Carlos Peniche

Self-curing membranes of chitosan/PAA IPNs obtained by radical polymerization: preparation, characterization and interpolymer complexation

Chitosan/polyacrylic acid I PNs were prepared by radical polymerization of acrylic acid, AA, activated at low temperature, in an aqueous/alcoholic chitosan dispersion. AA monomer to polymer conversion and membrane compositions were determined by elemental analysis and FTIR. Evidences of interpolyelectrolite complex formation were found from the FTIR spectra as well. The gravimetric measurements and the elemental analysis after some exhaustive PAA extraction support the existence of some PAA grafting on the reactive amine group of the chitosan. Swelling degree of the membranes is highly dependent on pH and composition, showing a higher swelling in membranes richer in AA and increased pH due to the breaking of interpolyelectrolite salt bonds.

Water sorption of flexible networks based on 2- hydroxyethyl methacrylate-triethylenglycol dimethacrylate copolymers

Abstract Cross-linked films of copolymer of 2-hydroxyethyl methacrylate (HEMA) and triethylenglycol dimethacrylate (TEGDMA) were prepared by free radical polymerization initiated at 60°C. The swelling behaviour of films prepared with 2, 5 and 10 mol% of TEGDMA was followed gravimetrically and the diffusion coefficients were determined according to the Fickian law at several temperatures in the interval 25–50°C. The apparent activation energy was independent of the composition of the networks, giving a value of 15.5 kJ mol−1 which corresponds to a typical diffusion process. The freezing point, the enthalpy of fusion and the amount of non-freezable water were determined by differential scanning calorimetry (DSC) on hydrated samples with different hydration degree. There is a critical hydration interval (W = 20–30 wt%) in which it is possible to distinguish the different states of water in the cross-linked hydrogel. The variation of the enthalpy ΔHf with the hydration degree gives a maximum amount of non-freezable water of about 23 wt%, independent of the TEGDMA content of copolymer systems.

Interpolymer complexes of chitosan and polymethacrylic derivatives of salicylic acid : preparation, characterization and modification by thermal treatment

Macromolecular interpolymer complexes were prepared by blending concentrated equimolar solutions of chitosan and poly(4-N-methacrylamidobenzoic acid) and evaporation of the solvents. The products obtained presented the structure of interpolymer complexes as indicated by FTIR spectroscopy. The thermal treatment of the solid products at 120°C gives rise to a partial dehydration together with the formation of covalent amide bonds between both polymeric components. The sorption behaviour of the systems is analysed on the basis of the structure of the macromolecular systems and a consideration of Fickian behaviour for highly hydrophilic materials. The diffusion coefficients determined are dependent on the thermal treatment applied to the interpolymer complexes.

Conductimetric study of the interpolyelectrolyte reaction between chitosan and polygalacturonic acid

The interpolyelectrolyte reaction between chitosan hydrochloride (CHI) and sodium polygalacturonate (NaPGA) has been investigated by conductimetric measurements. The composition of the reaction mixture, Z, was assessed by monitoring the conductivity when a CHI solution was added to a solution of NaPGA. It was determined to be unity at the equivalence point, indicating a 1:1 stoichiometry for the complex. The degree of complexation, θ, expressed as the fraction of groups reacted, was also obtained from the conductimetric measurements by means of a simple procedure. To this end the limiting ionic conductivities and transport coefficients of CHI and NaPGA were previously evaluated. It was found that θ varies with Z. It falls from unity to almost 0.8 as Z increases from 0.2 to 0.5 and then rises again up to 0.85 for Z=1.

Chitosan-based hydrogels: Synthesis and characterization

Chitosan (CHI) is a polysaccharide of β-1,4-linked 2-amino-2-deoxy-D-glucopyranose derived by N-deacetylation of chitin in aqueous alkaline medium. The shells of crustaceans such as crabs, shrimp, and lobster are the current source of chitosan. It is known to be non-toxic, odourless, biocompatible in animal tissues and enzymatically biodegradable. For these reasons much research interest has been paid to its biomedical, ecological, and industrial applications over the past decade. However, its rigid crystalline structure, poor solubility in organic solvents and poor processability have limited its use. To broadening its range of applications, a growth research effort has been devoted to explore ways of modifying Chitosan. Here it has been reported on the synthesis of new hydrogels, obtained by self-curing chitosan with acrylic acid (AA) and methyl acrylate (MA). The hydrogels were characterized by FTIR, swelling and rheological analysis. The results of this study showed that the swelling and mechanical properties of chitosan are highly improved by the presence of poly acrylate. The swelling degree of these materials does not depend upon the ratio MA/AA. It is possible to improve and modulate the mechanical properties of the hydrogels by changing the relative MA/AA ratio.© 2001 Kluwer Academic Publishers

Chitosan based polyelectrolyte complexes

Polyelectrolyte complexes (PECs) are formed through the electrostatic interactions between polymers carrying opposite charges. Here are presented results of basic studies on the PECs of chitosan with other polysaccharides such as sodium alginate, carboxymethyl cellulose, polygalacturonic acid and κ-carrageenan. An extensive study on chitosan/carboxymethyl cellulose membranes, regarding its swelling characteristics and water vapour sorption is offered. Also the interaction of chitosan with polyacrylic acid has been examined from the thermodynamic point of view.

Study of the thermal degradation of poly(furfuryl methacrylate) by thermogravimetry

Abstract The thermal degradation of poly(furfuryl methacrylate) (PFM) has been studied by means of dynamic thermogravimetric analysis (TGA) in the temperature range 100–600°C under nitrogen and oxygen atmospheres at various heating rates, and the apparent activation energy for the interval 230–340°C corresponding to the first degradation step was determined. Isothermal TGA at 250°C, 275°C and 300°C was carried out and the apparent activation energy values obtained were compared with those determined in dynamic experiments. The residues from isothermal degradation experiments were analysed by infrared spectroscopy and the results seem to indicate that in the thermal degradation of PFM the formation of cyclic structures of 2,4-dimethylglutaric anhydride occurs in the macromolecular chains, together with partial depolymerization of polymer segments, as well as intermolecular crosslinking through oxidation of the CH bond in position 5 of some furfuryl rings.

Chitosan/apatite composite beads prepared by in situ generation of apatite or Si-apatite nanocrystals

The objective of this work was to develop nanocrystalline apatite (Ap) dispersed in a chitosan (CHI) matrix as a material for applications in bone tissue engineering. CHI/Ap composites of different weight ratios (20/80, 50/50 and 80/20) and with CHI of different molecular weights were prepared by a biomimetic stepwise route. Firstly, CaHPO(4).2H(2)O (DCPD) crystals were precipitated from Ca(CH(3)COO)(2) and NaHPO(4) in the bulk CHI solution, followed by the formation of CHI/DCPD beads by coacervation. The beads were treated with Na(3)PO(4)/Na(5)P(3)O(10) solution (pH 12-13) to crosslink the CHI and to hydrolyse the DCPD to nanocrystalline Ap. This new experimental procedure ensured that complete conversion of DCPD into sodium-substituted apatite was achieved without appreciable increases in its crystallinity and particle size. In addition, composites with silicon-doped Ap were prepared by substituting Na(3)PO(4) by Na(2)SiO(3) in the crosslinking/hydrolysis step. Characterization of the resultant composites by scanning electron microscopy, X-ray powder diffraction (XRD), thermal analysis and Fourier transform infrared spectroscopy confirmed the formation, within the CHI matrix, of nanoparticles of sodium- and carbonate-substituted hydroxyapatite [Ca(10-x)Na(x)(PO(4))(6-x)(CO(3))(x)(OH)(2)] with diameters less than 20nm. Relatively good correspondence was shown between the experimentally determined inorganic content and that expected theoretically. Structural data obtained from its XRD patterns revealed a decrease in both crystal domain size and cell parameters of Ap formed in situ with increasing CHI content. It was found that the molecular weight of CHI and silicate doping both affected the nucleation and growth of apatite nanocrystallites. These effects are discussed in detail.

Chitin and chitosan

Publisher Summary Among the novel families of biological macromolecules, whose relevance in food systems is becoming increasingly evident, are chitin and its main derivative chitosan. The use of chitin and chitosan in food and other specialized applications is a good example of the recycling of organic solid waste and by-products generated by the food industry itself to obtain added-value products. This chapter provides an updated overview of the developments that have taken place over the past decades in the field of chitin science, particularly those that are relevant to food scientists and biotechnologists. The main goal here is to raise the awareness of the potential of these biopolymers and encourage further studies. Emphasis is on the key fundamental aspects of the physical and chemical behavior of these molecules, which underlie their specialized applications and on the methods to isolate them, including some of the current barriers to scale up some of these operations.

Free radical copolymerization of furfuryl methacrylate and N-vinylpyrrolidone

Abstract Copolymers of furfuryl methacrylate (F) and N -vinylpyrrolidone (P) were prepared by free radical polymerization in N , N -dimethylformamide solution at 50°C, using 2,2′-azobisisobutyronitrile as initiator. The reactivity ratios of both monomers were calculated according to the general copolymerization equation using the Fineman-Ross and Kelen-Tudos linearization methods, as well as the Tidwell and Mortimer non-linear least-squares treatment. The reactivity ratios obtained were r F = 3.92 and r P = 0.004. The microstructure of the copolymer chains is described on the basis of first-order Markov statistics, and the copolymer glass transition temperatures ( T g s) were determined calorimetrically. The variation of T g with copolymer composition is discussed according to modern methods, considering the sequence distribution of monomeric units along the copolymer chains. Also the T g of the corresponding homopolymers was determined giving the values T g (F) = 392 K and T g (P) = 358 K, whereas the T g of the corresponding alternating diad has an average value of T gFP = 347 K.