A. Arbelaiz

Effects of fibre treatment on wettability and mechanical behaviour of flax/polypropylene composites

Abstract Chemical treatment of natural reinforcements can enhance their adhesion to polymer matrices. This work reports the effects of different treatments on the fibre–matrix compatibility in terms of surface energy and mechanical properties of composites. The composites were compounded with two kinds of flax fibres (natural flax and flax pulp) and polypropylene. The applied treatments were maleic anhydride (MA), maleic anhydride-polypropylene copolymer (MAPP) and vinyl trimethoxy silane (VTMO). The treatment effects on the fibres have been characterised by Infrared Spectroscopy. Two techniques have been used to determine the surface energy values: the Dynamic Contact Angle method for the long flax fibres and the Capillary Rise method for the irregular pulps. The use of different methods involves a small discordance in the wettability values. Nevertheless, the three treatments reduce the polar component of the surface energy of the fibre. Composites containing MAPP-treated did the highest mechanical properties, whilst the MA and VTMO-treated fibre gave similar values to that for the untreated ones.

Mechanical behavior of wood/polypropylene composites: Effects of fibre treatments and ageing processes

Practical applications of wood based composites are limited by the hydrophilic nature of cellulose, which causes dispersion and moisture absorption problems. This work rests on the effects of wood treatment on the mechanical properties of composites made with wood flour and polypropylene (WF/PP). Two different fiber treatments (mercerization with a 10% NaOH solution and functionalization with Epolene E-43 MAPP copolymer), their combined action, and two compounding methods have been studied. In addition, the investigation includes the analysis of the mechanical behavior of composites after exposure to variable conditions of temperature and moisture.

Cellulose nanocrystals reinforced environmentally-friendly waterborne polyurethane nanocomposites

Focusing on eco-friendly materials, cellulose nanocrystals (CNC) have gained attention as nanoreinforcement due to their exceptional properties conferred by the elevated length/diameter aspect ratio and high specific mechanical properties. Furthermore, their water dispersibility makes them suitable nanoreinforcements for their incorporation in waterborne polyurethanes (WBPU). The possibility of tailoring the properties by varying the composition and nature of the reagents, opens the opportunity for a wide range of applications. Therefore, in this work a WBPU was synthesized for the preparation of nanocomposite films with different CNC content and the properties of the films were analyzed. The effective incorporation of CNC resulted in an increase in moduli and stress at yield besides in an increased thermomechanical stability, reaching the percolation threshold at a 3wt% CNC as determined theoretically. Nevertheless, above the percolation threshold, the presence of agglomerates reduced slightly these values. The prepared nanocomposites showed increased hydrophilicity after CNC addition.

Functional properties and in vitro antioxidant and antibacterial effectiveness of pigskin gelatin films incorporated with hydrolysable chestnut tannin.

The impact of the incorporation of 10% w/w of hydrolyzable chestnut tannin into pigskin gelatin (G) films plasticized with glycerol (Gly) on the physicochemical properties as well as the in vitro antioxidant and antibacterial effectiveness against food-borne pathogens such as Escherichia coli and Streptococcus aureus was investigated. A higher tendency to both redness (a*) and yellowness (b*) coloration characterized gelatin films incorporated with chestnut tannin. The reduced lightness (L) and transparency of gelatin–chestnut tannin films plasticized with 30% w/w Gly might be associated with certain degree of phase separation which provoked the migration of the plasticizer to the film surface. The incorporation of chestnut tannin and glycerol affected the chemical structure of the resultant films due to the establishment of hydrogen interactions between components as revealed by Fourier transform infrared spectroscopy. These interactions reduced gelatin crystallinity and seemed to be involved in the substantial decrease of the water uptake of films with tannin, irrespective of the glycerol level. Such interactions had minor effect on tensile properties being similar to those of the control films (without chestnut tannin) at the same glycerol level. Films modified with 10% w/w chestnut tannin showed significant (P < 0.05) 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity, ca. from 0 ± 0.033 to 87.1 ± 0.002% for chestnut tannin-free and chestnut tannin-containing gelatin films. The limited inhibitory activity of films incorporated with 10% w/w chestnut tannin against the selected bacteria evidenced by disk diffusion method probably resulted from the interactions within the film restricting the diffusion of the active agent into the agar medium. The more modest protective effect observed against a Gram-positive bacterium (S. aureus) was also discussed.

Bionanocomposites based on thermoplastic starch and cellulose nanofibers

The goals of this work are to obtain thermoplastic starch (TPS) with different glycerol/water ratios, verify its characterization by different techniques, and study the influence of addition of cellulose nanofibers in the matrix of TPS. The general procedure for processing starchy materials involves granular alteration with the combination of temperature, shear, and plasticizers. Distilled water and glycerol are used as plasticizers, and the influence of both of them has been studied in tensile properties. By infrared spectroscopy analysis, the addition of plasticizers created new physical links (hydrogen bonds) with starch molecules thereby shifting the characteristic peaks of native corn starch to higher wave number. The most suitable composition for the elaboration of bionanocomposites has been determined and bionanocomposites with different content of cellulose nanofibers have been obtained and their mechanical properties have been studied.

Water Uptake Behavior and Young Modulus Prediction of Composites Based on Treated Sisal Fibers and Poly(Lactic Acid)

The main aim of this work was to study the effect of sisal fiber surface treatments on water uptake behavior of composites based on untreated and treated fibers. For this purpose, sisal fibers were treated with different chemical treatments. All surface treatments delayed the water absorption of fibers only for a short time of period. No significant differences were observed in water uptake profiles of composites based on fibers with different surface treatments. After water uptake period, tensile strength and Young modulus values of sisal fiber/poly(lactic acid) (PLA) composites were decreased. On the other hand, composites based on NaOH + silane treated fibers showed the lowest diffusion coefficient values, suggesting that this treatment seemed to be the most effective treatment to reduce water diffusion rate into the composites. Finally, Young modulus values of composites, before water uptake period, were predicted using different micromechanical models and were compared with experimental data.

Testing the effect of processing and surface treatment on the interfacial adhesion of single fibres in natural fibre composites

Abstract: The main methods for mechanical characterization of the single fibre–polymer matrix interfacial adhesion are described: fibre pull-out, single fibre fragmentation and microdebonding tests. The basis of each method, assumptions and main advantages and drawbacks are discussed. A review of lignocellulosic polymer fibre–matrix interface adhesion data is presented. The effect of different surface treatments and also the effect of different processing parameters are also shown.

Effect of Diisocyanate Structure on Thermal Properties and Microstructure of Polyurethanes Based on Polyols Derived from Renewable Resources

Polyols derived from renewables resources are good candidates to obtaining segmented polyurethane elastomers. Diisocyanates with different chemical structure, aliphatic and aromatic, have been used to synthesize by a two step polymerization procedure polyurethane elastomers with different hard segment content. Microphase separation and thermal stability have been studied using attenuated total reflection Fourier transform infrared spectroscopy (ATR‐FTIR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The analysis of the H‐bonded and non H‐bonded urethane carbonyl stretching vibration in the amide I region, the glass transition temperature of the soft and hard segments and the melting temperature and enthalpies of hard segment reveal that aliphatic diisocyanate based polyurethanes present higher phase separation degree and harder segment crystallinity and also superior thermal stability than aromatic diisocyanate‐based polyurethanes.

Pretreatments of Natural Fibers for Polymer Composite Materials

The use of lignocellulosic fibers as reinforcement in polymer composites is attracting interest due to their properties such as mechanical properties and environmental benefits. Nevertheless, the hydrophilic character of lignocellulosic fibers reduces the compatibility with the hydrophobic matrices resulting in composites with poor mechanical properties. Therefore, in order to reduce the hydrophilic character of fiber and improve the fiber/matrix adhesion, is necessary to modify the fiber surface morphology. In this chapter, different lignocellulosic fiber treatments and the effect of these treatments on fiber properties as well as on composite mechanical performance were discussed. Even though chemical treatments are the most widely used, physical and biological treatments are environmentally friendly and promising alternatives.

Nanostructured Composite Materials Reinforced With Nature-based Nanocellulose

A better understanding of the relation between structure and function of cellulose-based hierarchical materials could provide the opportunity for developing new multi-functional composite materials and for designing nanostructured materials structurally optimised, using biodegradable renewable reinforcing materials. In this paper, recent advances by the authors’ research group in the study of nanocomposites, reinforced with natural nanocellulose from both vegetal and bacterial sources, are presented. The extraction process of cellulose nanofibres and nanocrystals as well as the composite manufacturing process are detailed. Two composite systems are considered: one based on vegetal cellulose nanocrystals and another based on bacterial cellulose nanofibres. The presented results concern the morphology, thermal behaviour, mechanical properties and optical performance of those hierarchical nanocomposites.