P. Guerrero

Functional properties of chitosan-based films.

Chitosan-based films plasticized with glycerol were prepared by casting with the aim to obtain environmentally friendly materials for packaging applications. Different contents of glycerol were incorporated into chitosan solutions to improve mechanical properties and all films obtained were flexible and transparent. It was observed that the transparency and good behaviour of the films against UV radiation were not affected by chitosan molecular weight or glycerol content. Moreover, chitosan-based films exhibited excellent barrier properties against water vapour and oxygen, even with the addition of glycerol. The effect of the plasticizer on the properties has been explained using Fourier transform infrared (FTIR) spectroscopic analysis. The changes observed in the intensity of the bands showed that glycerol interacts with chitosan, which could be confirmed by total soluble matter (TSM).

Chitosan as a bioactive polymer: Processing, properties and applications

Chitin is one of the most abundant natural polysaccharides in the world and it is mainly used for the production of chitosan by a deacetylation process. Chitosan is a bioactive polymer with a wide variety of applications due to its functional properties such as antibacterial activity, non-toxicity, ease of modification, and biodegradability. This review summarizes the most common chitosan processing methods and highlights some applications of chitosan in various industrial and biomedical fields. Finally, environmental concerns of chitosan-based films, considering the stages from raw materials extraction up to the end of life after disposal, are also discussed with the aim of finding more eco-friendly alternatives.

Influence of cure schedule and stoichiometry on the dynamic mechanical behaviour of tetrafunctional epoxy resins cured with anhydrides

Abstract Epoxy networks based on N,N,N′,N′ -tetraglycidyl-4,4′-diamino diphenylmethane (TGDDM) prepolymer were prepared with cis -1,2,3,6-tetrahydrophthalic anhydride (THPA) curing agent at anhydride/epoxy group ratios varying from 0.3 to 1.0. For post-cured mixtures, dynamic mechanical tests show that the glass transition temperature reaches the maximum value at stoichiometric ratios between 0.8 and 0.9. This behaviour has been related to the crosslink density of the formed networks, and also to etherification reactions occurring during cure which lower the amount of anhydride needed in order to complete the curing process. The study of cure cycle variations on the viscoelastic properties showed that for epoxy/anhydride mixtures high post-cure temperatures could be needed to reduce the amount of unreacted epoxy groups after curing. Fourier transform infra-red spectroscopy has been used to analyse the residual epoxy groups and also to study the influence of the different cure reactions on the physical properties of these networks.

FTIR characterization of protein–polysaccharide interactions in extruded blends

Soy protein-based blends were processed by double screw extrusion and the effects of different types and contents of polysaccharides were analyzed. Although extrusion has not been widely used for this type of blends, in this study it was observed that the increase in polysaccharide content in blends caused a decrease in specific mechanical energy (SME), facilitating extrusion process and showing the potential of this process, which is more cost effective at industrial scale. In order to explain this behavior, infrared spectroscopy analysis was carried out, mainly in the amide I and II regions. Moreover, curve fitting analysis showed the conformational changes produced in the blends due to the addition of polysaccharides, which affected protein denaturation. These changes also affected properties such as moisture content (MC) and total solubility matter (TSM). However, conformational changes did not show significant effects with respect to piece density (PD) or in the expansion ratio (ER) of the pellets. The quantitative analysis of the changes in the amide I and II regions provided novel information about the modifications produced in protein-based blends modified with polysaccharides. In this context, infrared spectroscopy provided a convenient and powerful means to monitor interactions between all ingredients used in the blend formulation, which is of great importance in order to explain changes in the functional properties of biodegradable materials used for industrial applications in food and pharmaceutical industries.

Kinetic and rheological studies of an unsaturated polyester cured with different catalyst amounts

An unsaturated polyester resin was cured with different catalyst contents. The crosslinking process was followed by static and dynamic viscosimetry and by differential scanning calorimetry (d.s.c.). Activation energies were determined from the gel times obtained by viscosimetry and from the variation in the maximum exotherm temperature obtained by d.s.c. at different heating rates. The existence of a threshold in the amount of catalyst to use is shown by analysis of the gel times. The effect of catalyst content on the glass transition temperatures of the different mixtures has been analysed taking into account the crosslink density, measured by means of the rubber modulus obtained by dynamic mechanical tests.

Extraction of agar from Gelidium sesquipedale (Rodhopyta) and surface characterization of agar based films

The chemical structure of the agar obtained from Gelidium sesquipedale (Rhodophyta) has been determined by (13)C nuclear magnetic resonance ((13)C NMR) and Fourier transform infrared spectroscopy (FTIR). Agar (AG) films with different amounts of soy protein isolate (SPI) were prepared using a thermo-moulding method, and transparent and hydrophobic films were obtained and characterized. FTIR analysis provided a detailed description of the binding groups present in the films, such as carboxylic, hydroxyl and sulfonate groups, while the surface composition was examined using X-ray photoelectron spectroscopy (XPS). The changes observed by FTIR and XPS spectra suggested interactions between functional groups of agar and SPI. This is a novel approach to the characterization of agar-based films and provides knowledge about the compatibility of agar and soy protein for further investigation of the functional properties of biodegradable films based on these biopolymers.

Comparative study by DSC and FTIR techniques of an unsaturated polyester resin cured at different temperatures

1 Escuela Universitaria de Ingenier•“a Te“cnica Industrial, Departamento de Ingenieria Qu•“mica y Medio Ambiente, Universidad delPa•“s Vasco/Euskal Herriko Unibertsitatea, Avda. Felipe IV, 1B. 20011 San Sebastia“ n, Spain2 Institute of Chemical Technologies, University of Perugia, Loc. Pentima Bassa, 21. 05100 Terni, Italy(Received 11 March 1997; revised version received 4 August 1997; accepted 8 October 1997)Abstract: The polymerization of a commercial polyester resin was investigatedby di†erential scanning calorimetry (DSC). The conversion proÐles wereobtained in the temperature range 60E80iC. The autocatalytic model satisfacto-rily describes the experimental data. Fourier transform infrared spectroscopy(FTIR) measurements were also made in order to obtain both the styrene andpolyester unsaturations conversions, which were compared to the overall conver-sion obtained by DSC. Overall conversion measured by DSC lies betweenstyrene and polyester CxC bond conversion obtained by FTIR. 1998 SCI.(Polym. Int. 45, 333E338 (1998)Key words: DSC; FTIR; conversion; kinetic model

Kinetic and rheological studies of two unsaturated polyester resins cured at different temperatures

Abstract The effect of temperature on the curing kinetics of two unsaturated polyester resins has been studied by Fourier transform infrared spectroscopy. It has been found that at the beginning of the reaction, the kinetic mechanism was dominated by near-azeotropic copolymerization, while conversion of polyester vinylene groups became much more favourable than styrene later in the reaction. Both styrene and vinylene group conversion at the end of isothermal cures were a function of the styrene content in the resin. The experimental results have been related to the rheological changes during cure. Activation energies have been obtained from both rheological and thermal techniques.

Characterization of agar/soy protein biocomposite films: Effect of agar on the extruded pellets and compression moulded films

Agar/soy protein biocomposite films were successfully processed by extrusion and compression moulding, obtaining transparent and homogeneous films. The conformational changes occurred during the extrusion process and the effect of agar on the final properties were analyzed. As shown by differential scanning calorimetry (DSC) and specific mechanical energy (SME) values, during the extrusion process protein denatured and unfolded protein chains could interact with agar. These interactions were analyzed by Fourier transform infrared spectroscopy (FTIR) and the secondary structure was determined from the amide I band. Those interactions were supported by the decrease of film solubility. Furthermore, the good compatibility between agar and soy protein was confirmed by the images from scanning electron microscopy (SEM).

Fracture behavior-morphology relationships in an unsaturated polyester resin modified with a liquid oligomer

An unsaturated polyester (UP) resin modified with a liquid polymer, polyoxypropylenetriamine (POPTA), at a concentration of 10 wt% has been precured at several temperatures. Phase separation takes place before gelation at all precure temperatures used. The glass-transition region has been analyzed by dynamic mechanical analysis. Mechanical properties have been related to microstructural features. With a precure temperature fixed, the unsaturated polyester (UP) resin has also been modified with different contents of POPTA. Fracture toughness of the mixtures has also been analyzed and results are compared to those for the unmodified mixture.