The effect of liquid anhydrous ammonia in the structure and morphology of cotton cellulose

Preparation of cellulose-based fluorescent carbon nanoparticles and their application in trace detection of Pb(ii)

Nanocrystalline cellulose (NCC) with a particle size of 23.80 ± 0.33 nm was prepared from microcrystalline cellulose by a mixed treatment with acids and ultrasound.

Effects of alkaline or liquid-ammonia treatment on crystalline cellulose: changes in crystalline structure and effects on enzymatic digestibility

BACKGROUND

In converting biomass to bioethanol, pretreatment is a key step intended to render cellulose more amenable and accessible to cellulase enzymes and thus increase glucose yields. In this study, four cellulose samples with different degrees of polymerization and crystallinity indexes were subjected to aqueous sodium hydroxide and anhydrous liquid ammonia treatments. The effects of the treatments on cellulose crystalline structure were studied, in addition to the effects on the digestibility of the celluloses by a cellulase complex.

RESULTS

From X-ray diffractograms and nuclear magnetic resonance spectra, it was revealed that treatment with liquid ammonia produced the cellulose IIII allomorph; however, crystallinity depended on treatment conditions. Treatment at a low temperature (25°C) resulted in a less crystalline product, whereas treatment at elevated temperatures (130°C or 140°C) gave a more crystalline product. Treatment of cellulose I with aqueous sodium hydroxide (16.5 percent by weight) resulted in formation of cellulose II, but also produced a much less crystalline cellulose. The relative digestibilities of the different cellulose allomorphs were tested by exposing the treated and untreated cellulose samples to a commercial enzyme mixture (Genencor-Danisco; GC 220). The digestibility results showed that the starting cellulose I samples were the least digestible (except for corn stover cellulose, which had a high amorphous content). Treatment with sodium hydroxide produced the most digestible cellulose, followed by treatment with liquid ammonia at a low temperature. Factor analysis indicated that initial rates of digestion (up to 24 hours) were most strongly correlated with amorphous content. Correlation of allomorph type with digestibility was weak, but was strongest with cellulose conversion at later times. The cellulose IIII samples produced at higher temperatures had comparable crystallinities to the initial cellulose I samples, but achieved higher levels of cellulose conversion, at longer digestion times.

CONCLUSIONS

Earlier studies have focused on determining which cellulose allomorph is the most digestible. In this study we have found that the chemical treatments to produce different allomorphs also changed the crystallinity of the cellulose, and this had a significant effect on the digestibility of the substrate. When determining the relative digestibilities of different cellulose allomorphs it is essential to also consider the relative crystallinities of the celluloses being tested.

Activation of crystalline cellulose to cellulose IIII results in efficient hydrolysis by cellobiohydrolase

The crystalline polymorphic form of cellulose (cellulose I(alpha)-rich) of the green alga, Cladophora, was converted into cellulose III(I) and I(beta) by supercritical ammonium and hydrothermal treatments, respectively, and the hydrolytic rate and the adsorption of Trichoderma viride cellobiohydrolase I (Cel7A) on these products were evaluated by a novel analysis based on the surface density of the enzyme. Cellobiose production from cellulose III(I) was more than 5 times higher than that from cellulose I. However, the amount of enzyme adsorbed on cellulose III(I) was less than twice that on cellulose I, and the specific activity of the adsorbed enzyme for cellulose III(I) was more than 3 times higher than that for cellulose I. When cellulose III(I) was converted into cellulose I(beta) by hydrothermal treatment, cellobiose production was dramatically decreased, although no significant change was observed in enzyme adsorption. This clearly indicates that the enhanced hydrolysis of cellulose III(I) is related to the structure of the crystalline polymorph. Thus, supercritical ammonium treatment activates crystalline cellulose for hydrolysis by cellobiohydrolase.

Pretreatment of corn stover by aqueous ammonia

Corn stover was pretreated with aqueous ammonia in a flow-through column reactor, a process termed ammonia recycled percolation (ARP). This method was highly effective in delignifying of the biomass, reducing the lignin content by 70-85%. Most lignin removal occurred within the first 20 min of the process. Lignin removal by ARP was further confirmed by FTIR analysis and lignin staining. The ARP process solubilized 40-60% of the hemicellulose but left the cellulose intact. The solubilized carbohydrate existed in oligomeric form. Carbohydrate decomposition during the pretreatment was insignificant. Corn stover treated for 90 min exhibited enzymatic digestibility of 99% with 60 FPU/g of glucan enzyme loading, and 92.5% with 10 FPU/g of glucan. The digestibility of ARP treated corn stover was substantially higher than that of alpha-cellulose. The enzymatic digestibility was related with the removal of lignin and hemicellulose, perhaps due to increased surface area and porosity. The SEM pictures indicated that the biomass structure was deformed and its fibers exposed by the pretreatment. The crystallinity index increased with pretreatment reflecting removal of the amorphous portion of biomass. The crystalline structure of the cellulose in the biomass, however, was not changed by the ARP treatment.

Structural data on the intra-crystalline swelling of beta-chitin

The intra-crystalline swelling of the highly crystalline beta-chitin from Tevnia jerichonana was investigated by X-ray crystallography and Fourier transform infrared (FTIR) spectroscopy, using hydrogenated and deuterated hydrochloric acids as swelling agents. Three levels of swelling were identified that could be defined as inter- and intra-sheet swelling. A moderate and reversible swelling in water and methanol gave crystalline beta-chitin cystallosolvates, namely dihydrate and methanolate, respectively. In these, an inter-sheet swelling was observed, corresponding to an expansion of only the b parameter of the unit cell of beta-chitin. Under these swelling conditions, the use of deuterated reagents had no effect on the amide N&z.sbnd;H⋯O&z.dbnd6;C hydrogen bonds that hold the structure of beta-chitin together, but only induced a partial and reversible deuteration of the chitin hydroxymethyl groups. A more severe swelling - but still reversible - occurred with 6 N HCl or DCl, which converted the crystals of beta-chitin into a paracrystalline gel-like product resulting from inter-sheet+intra-sheet swelling. With this acid strength, the deuteration pattern indicated that a fraction of the amide hydrogen bonds was broken and became susceptible to an irreversible deuteration. A very severe and irreversible swelling occurred with 8 N HCl or DCl. In that case, the inter- and intra-sheet swelling was extensive to the point where all memory of the parallel-chain beta-chitin was lost. In addition, this swelling was accompanied by a drastic and rapid depolymerization. The treatment with 8 N HCl led invariably to crystalline alpha-chitin when the samples were neutralized.