XRD studies of polyurethane elastomers based on chitin/1,4-butane diol blends

Chitin based polyurethane elastomers (PUEs) were synthesized by step growth polymerization techniques using poly (ε-caprolactone) (PCL), 4, 4′- diphenylmethane diisocyanate (MDI) and blends of chitin and 1,4-butanne diol (BDO). The conventional spectroscopic characterization of the samples with FT-IR, ¹H NMR and ¹³C NMR were in accordance with proposed PUEs structure. The crystalline behavior of the synthesized polymers were investigated by X-ray diffraction (XRD), differential scanning calorimetery (DSC), optical microscopic technique and loss tangent curves (tan δ peaks). Results showed that crystallinity of the synthesized PUEs samples was affected by varying the chitin contents used as chain extender. The contents of chitin favors the formation of more ordered structure, as higher peak intensities were obtained from the PU extended with chitin than 1,4-butane diol (BDO). X-ray diffraction experiments results correlates with optical microscopy findings. The higher ΔH value; 41.57 (J g^?1) was found in the samples extended with chitin than BDO (31.32 J g^?1).     

XRD studies of chitin-based polyurethane elastomers

Chitin-based polyurethane elastomers (PUEs) were synthesized by step growth polymerization techniques using poly(epsilon-caprolactone) (PCL) varying diisocyanate and chain extender structures. The viscosity average molecular weight (M(v)) of chitin was deduced from the intrinsic viscosity and found; M(v)=6.067 x 10(5). The conventional spectroscopic characterization of the samples with FTIR, (1)H NMR and (13)C NMR were in accordance with proposed PUEs structure. The crystalline behavior of the synthesized polymers were investigated by X-ray diffraction (XRD), differential scanning calorimetery (DSC) and loss tangent curves (tan delta peaks). The observed patterns of the crystalline peaks for the lower angle for chitin in the 2theta range were indexed as 9.39 degrees, 19.72 degrees, 20.73 degrees, 23.41 degrees and 26.39 degrees. Results showed that crystallinity of the synthesized PUEs samples was affected by varying the structure of the diisocyanate and chain extender. Crystallinity decreased from aliphatic to aromatic characters of the diisocyanates used in the final PU. The presence of chitin also favors the formation of more ordered structure, as higher peak intensities was obtained from the PU extended with chitin than 1,4-butane diol (BDO). The value of peak enthalpy (DeltaH) of chitin was found to be 47.13 J g(-1). The higher DeltaH value of 46.35 J g(-1) was found in the samples extended with chitin than BDO (39.73 J g(-1)).     

Surface characteristics of UV-irradiated chitin-based polyurethane elastomers

Chitin-based polyurethane elastomers (PUEs) constituted on 4,4′-diphenylmethane diisocyanate (MDI), poly(ε-caprolactone) (PCL) and extended with blends of chitin/1,4-butane diol were first synthesized via two step polymerization technique and then irradiated for 50, 100 and 200 h in an UV exposure chamber as such the spectral distribution of the light is good match for terrestrial solar radiation. The surface properties of the irradiated PU samples were investigated by contact angle measurements, surface free energy and water absorption (%), total work of water adhesion to polymer and equilibrium degree of swelling. The effects of UV-irradiation time and chitin contents in chain extenders (CE) proportion on surface properties were investigated. Results of the aforementioned surface techniques revealed that the UV-irradiated polyurethane samples were affected by varying the UV exposure period.     

Surface characteristics of polyurethane elastomers based on chitin/1,4-butane diol blends

Biodegradable polyurethane elastomers with tunable hydrophobicity were synthesized by step-growth polymerization techniques using poly(?-caprolactone) (PCL) and 4,4′-diphenylmethane diisocyanate (MDI). The prepolymer was extended with different mass ratios of chitin and 1,4-butane diol (BDO). The effect of chitin contents in chain extenders (CE) proportion on surface properties was studied and investigated. Incorporation of chitin contents into the final PU showed decrease in surface free energy and its polar component. Simultaneously, the work of water adhesion to polymer decreases significantly by increasing the chitin contents in the synthesized polymer. Contact angle measurement, water absorption and swelling behavior of the synthesized polyurethane samples were affected by varying the chitin contents in the chemical composition of the final PU. The interactions of the final PU films with solvents on the surface were displayed clear dependent on the contents of chitin in to the final polyurethane formulation. The results of different tests demonstrated that the synthesized products are a potential candidate as non-absorbable suture as previously investigated into their in vitro biocompatibility and non-toxicity [K.M. Zia, M. Zuber, I.A. Bhatti, M. Barikani, M.A. Sheikh, Int. J. Biol. Macromol. 44 (2009) 18–22].     

Evaluation of biocompatibility and mechanical behavior of polyurethane elastomers based on chitin/1,4-butane diol blends

Chitin based polyurethane elastomers with potential as biomedical implants with tunable mechanical properties were synthesized by step growth polymerization techniques using poly(epsilon-caprolactone) (PCL) and 4,4'-diphenylmethane diisocyanate (MDI). The prepolymer was extended with different mass ratios of chitin and 1,4-butane diol (BDO). Molecular characterization was done using FTIR, 1H NMR and 13C NMR techniques. The mechanical properties of these polymers were improved with increase in the chitin contents. Optimum mechanical properties were obtained from elastomers extended with chitin in comparison to elastomers extended with BDO. Cytotoxicity of the synthesized polyurethane samples was affected by varying the chitin contents in the chemical composition of the final polyurethane (PU). It is revealed that the final polymers extended with chitin are preferred candidates for surgical threads with on going investigations into their in vitro biocompatibility and non-toxicity.     

Light-scattering and infrared-spectrophotometric studies of chitin and chitin derivatives

A sample of chitin isolated from the shell of the crab Scylla serrata had, when in lithium thiocyanate solution, an average, weight-average molecular weight (1) of 1.036 x 10⁶ daltons, an intrinsic dissymmetry (2) of 1.93, and a Z-average radius of gyration (3) of 64.14 nm. Carboxymethylchitin and glycol chitin, in 0.5M sodium chloride, had, respectively, (1) 1.896 and 1.819 x 10⁶ daltons, (2) 3.25 and 4.31. and (3) 143.49 and 251.57 nm. They had similar degrees of polymerization, they underwent dissociation as the concentration of sodium chloride was increased to 2.5M, and the molecular packing of the chains was essentially side-by-side. Chitin in 5.55M lithium thiocyanate and carboxymethylchitin in 2.5M sodium chloride had similar degrees of polymerization. It is concluded that a small but significient number of the amino groups in the chitin molecule are not acetylated.     

A rapid technique for evaluating the biodeterioration potential of polyurethane elastomers

Summary The technique described provides a rapid method for screening thermoplastic polyurethanes against deteriogenic micro-organisms using thin films (0.4–0.5 mm thick) of plastic prepared in an electric plantens press. The films are inoculated with a spore suspension of Gliocladium roseum and can be viewed directly under the light microscope for evaluation of surface effects; selective staining can be used to reveal fungal mycelium. Results can be obtained within a week which correlate with longer term tests using commercial samples. The technique can also be used to isolate potential polyurethane deteriorating micro-organisms from the environment and to confirm their biodeteriogenic activities.     

Flexible chitin films: structural studies

Chitin gels were transformed into thin, flexible chitin films with minimal dimensional shrinkage and maximum flexibility and thickness in the range of 25-80 microm by a cold-press process. Solvent residue was removed by heating the films at 50 degrees C for 12 h, followed by rinsing in 95% ethanol. The crystallinity and mechanical properties of the flexible chitin films were found to be a function of the amount of shrinkage from the gel to the final film that was obtained. For 28-microm thick films with 30% shrinkage, transparency of up to 90% was found. X-ray diffractometry (XRD) showed that the number of diffraction peaks appearing at 2theta;=23 degrees and 2theta;=27 degrees became increasingly sharper with shrinkage. Topographical information obtained from scanning electron microscopy (SEM) and atomic force microscopy (AFM) attributed the structural morphology of the films to the formation of sub-microscopic micelles. Scanning transmission electron microscopy (STEM) showed that shrinkage resulted in coarser microstructure, affecting tensile properties, where the ductility and toughness were proportional to the amount of shrinkage. These flexible chitin films have potential as wound dressing materials.     

Sorption and desorption studies on chitin gels

The aim of this work was to study various transport phenomena in chitin gels obtained by N-acetylation of chitosan in a water-alcohol mixture. Three kinds of transport were investigated: the sorption of solutes interacting with chitin, the desorption of solutes without significant interaction with the polymer, and osmosis phenomena. In the case of interactive sorption, dyes having different chemical structures such as C.I. Acid Blue 74, C.I. Reactive Violet 5 or C.I. Direct Red 28 were tested. Sorptions of C.I. Acid Blue 74 and C.I. Reactive Violet 5 depend on the charge density of the polymer network and, as a consequence, on DA, pH and the dielectric constant of the media. This result reveals the importance of electrostatic interactions. On the other hand, the sorption of C.I. Direct Red 28 is mainly due to hydrophobic interactions and H-bonding, it is limited to the extreme surface of the gel. Concerning the non-interactive desorption, solutes of different steric hindrance such as PP vitamin, B1 vitamin and caffeine exhibit similar diffusion coefficients located within 3.7-5.6x10(-6) cm(2) s(-1). Finally, the osmotic behaviour of the gel immersed in a concentrated solution of gelatin allows us to multiply by 25 the concentration of chitin in the gel without any penetration of gelatin.     

XRD studies of beta-chitin from squid pen with calcium solvent

The crystalline structure of β-chitin from squid pen was investigated by X-ray diffraction (XRD). The purified β-chitin was prepared from bigfin reefsquid pen. β-Chitin was treated with saturated calcium chloride dihydrate/alchohol (CaCl₂·2H₂O/MeOH) solvent system at different conditions for XRD studies. The change of crystallinity of β-chitin from squid pen was studied by using the fiber photographs on imaging plates. The results showed that the diffraction peak (0 1 0) was shifted. It means that the lattice plane (0 1 0) interplanarilly spreaded to 3.4 Å, when the squid pen was washed with water after treatment of Ca solvent. Furthermore, when the squid pen was dried after treatment of Ca solvent and washing with water, interplanar spacing of (0 1 0) inversely shrank to 1.1 Å. These results suggested that Ca solvent especially influences the plane (0 1 0) of β-chitin structure.     

Biodegradation of polyurethane acrylate with acrylated epoxidized soybean oil blend elastomers by Chaetomium globosum

This paper studies the biodegradation features of a novel blend of polyurethane acrylate-acrylated epoxidized soybean oil-based cross-linked polyurethane elastomers in the presence of the soft-rot fungus Chaetomium globosum. After the specimens were incubated at 28 °C for 90 and 130 days, the degree of fungal damage was measured by analysis of weight loss and mechanical properties. The biodegradation of the films was also evidenced by SEM and FTIR spectroscopic studies. After fungal attack, the FTIR spectra indicate a degradation of urethane and ester groups of the polyurethane and especially of the ester groups from the modified soybean oil part. The polyurethane blend films exposed to fungal attack suffered a loss in strength of up to 55% and a loss in elongation of up to 80%, depending on the content of acrylated epoxidized soybean oil. The biodegradation of the blends was also confirmed by SEM analyses. The biodegradation results show that samples with a high content of acrylated epoxidized soybean oil are more biodegradable than mere polyurethane acrylate. These biodegradable polymer blends present an optimum balance of physical properties and biodegradable properties with the potential for application as eco-friendly biomaterials.     

Evaluation of biocompatibility and mechanical behavior of chitin-based polyurethane elastomers. Part-II: Effect of diisocyanate structure

Chitin-based polyurethane elastomers having potential for biomedical applications with tunable mechanical properties were synthesized by step growth polymerization techniques using poly(?-caprolactone) (PCL) with different diisocyanates. The prepolymer was extended using chitin and/or 1,4-butane diol (BDO). The structures of the resulted polymers were determined by Fourier transform infrared (FTIR), ¹H NMR and ¹³C NMR spectroscopic techniques. The effect of structure of diisocyanates and chain extenders on mechanical properties and in vitro biocompatibility were investigated. The results revealed that the final polymers extended with chitin are preferred candidates for surgical threads with on going investigations into their in vitro biocompatibility and non-toxicity.     

Morphologic and biochemical studies of chitin expression in Pneumocystis carinii.

Tomato lectin, which binds oligosaccharides of N-acetyl-D-glucosamine, and an antiserum against macromolecular chitin were used to probe sections of human and murine lungs infected with Pneumocystis carinii. By light, fluorescence and electron microscopy, lectin and antiserum binding patterns indicated that both human and murine strains of P. carinii express chitin at all identifiable stages of their life cycles. Light microscopic autoradiographs of murine P. carinii cultured in vitro with 3H-glucosamine revealed dense incorporation of the radiolabel into the cell walls in a pattern analogous to those of the antiserum and lectin binding studies. These investigations offer further evidence that chitin is an integral part of the cell wall of P. carinii trophozoites and cysts.     

Renewable-resource thermoplastic elastomers based on polylactide and polymenthide

An alpha,omega-functionalized polymenthide was synthesized by the ring-opening polymerization of menthide in the presence of diethylene glycol with diethyl zinc as the catalyst. Termination with water afforded the dihydroxy polymenthide. The reaction of this telechelic polymer with triethylaluminum formed the corresponding aluminum alkoxide macroinitiator that was used for the controlled polymerization of lactide to yield biorenewable polylactide-b-polymenthide-b-polylactide triblock copolymers. The molecular weight and chemical composition were easily adjusted by the monomer-to-initiator ratios. Microphase separation in these triblock copolymers was confirmed by small-angle X-ray scattering and differential scanning calorimetry. A representative triblock was prepared with a hexagonally packed cylindrical morphology as determined by small-angle X-ray scattering, and tensile testing was employed to assess the mechanical behavior. On the basis of the ultimate elongations and elastic recovery, these triblock copolymers behaved as thermoplastic elastomers.     

Peculiarities of metabolism of UV-irradiated lymphocytes

The influence of UV-light (240-390 nm) at a dose of 151 and 755 J/m2 on the functional properties of lymphocyte metabolism key enzymes from donors' human blood: lactate dehydrogenase (LDH), cytochrome c oxidase, succinate dehydrogenase (SDH), Ca2(+)-ATPase of plasma membranes has been investigated. It has been revealed that photoinactivation of enzymes immediately after UV-irradiation which leads to the decrease of the ATP content in lymphocytes is replaced by the increased activity of the enzymes under investigation during daily incubation of lymphocytes. As a result, the level of ATP in photo-modified lymphocytes does not differ from that in native cells before incubation. This indicates the normalization of biochemical processes in lymphocytes influenced by UV-light applied in autotransfusion of UV-irradiated blood.     

Electrophoretic mobility of UV-irradiated bacterial cells

Electrophoretic mobility of Escherichia coli cells exposed to various doses of UV-radiation was investigated. The method of free flow electrophoresis was used to study a correlation between membrane protein charge and cell surface electric charge. The change in the cell surface charge and electrophoretic motility was associated with the damage to membrane proteins and the survival of UV-irradiated bacteria.     

Biomaterials based on chitin and chitosan in wound dressing applications

Wound dressing is one of the most promising medical applications for chitin and chitosan. The adhesive nature of chitin and chitosan, together with their antifungal and bactericidal character, and their permeability to oxygen, is a very important property associated with the treatment of wounds and burns. Different derivatives of chitin and chitosan have been prepared for this purpose in the form of hydrogels, fibers, membranes, scaffolds and sponges. The purpose of this review is to take a closer look on the wound dressing applications of biomaterials based on chitin, chitosan and their derivatives in various forms in detail.     

Physical properties of canola oil based polyurethane networks

A new generation polyol (generation-II) with significantly higher triol content and higher hydroxyl value was synthesized from canola oil by introducing a mild solvent (ethyl acetate) and a more efficient reductive reagent (zinc) to the previous synthetic procedure (Narine, S. S.; Yue, J.; Kong, X. J. Am. Oil Chem. Soc. 2007, 84, 173-179). Polyurethane (PUR) elastomers were prepared by reacting this type of polyol with aliphatic diisocyanates. The physical and thermal properties of the PUR elastomers were studied using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) and compared to the elastomers made from the old generation polyol (generation-I). The concentration of elastically active network chains (nue) of the polymer networks was calculated based on rubber elasticity theory. Larger nue and narrower distribution of nue was observed in the case of the PURs prepared from the generation-II polyol. The relatively faster relaxation at higher temperature for this type of PUR elastomer, suggests a tighter cross-linked network structure by reducing the dangling chains effect. With the same OH/NCO molar ratio, the PURs prepared from the generation-II polyol showed higher glass transition temperatures (Tg), higher Young's modulus and tensile strength, and longer elongation at break.     

Peripheral enzymatic deacetylation of chitin and reprecipitated chitin particles

The enzymatic deacetylation of various chitin preparations was investigated using the fungal chitin deacetylase (CDA) isolated from Rhizopus oryzae growth medium. Specific extracellular enzyme activity after solid state fermentation was 10 times higher than that after submerged fermentation. Natural crystalline chitin is a very poor substrate for the enzyme, but showed a five-time better deacetylation after dissolution and reprecipitation. Chitin particles, enzymatically deacetylated for only 1% exhibited a strongly increased binding capacity towards ovalbumin, while maintaining the rigidity and insolubility of chitin in a moderate acidic environment. Because of the unique combination of properties, these CDA treated chitin materials were named "chit-in-osan". Chitinosan was shown to be an attractive matrix for column chromatography because no hydrogel formation was observed, that impaired the flow of eluent. Under the same conditions, partially deacetylated chitosan swelled and blocked the flow in the column.