twin-screw-extrusion-process-to-produce-renewable-fiberboards

Twin-Screw Extrusion Process to Produce Renewable Fiberboards

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pre-treatment on lignocellulosic biomass before using it as ...

Université de Toulouse, INRAE, INPT

Thermoplastic sugar beet pulp (thermo-mechanical processing was discussed in previous studies) was formed into film strips by extrusion. Film tensile properties are discussed according to the molecular structure of external plasticizer. Sorbitol, fructose and adipic acid have a marked antiplasticizing effect, while urea and xylitol gave higher ultimate tensile stress than glycerol for a comparable strain at break. Xylitol can be considered as the best plasticizer with UTS and EL of, respectively, 4.9 MPa and 11.3% and water absorption (85% RH, 25 degrees C) was less than 25%. Glycidyl methacrylate was directly used in the extrusion process as cross-linker. In high humidity atmosphere (97% RH, 25 degrees C), film water absorption was then kept under 40% while tensile strength and strain were improved of 50% and with a 30 min UV post-treatment the mass gain in absorption was even less than 30% after 5 days.

Thermo-mechanical processing of sugar beet pulp. III. Study of extruded films improvement with various plasticizers and cross-linkers.

In this study, five different types of maltodextrins (DE-2, DE-6, DE-12, DE-17 and DE-19) were characterized for the physico-chemical properties. TGA, DVS and SEC analyses were carried out and additionally apparent melt-viscosity (in a micro-extruder) and the glass transition temperature (analyzed by DMA) of maltodextrin/plasticizer mixtures were also measured in order to evaluate both the effect of plasticizer nature and content and the effect of the DE-value. For this, three plasticizing agents were compared: water, d-sorbitol and glycerin. The adsorption isotherms showed that depending on the DE-value and the relative humidity they were exposed to, different behavior could be obtained. For example, for relative humidities below 60% RH maltodextrin DE-2 was the least hygroscopic. And on the contrary for relative humidities above 75% RH maltodextrin DE-2 was the most hygroscopic. The rheology measurements showed that the viscosity decreased with the increase of the DE-value and with the plasticizer content, as expected. On the contrary, no direct correlation could be established between the DE-value and the glass transition temperature. These results demonstrated that to predict maltodextrins behavior and to better adapt the process conditions, combined analyses are mandatory as the DE-value alone is not sufficient. The most compelling evidence was obtained by size exclusion chromatography, which pointed out that maltodextrins had a bimodal molecular weight distribution composed of high and low molecular weight oligo-saccharides. Indeed, maltodextrins are highly polydisperse materials (i.e. polydispersity index ranging from 5 to 12) and that should be the reason why such distinct behaviors were observed in some of the physico-chemical analyses that were preformed. 

Influence of DE-value on the physicochemical properties of maltodextrin for melt extrusion processes.

This work deals with the modifications resulting from the dissolution of four commercial cellulosic samples, with different crystallinity rates and degrees of polymerization (DPs), in four solvent systems, known and used to dissolve cellulose. The dissolution conditions were optimized for the 16 various systems and followed by turbidity measurements. After regeneration, the samples were analyzed by thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray diffractometry (XRD) to study their modification. Viscosimetry measurements were used to evaluate the potential decrease of the DP after dissolution. The observed structural modifications established that, for low DP, all the solvent systems were efficient in dissolving the cellulose without altering the DP, except BMIM [Cl], which provoked a decrease of up to 40 % and a decrease of around 20 % of the degradation temperature (onset temperature, T o). For high molecular weight (MW) celluloses, DMSO/TBAF was the only system to allow a complete dissolution without any molar mass loss and degradation temperature modification.

Structural modifications of cellulose samples after dissolution into various solvent systems.

Commercial α-cellulose was compression-molded to produce 1A dog-bone specimens under various operating conditions without any additive. The resulting agromaterials exhibited a smooth, plastic-like surface, and constituted a suitable target as replacement for plastic materials. Tensile and three-points bending tests were conducted according to ISO standards related to the evaluation of plastic materials. The specimens had strengths comparable to classical petroleum-based thermoplastics. They also exhibited high moduli, which is characteristic of brittle materials. A higher temperature and higher pressure rate produced specimens with higher mechanical properties while low moisture content produced weaker specimens. Generally, the strong specimen had higher specific gravity and lower moisture content. However, some parameters did not follow the general trend e.g., thinner specimen showed much higher Young's Modulus, although their specific gravity and moisture content remained similar to control, revealing a marked skin-effect which was confirmed by SEM observations.

High Pressure Compression-Molding of α-Cellulose and Effects of Operating Conditions.

This paper deals with the use of tetrabutylammonium fluoride/dimethylsulfoxide (TBAF/DMSO) to characterize the molar mass distribution of non-derivatized cellulosic samples by size exclusion chromatography (SEC). Different cellulose samples with various average degree of polymerization (DP) were first solubilized in this solvent system, with increasing TBAF rates, and then analyzed by SEC coupled to a refractive index detector (RID), using DMSO as mobile phase. The Molar Masses (MM) obtained by conventional calibration were then discussed and compared with suppliers' data and MM determined by viscosimetry measurements. By this non-classic method, molar mass of low DP samples (Avicel and cotton fibers) have been determined. For high DP samples (α-cellulose and Vitacel), dissolution with TBAF concentration of 10 mg/mL involved elution of cellulose aggregates in the exclusion volume, related to an incomplete dissolution or the dilution of TBAF molecules in elution solvent, preventing the correct evaluation of their molar mass.

Antoine Rouilly

Laboratoire de Chimie Agro-industrielle (LCA)

Université de Toulouse, INRAE, INPT

Twin-Screw Extrusion Process to Produce Renewable Fiberboards

Antoine Rouilly

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Laboratoire de Chimie Agro-industrielle (LCA)

Université de Toulouse, INRAE, INPT

Twin-Screw Extrusion Process to Produce Renewable Fiberboards

Laboratoire de Chimie Agro-industrielle (LCA)