Showing papers in "Polymer Bulletin in 2017"

Cellulosic materials as natural fillers in starch-containing matrix-based films: a review

Abstract: In this work, the different cellulosic materials, namely cellulose and lignin are analyzed. In addition, the starch-containing matrices (isolated starch and flour) reinforced with cellulosic materials to be used in packaging applications are described. Many efforts have been exerted to develop biopackaging based on renewable polymers, since these could reduce the environmental impact caused by petrochemical resources. Special attention has had the starch as macromolecule for forming biodegradable packaging. For these reasons, shall also be subject of this review the effect of each type of cellulosic material on the starch-containing matrix-based thermoplastic materials. In this manner, this review contains a description of films based on starch-containing matrices and biocomposites, and then has a review of cellulosic material-based fillers. In the same way, this review contains an analysis of the works carried out on starch-containing matrices reinforced with cellulose and lignin. Finally, the manufacturing processes of starch/cellulose composites are provided as well as the conclusions and the outlook for future works.

Evaluation of highly filled epoxy composites modified with walnut shell waste filler

Abstract: Epoxy composites modified with ground walnut shell used as organic waste fillers were prepared and examined. Post-agricultural waste materials after grinding were characterized by evaluation of grain size distribution and structure observations realized using scanning electron microscope (SEM). The influence of filler addition on the mechanical properties of epoxy-based composites was determined by: static tensile test, Charpy impact test, and ball indentation hardness measurements. Composite samples containing 20, 30, 40, and 50 wt% of walnut shell were characterized by increased stiffness and hardness in comparison to the unmodified resins. Moreover, the incorporation of the filler resulted in a decrease of composite material tensile strength and impact resistance. Thermo-mechanical properties of the composites were investigated by dynamic mechanical thermal analysis (DMTA). Results obtained from DMTA tests showed a growth in the composites’ stiffness at elevated temperatures as a function of the increasing natural filler content. The material characterization was supplemented by thermal stability evaluation realized by thermogravimetric analysis (TGA). It was found that the incorporation of ground walnut shell led to an improved thermal stability of composite materials. The analysis of the change in composite material properties, caused by natural filler incorporation, was complemented by material microstructure observations.

Polyvinyl alcohol/tannic acid hydrogel prepared by a freeze-thawing process for wound dressing applications

Abstract: The objective of this study was to develop an effective, potential wound dressing consisting of a blended hydrogel of polyvinyl alcohol (PVA) and tannic acid (TA). PVA is known for its biocompatibility and hydrophilicity, and TA is known for being a natural compound which can serve as a cross-linking agent and a therapeutic agent. To prepare the PVA/TA hydrogel, a blended aqueous solution of PVA and TA was processed through three cycles of freezing at −20 ± 3 °C for 18 h followed by thawing at 25 °C for 6 h. Consequently, the PVA/TA hydrogel was successfully prepared through the freeze-thawing process. In an investigation of the hydrogel, it was found that the mechanical strength and hardness increased and that the moisture content decreased as the TA concentration was increased. Moreover, the PVA/TA hydrogel showed excellent antibacterial ability (>99.99%) and antioxidant ability (>92%).

Synthesis, characterization, and fertilizer release study of the salt and pH-sensitive NaAlg-g-poly(AA-co-AAm)/RHA superabsorbent nanocomposite

Abstract: New slow release nitrogen (N), phosphorous (P), and potassium (K) (NPK) fertilizer formulation was synthesized by in situ free-radical graft copolymerization of sodium alginate (NaAlg), acrylic acid (AA), and acrylamide (AAm) in the presence of rice husk ash (RHA) and fertilizer compound solution. FTIR results confirmed that NaAlg chains have been grafted onto acrylate monomers successfully. The water absorbency of hydrogel sample was affected greatly by different salt and pH solutions. The swelling ratio of the hydrogel sample was increased from 830 to 1070 g/g by the addition of RHA up to 15 wt%. The experimental findings indicated that incorporation of RHA into the hydrogel network not only improved its water retention capability, but also caused the system to liberate fertilizer in a more controlled manner compared with the neat hydrogel. Consequently, this new environment-friendly product with good slow release property and high water retention capacity can be useful in agricultural and horticultural applications.

Synthesis and surface analysis of self-matt coating based on waterborne polyurethane resin and study on the matt mechanism

Abstract: Self-matt coating of waterborne polyurethane (WBPU) was synthesized by combining prepolymer and self-emulsification methods. The emulsion was fabricated from both hydroxy carboxylic acid and aminosulfonic acid types of hydrophilic chain-extending agents, in which the 2-[(2-aminoethyl) amino] ethane sulphonate sodium (AAS salt) was produced in laboratory. This emulsion demonstrated an excellent matt performance without the addition of extra matting agents after filming. Four different kinds of surface properties were measured on the film: the specular gloss (60° gloss meter), the contact angle (CA), the surface roughness degree (3D Surface Profilometer), and the topography of the coatings surface (SEM). The results showed that tons of spherical particles with diameter in a few micrometers were aggregated on the film surface. The effect of the roughness parameters (R a and R q ) and the average particle size of the emulsions on the specular gloss degree were probed. The research indicated that the emulsion with average particle size in the range of 2.5–3.0 µm and, meanwhile, the film with roughness parameters R a and R q both greater than 1 µm could attain the best matt effect. The WBPU emulsions showed good physical and mechanical properties, and were introduced into wood varnish for matting purpose.

High thermal conductivity and low absorptivity/ emissivity properties of transparent fluorinated polyimide films

Abstract: Polyimide film materials are a very promising and high-performance polymer in space application. However, the deep coloration of conventional polyimide films greatly limits the wide use in areas where transparency and low solar absorptance are the essential requirement. Here, we prepared the transparent polyimide from 4,4 $$^{\prime }$$ -(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and different ratios of 2,2 $$^{\prime }$$ -bis(trifluoromethyl)-benzidine (TFB) and 2,2-bis(4-(4-aminophenoxy)-phenyl) hexafluoropropane (BAPP) with a low solar absorptance. Properties, such glass-transition temperature, thermal decomposition temperature, thermal conductivity and transmittance, were investigated, It is suggested that the introduction of fluorine into polyimide will significantly increase transmittance and in turn decrease solar absorptance, The polyimide film with fluorinated groups exhibited superior optical transparency, low absorptivity/emissivity, high thermal conductivity, and good resistance to ultraviolet radiation. The transparent polyimide exhibits a low solar absorptivity of 0.04 and infrared emissivity of 0.6.

Toughening effect of liquid natural rubber on the morphology and thermo-mechanical properties of the poly(lactic acid) ternary blend

Abstract: In this work, poly(lactic acid) (PLA) was melt blended with liquid natural rubber (LNR) and linear low-density polyethylene (LLDPE) to fabricate a PLA–LNR–LLDPE ternary blend. The torque rheology demonstrates the melt mixing behavior of PLA–LLDPE binary and PLA–LNR–LLDPE ternary blends. Mechanical properties of ternary blend illustrate the highest toughness as compared to neat PLA and PLA–LLDPE binary blend. Fracture morphology reveals the plastic deformation behavior in the ternary blend which is illustrated in TEM micrograph. The cold crystallization temperature of the ternary blend appears at a lower temperature as compared to the binary blend. The thermal stability of PLA is improved due to blending with LLDPE and LNR. The ternary blend exhibits greater storage modulus in the glassy state as well as in the rubbery state as compared to neat PLA and binary blend. Finally, LNR performed as an effective compatibilizer between PLA and LLDPE.

Properties of UV protective films of poly(vinyl-chloride)/TiO2 nanocomposites for food packaging

Abstract: This work studies the UV protection properties of poly(vinyl-chloride) (PVC) nanocomposites. A functional property of UV protection is achieved by adding the active component (titanium dioxide (TiO2) or titanium dioxide modified with silver nitrate and copper nitrate) to the PVC matrix. PVC nanocomposites were prepared by extrusion and then pressed into films. Prepared PVC nanocomposites were characterized by thermogravimetric analysis, UV–Vis spectroscopy, X-ray diffraction and scanning electron microscopy. The mechanical properties and antimicrobial activity were also studied. The results show that PVC nanocomposites’ thermal stability is improved in relation to a pure PVC polymer. The thermal stability and antimicrobial efficiency increase when higher silver nitrate content is used. The sample prepared with silver and copper nitrate shows the best thermal stability due to a modified mechanism of thermal degradation. Samples where nanoparticles are homogeneously dispersed in the polymer matrix show good mechanical properties. The results also show that adding the active component TiO2 modified with silver ions contributes to the improved UV protection property of nanocomposite materials.

Radiation synthesis and characterization of polyvinyl alcohol/chitosan/silver nanocomposite membranes: antimicrobial and blood compatibility studies

Abstract: Polyvinyl alcohol/chitosan/silver (PVA/CS/Ag) nanocomposite membranes were synthesized by γ-radiation with promising antimicrobial and biomedical applications. The nanocomposite membranes were prepared by mixing PVA and CS solutions with different copolymer compositions in the presence of silver nitrate (AgNO3) and glutaraldehyde as cross-linker, followed by in situ reduction with γ-radiation at different doses. The nanocomposite membranes were characterized by ultraviolet spectroscopy (UV), Fourier transform infrared, X-ray diffraction (XRD) and transmission electron microscopy (TEM). UV studies showed a strong peak around λ max at 430 nm due to surface plasmon resonance of silver nanoparticles formed during irradiation. As the irradiation dose increased from 25 to 75 kGy, the plasmon band is shifted from 430 to 418 nm with high intensity, indicating the formation of smaller particles. TEM investigation showed uniform distribution of silver nanoparticles (AgNPs) in the membranes with mean diameter of 32–19 nm. XRD results confirmed that the mean diameter of AgNPs estimated from the Debye–Scherrer formula was in the range of 27.5–12.8 nm which confirms the TEM results. The PVA/CS/Ag nanocomposite membranes exhibited good antibacterial activity and were found to cause significant reduction in microbial growth. The nanocomposite membranes showed non-thrombogenicity effect and slightly haemolytic potential, suggesting their promising use in biomedical applications.

Water absorption, residual mechanical and thermal properties of hydrothermally conditioned nano-Al2O3 enhanced glass fiber reinforced polymer composites

Abstract: The durability of the nano-Al2O3 enhanced glass fiber reinforced polymer (GFRP) composites in hydrothermal environment is necessary for hydro/hygro thermal applications. The present investigation emphasizes the effect of nano-Al2O3 filler concentration on moisture absorption kinetics, residual mechanical and thermal properties of hydrothermally treated GFRP nano-composites. Nano-Al2O3 particles were mixed with epoxy matrix through temperature assisted magnetic stirrer and followed by ultrasonic treatment. It has been observed that, the addition of 0.1 wt% of nano-Al2O3 into the GFRP nano-composites reduces the moisture diffusion coefficient by 10%, as well as improves the flexural residual strength by 16% and interlaminar residual shear strength by 17% as compared to the neat epoxy GFRP composites. However, the glass transition temperature has not been improved by the addition of nano-Al2O3 filler. Weibull design parameters have been determined for dry and hydrothermally conditioned nano-composites. A good agreement between the experimental and the simulated stress–strain results has been observed. The interface failure mechanism has been evaluated by field emission scanning electron microscope to support the new findings.

Preparation of the chitosan/polyacrylonitrile semi-IPN hydrogel via glutaraldehyde vapors for the removal of Rhodamine B dye

Abstract: In the present study, a chitosan/polyacrylonitrile semi-IPN hydrogel system was developed. To do so various blends of chitosan/polyacrylonitrile were prepared. The miscibility of the polymers, crosslinking of chitosan via glutaraldehyde vapors to produce semi-IPN and microstructures of the hydrogels were determined with DSC, FT-IR and FE-SEM, respectively. The DSC thermograms of hydrogels blends showed a single Tg (at 179–152 °C for Gel1–Gel4), which suggested good miscibility between the two polymers. For semi-IPN (Gel7) the Tg appeared at slightly lower temperature (128 °C), which suggested reduced intermolecular interactions between the two polymers due to the crosslinking of the chitosan. FT-IR showed no change in the characteristic bands positions of the two polymers for hydrogel blends(Gel1–Gel4) and a characteristic doublet at 1563 cm−1 and 1630 cm−1 (for the crosslinking of chitosan with glutaraldehyde) for semi-IPN hydrogel (Gel7). The FE-SEM micrographs showed homogenous (with no phase separation) surface and cross section morphologies for the blends hydrogels (Gel1–Gel4) and semi-IPN hydrogel (Gel7). The aqueous behaviors of the blend hydrogel (Gel1) and semi-IPNs (Gel5–Gel7) were investigated with the reported methods. The % degree of swelling was observed to decrease whereas stability increased as the crosslinking time was increased. The semi-IPN hydrogel (Gel7) showed improved stability and fair swelling. The potential of blend hydrogel (Gel1) and semi-IPNs hydrogel (Gel7) as adsorbents for the adsorption of Rhodamine B dye was studied. Rhodamine B dye showed significant adsorption affinity for semi-IPN hydrogel (Gel7). The data fitted best to pseudo-second-order kinetic and Langmuir isotherm. Intraparticle diffusion model confirmed that diffusion is not the only rate-limiting step, some degree of boundary layer control may be also operating.

Synthesis and swelling behavior of metal-chelating superabsorbent hydrogels based on sodium alginate-g-poly(AMPS-co-AA-co-AM) obtained under microwave irradiation

Abstract: A metal-chelating superabsorbent hydrogel based on poly(2-acrylamido-2-methylpropanesulfonic acid-co-acrylic acid-co-acrylamide) grafted onto sodium alginate backbone, NaAlg-g-poly(AMPS-co-AA-co-AM) is prepared under microwave irradiation. The Taguchi method is used for the optimization of synthetic parameters of the hydrogel based on water absorbency. The Taguchi L9 (34) orthogonal array is chosen for experimental design. Mass concentrations of crosslinker MBA $$C_{\text{MBA}}$$ initiator KPS $$C_{\text{KPS}}$$ , sodium alginate $$C_{\text{NaAlg}}$$ and mass ratio of monomers $$C_{\text{AM/AA/AMPS}}$$ are chosen as four factors. The analysis of variance of the test results indicates the following optimal conditions: 0.8 g L−1 of MBA, 0.9 g L−1 of KPS, 8 g L−1 of NaAlg and $$R_{\text{AM/AA/AMPS}}$$ equals to 1:1.1:1.1. The maximum water absorbency of the optimized final hydrogel is found to be 822 g g−1. The relative thermal stability of the optimized hydrogel in comparison with sodium alginate is demonstrated via thermogravimetric analysis. The prepared hydrogel is characterized by FTIR spectroscopy and scanning electron microscopy. The influence of the environmental parameters on water absorbency such as the pH and the ionic force is also investigated. The optimized hydrogel is used as adsorbent for hazardous heavy metal ions Pb(II), Cd(II), Ni(II) and Cu(II) and their competitive adsorption is also discussed. Isotherm of adsorption and effect of pH, adsorption dosage and recyclability are investigated. The results show that the maximum adsorption capacities of lead and cadmium ions on the hydrogel are 628.93 and 456.62 mg g−1, respectively. The adsorption is well described by Langmuir isotherm model. The hydrogel is also utilized for the loading of potassium nitrate as an active agrochemical agent and the release of this active agent has also been investigated.

Synthesis and characterization of agarose–bacterial cellulose biodegradable composites

Abstract: Agarose is an abundant and biodegradable polymer with strength comparable or higher than other commonly used natural polymers. Agarose can be used for wound dressing and tissue engineering applications. Excessive water uptake and moderate strength limit its applicability for various applications. The objective of this study was to enhance its strength by reinforcing with bacterial cellulose. The addition of bacterial cellulose exhibited remarkable enhancement of 140% in the tensile strength of agarose bioplastic. The strength increased from 25.1 MPa for agarose bioplastic to a maximum of 60.2 MPa for 20% (w/w) of bacterial cellulose. There was a decrease in the amount of water absorption; at 37 °C, the composite films absorbed 450% of their own weight of water, as against 700% absorption by un-reinforced bioplastic films at the same temperature. Thermogravimetric analysis did not reveal any perceivable change in the thermal stability of the bioplastic. Biodegradability of composite films was also established.

Preparation, morphology and properties of natural rubber composites filled with untreated short jute fibres

Abstract: Green composites were obtained by incorporation of short jute fibres in natural rubber matrix using a laboratory two-roll mill. The influence of untreated fibre content (1, 2.5, 5, 7.5 and 10 phr) on the mechanical properties, dynamic mechanical properties, swelling properties was examined. The behaviour of prepared green composites under cyclic compression was also investigated. Fibre dispersion in rubber matrix was studied by scanning electron microscopy. The highest tensile strength (21.1 MPa) and highest tear strength (39.9 N/mm) were found for composites containing 2.5 and 5 phr of short jute fibres, respectively. The results also suggested that increasing fibrous filler content resulted in increasing of tensile moduli 100, 200 and 300 % of elongation and hardness, and decreasing of rebound resilience and abrasion resistance of prepared jute/natural rubber composites. The cyclic compression test showed that increasing the amount of short jute fibres in the rubber matrix is related to increase of the energy dissipated in the composite. The incorporation of short jute fibres into the rubber matrix improves the stiffness of the composites, and it is related to the interaction between fibre surface and rubber matrix. The application of short fibres in higher amounts leads to formation of fibre agglomerates reducing the mobility of the rubber polymer chains. The mentioned agglomerates act as defects in rubber matrix, which caused decreasing of some properties, e.g. relative elongation at break.

A review on recent researches on polylactic acid/carbon nanotube composites

Abstract: As multifunctional high-performance materials, polylactic acid/carbon nanotube (PLA/CNT) composites are currently of great interest for using in an extensive range of medical and industrial applications. The main focus of the present work, accordingly, is to review the recent developments on PLA/CNT composites. In addition, the dependence of thermal, mechanical, electrical, and rheological properties on the type, aspect ratio, loading, dispersion state, and alignment of CNTs within PLA matrix was reviewed. The discussion of the different properties revealed that the CNTs additive could be an effective method to improve the performance of PLA materials for medical and industrial applications.

A novel hydrogel based on agricultural waste for removal of hazardous dyes from aqueous solution and reuse process in a secondary adsorption

Abstract: A novel hydrogel based on the orange peel (OP) and N-vinyl-2-pyrrolidone was prepared by free-radical polymerization using gamma irradiation. The effect of radiation dose and hydrogel composition on gel content was studied. The formed hydrogel was characterized by FT-IR, TGA, and SEM. The swelling behavior was determined as a function of swelling time, pH, and OP content. The hydrogel swelling was found to be pH dependent, and the diffusion mechanism of water into the hydrogel was found Fickian. The developed hydrogel was used for the removal of Congo red (CR) and methyl orange (MO) dyes from wastewater. The effects of various operating parameters, such as initial pH, contact time, initial dye concentration, and temperature on the removal of dyes, have been investigated. The Langmuir and the Freundlich adsorption models were applied to study the adsorption isotherm. The pseudo-first-order model was proved compatible for CR adsorption and the pseudo-second-order model well described the adsorption of MO. The adsorption of dyes increased with increasing temperature indicating that the endothermic nature of the adsorption process and the thermodynamic parameters was evaluated. Second, the adsorption cycle of dyes was also examined and discussed utilizing the loaded hydrogel with the other dye and cobalt metal ions.

Ionic conductivity and conduction mechanism studies on cellulose based solid polymer electrolytes doped with ammonium carbonate

Abstract: The present work deals with the formation of solid polymer electrolytes (SPE) from carboxy methylcellulose (CMC) and doped with ammonium carbonate ((NH4)2CO3). The CMC–(NH4)2CO3 SPE was characterized with electrical impedance spectroscopy (EIS) and transference number measurement (TNM) to understand its electrical and conduction mechanism. Fourier transform infrared (FTIR) were conducted to correlate the complexation of the SPE with conductivity and conduction mechanism. Complexation appears to occur mainly in CMC carboxyl group (C=O). The highest ionic conductivity obtained is 7.71 × 10−6 Scm−1 for samples incorporated with 7 wt% of (NH4)2CO3. Lowest activation energy, E a achieved is 0.21 eV corresponds to the highest conductivity sample. Ionic conductivity measurement at elevated temperature follows Arrhenius model. Dielectric study of the sample shows dependence to temperature, but not to the frequency. CMC–(NH4)2CO3 SPE sample with the highest conductivity has transference number, $$t_{ + }$$ of 0.98 proving of its conduction is predominantly cation. Quantum mechanical tunneling (QMT) was the best model to explain the conduction mechanism of the highest conductivity sample.

Synthesis, characterisation and flame, thermal and electrical properties of poly ( n -butyl methacrylate)/titanium dioxide nanocomposites

Abstract: Nanocomposites based on poly (n-butyl methacrylate) (PBMA) with various concentrations of titanium dioxide (TiO2) nanoparticles were synthesised by in situ free radical polymerisation method. The formation of nanocomposite was characterised by FTIR, UV, XRD, DSC, TGA, impedance analyser and flame retardancy measurements. FTIR and UV spectrum ascertained the intermolecular interaction between nanoparticles and the polymer chain. The XRD studies indicated that the amorphous region of PBMA decreased with the increase in content of metal oxide nanoparticles. The SEM revealed the uniform dispersion of nanoparticles in the polymer composite. The DSC and TGA studies showed that the glass transition temperature and thermal stability of the nanocomposites were increased with the increase in the concentration of nanoparticles. The conductivity and dielectric properties of nanocomposites were higher than pure PBMA and the maximum electrical property was observed for the sample with 7 wt% TiO2. As the concentration of nanoparticles increased above 7 wt%, the electrical property of nanocomposite was decreased owing to the agglomeration of nanoparticles in the polymer. Nanoparticles could impart better flame retardancy to PBMA/TiO2 composite and the flame resistance of the materials improved with the addition of nanoparticles in the polymer matrix.

Ibuprofen and acetylsalicylic acid loaded electrospun PVP-dextran nanofiber mats for biomedical applications

Abstract: The aim of this work is to investigate the suitability of electrospinning for biomedical applications and to produce fast-dissolving drug delivery through uniform dextran nanofiber nonwoven maps. To prepare oral fast-dissolving drug delivery nonwoven maps via electrospinning technology, ibuprofen (Ibu) and acetylsalicylic acid (ASA) as the model drugs, and polyvinylpyrrolidone (PVP), dextran T10 (Dext T10) and dextran T40 (Dext T40) as the filament-forming polymer and drug carrier were selected. Morphology of nanofiber samples was characterized by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS). SEM images showed homogeneous dispersion of drugs into the polymer blends. The structure analysis made by attenuated total reflectance/Fourier transform infrared spectroscopy suggested that PVP/dextran and drug blended very well in the nanofibers. The amount of ibuprofen and acetylsalicylic acid in a nanofiber samples was determined using reverse-phase high-performance liquid chromatography. The results showed that the ibuprofen content in PVP/Dext T40-Ibu and PVP/Dext T10-Ibu nanofiber samples (431.7 ± 39.7 and 528.3 ± 24.7 µg/mL, respectively) is significantly higher than acetylsalicylic acid content in PVP/Dext T40-ASA and PVP/Dext T10-ASA nanofiber samples (145.5 ± 5.6 and 168.3 ± 7.3 µg/mL, respectively). Antibacterial properties of the fiber samples containing drug against Gram-negative (Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922) and Gram-positive bacteria (Staphylococcus aureus ATCC 25923, Bacillus subtilis ATCC 6633) were examined. The PVP-drug containing nanofibers resulted in a superior antibacterial activity than PVP/dextran-drug containing nanofibers. PVP/Dext T10 and PVP/Dext T40 nanofibers have the potential to be used as solid dispersions to improve the dissolution profiles of poorly water-soluble drugs and/or fast disintegrating drug delivery systems.

Thermal stability and thermal degradation kinetics of bio-based epoxy resins derived from cardanol by thermogravimetric analysis

Abstract: Cardanol is a naturally occurring chemical compound consisting of meta substituted alkyl phenol. Two types of epoxy resins have been synthesized from cardanol. The synthesized epoxy resins have been characterized by FTIR and NMR spectroscopic analyses. The thermal stabilities and kinetics of the thermal degradation of cardanol-based resins were studied by thermogravimetric analysis under a nitrogen atmosphere with heating rates of 5, 10, 15 and 20 °C min−1. The molecular weights of the prepared novolac and epoxidized novolac resins were determined by gel permeation chromatography analysis. There is intense interest in understanding the degradation behavior and properties of cardanol-based epoxy resins. Three model-free methods, Kissinger, Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO), and the model-fitting Coats–Redfern method were employed to identify the kinetic triplet including activation energy, pre-exponential factor and reaction model. It was established that the Coats–Redfern model-fitting method is suitable for determining the kinetic reaction mechanism, but the most probable reaction functions R3 and D3 can be evaluated on the basis of the activation energy value which is nearest to the value of activation energy obtained by the FWO and KAS methods. A kinetic compensation effect was also observed for the above-mentioned bio-based epoxy resins.

PBAT/organoclay composite films: preparation and properties

Abstract: Environmental problems caused by the increased waste associated with short-term use of plastic materials, particularly by the food packaging industry, prompted the search for biodegradable alternatives. This contribution studied one of these alternatives, poly(butylene adipate-co-terephthalate)—PBAT, a polymer that is fully biodegradable in common landfills, compounded with a small amount of Cloisite 20A organoclay. Materials were mixed in a laboratory internal mixer and films prepared in a chill roll extruder. Results show that the presence of organoclay does not increase degradation of the polymer matrix during processing, nor affects its crystallization characteristics. However, organoclay addition significantly diminished oxygen and carbon dioxide permeability of the films, making them a very interesting alternative for the food packaging industry.

Biodegradable and antimicrobial films based on poly(butylene adipate-co-terephthalate) electrospun fibers

Abstract: Biodegradable poly(butylene adipate-co-terephthalate) (PBAT) films incorporated with different levels of the antimicrobial peptide nisin were developed using the electrospinning technique. The characterization included thermal, structural, morphological, mechanical and antimicrobial properties. Thermal analysis indicated good thermal stability of PBAT. Nisin incorporation seems to increase nanofiber stability. The PBAT/nisin fibers presented no significant differences in the melting temperature (124–125.4 °C) and the glass transition temperature. PBAT showed characteristic diffraction peaks of the crystal structure. PBAT fibers were uniformly distributed and nisin was well dispersed throughout the fiber. The samples showed similar mechanical properties, and the addition of nisin caused no significant changes in the values of tensile strength, although Young’s modulus tended to decrease with higher nisin levels. Antimicrobial fibers inhibited the Gram-positive bacterium Listeria monocytogenes. These results provided insights into the interaction of nisin and PBAT in nanofibers produced by the electrospinning technique and their application in the food packaging industry.

Influence of melt-mixing processing sequence on electrical conductivity of polyethylene/polypropylene blends filled with graphene

Abstract: In this paper, we produced composites of high-density polyethylene (PE)/polypropylene (PP) filled with graphene by melt compounding. Comparing composites produced in three processing sequences, we explored whether the sequence improved the composites’ electrical conductivity. The (graphene/PE)/PP composite, prepared by simultaneous compounding, exhibited an electrical percolation threshold of 1.25 vol.%. In contrast, the (graphene/PP)/PE composite, prepared by blending the graphene with PP first and then blending the graphene/PP with PE, had a much lower electrical percolation threshold at less than 0.83 vol.%. At its percolation threshold, the (graphene/PP)/PE composite had a conductivity about two orders of magnitude higher than the (graphene/PE)/PP composite. We attribute this difference in conductivity to differences in the graphene distributions in the composites. In the (graphene/PE)/PP composite, the graphene sheets were selectively dispersed in the PE phase; in the (graphene/PP)/PE composite, some of the graphene was localized at the interface of the PE/PP blend. We also showed how the different processing sequences affected the composites’ measured rheological and mechanical properties.

Synthesis of comb-type amphiphilic graft copolymers derived from chlorinated poly(ɛ-caprolactone) via click reaction

Abstract: This work refers to the synthesis of a series of novel chlorinated poly(ɛ-caprolactone) (PCL) for further functionalization of PCL. For this aim, chlorine gas was passed through into the chloroform solution to obtain chlorinated polycaprolactone. The chlorine contents in chlorinated PCL were between 0.9 and 1.6 mol%. The molecular weights of the polymers (M n) changed from 4853 to 9497 g/mol. As the amount of passing chlorine gas increases, the molecular weight of the chlorinated PCL was found to decrease. Pendant chloride groups of PCL were reacted with sodium azide to prepare PCL with pendant azide groups (PCL-N3). Poly-(ethylene glycol) methyl ether (mPEG) was reacted with propargyl chloride to achieve alkynyl mPEG (mPEG-alkyn). Click reaction was then carried out by the reaction between PCL-N3 and mPEG-alkyn to obtain PCL-g-PEG comb-type amphiphilic graft copolymer. Interestingly, SEM images of the PCL-g-PEG comb-type amphiphilic graft copolymers showed the highly microporous structure. The resulting products were characterized by 1H NMR, FT-IR, gel-permeation chromatography, SEM, surface tension, contact angle and water uptake measurements, differential scanning calorimeter and thermogravimetric analyses techniques.

Effect of polydopamine coating on improving photostability of polyphenylene sulfide fiber

Abstract: The effect of polydopamine coating on improving photostability of polyphenylene sulfide (PPS) fiber was investigated in detail. Due to strong adhesion ability and self-polymerization of dopamine in alkaline solution, the polydopamine could be easily coated on polyphenylene sulfide fiber under mild conditions. XPS, ATR-FTIR and SEM, which indicated the polydopamine coating was homogeneous, confirmed the polydopamine coating on PPS fiber. The UV-spectra analysis of polydopamine coating showed that it had a strong absorbance in ultraviolet wavelength and was very stable to it, which implied that the polydopamine was a potential photoprotection agent. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) experiment further revealed that the PDA could quench free radicals, suggesting PDA was a good antioxidant. This scavenging ability of PDA might contribute to improving photostability of PPS fiber. Compared to pristine PPS fiber, the PPS fiber coated by polydopamine obviously had better photostability after ultraviolet irradiation according to mechanical test, which proved that polydopamine coating did improve the photostability of PPS fiber.

Thermal stability and decomposition kinetic studies of antimicrobial PCL/nanoclay packaging films

Abstract: In our previous research, we had successfully developed antimicrobial PCL/nanoclay nanocomposite films with enhanced mechanical and water vapor barrier properties for food packaging field. Now, in this present work, we complete our study by investigating the thermal stability and decomposition kinetics of these materials using thermogravimetry technique (TGA). The TGA results revealed that the incorporation of 3% of organoclay in the PCL matrix reduced the thermal stability of PCL nanocomposite films. In addition, the decomposition kinetic study showed that the apparent activation energies Ea of the thermal degradation of the PCL nanocomposites are lower compared to those calculated for pristine PCL, confirming the catalytic effect of the organoclay upon the PCL decomposition. The master plots of g(α) function showed a similar thermal degradation mechanism of PCL and its PCL nanocomposites. All the studied samples followed Avrami–Erofeev, m = 1.5 model. Also, the thermodynamic parameters such as ∆H #, ∆S # and ∆G # were calculated and discussed.

Chitosan/oxidized pectin/PVA blend film: mechanical and biological properties

Abstract: This paper describes the preparation and characterization of flexible crosslinked chitosan (CH)/poly(vinyl alcohol) (PVA) films. These chitosan-based films are prepared using oxidized pectin as crosslinking agent, and PVA as plasticizer. The chemical structure of the obtained blend films were investigated using FTIR spectroscopy. Swelling behavior of hydrogels obtained was studied in various pH media. The blending of PVA with chitosan or chitosan/oxidized pectin (OP) was found to highly enhance the swelling of the prepared films compared to those obtained from pure chitosan. On the other hand, the use of lactic acid as solvent and the incorporation of PVA improve the flexibility of chitosan matrices. Examination of the hemolytic potential showed that the hydrogels were non hemolytic in nature. The hydrogels were non-toxic and blood-compatible. Reducing power was used to determine in vitro antioxidant activity and anti-inflammatory activity of chitosan films was investigated by protein denaturation method. The biological activity of CH/OP/PVA towards Pseudomonas aeruginosa, Staphylococus aureus, Bacillus subtilis and Escherichia coli has been examined in this study.

Synthesis and characterization of an novel flame retardant based on phosphaphenanthrene for epoxy resin

Abstract: A simple route to synthesize a new type of charring agent in high yield is reported. The polyphosphate oligomer polyphosphate poly(6-oxido-6H-dibenzo[c,e][1,2]oxa-phosphinin-6-yl phenyl phenylphosphate) (POBPP) was synthesized by addition reaction between 10-(2,5-dihydroxyl phenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-BQ) and phenyl dichlorophosphate. The structure of this product was characterized by means of the Fourier transform infrared spectra (FTIR) and nuclear magnetic resonance spectroscopy (1H–, 13C– and 31P-NMR. The molecular weight was determined by Gel Permeation Chromatography (GPC). By blending this flame retardant resin with diglycidyl ether of bisphenol-A (DGEBA) resin, a flame retardant and anti-dripping epoxy resin was obtained. Thermal stability of flame retardant (FR) and cured composites was studied by the Thermal Gravimetric Analysis (TGA). Flame retarding performances of this epoxy were characterized by limiting oxygen index (LOI) and vertical burning test (UL94). Morphology of residue was investigated by a scanning electron microscope (SEM). The results reveal that FR improve the thermal stability of epoxy resin and help matrix to leave more residue by forming net structure in char.

Conjugated dual-phase transitions in crystalline/crystalline blend of poly(vinylidene fluoride)/poly(ethylene oxide)

Abstract: Blends of two semi-crystalline polymers, poly(vinylidene fluoride) (PVDF) and poly(ethylene oxide) (PEO), were prepared via solution mixing method over the whole composition range. The research focuses on the liquid–liquid phase separation (LLPS) and miscibility window in the PVDF/PEO blends by employing several techniques. Small-amplitude oscillatory shear measurements were carried out to detect LLPS and determine spinodal and binodal decomposition temperatures in its early stages. An asymmetrical lower critical solution temperature (LCST) phase diagram was observed from dynamic temperature sweep experiments in which the system became immiscible after the solid–liquid phase transition (SLPS) temperatures in the PEO-rich blends. In fact, a one-way partial miscibility of PEO in the PVDF-rich phase blends was observed. The rheologically determined phase diagram was also verified by means of optical microscopy and cloud point technique. The results revealed that the PVDF/PEO blends undergo a viscoelastic phase separation (VPS). This was attributed to the large viscoelastic asymmetry of the components in the blend. A compressible regular solution free energy model was employed to determine the spinodal temperatures theoretically. The comparison between the experimental results and the mathematical modeling indicated that the model is able to predict the phase behavior qualitatively.

UV-induced switchable wettability between superhydrophobic and superhydrophilic polypropylene surfaces with an improvement of adhesion properties

Abstract: Polypropylene (PP) surfaces with reversible switching between superhydrophobicity and superhydrophilicity were fabricated by a simple dip-coating method. The reversibility was obtained using a combination of UV and thermal treatment cycles. Superhydrophobic polymeric surfaces were prepared by dipping PP substrates in a hot suspension of xylene containing TiO2 nanoparticles (NPs) functionalized with trimethoxypropyl silane (TMPSi). This resulted in superhydrophobic PP surfaces with water contact angles (WCA) of 158° that were converted to superhydrophilic (WCA ~0°) by UV irradiation. However, the superhydrophobic state can be easily recovered using a soft thermal treatment (100 °C for 2 h). A continuous switch in the extreme wettability properties of the surfaces was achieved using cycles of UV irradiation and thermal treatments. Additionally, the hydrophilicity obtained by UV illumination improved the weak adhesion that existed between the nanocoating and the PP surface before the UV treatment by about 90 %. Detailed high-resolution X-ray photoelectron spectroscopy data showed that the relative concentration of the hydrophilic component, Ti–OH, in the O 1s signal increased from 32 % to more than 50 % when the surface was irradiated. Simultaneously, the Ti 2p signal showed a reduction of Ti(IV) to Ti(III) after the photochemical treatment leading to a surface hydroxylation and the superhydrophilicity found after UV irradiation. This paper reports the preparation of PP surfaces with excellent controllable wettability with important applications where improvement in the coating adhesion is necessary.