Fabrication and characterization of gamma-irradiated recycled (thermoplastic/elastomer) matrix filled with feldspar composites

A composite of waste polyethylene, recycled waste rubber powder and reactive compatibilizing agent maleic anhydride, 60/40/2 mass%, was loaded with increasing contents, up to 20 mass%, of the reinforcing filler, feldspar [K (Al SiO₃O₈)]. The composites were gamma-irradiated at various doses up to 150 kGy. Selected physical, mechanical, and thermal parameters were investigated as functions of radiation dose and filler content. Gamma irradiation led to a significant improvement in the properties for all composites irradiated with 150 kGy. Similarly, the increase in feldspar content provided substantial improvement in properties as a result of development in the interfacial adhesion between the filler particles and composite components. The results were confirmed by examining the fracture surfaces using scanning electron microscopic techniques.     

Graphene oxide improved thermal and mechanical properties of electrospun methyl stearate/polyacrylonitrile form-stable phase change composite nanofibers

In the present work, a novel PAN-based form-stable composite phase change materials with the methyl stearate (MES) encapsulated in the supporting matrices of polyacrylonitrile (PAN) nanofibers were fabricated through electrospunning for the storage and retrieval of thermal energy. Influences of graphene oxide (GO) addition on the chemical properties, structural morphologies, mechanical properties, thermal energy storage properties, thermal stability, and thermal energy storage/retrieval rates of electrospun MES/PAN/GO phase change composite nanofibers were systematically investigated by FT-IR, FE-SEM, tensile testing, DSC, TG, and measurement of melting/freezing times, respectively. The results revealed that the incorporation of GO effectively enhanced the mechanical properties, thermal stability, as well as heat storage and release rates of the phase change composite nanofibers. The averaged tensile strength of electrospun MES/PAN/GO phase change composite nanofibers increased significantly by 573 % with 10 mass% loading of GO, while elongation at break had a maximum 107 % increment when adding 3 mass% of GO. The DSC results indicated that the electrospun PAN-based phase change composite nanofibers with various GO loadings had suitable phase transition temperatures with the latent heat ranging from about 92 to 109 kJ kg^?1 and exhibited good thermal reliability in terms of DSC measurements during 50 melting-freezing cycles. Moreover, the melting and freezing time were significantly decreased about 44 and 43 % for the MES/PAN/GO5, as well as 59 and 64 % for the MES/PAN/GO10 after introducing the GO into the composite nanofibers systems.     

Thermal and mechanical properties of nanofibers-based form-stable PCMs consisting of glycerol monostearate and polyethylene terephthalate

An innovative type of nanofibers-based form-stable composite phase change materials for the storage and retrieval of thermal energy was successfully prepared by encapsulating glycerol monostearate (GMS) into the porous structure of polyethylene terephthalate (PET)-supporting matrices on the nanoscale through electrospinning. The field-emission scanning electron microscopy and transmission electron microscopy images revealed that the composite nanofibers possessed desired morphologies with the average fiber diameters ranging from about 290 to 1000 nm which increased with the contents of GMS. The two phase separation (e.g., GMS phase and PET phase) was clearly observed from the images. When GMS content reached 60 %, the amount of the GMS distributing on the surface of the composite nanofibers was significantly increased during the electrospinning. The Fourier transform infrared spectroscopy spectrum proved that the PET supporting matrices were physically combined with GMS molecules. The differential scanning calorimetry analysis indicated that the GMS/PET composite nanofibers had reversible phase change behaviors, and the melting enthalpies increased from 32.63 to 66.99 kJ kg^?1 with increasing GMS amount. The TG results showed that both the onset thermal degradation temperature and charred residue of the GMS/PET composite nanofibers at 700 °C were higher than those of pristine GMS powder owing to the better thermal stability of the PET molecules. The tensile testing revealed that the averaged tensile strength and elongation at break of the all GMS/PET composite nanofibers varied from 3.29 to 10.30 MPa and from 2.42 to 42.30 %, respectively.     

Casting of poly (vinyl alcohol)/glycidyl methacrylate reinforced with titanium dioxide nanoparticles for proton exchange fuel cells

Gamma irradiation was used for cross-linking poly (vinyl alcohol) (PVA) and glycidyl methacrylate (GMA) mixtures of different compositions. Specifically, 0.5 wt% titanium dioxide (TiO₂) nanoparticles were added and blended well with the casting mixture prior to exposure to the irradiation dose. Next, 10 kGy was found to be the optimum dose for achieving the desired physical and chemical properties of the membrane. Characterizations of the cast membranes were carried out by Fourier transformer infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and positron annihilation lifetime spectroscopy (PALS). The properties of the membrane were also characterized by ion exchange capacity (IEC), water uptake, and tensile strength and were assessed in relation to application in proton exchange membrane fuel cells (PEMFCs). A maximum proton conductivity of 7.3 × 10^?2 S cm^?1 was obtained for the membrane having 20 % GMA, 80 % PVA, and 0.5 % TiO₂, and its activity and durability in a membrane electrode assembly (MEA) were compared to those of a commercial Nafion® 1350.     

Thermal decomposition kinetics of potassium iodate

The effect of gamma ray irradiation on the rate and kinetics of thermal decomposition of potassium iodate (KIO₃) has been studied by thermogravimetry (TG) under non-isothermal conditions at different heating rates (3, 5, 7, and 10 K min^?1). The thermal decomposition data were analyzed using isoconversional methods of Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Friedman. Irradiation with gamma rays increases the rate of the decomposition and is dependent on the irradiation dose. The activation energy decreases on irradiation. The enhancement of the rate of the thermal decomposition of KIO₃ upon irradiation is due to the combined effect of the production of displacements and extended lattice defects and chemical damage in KIO₃. Non-isothermal model fitting method of analysis showed that the thermal decomposition of irradiated KIO₃ is best described by the contracting sphere model equation, with an activation energy value of ~340 kJ mol^?1.     

Kinetic analysis for non-isothermal decomposition of un-irradiated and gamma-irradiated potassium bromate

The thermal decomposition of un-irradiated and gamma-irradiated potassium bromate (KBrO₃) was performed under non-isothermal conditions at different heating rates (5, 10, 15 and 20 K min^?1). The data was analysed using isoconversional and non-isoconversional methods. The kinetic parameters of thermal decomposition process were obtained by three model-free isoconversional methods: Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and Friedman. Irradiation enhances the decomposition and the effect increases with the irradiation dose. The activation energy decreases on irradiation. Kinetic analysis of data in view of various solid-state reaction models showed that the decomposition of un-irradiated and irradiated anhydrous KBrO₃ is best described by the Avrami–Erofeev model equation, [?ln(l?α)]^1/2 = kt.     

Gamma-Irradiated Gelatin-Based Films Modified by HEMA for Medical Application

The present article describes the synthesis and characterization of bi-component polymer systems based on gelatin films incorporated with 2-hydroxyethyl methacrylate (HEMA) monomer, developed for medical application. Gelatin films were prepared by the addition of HEMA of different concentrations (0–30 wt.%) and irradiated with various radiation doses (0–5 kGy). Tensile strength and tear strength of the irradiated gelatin films were found to increase with increasing HEMA up to 20 wt.% as well as radiation doses (1 kGy) as optimized. The maximum tensile and tear strengths of irradiated gelatin films with HEMA were found to be 79.1 MPa and 83.2 N/mm, respectively, at the optimum conditions, and these values were about double that of a reference film prepared without additives. In addition, morphological analysis was done by scanning electron microscopy (SEM) and showed how HEMA cemented and was covered with gelatin in the blend. Thermomechanical analysis was carried out to investigate the shifting of glass transition temperature (T_g) towards higher temperature due to HEMA addition, and the effect of this film was tested on the human body in order to determine whether it can be applied for medical purposes.     

Monomer and Radiation-Mediated Sago Starch Blend Film: Mechanical and Thermal Property Optimization

Bio-blend films were prepared with sago starch and N-vinyl-2-pyrrolidone (NVP) by the casting method, varying the concentrations of sago starch (100 to 93%) and NVP (0 to 7%). The formulations were designated as F1 (starch 100%), F2 (starch 97%), F3 (starch 95%), and F4 (starch 97%). The highest tensile strength (TS), tensile modulus (TM), and elongation at break (Eb%) were found correspondingly to be 30.47 MPa, 407.74 MPa, and 8.25% for the F3 formulation. Gamma radiation was applied to films to modify their performance through grafting and cross-linking. The highest TS, TM, and Eb% were found at 500 krad dose and they were 38.12 MPa, 481.00 MPa, and 9.78%, respectively for F3 formulation. The water uptake nature and thermal properties of the treated and untreated films were also investigated.     

Effect of electron beam irradiation on mechanical and thermal properties of waste polyamide copolymer blended with nitrile‐butadiene rubber

In the present study, the effect of electron beam irradiation on the morphological, thermal, and mechanical properties of waste polyamide copolymer (WPA‐66/6) blended with different contents of acrylonitrile butadiene rubber (NBR) were studied. The prepared blends were subjected to irradiation doses up to 150 kGy and the structural modifications were discussed; non‐irradiated blends were used as control. Mechanical properties, namely, tensile strength (TS), yield strength, elongation at break, and hardness, were followed up as functions of irradiation dose and degree of loading with rubber content. On the other hand, the influence of irradiation dose on the thermal parameters, melting temperature, heat of fusion, ΔH_m of the recycled PA copolymer, and its blend with NBR were also investigated. Copyright © 2009 John Wiley & Sons, Ltd.     

Identification of gamma-irradiated Chinese herbs by thermoluminescence analysis

The feasibility of thermoluminescence (TL) to differentiate irradiated Chinese medicinal herbs from non-irradiated was investigated. Thirty different dried Chinese herbs were tested, including root, flower, ramulus, rhizome, cortex, and whole plant samples. Irradiation of Chinese herbs was associated with strong TL peaks at ~150–250 °C, while TL curves of non-irradiated herbs had very low intensities above 250 °C, which was also confirmed by the TL ratio (non-irradiated, TL₁/TL₂ < 0.1). The ability to determine the irradiation dose by the TL method was influenced by the amount and types of minerals in the samples. All levels of irradiation doses could be detected when between 0.1 and 1.0 kGy, except for three herbs at 0.1 kGy dose. Different blends with small quantities (0.1–10 %) of irradiated herbs were also tested in this study. Samples with powder mixtures containing 1 % irradiated components could be differentiated (TL₁/TL₂ > 0.1) except for sterculia lychnophora, semen cassia, flos inulae, and anemone root. TL ratios of some herbs indicated irradiation (TL₁/TL₂ > 0.1) even if the irradiated components were as low as 0.1 %. Thus we demonstrated that TL analysis had excellent sensitivity and reliability for the identification of irradiated Chinese herbs.     

The effect of gamma irradiation on mechanical, and thermal properties of recycling polyethylene terephthalate and low density polyethylene (R-PET/LDPE) blend compatibilized by ethylene vinyl acetate (EVA)

A study has been made on the compatibility of recycled polyethylene terephthalate (R-PET) and low density polyethylene (LDPE) blend in the presence of ethylene vinyl acetate (EVA) as a compatibilizing agent prepared by extrusion hot stretching process. EVA content in the blend as a compatibilizing agent was an enhancement effect on radiation crosslinking of R-PET/EVA/LDPE blends and the highest radiation crosslinking was obtained when the EVA content was reached at 10 % EVA when irradiated by gamma irradiation. Blends containing different (EVA) ratios were irradiated to different doses of gamma irradiation 25, 50 and 100 kGy. The effect of the compatibilizer and radiation on mechanical, thermal properties of R-PET together with LDPE and morphology has been investigated. It was found that gamma irradiation together with the presence of compatibilizing agent (EVA) has positive effect on the mechanical and thermal properties of R-PET/LDPE blend. The structural properties of R-PET/LDPE modified by gamma irradiation and EVA as compatibilizing agent was examined by SEM. Also, it was found that the optimum concentration of EVA and gamma irradiation dose was found to be 10 % EVA and 100 kGy, respectively.     

Investigation of polymer degradation by addition of magnesium

The effect of alkali metal magnesium on polymer degradation of physico-mechanical properties of radiation-vulcanized natural rubber latex (RVNRL) films was investigated. RVNRL films were prepared by the addition of Mg of different concentrations (0–30 ppm) to natural rubber latex and irradiation with various radiation doses (0–20 kGy). The radiation doses were optimized (12 kGy), and the adverse effect of Mg was studied against a reference film prepared without metal. Tensile strength, tear strength, and cross-linking density of the irradiated rubber films were decreased with increasing metal ion concentrations and decreasing radiation doses. The mechanical properties of the films were reduced by nearly 10% for 30 ppm Mg ions and at the optimum dose. In contrast, elongation at break, permanent set, and swelling ratio of the films were increased at the same conditions. The maximum tensile and tear strengths of irradiated rubber films without additive were 29.33 MPa and 47.95 N/mm, respectively, at a radiation dose of 12 kGy, and these values were about six times higher than those of blank samples. With the addition of Mg, the corresponding values decrease continuously, and the minimum values were found to be 26.35 MPa and 42.675 N/mm, respectively. The effect of divalent alkali metal on polymer chain scission can be explained by the classical electron concept reported in this article.     

Characterization of New Natural Cellulosic Fiber from Acacia leucophloea Bark

There is a need to explore the possibility of natural fibers as a novel reinforcement to fabricate lightweight composite structures. This investigation was aimed at understanding the characteristics of fiber extracted from the bark of the Acacia leucophloea (AL) plant and its physico-chemical properties. Cellulose content (68.09 wt.%), density (1385 kg/m³), crystallinity index (51%), tensile strength (317–1608 MPa), and Young’s modulus (8.41 ? 69.61 GPa) properties were identified in the AL fibers, and thermal studies using TG and DTG analysis revealed that they degraded at a temperature of 220°C with kinetic activation energy of 73.1 kJ/mol.     

Tensile and Thermal Properties of Poly(lactic acid)/Eggshell Powder Composite Films

Biodegradable composite films of poly(lactic acid) (PLA)/eggshell powder (ESP) were prepared by the composite film casting method using chloroform as the solvent. ESP was loaded in PLA in 1 to 5 wt.%. The films were subjected to tensile, FT-IR spectral, thermogravimetric, X-ray, and microscopic analyses. The tensile strength and modulus of the composite films were found to be higher than those of PLA and increased with ESP content up to 4 wt.% and then decreased. A reverse trend was observed in the case of percentage elongation at break. The X-ray diffractograms of the composite films indicated an increase in crystallinity with ESP content. The optical micrographs indicated uniform distribution of ESP particles in the composite films. However, the fractographs indicated agglomeration of ESP particles at 5 wt.% loading. The FT-IR spectra revealed no specific interactions between PLA and ESP. The thermal stability of the composite films increased with ESP content.     

Eco-friendly synthesis, characterization and properties of a sodium carboxymethyl cellulose/graphene oxide nanocomposite film

A previously unreported nanocomposite (CMC/GO) high-performance film was prepared by a simple solution mixing-evaporation method. The structure, thermal stability, and mechanical properties of the composite films were investigated by wide-angle X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, thermogravimetry analysis, and mechanical testing. The results obtained from these different studies revealed that CMC and graphene oxide were able to form a homogeneous mixture. Compared with pure CMC, the tensile strength and Young’s modulus of the graphene-based materials were improved significantly upon incorporation of 1 wt% graphene oxide by 67 ± 6 % and 148 ± 5 %, respectively. In addition, the DMA composite films also showed a high storage modulus up to 250 °C.     

Characterization of new natural cellulosic fiber from the Ipomoea staphylina plant

Natural fibers extracted from plants play a major role as reinforcement in polymer composite materials due to their superior properties. This work aims to comprehensively characterize the physical and chemical properties of Ipomoea staphylina fibers (ISFs), which are extracted from the stem of the Ipomoea staphylina plant. The ISFs show cellulose content (72.76 wt%), hemicelluloses content (13.6 wt%), density (1401 kg cm^?3), and tensile strength of 173–658 MPa with a strain rate of 2.03–6.63%. The thermal stability of ISFs illustrate that the fibers are stable up to a temperature of 311°C with kinetic activation energy of 99.82 kJ mol^?1.     

Effect of nanosilica on thermal oxidative degradation of SBR

The effect of silica content on thermal oxidative stability of styrene–butadiene rubber (SBR)/silica composites has been studied. Morphologies of silica in SBR with different contents are investigated by scanning electron microscopy, which indicates that silica can well disperse in SBR matrix below the content of 40 %, otherwise aggregates or agglomerates will generate. Composites with around 40 % silica content show excellent mechanical properties and retention ratios after aging at 85 °C for 6 days. The values of activation energy (E _a) of pure SBR and its composites are calculated by Kissinger and Flynn–Wall–Ozawa methods based on thermogravimetric (TG) results, which suggests that composite with about 20 % silica has minimum E _a, and composite with 30–40 % silica has maximum E _a. According to TG curves, it is found that silica can suppress the formation of char leading to decline in stability to some extent. On the other side, silica also has positive effect on improving thermal stability of the matrix as filler. Thus, the SBR/silica composites with silica content of 30–40 % can possess both excellent resistance to thermal oxidative degradation and superior mechanical properties.     

Biocomposites based on Alfa fibers and starch‐based biopolymer

Biocomposite materials based on Alfa cellulose fibers (esparto grass plant) as reinforcing element and starch‐based biopolymer matrix were prepared and characterized in terms of mechanical performance, thermal properties, and water absorbance behavior. The fibers and the matrix were first mixed in the melted state under mechanical shearing using a plastograph and the obtained composites were molded by injection process. The tensile mechanical analysis showed a linear increase of the composite flexural and tensile modulus upon increasing the fiber content, together with a sharp decrease of the elongation at break. The fibers′ incorporation into the biopolymer matrix brings about an enhancement in the mechanical strength and the impact strength of the composite. Dynamic mechanical thermal analysis (DMTA) investigation showed two relaxations occurring at about ?30 and 35°C. The addition of Alfa fibers enhanced the storage modulus E′ before and after T_α, which is consistent with the reinforcing effect of Alfa cellulose fibers. Copyright © 2008 John Wiley & Sons, Ltd.     

Irradiation crosslinking and halogen-free flame retardation of EVA using hydrotalcite and red phosphorus

Halogen-free flame retarded ethylene vinyl acetate copolymer (EVA) composites using Mg-Al-CO₃ hydrotalcite (MALDH) and microcapsulated red phosphorus (MRP) have been prepared in a melt process. The flame retardation of the composites has been studied by the limited oxygen index (LOI) and UL-94 methods, and the thermal decomposition by the thermogravimetric analysis (TGA). The changes of their properties of the composites before and after the Gamma irradiation are compared. The synergistic effect in the flame retardation between MALDH and MRP in EVA has been found. The EVA/MALDH/MRP composites after the irradiation crosslinking result in a great increase in the Vicat softening point. The LOI value, the mechanical properties and thermal stability are also improved for the composites irradiated by a suitable irradiation dose.     

Properties of poly(acrylamide)/TEMPO-oxidized cellulose nanofibril composite films

Self-standing composite films consisting of 2,2,6,6-tetramethylpiperidine-1-oxyl-oxidized cellulose nanofibril (TOCN) and anionic poly(acrylamide) (PAM) in various weight ratios were prepared by casting and drying of homogeneous mixtures of aqueous TOCN dispersion and PAM solution. PAM/TOCN composite films consisting of 25 % PAM and 75 % TOCN had clearly higher Young’s modulus (13.9 GPa) and tensile strength (266 MPa) than 100 % TOCN film (10.8 GPa and 223 MPa, respectively) or 100 % PAM film (4.9 GPa and 78 MPa, respectively), showing that PAM molecules have mechanical reinforcement ability in TOCN matrix. Some attractive interactions are likely formed between TOCN element surfaces and PAM molecules. In contrast, no such mechanical improvements were observed for poly(vinyl alcohol)/TOCN or oxidized starch/TOCN composite films prepared as references. Moreover, the mechanical properties of the PAM/TOCN composite films were further improved by controlling molecular mass and branching degree of the PAM. The high optical transparency and low coefficient of thermal expansion of the 100 % TOCN film were mostly maintained in the TOCN composite film containing 25 % PAM.