficient processing technique.The pretreated substrate with crystallinity index of 37.14%was suitable for the subsequent preparation of cellulose nanocrystal(CNC).Secondly,a two-stage process invovling ionic liquid swelling and solid acid hydrolysis is used to prepare corncob CNC.The ionic liquid Amim Cl swells the cellulose in the first stage to improve the reactivity of the amorphous region.Then,the solid acid Armbyst-40 selectivly hydrolyzes cellulose to produce CNC.The optimal conditions of the ionic liquid swelling treatment are:temperature at 45?,water content of 2.0%,biomass-liquid ratio of 1:20,treatment time of 30 min.Compared to the conventional heating,microwave and ultrasonic heating have better swelling effect,which can reduce swelling time and improve swelling index.The conditions of solid acid hydrolysis are optimized(solid acid dosage based on cellulose of60 wt%,temperature at 60°C,hydrolysis time for 8.0 h).CNC has high yield and crystallinity.Moreover,the ionic liquid and solid acid can be readily recycled and reused for multiple times.Thirdly,the organic acids(oxalic acid and maleic acid)were used to prepare the carboxylated CNC,carboxylic acid groups of the resultant OACNC and MACNC are 0.24 and0.19 mmol/g,respectively;and zeta potentials are-42.1±0.7 m V and-32.7±0.6 m V,respectively.This facilitated functionalization and dispersion in aqueous processing.The prepared CNCs also exhibited excellent properties of high crystallinity and good thermal stability.The hydrolyzed material is pulverized by an ultrafine grinder to obtain nanofiber filaments.Organic acids can be recycled and reused through low-temperature recrystallization,which reduces production costs and reduces the pollution load on the environment.In addition,p-Ts OH/formaldehyde-cellulase system was established to prepare CNC,which can realize the preparation of CNC and CNF.The pretreatment conditions were p-Ts OH concentration of 80 wt%,temperature at 80°C,reaction time for 60 min,and the enzymatic hydrolysis time ranged from 60-72 h.The CNCs were analyzed using XRD,FTIR,AFM and morphology,which showed excellent performances.Finally,nano-cellulose was introduced into polyether polyol to prepare composite polyurethane foam,and the composite foam material was analyzed for dynamic thermodynamics,rheology,infrared,scanning electron microscopy,and compression deformation characteristics.Nano cellulose significantly affects the cell morphology and structure of polyurethane foams.An appropriate amount of nano cellulose facilitates to form a continuous cell wall structure.Excessive dosage of nano cellulose causes cell wall rupture.Nano cellulose can significantly improve the compressive strength and mechanical modulus of polyurethane foam,whereas a high content will cause an increase in the proportion of open cells,resulting in a decrease in the overall compressive strength of the foam.The reasonable size and proportion of nano cellulose play an important role in the optimization of the performance of polyurethane foam.