Francesc Ferrando

Suitability of steam exploded residual softwood for the production of binderless panels. Effect of the pre-treatment severity and lignin addition

Abstract A steam explosion pre-treatment was applied at various severities to softwood residual substrate to determine the most suitable pre-treatment for the manufacture of binderless panels. The effect of adding acid to the pre-treatment of fibres was also evaluated. The changes in the chemical composition and morphology of the original material were investigated by fractionation analyses and scanning electron micrographs. High severities caused defibrillation of the material allowing to build links to form the panels. Prehydrolysis with acid had a great effect on the structure of the material even at low acid concentration. The physical and mechanical properties of the panel improved as the severity of the pre-treatment increased up to a point where mechanical properties deteriorated. The composites with highest internal bond had a high cellulose content and a medium lignin content. All these factors suggested that steamed pre-treated residual could be improved by adding a natural binder to produce the panels. A test of producing panels with addition of several kinds of lignin (up to 20%) was performed. With no significant changes in density, water stability (thickness swelling and water absorption) internal bond and mechanical properties were greatly improved. Results after accelerated ageing test were also enhanced.

Binderless composites from pretreated residual softwood

Residual softwood was thermomechanically pretreated and used to produce composites with no synthetic binders. The lignocellulosic material was steam exploded with a thermomechanical aqueous vapor process in a continuous tubular reactor. The study attempts to use the intrinsic bonding capacity of the steamed fiber, which is due to the plastification of the lignin. Chemical and structural changes in the pretreated substrate were evaluated by analytical characterization and scanning electron micrographs (SEM). The effect of the pressing conditions was evaluated in accordance with the physicomechanical responses of the composites. The physical and mechanical properties of the panels obtained were tested using UNE EN Spanish standard-European standards. In order to get more information about the degree of adhesion between the lignin and the fibers, SEM micrographs were taken of the broken surfaces of the material tested by the internal bond method. The results show that the thermomechanical pretreatment, pressing temperature, and time have a great effect on the mechanical and physical properties of binderless composites. The steam explosion aqueous vapor pretreatment is a good way for conditioning softwood sawdust for production of composites.

Binderless fiberboard from steam exploded Miscanthus sinensis: The effect of a grinding process

Miscanthus sinensis was thermomechanically pretreated and used to produce fiberboard with no synthetic binders. The lignocellulosic material was steam exploded using an aqueous vapor process in a batch reactor. Part of the resultant pulp was ground to pass through a 4-mm sieve. The effect of the grinding on the physicomechanical responses of the fiberboard was evaluated. ANOVA methodology was used. The boards obtained with the ground pulp were of better quality that those obtained with the non-ground pulp. The milling process considerably improved the internal bond strength and diminished the density of the board. The other measured properties (MOE, MOR, WA and TS) were not significantly affected by the process. Scanning electron micrographs show that the changes are due to the segregation of packages of fibers and not to the cut of the fibers. This segregation increases the inter-fiber bonding area.Miscanthus sinensis wurde thermomechanisch vorbehandelt und für Faserplatten ohne synthetische Kleber verwendet. Die Dampfexplosion erfolgte mit Wasserdampf in einem Trommelreaktor. Ein Teil des so gewonnenen Zellstoffes wurde gemahlen bis er durch ein 4-mm-Sieb paßte. Der Einfluß des Mahlens auf die pysikalisch-mechanischen Eigenschaften wurde verfolgt. Dabec wurde die ANOVA-Methode benutzt. Die Platten aus gemahlenem Zellstoff waren von besserer Qualität als die aus nicht gemahlenem. Insbesondere wurde die Querzugfestigkeit erhöht und die Dichte vermindert. Die übrigen gemessenen Parameter (MOE, MOR, WA und TS) wurden durch den Mahlprozeß nicht signifikant beeinflußt. Aufnahmen mit dem Rasterelektronenmikroskop zeigen, daß die Verbesserungen auf die Auflösung von Faserbündeln zurückzuführen ist und nicht auf gebrochene Fasern. Die fein zerteilten Faserbündel erhöhen die innere Oberfläche für die Faser-Faser-Bindung.

A New Epoxy-Based Layered Silicate Nanocomposite Using a Hyperbranched Polymer: Study of the Curing Reaction and Nanostructure Development

Polymer layered silicate (PLS) nanocomposites have been prepared with diglycidyl ether of bisphenol-A (DGEBA) epoxy resin as the matrix and organically modified montmorillonite (MMT) as the clay nanofiller. Resin-clay mixtures with different clay contents (zero, two, five and 10 wt%) were cured, both isothermally andnon-isothermally, using a poly(ethyleneimine) hyperbranched polymer (HBP), the cure kinetics being monitored by differential scanning calorimetry (DSC). The nanostructure of the cured nanocomposites was characterized by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), and their mechanical properties were determined by dynamic mechanical analysis (DMA) and impact testing. The results are compared with an earlier study of the structure and properties of the same DGEBA-MMT system cured with a polyoxypropylene diamine, Jeffamine. There are very few examples of the use of HBP as a curing agent in epoxy PLS nanocomposites; here, it is found to enhance significantly the degree of exfoliation of these nanocomposites compared with those cured with Jeffamine, with a corresponding enhancement in the impact energy for nanocomposites with the low clay content of 2 wt%. These changes are attributed to the different cure kinetics with the HBP, in which the intra-gallery homopolymerization reaction is accelerated, such that it occurs before the bulk cross-linking reaction.

Influence of Holding Time on Shape Recovery in a Polyurethane Shape-Memory Polymer

Shape-memory polymers have attracted a lot of interest in recent years. A shape-memory polymer can be deformed and fixed into a temporary shape and subsequently made to recover its original shape when a suitable stimulus is applied. This is accomplished by means of a thermomechanical cycle called programming. Programming can be performed in a stress- or strain-controlled mode. The thermomechanical conditions of the programming affect shape-memory properties differently in each programming mode. One of the parameters which significantly affects shape-memory properties in a stress-controlled procedure is stress-holding time (tH) at high temperature. This paper studies how stress-holding time affects the most significant shape-memory properties under successive thermomechanical cycles. The experiments were conducted using two different programming temperatures in the vicinity of the Tg. The shape-recovery ratio decreased dramatically with cycling even when the holding time was just a few seconds, however, the impact of the stress-holding time depends on the temperature at which it has been applied. Shape-fixity ratio and switching temperature were also studied, but stress-holding time and successive cycles do not seem to affect either of these factors.

Cynara cardunculus as Raw Material for the Production of Binderless Fiberboards: Optimization of Pretreatment and Pressing Conditions

Abstract Cynara cardunculus was pretreated and used to produce fiberboards without synthetic adhesives. The lignocellulosic material was steam exploded through a thermo-mechanical vapor process in a batch reactor. After pretreatment the material was dried, ground, and pressed to produce the boards. The effects of pretreatment factors and pressing conditions on the chemical and physico-mechanical properties of the fiberboards were evaluated and the conditions that optimize these properties were found. Response surface methodology based on a central composite design and multiple response optimization were used. The variables studied and their respective variation ranges were: pretreatment temperature, 160–240°C; pretreatment time 2.5–12.5 min; pressing temperature, 190–230°C; initial and final pressing pressures, 4–20 MPa, and initial and final pressing times, 1–9 min. Good properties were obtained at optimum conditions found (modulus of elasticity up to 5970 MPa, modulus of rupture up to 59 MPa, internal bond up to 0.8 MPa, thickness swelling as low as13.5%, and water absorption as low as 18.5%). Some of the boards fully satisfy the standard specifications although they were not produced at the optimum combination of process factors. Optimum operational conditions for producing binderless fiberboards from Cynara cardunculus that fully satisfy the European standards were found based on multiple response optimization methodology.

New Epoxy-Anhydride Thermosets Modified with Multiarm Stars with Hyperbranched Polyester Cores and Poly(ϵ-caprolactone) Arms

Multiarm star polymers with hyperbranched aromatic or aromatic-aliphatic cores and poly(ϵ-caprolactone) arms have been used as toughness modifiers in epoxy-anhydride formulations catalyzed by benzyldimethylamine. The curing process has been studied by dynamic scanning calorimetry, demonstrating little influence of the mobility of the reactive species and the hydroxyl content on the kinetics of this process. The obtained materials were characterized by thermal and mechanical tests and the microstructure by electron microscopy. Homogeneous thermosets have been obtained with a remarkable increase in impact strength without compromising glass transition temperature, thermal stability or hardness.

Comparison of the Nanostructure and Mechanical Performance of Highly Exfoliated Epoxy-Clay Nanocomposites Prepared by Three Different Protocols

Three different protocols for the preparation of polymer layered silicate nanocomposites based upon a tri-functional epoxy resin, triglycidyl para-amino phenol (TGAP), have been compared in respect of the cure kinetics, the nanostructure and their mechanical properties. The three preparation procedures involve 2 wt% and 5 wt% of organically modified montmorillonite (MMT), and are: isothermal cure at selected temperatures; pre-conditioning of the resin-clay mixture before isothermal cure; incorporation of an initiator of cationic homopolymerisation, a boron tri-fluoride methyl amine complex, BF3·MEA, within the clay galleries. It was found that features of the cure kinetics and of the nanostructure correlate with the measured impact strength of the cured nanocomposites, which increases as the degree of exfoliation of the MMT is improved. The best protocol for toughening the TGAP/MMT nanocomposites is by the incorporation of 1 wt% BF3·MEA into the clay galleries of nanocomposites containing 2 wt% MMT.

Axial Force Test and Modelling of the V-Belt Continuously Variable Transmission for Mopeds

This article discusses the experiments and modelling carried out on a V-belt continuously variable transmission (CVT) of the type that is used in mopeds. Our aim was to characterize the forces which determine how the system functions. A test bench was designed for them to be determined experimentally and a series of tests which cover the variable conditions of speed, torque, transmission ratio and tension of a CVT are carried out. Estimates of the principal existing models are compared and an empirical model for assessing these forces is discussed.

Effect of Different Shape-Memory Processing Methods on the Thermomechanical Cyclic Properties of a Shape-Memory Polyurethane

Shape-memory polymers are materials that are capable of changing their shape when an external stimulus is applied. This effect is called the shape-memory effect (SME) and takes place by means of a thermomechanical cycle called programming. The SME depends on the thermomechanical conditions at which programming is performed, and the influence of these conditions differs depending on whether the programming is performed with a strain- or stress-controlled protocol. This study focuses on finding the thermomechanical cycling conditions in stress-controlled programming (Tprog and σm) that stabilize the material in the fewest cycles while obtaining the best mechanical and shape-memory properties over the highest number of cycles. Using a Tprog above or below, the glass transition temperature makes a big difference in terms of shape recovery and the maximum stress is a key factor in the stabilization of shape-memory properties.