Georgeta Cazacu

Lignin/epoxy composites

Abstract This paper presents some possibilities for the use of lignin/epoxy resins in blends and composites with epoxy resins. A compatibility study was carried out by optical and electron microscopy, viscosimetric determinations and thermo-optical analysis in order to establish optimum synthesis conditions of molding mass (cast resins). Lignin/epoxy composites including various fillers (lead soap, alum earth, talc, chalk, sand, trihydrate aluminium oxide, glass fibers), plasticizer (dibutylphthalate and polyester C6) and pigments (iron-oxide and titanium dioxide) have been obtained. Lignin/epoxy composites are characterized by good dielectric, mechanical and adhesive properties. These composite materials can be used in the electronics industry.

Semi-interpenetrating Polymer Networks Containing Polysaccharides. I Xanthan/Lignin Networks

The polysaccharides are important materials in food, pharmaceutical, cosmetic and related biomedical applications. Xanthan gum is a microbial polysaccharide of great commercial significance. It is well known as one of the best thickening polymers due to its high intrinsic stiffness related to the helical conformation stabilized in the presence of excess salt. It is used in a wide variety of foods for a number of important reasons, including emulsion stabilization, temperature stability, compatibility with food ingredients, and its pseudoplastic rheological properties. Due to its properties in thickening aqueous solutions, as a dispersing agent, and stabilizer of emulsions and suspensions, xanthan gum is used in pharmaceutical formulations, cosmetics, and agricultural products, as well as in textile printing pastes, ceramic glazes, slurry explosive formulations, and rust removers. In this work the crosslinking of a mixture of xanthan and lignins in the presence of the epichlorohydrin, leading to superabsorbant hydrogels with high swelling rate in aqueous mediums, was studied. The swelling properties of these composite hydrogels were investigated. Three different types of lignin have been used namely: aspen wood lignin (L), annual fiber crop lignin (GL) and lignin epoxy-modified resin (LER). Semi-interpenetrating polymer network hydrogels in various ratios were prepared. The influence of gravimetric ratio between components of the semi-interpenetrating polymer networks, as well as the kinetics of water sorption will be discussed. The maximum swelling degree of the hydrogels and the swelling rate constant were determined as a function of the hydrogels composition. It has been established that the nature of lignin significantly influences swelling process, the chemical modified lignin having a particular behavior.

Polyester/lignosulfonate blends with enhanced properties

The compatibility of poly(ethylene terephthalate) and its copolymer containing isophthalate units with epoxy-modified lignin has been studied. The following methods have been used: DSC, thermogravimetry, IR spectroscopy, contact angle measurements and dielectric properties determination. The optimum compatibility ratios and the necessity of a partial crosslinking with 4,4′-diaminodiphenylmethane to obtain a stable morphology have been established. Die Vertraglichkeit von Polyethylenterephthalat und des Copolymeren mit Isophthalsaureeinheiten mit epoxy-modifiziertem Lignin wurde mittels DSC, Thermogravimetrie, IR-Spektroskopie, Kontaktwinkelmessungen und der Bestimmung dielektrischer Eigenschaften untersucht. Das optimale Vertraglichkeitsverhaltnis wurde ermittelt, und die Notwendigkeit der teilweisen Vernetzung mit 4,4′-Diaminodiphenylmethan wurde festgestellt.

Polyester/lignosulfonate blends, 2. Accelerated aging behavior

The behavior of the poly(ethylene terephthalate)-co-(ethylene isophthalate)] copolymer/epoxy-modified lignosulfonate (LER) blends has been studied during aging, in the conditions of sewage sludge test. The bulk and surface properties of the aged blends have been followed by electron microscopy, DSC, TG/DTG, IR spectroscopy and contact angle measurements, and compared with undegraded samples. It has been established that the UV-irradiated blends undergo more important changes in their properties after aging than the unirradiated samples. The physical treatment and increase of LER content in the blend could be a way to obtain materials with a good balance of properties and environmental degradation.

Alginate/Lignosulfonate Blends with Photoprotective and Antioxidant Properties for Active Packaging Applications

Sodium alginate/ammonium lignosulfonate blend solutions and thin films with different compositions have been prepared and studied. The rheology of the film forming solutions was comparatively evaluated and was established the effect of lignosulfonate incorporation onto sodium alginate solution properties and partial compatibility of components was found. The shear-thinning behaviour of the ALG/LS solutions was better evidenced at high ALG content, suggesting that the time required for the reorganization of the network structure is longer for the samples containing predominantly ALG, because its structure is damaged by increasing shear rate. The structural, morphological, optical and antioxidant properties of the crosslinked ALG/LS blend films were investigated with the aim to identify their potential as new active materials with photoprotective and antioxidant properties. The ATR-FTIR spectroscopy revealed the hydrogen bonding interactions between the components and scanning electron microscopy showed the modified microstructure of the blend films depending on composition. The surface topography changes have been evidenced by atomic force microscopy, showing an increased average surface roughness when the increasing lignosulfonate amount was incorporated into ALG matrix. The optical properties measurements revealed the light barrier properties of the blend films and the antioxidant activity evaluation showed the enhanced radical scavenging activity of the films with higher lignosulfonate content.

Environmentally Friendly Polylactic Acid/Modified Lignosulfonate Biocomposites

Ammonium lignosulfonate was modified with carboxylic acids (lactic, oleic) and butyrolactone by physical non-polluting radio frequency cold plasma method. Modified lignosulfonates/polylactic acid (PLA)-based biocomposites with enhanced dielectric and thermal properties have been prepared by melt mixing technique. Some modified lignosulfonates improved processability and rheological properties of PLA. A homogeneous dispersion of lignosulfonates in PLA matrix assures the improvement of hydrophilicity, dielectric, rheological properties and thermal performance of the PLA polymer as they act as nucleating agents increasing crystallinity degree. The dielectric characteristics followed in a large frequency and temperature range. Relaxation transitions and their activation energies were found to be dependent on modified lignosulfonate type incorporated in biocomposites. As PLA is recognized by its biodegradability and the composites containing modified lignosulfonates disintegrate by bio- and environmental degradation even they are incorporated in much resistant matrices as polyolefins, it can supposed that such biocomposites could be considered as medium term degradable ones. Increasing modified lignosulfonates content environmental disintegration period could be shorten.

New Green Hydrogels Based on Lignin

The development of various green materials from lignin, which is most often considered as waste, is of prime interest from environmental and economic points of view. In the last years, only few studies regarding the use of lignin as a backbone component in the hydrogels have been made. The potential efficacy of lignin in hydrogels with particular emphasis on synthesis and characterization was investigated. By using steam explosion lignin from aspen wood or the corresponding epoxy-resin mixed with poly(vinyl alcohol), a series of new green hydrogels were prepared by covalent crosslinking in the presence of the epichlorohydrin. The unmodified and modified lignins were characterized by determination of functional groups content (OHT, OHph, OCH3 and epoxy groups), average particle size and zeta potential. The intermolecular interactions between lignin and poly(vinyl alcohol) was evaluated by Fourier transform infrared spectroscopy (FTIR), when the achievement of the cross-linking reaction was proved. The structural features of lignin-based hydrogels were revealed by X-ray diffraction (XRD) analysis. The scanning electron microscopy (SEM) images showed the porous nature of the hydrogels and that the pore size increase with increasing the lignin content. The yield in hydrogel showed a dependence on the structure of the lignins. In addition, it has been established that the lignin nature significantly influences the swelling process of hydrogels.

Influence of the polyethyleneglycol content on the properties of ethyleneglycolterephthalate/ polyethyleneglycol terephthalate copolymers

The effect of the polyethyleneglycol (PEG) content on the properties of the ethyleneglycol terephthalate (EGT)/polyethyleneglycol terephthalate (PEGT) copolymers has been studied. The PEG content varied over a wide range (5-70% PEG). To obtain information on the solubility and on the thermal properties, the following methods: turbidimetry, differential scanning calorimetry (DSC), thermogravimetry and differential thermogravimetry (TG, DTG) have been used. The turbidimetric characteristics are dependent on composition copolymers. The incorporation of increasing amount of PEG 4000 in EGT/PEGT copolymers has a pronounced effect on the properties: increases viscosity and solubility of copolymers, decreased glass transition, cold crystallization and melting temperatures and also decreased crystallization and melting heat. These changes are desirable for better processing of these copolymers comparatively with PET in products with higher elasticity and hydrophilicity. It must be take into account, however, that above 20 wt% PEG the copolymers the thermal stability is significantly affected.