Showing papers in "Polymer Bulletin in 2014"

Effect of degree of cross-linking on swelling and on drug release of low viscous chitosan/poly(vinyl alcohol) hydrogels

Abstract: In the present work, a series of cross-linked LVCS/PVA hydrogels with various feed compositions were prepared using glutaraldehyde as cross-linking agent. The prepared hydrogels were used for dynamic and equilibrium swelling studies. The swelling behavior of these hydrogels was investigated as functions of effect of pH, polymeric compositions and degree of cross-linking. Swelling studies were performed in 0.05 M USP phosphate buffer solutions of varying pH 1.2, 5.5, 6.5 and 7.5. Results showed that swelling increased by increasing PVA contents in the structure of hydrogels in solutions of higher pH values. This is due to the presence of more hydroxyl groups (–OH) in the PVA structure. On the other hand, by increasing LVCS contents, swelling increased in a solution of acidic pH and it is due to ionization of amino groups (–NH2), but this swelling was not significant. Swelling of hydrogels was decreased with increase in cross-linking ratio due to tighter hydrogel structure. Porosity and sol–gel fraction were also investigated. It was found that with increase in LVCS and PVA contents porosity and gel fraction increased, whereas by increasing glutaraldehyde content gel fraction increased and porosity decreased. Diffusion coefficient (D) and network parameters, i.e., the average molecular weight between cross-links (MC), solvent interaction parameters (χ), polymer volume fraction in swollen state (V2S) and cross-linked density (q) were calculated using Flory–Rehner theory. Selected samples were loaded with model drug diphenhydramine HCl. The release of diphenhydramine HCl was studied for 12 h period in 0.05 M USP phosphate buffer solutions of varying pH 1.2, 5.5 and 7.5. It was observed that drug release increased with increasing PVA contents in the hydrogels, while release of drug decreased as the ratio of cross-linking agent increased in the hydrogel structure owing to strong physical entanglements between polymers. The release mechanisms were studied by fitting experimental data to model equations like zero order, first order, Higuchi and Peppas. Results showed that the kinetics of drug release from hydrogels in buffer solutions of pH 1.2, 5.5 and 7.5 was mainly non-fickian diffusion. Hydrogels were characterized by Fourier transform infrared and X-ray diffraction to confirm the structure and study the crystallinity of hydrogel, respectively.

A study on polymer blend electrolyte based on PVA/PVP with proton salt

Abstract: Proton-conducting polymer blend electrolytes based on PVA–PVP–NH4NO3 were prepared for different compositions by solution cast technique. The prepared films are investigated by different techniques. The XRD study reveals the amorphous nature of the polymer electrolyte. The FTIR and laser Raman studies confirm the complex formation between the polymer and salt. DSC measurements show decrease in T g with increasing salt concentration. The ionic conductivity of the prepared polymer electrolyte was found by ac impedance spectroscopy analysis. The maximum ionic conductivity was found to be 1.41 × 10−3 S cm−1 at ambient temperature for the composition of 50PVA:50PVP:30 wt% NH4NO3 with low-activation energy 0.29 eV. The conductivity temperature plots are found to follow an Arrhenius nature. The dielectric behavior was analyzed using dielectric permittivity (e*) and the relaxation frequency (τ) was calculated from the loss tangent spectra (tan δ). Using this maximum ionic conducting polymer blend electrolyte, the primary proton battery with configuration Zn + ZnSO4·7H2O/50PVA:50PVP:30 wt% NH4NO3/PbO2 + V2O5 was fabricated and their discharge characteristics studied.

Effects of nano-graphene on the physico-mechanical properties of bagasse/polypropylene composites

Abstract: This study was aimed at identifying the best approach of incorporating nano-graphene (NG) into bagasse/polypropylene composites to enhance their mechanical and physical properties. The composites with different NG contents were produced by melt compounding in a twin-screw extruder and then by injection molding. The mass ratio of the bagasse flour (BF) to polymer was 15/85 and 30/70 (w/w). Water absorption, thickness swelling, tensile strength, bending characteristics, impact strength and morphological properties of the produced composites were evaluated. In general, applying NG would improve mechanical properties of the composites. The mechanical test results indicated that when only 0.1 wt % of NG was added, tensile and flexural properties reached their maximum values, while the notched impact was slightly decreased. The composites containing 0.1 wt % NG and 30 wt % BF exhibited the highest tensile, flexural and notched impact strength values. Although incorporating NG into the polymer matrix effectively improves mechanical properties, this improvement comes at proper nanofiller loading (0.1 wt %). Addition of NG almost did not change the average water uptake and thickness swelling, compared to the control (without NG) samples. Morphological study confirmed that high contents (0.5–1 wt %) of NG were easily agglomerated. Thermal analysis showed slight increase in thermal stability of WPCs after incorporation of NG particles. In addition, it was found that the effect of BF was notable in material properties of the composites.

Influence of talc particle size and content on crystallization behavior, mechanical properties and morphology of poly(lactic acid)

Abstract: This research aimed to employ inorganic filler such as talc to promote crystallization in poly(lactic acid) (PLA). Three different talc particle sizes, namely 1, 5 and 30 µm, were used as nucleating agents; each was compounded with PLA at various contents from 0 to 10 wt%. The crystallization temperature (T c) reduced most rapidly from 128 to 107 °C with the presence of 1 wt% talc. Beyond this concentration, the T c still decreased but only minutely. Compared to other sizes, finer talc particles were found to promote a slightly higher degree of crystallinity. X-ray diffraction peaks indicated that the α-crystal was formed in all PLA/talc compositions. The heat distortion temperature values suggested that the modified PLA could resist the thermal deformation from 58 °C to a maximum value of 139 °C when 1 µm talc was added at 10 wt%. With the presence of talc, the composites were more brittle and both tensile elongation at break and impact strength were decreased.

Nanocomposites based on transition metal oxides in polyvinyl alcohol for EMI shielding application

Abstract: In the present work, the nanocomposites based on different transition metal oxides like iron oxide (Fe2O3), zinc oxide (ZnO), silicon dioxide (SiO2), zirconium dioxide (ZrO2), and titanium dioxide (TiO2) in PVA matrix have been studied for their suitability as electromagnetic interference (EMI) shielding materials in the frequency range of 4–8 GHz (C-band) and 8–12 GHz (X-band). The nanocomposites containing 0.1, 0.5, 1.0, 5.0, and 10.0 wt% of oxides in the matrix were synthesised by solvent casting method. The EMI attenuation studies in 4–12 GHz frequency range were carried out using the Vector Network Analyzer R & S: ZVA40 method by measuring the loss due to reflection. The minimum reflectivity values for the composites containing Fe2O3, ZnO, SiO2, ZrO2, and TiO2 in PVA matrix at 10 wt% concentration level in the matrix were found to be −38.85 dB (10.4 GHz), −33.65 dB (10.4 GHz), −41.90 dB (10.4 GHz), −24.90 dB (11.0 GHz), and −32.90 dB (9.76 GHz), respectively. Based on these results, the SiO2- and Fe2O3-based composites, which also exhibit high thermal stability and mechanical strength, are found to be low-cost and efficient EMI shielding materials.

Controlled release of highly water-soluble antidepressant from hybrid copolymer poly vinyl alcohol hydrogels

Abstract: This paper reports the development of hybrid copolymer poly vinyl alcohol hydrogel (H-PVA) based on acrylic acid (AA), 2-acrylamido-2-methyl propane sulfonic acid (AMPSA) and ethylene glycol dimethacrylate (EGDMA) The H-PVA hydrogels were used for controlled release study of highly water-soluble antidepressant drug (venlafaxine) The formation of new structure was confirmed by Fourier transform infrared spectroscopy The morphology of dry hydrogel slabs was examined by scanning electron microscopy Thermal gravimetric analysis of hydrogels showed that there was an increase in thermal stability of H-PVA hydrogels Swelling experiments performed in acidic and basic media provided important information on drug release properties of hydrogels The release of venlafaxine was significantly retarded in pH 12, while rapid release was observed in pH 74 The release rate of venlafaxine increased with increasing ratio of AA and AMPSA However, extent of drug release was significantly reduced on increasing ratio of EGDMA Mechanism of release has been analyzed using various mathematical models H-PVA hydrogel slabs were able to sustain the release of venlafaxine more than 20 h The results of the study suggest that optimized H-PVA hydrogels could serve as suitable controlled release matrices

Preparation method and physical, mechanical, thermal characterization of poly(vinyl alcohol)/poly(acrylic acid) blends

Abstract: A series of blends of poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) were prepared by solution mixing and casting. Glycerol was used as plasticizer. The blends were characterized for their physicochemical and thermo-mechanical properties. The FTIR results revealed the molecular level interaction between PVA and PAA at all blend ratios. The incorporation of PAA significantly reduced the storage modulus of PVA at a given temperature. PVA gradually lost its crystalline character with the increase of PAA and became fully amorphous when the PAA content in the blend exceeded 50 wt%. The kinetic parameters of the semi-crystalline blends were determined using the Avarami–Erofeev model, which showed excellent fitting with the experimental data from DSC. The loss in crystallinity of PVA also contributed to an increase in swelling of the blend when the PAA content is increased. The morphology study by FE-SEM demonstrated that there is no phase separation among the blend components at all blend ratios.

Development of novel hybrid nanocomposites based on natural biodegradable polymer–montmorillonite/polyaniline: preparation and characterization

Abstract: The problems with non-degradable materials in different applications have led to an interest in materials based on bionanocomposites. In this study, polymer–montmorillonite nanocomposites based on natural polymers (chitosan, alginate, gelatin and starch) and montmorillonite (MMT) were prepared using solution intercalation method. Then hybrid nanocomposites were synthesized by chemical oxidative polymerization of aniline in the presence of polymer–MMT nanocomposites. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) were employed to characterize the nanocomposites. FT-IR confirmed the successful preparation of hybrid nanocomposites. From the XRD results, intercalation of the MMT platelets in the matrix of polymers was examined. Further investigation by TEM images showed a mixed intercalated and flocculated structure for nanocomposites. Moreover, the TGA results showed improved thermal stability for the nanocomposites. The results presented in this study showed the feasibility of using these hybrid nanocomposites with improved properties in wide range of applications.

Synthesis and characterization of citric acid-based pH-sensitive biopolymeric hydrogels

Abstract: Biocompatible hydrogels based on citric acid (CA) with varying glycol unit, viz., ethylene glycol (EG), diethylene glycol and triethylene glycol were prepared along with acrylic acid. The formations of various hydrogels were confirmed using spectral techniques such as FT-IR and 1H NMR. Thermal stability (thermogravimetric analysis, DTA and differential scanning calorimetry) and morphology (SEM) of the synthesized hydrogels were investigated. Swelling studies of hydrogels at various pH values ranging from 4.0 to 10.0 were also investigated. The results of swelling studies show that the percentage of swelling is comparatively higher at higher pH than lower pH. Swelling equilibrium for various hydrogels was also found. Increased composition of CA in hydrogels at different pH values of 4.0, 6.0, 7.4, 8.0 and 10.0 enhanced the swelling equilibrium.

Mechanical behavior and optical transparency of polyamide 6 of different morphology formed by variation of the pathway of crystallization

Abstract: The phase composition and supermolecular structure of polyamide 6 (PA 6) melt-crystallized on cooling at different rates or cold-crystallized at different temperatures were characterized and related to the optical transparency, stiffness and the stress–strain behavior. Cold-crystallization results in non-spherulitic formation of γ-mesophase or α-crystals, depending on the maximum annealing temperature. Both mesophase and crystals are of nodular shape. Melt-crystallization at low supercooling leads to formation of lamellar α-crystals and spherulites, while at high supercooling the nodular mesophase is forming. The absence of spherulites in cold-crystallized PA 6 films leads to high see-through clarity which is in contrast to the slowly melt-crystallized samples with opaque appearance. While Young’s modulus and the glass transition temperature increase with increasing crystallinity, for samples of identical crystallinity stiffness is considerably higher if the crystals are of lamellar rather than of nodular shape. The higher glass transition temperature of cold-crystallized PA 6 is related to a higher rigid amorphous fraction than in melt-crystallized samples pointing to a stronger coupling of the amorphous phase to ordered domains.

Radiation vulcanization of natural rubber with polyfunctional monomers

Abstract: This study presents the effect of the polyfunctional monomers (PFMs) triallylcyanurate (TAC), triallylisocyanurate (TAIC), trimethylolpropane trimethacrylate (TMPT), ethylene glycol dimethacrylate (EDMA) and zinc diacrylate (ZDA) on the mechanical properties of natural rubber (NR) crosslinked by electron beam (EB) processing. Dependence of mechanical properties and crosslink density on irradiation dose was determined from a dose range of 50 to 200 kGy. The control blends, obtained with benzoyl peroxide as curing agent, were prepared by blending on a laboratory roller and the control sample curing was accomplished on hydraulic press at 160 °C. The results showed an increase in mechanical properties and crosslink density due to the introduction of PFMs. Also, based on the comparison between EB irradiation and dibenzoyl peroxide vulcanization efficiency, the experimental results show that EB irradiation gave the best results.

Collagen-based hydrogel films as drug-delivery devices with antimicrobial properties

Abstract: Collagen (coll)-containing hydrogel films were prepared by mixing degraded collagen with monomers such as acrylamide (AAm), and 2-hydroxy ethylmethacrylate (HEMA) before the polymerization/cross-linking of composites as p(coll-co-AAm), and p(coll-co-HEMA), respectively. These materials were used as drug-delivery devices for potential wound dressing materials by loading and releasing of model drugs such as gallic acid (GA) and naproxen (NP). A linear release profile was obtained up to 32-h release from GA-loaded p(coll-co-AAm) interpenetrating polymeric networks films, and 36-h linear release profile of NP for p(coll-co-HEMA). Furthermore, metal nanoparticles such as Ag and Cu prepared within these hydrogel films offered antimicrobial characteristic against known common bacteria such as Escherichia coli, Bacillus subtilis, and Staphylococcus aureus.

Biodegradable polymeric microspheres of gelatin and carboxymethyl guar gum for controlled release of theophylline

Abstract: Carboxymethyl guar gum (CMGG) was synthesized by carboxymethylation of guar gum (GG), which was blended with gelatin (GE) to obtain a novel semi-interpenetrating polymer network (semi-IPN) in the form of microspheres prepared by water-in-oil emulsion method to investigate the controlled release of theophylline (THP), an antiasthmatic drug. Electronic spectroscopy revealed the drug encapsulation ranging from 56 to 74 %. Fourier Transform infrared spectroscopy confirmed the carboxymethylation of GG as well as the semi-IPN structure of the blend polymer. Scanning electron microscopy indicated the smooth surfaces with spherical microspheres. Differential scanning calorimetric and X-ray diffraction studies showed the molecular level dispersion of drug in the microspheres. The in vitro drug release profiles were analyzed to study the effect of polymer blend composition, % drug loading and amount of glutaraldehyde added as a crosslinker. The drug release was extended up to 26 h. The in vitro release data performed in acidic and alkaline media were analyzed using the empirical equations to understand the release profiles of THP.

Characterization and proof testing of the halochromic shape memory polyurethane

Abstract: Polyurethane (PU) grafted with several well-known pH indicators (alizarin yellow, bromocresol green, bromocresol purple, or thymol blue) via spacer is characterized for thermal, spectroscopic, mechanical, and shape memory properties, as well as for PU color change to aqueous solution with various pH values. The PU polymer frame is composed of 4,4′-methylenebis(phenylisocyanate) (MDI), which acts as a hard segment, poly(tetramethyleneglycol) (PTMG) as a soft segment, and a covalently linked pH indicator. The four different PU series studied in this work display characteristic color dependent upon the grafted indicator type. The PU series also exhibit a small degree of cross-linking due to the grafting agent used to covalently link the indicator to the PU frame. The tensile mechanical strength and the shape recovery of the indicator-grafted PU remain high after repeated tests compared to that of the plain linear PU. Regarding the tensile mechanical properties, the maximum stress and the strain increase to 424 and 1,880 %, respectively, for indicator-grafted PU compared to the linear PU. Furthermore, the shape recovery is observed to reach 98 % and improves after each test cycle. A reversible color change is observed after repeated exposure to aqueous solutions with varying pH values and is confirmed with UV-VIS spectra results.

How does a chain-extended polylactide behave?: a comprehensive analysis of the material, structural and mechanical properties

Abstract: The presented contribution deals with the material properties of chain-extended polylactide. In the course of this study, two different functional additives were used, namely an epoxidized and a maleated styrene-acrylic copolymer. Both additives were compounded together with polylactide using a conventional twin-screw extruder, and were then injection moulded to standardized testing specimens. The main focus of the investigation is on structural changes as well as the mechanical performance, e.g. crack propagation and arresting mechanisms that are affected by reactive chain extension. The first section of the experimental part consists of results regarding modifications achieved on the macromolecular level. Based on size exclusion chromatography and DSC-OIT experiments, different structural changes and their influence on the material behaviour are presented. Subsequently, a comprehensive analysis of the quasi-static tests and the impact strength of notched and unnotched specimens was performed, and correlated with the following fatigue experiments. A discussion concerning morphological aspects and finally a correlation to the fracture surface topography after fatigue test completes the experimental part.

Structural changes and enhanced accessibility of natural cellulose pretreated by mechanical activation

Abstract: A kind of natural cellulose, bleached pine pulp (BPP), was pretreated by mechanical activation (MA) using a self-designed stirring ball milling. The effect of MA pretreatment on the dissolving capacity and molecular chain structure of BPP were investigated by the determination of alkaline solubility (Sa) and degree of polymerization (DP). In addition, the changes in crystal structure of MA-pretreated BPP with different milling times were qualitatively and quantitatively measured by X-ray diffraction and Fourier transform infrared spectroscopy, and the morphology modification was observed by scanning electron microscopy. It was found that MA significantly increased the Sa and reduced the DP of BPP, contributing to the destruction of inter- and intramolecular hydrogen bonds and macromolecular chains in cellulose. The stable crystal structure of BPP was also remarkably damaged during MA processing, resulting in the variation of surface morphology, the increase of amorphous region ratio and hydrogen bond energy, and the decrease in crystallinity and crystalline size, which efficiently increased the accessibility of natural cellulose and would have positive effects on subsequent treatments. The crystalline form of natural cellulose was not changed by MA, and no new functional groups generated during milling.

Investigation of the effect of nano-clay type on the non-isothermal crystallization kinetics and morphology of poly(3(R)-hydroxybutyrate) PHB/clay nanocomposites

Abstract: PHB is a thermoplastic biopolymer produced by fermentation of renewable resources. Secondary crystallization during storage leading to an increased degree of crystallinity is a principal reason of PHB brittleness. In addition, pure PHB has no residues of catalysts, meaning low nucleation density and slow crystallization rates, leading to the formation of large spherulites with cracks and brittleness. To overcome the brittleness of PHB, polymer composites based on PHB, plasticizers, and nano-clays A and B were prepared by solvent casting. The addition of plasticizer decreases T g from 5 to −13 °C in all composites. Furthermore, the addition of nano-clays acts as a nucleating agent to PHB. The effect of nano-clays A and B on spherulites morphology, thermal behavior, and crystal structure of PHB composites were tested by several techniques. Differential scanning calorimetry analysis shows that the addition of nano-clay A does not change the crystallization temperature and the crystallization half-time (t 1/2) of the PHB matrix but that nano-clay B accelerates the crystallization process. Thermogravimetric analysis revealed an increase in thermal stability of composites containing nano-clay B. Polarized optical microscopy showed that nano-clays serve as nucleating agents in PHB matrix. Therefore, the spherulites become smaller and the nuclei density increases at the selected crystallization temperature, compared to pure PHB.

Effects of benzoyl peroxide on some properties of composites based on hemp and natural rubber

Abstract: The obtaining and characterization of polymer composites based on natural rubber and hemp, in which the elastomer crosslinking has been achieved with benzoyl peroxide, are presented. The mechanical characteristics, gel fraction, crosslink density, water uptake swelling parameters and FTIR of the composites based on natural rubber and hemp fiber vulcanized by dibenzoyl peroxide have been investigated as a function of the hemp content. The hardness, modulus at 100 % elongation, tearing strength, tensile strength and elongation at break have been improving with the increasing of fiber content in composites materials due to the better interaction of fiber in natural rubber composites. These results indicate that hemp has a reinforcing effect on natural rubber. Gel fraction value is over 95 % for all blends and varies irregularly depending on the amount of hemp in the composites. The crosslinking density (ν) of samples increases as the amount of hemp in blends increases, because hemp act as a filler in natural rubber blends and leads to reinforcement of the blends. The water uptake and swelling parameters also increases with the increasing of the amount of fiber content, because of the hemp hydrophilic characteristics.

Microencapsulation of n-hexadecane phase change material by ethyl cellulose polymer

Abstract: Microencapsulation of phase change materials (PCMs) is an attractive opportunity for broadening their applications. In this respect, a novel encapsulating polymer, ethyl cellulose (EC) was used to entrap n-hexadecane (HD) PCM by an emulsion-solvent evaporation method. Emulsifiers strongly influenced the size and morphology of the forming EC–HD composite microcapsules, and they also had a great impact on their thermal properties. All of the three emulsifiers were suitable to prepare quasi core–shell microparticles, though the high porosity of shells resulted in serious leakage in composites prepared by Tween 80, and permeability of particles manufactured by poly(vinyl alcohol) (PVA), as can be stated from scanning electron microscopy and differential scanning calorimetry analysis. Interfacial tension measurements and spreading coefficient analysis enabled the prediction of preparation conditions for usable core–shell microcapsules. Volume-weighted mean diameters of the microparticles were 319, 92 and 85 μm formed by Tween 80, PVA and poly(methacrylic acid sodium salt) (PMAA), respectively. A significantly higher HD content and latent heat storage capacity could be achieved using PVA and PMAA than with Tween 80. The thermal cycling test indicated good thermal reliability of microcapsules prepared by PMAA, while the energy-storing capacity of composites prepared by PVA decreased substantially, and a dramatic reduction was found in microparticles using Tween 80.

Investigation on the structure and crystallization behavior of controlled-rheology polypropylene with different stereo-defect distribution

Abstract: Understanding concerning the influence of peroxide degradation on the stereo-defect distribution and related crystallization kinetics of controlled-rheology polypropylene are of great importance. In this study, two iPP samples (PP-A, PP-B) with similar molecular weights and average isotacticities, but different stereo-defect distributions and their degradation productions after the addition of dicumyl peroxide (DCP) were prepared. Their melt flow indexes (MFI), stereo-defect distributions, crystallization behaviors and kinetics were studied using MFI measurement, differential scanning calorimetry, wide-angle X-ray diffraction, non-isothermal crystallization kinetics and successive self-nucleation and annealing fractionation. The results showed that as the content of DCP increased, the MFI, the crystallization temperature and crystallization rate of PP increased gradually, the crystallization peak width became narrower, and the crystallite size decreased. Meanwhile, the addition of DCP greatly restrained the formation of thick lamellae and narrowed its stereo-defect distribution [meso-sequence length (MSL) distribution]. On the other hand, results showed that PP resins with different stereo-defect distribution have similar MFI variations after degradation. PP-A (whose stereo-defect distribution was less uniform than PP-B) and its degradation products still possess higher crystallization rate, stronger crystallizability, smaller crystallite size and higher fractions of long MSL, compared with their counterparts of PP-B.

Selected biotrends in development of epoxy resins and their composites

Abstract: Epoxy resins and their fibre or particulate composites are widely used in various industries, including building, naval, aircraft, automotive and aerospace. Modern polymer science and technology focus on the development of green polymers and composites. There are two major areas of interest in the case of epoxy resins: the development of bio-based resins and the production of composites with natural fibres. One of the most interesting challenges is developing fully bio-based composites: that is, epoxy resins based on renewable resources and natural fibres. This paper presents a review of literature on epoxy resins and hardeners based on renewable resources (especially vegetable oils) and epoxy composites with natural fibres. We also describe some of the effective methods of improving the mechanical properties of epoxy–natural fibres composites, including chemical modification of the fibre surface and the application of hybrid reinforcements.

Chitosan/poly(vinyl alcohol) hydrogels for amoxicillin release

Abstract: Chitosan and poly(vinyl alcohol)-based hydrogel films were synthesized using tartaric acid as a crosslinking agent. The films denoted as CVT were then characterized using Fourier transform infrared, Nuclear magnetic resonance, X-ray diffraction, and scanning electron microscopy analysis. TG/DTG and DSC analysis were also carried out for the determination of thermal properties of hydrogel films. Swelling properties of these hydrogel films were investigated at two different pHs and temperatures. The swelling behaviors of all samples were increased in acidic medium, while decreased in alkaline medium. The enzymatic degradation of the hydrogels was studied using lysozyme, and degradation rates were found to be parallel with the swelling ratio for CVT hydrogel. The hydrogels were also used for the amoxicillin release in KCl/HCl and PBS buffer solutions. The release behaviors of CVT hydrogel films were slower and can be controlled as compared with commercial drug release systems. CVT hydrogel films may be more appropriate for controlled release of amoxicillin.

Effects of crosslinking degree of poly(vinyl alcohol) hydrogel in aqueous solution: kinetics and mechanism of copper(II) adsorption

Abstract: Recently, a renewed interest in hydrogels for heavy metal removal of wastewater has been growing because of embarking opportunities in industrial applications. One of the most interesting hydrogels potentially used as absorbent is poly(vinyl alcohol) (PVA), owing to its biocompatibility. In this study, the adsorption capacity of copper(II) ion onto PVA hydrogel (PVAH) adsorbents with different crosslinking degrees of 1, 3 and 5 % from aqueous solution was investigated. The PVAH adsorbents were prepared from PVA, using glutaraldehyde as a crosslinking agent. Their properties were determined by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and water absorption measurement. The results showed that PVA was crosslinked with glutaraldehyde. It exhibited an equilibrium swelling ratio in the range of 195–250 %, depending on the crosslinking degree with different PVAH structures defined from SEM micrographs. The adsorption capacity of copper(II) ion onto PVAH adsorbents was investigated and found that higher crosslinking degree decreased the absorption capacity. This behavior is due to the decrease in reactive sites, resulting in the decrease of interaction between copper(II) ion and PVA. Besides, the adsorption capacity also depended on contact time, pH and temperature. The adsorption process followed pseudo-second-order kinetic, having a 0.99 correlation coefficient. Intraparticle diffusion was confirmed by the adsorption mechanism controlled by particle and film diffusions.

Enhancement in crystallization kinetics of the bacterially synthesized poly(β-hydroxybutyrate) by poly(butylene succinate)

Abstract: Poly(β-hydroxybutyrate), PHB, is a bio-based and biodegradable material. However processing and application of the PHB are disturbed by its low crystallization rate. In this manuscript the crystallization behavior of the PHB was improved via incorporation of another biodegradable polymer, i.e. poly(butylene succinate), PBS. The two polymers show phase separation in the blends. PBS varies from a dispersed phase to a continuous phase with increasing its content from 20 to 70 wt% and a co-continuous morphology is observed at PBS 50 wt%. Although the spherulitic radial growth rate of the PHB is retarded to a certain extent by the PBS, the non-isothermal crystallization temperature is increased by around 30 °C while the half-life crystallization time is reduced significantly, indicating an increased overall crystallization rate of the PHB. The increased crystallization rate of PHB is attributed to a modified multi-nucleation mechanism, i.e. homogeneous nucleation, heterogeneous nucleation and self-enhanced nucleation.

High strain rate compressive behavior of PMMA

Abstract: Polymethylmethacrylate (PMMA) materials are extensively used for diverse applications e.g., protective vehicular windows to eye protection devices. However, the high strain rate deformation and fracture mechanisms of PMMA are far from well understood. Therefore, controlled split Hopkinson pressure bar (SHPB) experiments that could lead to deformation with and without fracture were conducted on PMMA samples at strain rates of ~4 × 100 to 1.3 × 103 s−1. With increase in strain rate, the maximum compressive yield strength of PMMA is enhanced by about 25 %. Absence of global failure characterized the deformation at relatively lower strain rates (e.g., ~4.75 × 102 to 6.75 × 102 s−1), while its marked presence characterized the same at comparatively higher strain rates (e.g., ~7.69 × 102 to 9.31 × 102 s−1). Attempts were made to explain these observations by the subtle changes in failure mechanisms as revealed from the fractographic examinations of the PMMA samples deformed with and without failures. The implications of the test-condition induced restrictions on the degrees of freedom locally available to the polymeric chains were discussed in the perspective of the relative strain rate dependencies of the yield behaviors of the present PMMA samples.

[6]-Gingerol-loaded cellulose acetate electrospun fibers as a topical carrier for controlled release

Abstract: [6]-Gingerol (6 % w/v)-loaded cellulose acetate (12 % w/v CA; MW ~ 3 × 104 g/mol) fibers (375 ± 107 nm) were prepared by electrospinning at 7.5 kV. ATR-FTIR spectra indicated that the mixture was miscible at this composition. Differential scanning calorimetry revealed that [6]-gingerol was uniformly dispersed in the CA matrix and interrupted the hydrogen bond formation among the CA chains. Controlled release study showed that ~97 % of the loaded [6]-gingerol could be released from the loaded fibers to the acetate buffer solution at 37 °C, whereas only ~74 % of it could be done from the corresponding films. About 92 % of [6]-gingerol in the fibers was dramatically released within 4 h. Release was mainly governed by a diffusion-controlled mechanism. The radical scavenging assay showed antioxidant activity of the loaded fibers. The in vitro cytotoxicity test revealed that the viability of L-929 mouse fibroblast cells to the loaded fibers was ~65 %.

Thermal and mechanical properties of poly(lactic acid) modified by poly(ethylene glycol) acrylate through reactive blending

Abstract: Poly(lactic acid) (PLA) was modified using a simple reactive blending method, where a low molecular weight poly(ethylene glycol) acrylate (PEGA) was blended with PLA in the presence of a radical initiator. To examine the initiation effect on the modification of PLA, various amounts of radical initiator (between 0 and 1.5 %) were added to the PLA/PEG acrylate mixture. The modified PLAs (PLMs) were characterized by gel permeation chromatography, Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, and solvent extraction. The properties of the PLMs were investigated using tensile testing, differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and hydrolytic degradable analysis. The PEGA significantly influenced the molecular structure and properties of the modified PLA. The glass transition temperature of the PLMs was decreased by approximately 15 °C (for PLM15) from 59.3 °C of PLA, whereas their toughness increased considerably compared to PLA. In addition, PEG acrylate facilitates hydrolytic degradation, even after radical polymerization by reactive blending.

Microwave-assisted synthesis of alginate-g-polyvinylpyrrolidone copolymer and its application in controlled drug release

Abstract: The aim of this study is to synthesize graft copolymer (NaAlg-g-PVP) in microwave oven and prepare pH-responsive beads with high entrapment efficiency. For this purpose, PVP was grafted onto sodium alginate using microwave radiation. The copolymer obtained was characterized using FTIR, 1H-NMR, elemental analysis and thermogravimetric analysis. A series of NaAlg-g-PVP beads were prepared as drug delivery matrices for ibuprofen (IB) by cross-linking into beads via glutaraldehyde. The chemical stability of IB after encapsulation into beads was confirmed by FTIR, DSC, and X-RD analysis. Synthesis conditions of beads were optimized by considering entrapment efficiency, particle size, swelling capacity and their release data. Effects of such variables as graft yield and drug/polymer ratio were investigated at 1.2 and 7.4 pH values. Increasing the drug/polymer ratio and extent of cross-linking caused decrease in the IB release. On the other hand, increase in the graft yield led to increase in the IB release as well. The results also showed that NaAlg-g-PVP beads were positive pH-responsive.

Synthesis and application of salt tolerance amphoteric hydrophobic associative flocculants

Abstract: A series of amphoteric hydrophobic-associative flocculants with outstanding flocculation efficiency and salt tolerance, poly(acrylamide/acrylic acid/dimethyl benzyl aminoethyl acrylate chloride), are successfully prepared (named AAB series) and used to flocculate the montmorillonite suspensions. The solution properties of AAB copolymer are systematically evaluated by viscometer, rheology and steady-state fluorescence analysis. The results suggest that the space network structure forming via hydrophobic-associating interaction can increase solution viscosity and improve the bridging capacity of copolymers. Meanwhile, the apparent viscosity in salt solution increases with increase in the concentration of salt stemming from the anti-polyelectrolyte effect of polyampholyte. Further, the flocculation performances of flocculants in 1 wt% montmorillonite suspensions are evaluated by turbidity, optimal dosage and settlement rate measurement. The results elaborate that the flocculation performances of amphoteric hydrophobic-associating AAB flocculants are better than that of commercial flocculants (cationic and anionic polyacrylamide) and homemade cationic flocculant (AAB-0-5) independent of the type and concentration of salt. The novel ampholyteric hydrophobic-associative flocculants will exhibit intriguing prospective in industry water treatment, in that the anti-polyelectrolyte effect of polyampholyte and hydrophobic-associating interaction can endow excellent flocculation efficiency and salt tolerance.

Inter-polymer complex microspheres of chitosan and cellulose acetate phthalate for oral delivery of 5-fluorouracil

Abstract: Inter-polymer complexes (IPCs) of chitosan (CS) and cellulose acetate phthalate (CAP) have been prepared to develop spherical microspheres by a novel emulsion-solvent evaporation technique. The microspheres were used for the oral delivery of 5-fluorouracil (5-FU), an antimetabolite and antineoplastic agent, whose release time was extended up to 12 h. Formulations were prepared by varying the concentrations of CS, CAP and 5-FU. FTIR confirmed the formation of IPC, indicating no chemical interactions of 5-FU with the polymer matrix. Scanning electron microscopy suggested spherical shape of the microspheres with smooth surfaces. Average particle size measured by optical microscopy varied between 2.7 and 5.5 μm. Differential scanning calorimetry showed amorphous dispersion of 5-FU particles into the IPC matrix. Encapsulation efficiency as estimated by UV was dependent on polymer composition with the highest value of 96 %. Water uptake by the IPC microspheres was higher at higher concentration of CS in the matrix. In vitro drug release performed in pH 1.2 and pH 7.4 buffer media showed a dependence on compositions of CS, CAP and drug loading. Molar mass between cross-links (M c) and cross-link density (d x ) values of the polymer matrix calculated from swelling data indicated the formation of a dense matrix between CS and CAP; the matrix was able to control the release of 5-FU. The in vitro release data have been fitted to empirical equations to understand the nature of drug release mechanism.