Bonaventura Focher

Alkaline N-deacetylation of chitin enhanced by flash treatments. Reaction kinetics and structure modifications

A new method for N-deacetylation of chitin is proposed in which a polymer almost free of N-acetyl groups is obtained by flash treatment. The reaction is carried out in 40% NaOH solution for 30–270 s at 140–190°C, using saturated steam. Flash treatment was found to proceed faster and with a higher activation energy for the deacetylation reaction (Ea = 36 kcal mol−1) compared with the traditional treatment (Ea = 11 kcal mol−1). X-Ray diffractometry, CP-MAS 13C-NMR and FTIR spectroscopy show that the flash treatment induces structure modifications; in particular, higher crystallinity indexes and specific area values are observed together with changes in the local and chain conformation.

Structural differences between chitin polymorphs and their precipitates from solutions—evidence from CP-MAS 13C-NMR, FT-IR and FT-Raman spectroscopy

Abstract Structural differences between α-chitin from shrimp ( Crangon crangon ) and β-chitin from squid (Loligo), as well as between their precipitated products from N,N-dimethylacetamide-LiCl solutions, are indicated by the CP-MAS 13 C-NMR, FT-IR, FT-Raman spectra and the X-ray diffractograms. The 13 C-NMR spectra in the solid state of α-chitin consisting of eight major resonances suggest a high degree of structural homogeneity. In the spectrum of β-chitin, the C-3 and C-5 signals merged in a single resonance. The bands contour of deconvoluted and curve-fit FT-IR and FT-Raman spectra shows a more detailed structure of α-chitin in the region of OH, NH and CO stretching regions; in particular the Amide I band is split, whereas a single broad band dominates in the corresponding β-form. Precipitation treatments induce a general disorder in α-chitin, while the metastable structure of β-chitin tends toward a more ordered architecture. All the present spectroscopic data of chitin samples are consistent with the corresponding X-ray diffraction patterns.

Chitosans from Euphausia superba. 2: Characterization of solid state structure

Abstract Chitosans from Euphausia superba of different degrees of acetylation (42%, 28% and The X-ray powder patterns indicated a decrease of order with decreasing the degree of acetylation as well as after regeneration and acid treatments. Similarly, the CP-MAS 13C-NMR and FTIR spectra exhibited a general broadening of signals suggesting the occurrence of new conformations for chitosans after regeneration. Furthermore, samples treated with hydrochloric acid showed some structural modifications which accounted for their behaviour in solution as reported in the first part of this study.

Broom fibers as reinforcing materials for polypropylene‐based composites

Broom fibers have been used as reinforcement for the conventional polypro- pylene (iPP) and a maleate modified one (iPPMA). A conventional alkaline treatment and a steam explosion extraction process were applied to obtain the cellulosic material from broom branches. Composites were prepared by melt mixing materials with differ- ent weight percentages of broom fibers. Also ternary blends (iPPMA/iPP/broom fibers 5/45/50 wt) were obtained to examine the possibility of utilizing the maleate polypro- pylene as a compatibilizing agent. The fibers and the composites were thermally, mor- phologically, and mechanically characterized. Water absorption tests, to examine the behavior of these materials in wet conditions, were also performed. Particular attention was addressed to the study of the fiber/matrix interfacial adhesion. The results showed that the iPPMA-based composites, reinforced with alkaline extracted broom fibers, present specific mechanical properties competitive with those of the homologous poly- propylene-based materials reinforced with short glass fibers. The ternary blends gave similar properties to those of the corresponding whole iPPMA-based composites. It is considered that the esteric linkage between the cellulose {OH, and the maleic anhy- dride groups grafted on the polypropylene backbone is greatly responsible for the simi- larity in the properties. In spite of better adhesion observed in the samples reinforced by the steam-exploded fibers, less improvement of the mechanical properties was observed, owing to significant damage of the structure of the fibers during the steam explosion process. A general decrease of mechanical properties is observed in normal polypropyl- ene-based composites. The results are also supported by the water absorption tests: whereby the iPPMA-based composites showed good capability to return their dry prop- erties when kept in an oven after wetting for many days. q 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1077-1089, 1998

Fractionation and bioconversion of steam-exploded wheat straw

Abstract Wheat straw was pretreated by steam explosion under various conditions. The capability of the process in inducing a high fractionation of the lignocellulosic material in its major components and the influence of the explosion conditions on the substrate susceptibility to the attack of cellulolytic enzymes have been investigated. Bioconversion was studied considering the cellulose-rich fraction obtained from product fractionation as well as the product directly obtained from the explosion treatment. Quantitative data in terms of rate and yield of hydrolysis have been obtained for the different conditions.

Chitosans from Euphausia superba. 1: Solution properties

Abstract A technological development of chitosan (copolymer of N -acetylglucosamine and glucosamine) is based on the knowledge of parameters such as composition. types of sequence, chain length and distribution. In addition to the sample source, these factors are related to preparation and purification methods. In this connection the authors examined chitosan samples having the same origin ( Euphausia superba ), but different degrees of acetylation, as well as materials which were subjected to regeneration and beating processes. In addition, the authors prepared chitosan samples of different degrees of polymerization by hydrolysis of commercial chitosan of high degree of acetylation under different pH and temperature conditions. The samples were characterized in 0·1 n CH 3 COOH (HAc) - 0·2 m NaCl by intrinsic viscosity ([η]) and light scattering techniques. The viscometric behaviour of the starting chitosans and of all depolymerization products follows an expected pattern. On the other hand, light scattering shows important differences among samples having identical [η], but obtained under different hydrolysis conditions. A tentative explanation is suggested for the discrepant responses.

Regenerated and graft copolymer fibers from steam‐exploded wheat straw: Characterization and properties

Steam explosion treatment has been proven to effectively induce such marked modifications to the chemical and supramolecular structure of wheat straw cellulose as to make this cellulose a suitable raw for dissolving processes. Regenerated and poly(acrylonitrile) (PAN) and poly(methyl methacrylate) (PMMA) grafted wheat straw fibers obtained on the laboratory scale were characterized by various techniques (X-ray diffraction, cross polarization-magic angle spinning (CP-MAS) 13C nuclear mag-netic resonance and vibrational spectroscopy, scanning electron microscopy, differential scanning calorimetry), and the relationships between the morphological–structural features and physicomechanical and end-use properties have been evidenced.

High-performance gel-permeation chromatography of chitosan samples

Abstract The conformational properties of chitosan, a copolymer of 2-acetamido-2-deoxy- d -glucose and 2-amino-2-deoxy- d -glucose, have been examined both in solution and in the solid state. Little has been reported previously on the determination of molecular weight using high-performance gel-permeation chromatography (HPGPC) and no attempt has been devoted to an examination of molecular weight distribution. An HPGPC method for evaluating the above-mentioned parameters for chitosan samples having different molecular weights and different degrees of acetylation was therefore developed. Calibration using sodium polystyrene sulfonate commercial standards of narrow molecular weight distribution could not be carried out in the solvent system used for chitosan. Calibration was therefore performed by means of chitosan samples obtained by depolymerization.

Steam exploded biomass for the preparation of conventional and advanced biopolymer-based materials

Abstract Lignocellulosic materials treated by the steam explosion technique alone, or in the presence of chemical reagents, undergo remarkable modifications at the level of both the chemical composition and supramolecular structure, developing features suitable for the production of conventional and advanced materials with improved properties. Experience in the production of high yield pulps, composite materials with microbial (PHB) and synthetic (polypropylene) thermoplastic matrices and high modulus lignocellulosic fibers is reported.

β-d-Galactosidases immobilized on soluble matrices: Kinetics and stability

Abstract Three β- d -galactosidases (β- d -galactoside galactohydrolase, EC 3.2.1.23) from different origins have been immobilized on sucrose-polyacrolein and sucrose sulphate-polyacrolein. This gave enzyme conjugates insoluble in the immobilization medium but which could be made soluble by reduction with sodium borohydride before use. The optimum conditions for both copolymer synthesis and the immobilization reaction were investigated. I.r. and 13 C n.m.r. spectroscopy were used to follow the sulphation and the copolymerization reaction. The characteristics of the enzyme conjugates were compared with those of the free enzymes: the V max values of the enzyme conjugates were lower than those of the corresponding free enzymes, whilst the K m values were similar. The thermal stability of the enzyme conjugates depended on the enzyme origin, while their pH stability was in all cases higher than that of the free enzymes. These data suggest some advantages in using enzyme immobilization supports which can be made soluble after separation of the immobilized enzyme without altering the enzyme characteristics .