Preparation Of Microcrystalline Cellulose For Synthetic Leather Form Wheat Straw Decomposed By Pollution-Free Process

The wheat straw stalk is a kind of abundant and renewable bioresources contains rich cellulose, hemicelluloses and lignin, but the value-added utilization of stralk is not enough or there are several serious environmental problems existed in the course of utilization. The belief of value-added utilization process is to decompose cellulose, lignin and hemi-cellulose from wheat straw, and utilize the three compositions respectively or convert them into other chemical products, and pollution-free is the characteristic in the process of separation and utilization.Microcrystalline cellulose (MCC), which has limited polymerization degree, is a high mobility polymer. It was prepared from natural cellulose by diluted acid hydrolysis and subsequent a series of processes. It could be used in the fields of light industry, chemical and daily-use chemical and so on, and it has become a new functional cellulosic material. MCC used in the wet synthetic leather industry was a kind of cellulosic micro-pore agent which could make the products flexible and soft, and the permeability and strength were higher than the dry synthetic leather products. Moreover, MCC as a kind of viscosity controlling agent to smooth coating slurry liquid could make the product properties stable and superior.At present, the main raw materials of MCC for synthetic leather were cotton pulp and wood pulp with high cost. Wheat straw stalk could be one kind of fine fiber resources to prepare and produce microcrystalline cellulose applied for synthetic leather industrially due to the wide varieties and low costs.Preparation of wheat straw stalks MCC for synthetic leather by pollution-free process was discussed in this study. Refining process of ethanol wheat straw pulp and preparation of dissolving pulp from ethanol wheat straw pulp using xylanase enzymatic treatment were discussed briefly, followed by the hydrochloric acid hydrolysis refining process of ethanol wheat straw coarse cellulose, alkali treatment method of reducing the ash content of wheat straw refining cellulose, crushing process of MCC for synthetic leather. The quality, performance indicators and application effects of the final product were analyzed to determine the optimal process route and process parameters.Refining process of ethanol wheat straw pulp through xylanase enzymatic treatment was studied with the purpose of improving a-cellulose content and whiteness. Results showed that it was feasible to degrade the pentosan of refined ethanol bleached wheat straw cellulose only using xylanase. The a-cellulose content could be significantly improved as the increasing of xylanase content. At the same time, the pentosan content could be reduced accordingly. The optimal xylanase dosage was 1.0IU/g, and a-cellulose content of refined cellulose could reach up to 90%. Compared with untreated refined cellulose, the increasing ratio of a-cellulose content could be higher than 7.68%. The pentosan content could be reduced from 9.01%to 5.81%. Whiteness 86.1%ISO and DP 631 could be obtained.Single factor experiment method was adopted to discuss the effect of hydrochloric acid concentration, liquid-solid ratio, hydrolysis time and hydrolysis temperature on the yield, crystallinity, DP and a-cellulose content of MCC. Results showed that the optimal hydrolysis process parameters were:hydrochloric acid concentration 2mol/L, liquid-solid ratio 1:15, hydrolysis temperature 70℃, hydrolysis time 90min. In order to reduce the ash content, the common method alkaline solution was utilized to treat the refined cellulose. The optimal alkaline treatment conditions were:alkali dosage 15%, temperature 80℃, MCC concentration 10%, treatment time 30min. At this point, the ash content of refined cellulose can be reduced to 0.32%, but the whiteness may be slightly decreased. The planetary ball mill grinding was adopted to crush MCC. The optimal crushing time was 100min under the condition of the pellet ratio 1:1. More than 90% of MCC through 320 mesh (particle size corresponding to 45μm) screen was obtained.The quality indicators of the product were in line with MCC for Synthetic Leather Forestry Industry Standards (LY/T1333-1999) released by State Forestry Administration. Using self-made MCC for synthetic leather as the filler, permeability, longitudinal and transverse tensile and tear strength of the wet PU film were better than domestic wood flour for the synthetic leather. Comparative application experiment results showed that other indicators of self-made MCC for synthetic leather reached and even exceeded imported lingo-MCC except the swelling ratio, horizontal tensile load and elongation. And this product had more advantages compared to the domestic high-grade MCC for synthetic leather.