Study of the effect of different electron irradiation doses on the decomposition temperature of azodicarbonamide

Azodicarbonamide (ADCA) is a well‐known chemical blowing agent used in the fabrication of polyolefin foams which decomposes into gases at temperatures above the melting temperature of the polymer. In these polymer foams, the polymer is usually crosslinked before or during the foaming process to increase its viscosity and make it capable of supporting the pressure of the gas during foaming. This crosslinking process allows producing low‐density foams with homogeneous cellular structures. A typical procedure to crosslink the polymer is to irradiate it using a high energy‐electron beam. When ADCA is incorporated into the polymer before the irradiation process, it is also exposed to the high energy electron beam. However, the effect of the irradiation on the decomposition process of ADCA has not been explored yet. In this research, it has been found that there is a reduction of the thermal decomposition temperature of ADCA when this material is electron irradiated with different doses ranging from 25 to 150 kGy, being this reduction higher when the irradiation dose is increased. It has also been found, that the reduction of the decomposition temperature is due to a modification of the lattice parameters of the crystalline structure of ADCA. POLYM. ENG. SCI., 59:791–798, 2019. © 2018 Society of Plastics Engineers     

Effect of Electron Beam Irradiation,EPDM and Azodicarbonamide on the Foam Properties of LDPE Sheet

The effect of electron beam irradiation, EPDM blending, and Azodicarbonamide (ACA) concentration on the foaming properties of LDPE sheet was investigated. The studied properties are foaming degree, cell densities, mechanical properties and thermal decomposition properties. The data showed that the increasing of foaming agent (ACA) concentration reduces the mechanical properties and increases the gel content. Also, electron beam irradiation has a clear effect on increasing the cell density, mechanical properties gel content and thermal properties of irradiated samples when compared with unirradiated samples. EPDM blending with LDPE at a concentration of 20% reduces the doses required to obtain the foaming degree (71.4%) from 50 kGy in LDPE to 5 kGy in LDPE/EPDM (80/20%). This effect may be attributed to enhancement of radiation cross-linking for LDPE by blending with the amorphous polymer (EPDM).     

A strategy for the preparation of closed‐cell and crosslinked polypropylene foam by supercritical CO2 foaming

We report the preparation of a closed‐cell polypropylene (PP) foam material by supercritical carbon dioxide foaming with the assistance of γ‐ray radiation crosslinking. Styrene–ethylene–butadiene–styrene (SEBS) copolymer was added to PP to enhance radiation crosslinking and nucleation. Radiation effects on the foaming of the PP/SEBS blend with different ratios were investigated. A significant improvement in the foaming of the crosslinked PP/SEBS blend was achieved as compared to pristine PP. The cell density of the crosslinked PP/SEBS foam greatly increased at a dose of 10 kGy and a high closed‐cell ratio was obtained. The tensile strength of the crosslinked PP/SEBS foams (10 kGy) was improved from 14 to 20.7 MPa compared to pristine PP foam (0 kGy). In addition, the crosslinked PP/SEBS blend exhibited a wider foaming temperature window (10 °C) as compared to the non‐crosslinked ones (4 °C). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45809.     

Effect of gamma irradiation on the interpenetrating networks of gelatin and polyacrylonitrile: Aspect of crosslinking using microhardness and crosslink density measurements

The present article reports the effect of gamma irradiation on the hardness behavior of the interpenetrating polymer networks (IPNs) of gelatin and polyacrylonitrile (PAN). Various compositions of gluteraldehyde‐crosslinked gelatin and N, N′‐methylene bis acrylamide (MBA)‐crosslinked PAN were prepared and investigated for microhardness studies. The pre‐ and post‐irradiated IPNs were characterized for their crosslinking density, determined with swelling ratio measurements. It was found that the crosslinked IPNs get further hardened because of radiational hardening at specific doses in the range from 2 to 250 kGy. The role of acrylonitrile and crosslinker (MBA) in the IPNs, as a consequence of irradiation, has also been explained. A fair consistency has been observed between the microhardness results and crosslinking density measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2581–2586, 2006     

Production of non‐crosslinked thermoplastic foams with a controlled density and a wide range of cellular structures

A novel foaming route, with respect to existing industrial foaming processes, called “Improved Compression Molding” (ICM), which allows producing non‐crosslinked thermoplastic foams in a wide density range, is described in this work. This process is different from others because it is possible to control independently density and cellular structure and therefore, tailored cellular polymers can be produced. To understand the process, a collection of polypropylene foams, with relative densities ranging from 0.3 to 0.6 were produced. The influence of foaming parameters, on foams microstructure and mechanical response was analyzed. Results revealed that for similar densities, foams with different open cell content and cell size can be achieved. In addition, it was proved that mechanical behavior strongly depends on the degree of interconnectivity of the cells. The analysis of the relative mechanical properties allowed determining the influence of microstructure on mechanical behavior as well as quantifying the efficiency of the foaming process to produce light‐weight stiff materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42324.     

Dielectric properties of irradiated polymer/multiwalled carbon nanotube and its amino functionalized form

The polymer/multiwalled carbon nanotube [poly(vinyl alcohol) (PVA)/carboxyethyl acrylate (CEA)]‐multiwalled carbon nanotube (MWCNT) and its amino functionalized (PVA/CEA)‐MWCNT‐NH₂ nanocomposite samples were successfully synthesized by the chemical method in the form of films. The samples were irradiated with gamma‐ray doses of 50 and 100 kGy and with ion beam fluence of 2.5 × 10¹⁸ and 3.75 × 10¹⁸ ions cm^?2. The prepared nanocomposite samples were characterized using X‐ray diffraction and thermogravimetric analysis. The X‐ray diffraction and thermogravimetric analysis confirm the existence of the chemical crosslinking occurred in the polymer compositions. The AC electrical conductivity, electrical modulus, dielectric constant, and dielectric loss in the frequency range 10²–10⁶ Hz are measured at room temperature. The electrical conductivity is increased with MWCNT doping, gamma‐irradiation, and by ion beam irradiation. A comprehensive analysis of the results revealed that dielectric properties are improved due to the induced physicochemical changes and conductive networks induced by ion beam irradiation. The behavioral effect of these embedded nanoparticles in a PVA matrix on the microstructural, dielectric, and electric properties is analyzed for possible device applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46647.     

Extruded foams from microbial poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) and its blends with cellulose acetate butyrate

Extrusion foaming of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) and two blends of PHBV with cellulose acetate butyrate (CAB) were studied using an azodicarbonamide (AZ) blowing agent and a single‐screw extruder. The concentration of the blowing agent was systematically varied from 0 to 4.0 phr to achieve maximum density reduction reaching 41%, as well as to obtain information on the dependence of cell growth on blowing agent concentration. Extruded foams were characterized in terms of their bulk densities and cellular morphologies. Stereological and statistical methods permitted full characterization of the three‐dimensional cell size distributions, assessing the average cell diameters (ranging from 58 to 290 μm) and cell densities (ranging from 650 to 180,000 cm^?3). The variation in cellular morphology among foams consisting of different polymer matrix or blowing agent concentration was compared. The results were analyzed by considering the influence of viscoelastic properties of the polymer matrix on the bubble growth during foaming. Significantly higher melt viscosity and elasticity and reduced gas solubility of the PHBV/CAB blends are believed to retard cell coalescence and collapse during foam expansion, resulting in more uniform cell size distribution and better homogeneity of cellular morphology. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Influence of the viscosity of poly(methyl methacrylate) on the cellular structure of nanocellular materials

Three different grades of poly(methyl methacrylate) (PMMA) with different rheological properties are used for the production of nanocellular materials using gas dissolution foaming. The influences of both the viscosity of the different polymers and the processing parameters on the final cellular structure are studied using a wide range of saturation and foaming conditions. Foaming conditions affect similarly all cellular materials. It is found that an increase of the foaming temperature results in less dense nanocellular materials, with higher cell nucleation densities. In addition, it is demonstrated that a lower viscosity leads to cellular polymers with a lower relative density but larger cell sizes and smaller cell nucleation densities, these differences being more noticeable for the conditions in which low solubilities are reached. It is possible to produce nanocellular materials with relative densities of 0.24 combined with cell sizes of 75 nm and cell nucleation densities of 10¹⁵ nuclei cm^?3 using the PMMA with the lowest viscosity. In contrast, minimum cell sizes of around 14 nm and maximum cell nucleation densities of 3.5 × 10¹⁶ nuclei cm^?3 with relative densities of 0.4 are obtained with the most viscous one. © 2019 Society of Chemical Industry     

Study of a Polydimethylsiloxane (PDMS) Elastomer Generated by γ Irradiation: Correlation Between Properties (Thermal and Mechanical) and Structure (Crosslink Density Value)

The present study investigates the structural modification of polydimethylsiloxane (PDMS) with a molecular weight of 35 kDa, using varying high doses of gamma irradiation. Elastomeric structures with different crosslinked density values were obtained as a function of the gamma irradiation dose (250, 300, 350 and 400 kGy). The structural characterization of the obtained elastomers was performed by employing Fourier Transform Infrared, ²⁹Si Magic Angle Spinning Nuclear Magnetic Resonance and X-Ray Diffraction (FTIR, ²⁹Si MAS NMR and XRD), showing integration with the polymer chains by siloxane crosslinks (Type-Y) and methylene crosslinks (Type-H). The mechanical and thermal characterizations were carried out by employing dynamical-mechanical analysis (DMA) and modulated differential scanning calorimetry (MDSC). The results showed an important correlation between the thermo-mechanical behavior and the irradiation dose. The thermal stability, analyzed by a thermo-gravimetric analysis (TGA), exhibited interesting behavior that suggested a direct correlation between the decomposition temperature and the structure generated by the gamma irradiation. These results suggest that the obtained elastomers could potentially be considered shape changing materials (SCM).     

EB‐crosslinked Polymer Electrolyte Membranes Based on Highly Sulfonated Poly(ether ether ketone) and Poly(vinylidene fluoride)/Triallyl Isocyanurate

In this study, crosslinked polymer electrolyte membranes for polymer electrolyte membrane fuel cell (PEMFC) applications are prepared using electron beam irradiation with a mixture of sulfonated poly(ether ether ketone) (SPEEK), poly(vinylidene fluoride) (PVDF), and triallyl isocyanurate (TAIC) at a dose of 300 kGy. The gel‐fraction of the irradiated SPEEK/PVDF/TAIC (95/4.5/0.5) membrane is 87% while the unirradiated membrane completely dissolves in DMAc solvent. In addition, the water uptake of the irradiated membrane is 221% at 70 °C while that of the unirradiated membrane completely dissolves in water at above 70 °C. The ion exchange capacity and proton conductivity of the crosslinked membrane are 1.57 meq g⁻¹, and 4.0 × 10⁻² S cm⁻¹ (at 80 °C and RH 90%), respectively. Furthermore, a morphology study of the membranes is conducted using differential scanning calorimetry and X‐ray diffractometry. The cell performance study with the crosslinked membrane demonstrates that the maximum power density is 518 mW cm⁻² at 1036 mA cm⁻² and the maximum current density at applied voltage of 0.4 V is 1190 mA cm⁻².     

Effect of die temperature on the morphology of microcellular foams

A study on the extrusion of microcellular polystyrene foams at different foaming temperatures was carried out using CO₂ as the foaming agent. The contraction flow in the extrusion die was simulated with FLUENT computational fluid dynamics code at two temperatures (150°C and 175°C) to predict pressure and temperature profiles in the die. The location of nucleation onset was determined based on the pressure profile and equilibrium solubility. The relative importance of pressure and temperature in determining the nucleation rate was compared using calculations based on classical homogeneous nucleation theory. Experimentally, the effects of die temperature (i.e., the foaming temperature) on the pressure profile in the die, cell size, cell density, and cell morphology were investigated at different screw rotation speeds (10 ～ 30 rpm). Experimental results were compared with simulations to gain insight into the foaming process. Although the foaming temperature was found to be less significant than the pressure drop or the pressure drop rate in deciding the cell size and cell density, it affects the cell morphology dramatically. Open and closed cell structures can be generated by changing the foaming temperature. Microcellular foams of PS (with cell sizes smaller than 10 μm and cell densities greater than 10 cells/cm³) are created experimentally when the die temperature is 160°C, the pressure drop through the die is greater than 16 MPa, and the pressure drop rate is higher than 10⁹ Pa/sec.     

Microcellular PVC

Novel microcellular PVC foams with a very homogenous cell distribution and cell densities ranging from 10⁷ to 10⁹ cells/cm³ have been created using carbon dioxide as the nucleating gas. Microcellular foams with relative densities (density of foam divided by the density of unfoamed polymer) ranging from 0.15 to 0.94 have been produced. It was found that the bubble nucleation density has and Arrhenius-type dependence on temperature, while the average bubble diameter is relatively independent of the foaming temperature. A majority of the cell growth was found to occur in the early stages of foaming.     

Improvement of the magnesium battery electrolyte properties through gamma irradiation of nano polymer electrolytes doped with magnesium oxide nanoparticles

Nanocomposite polymer electrolytes (NCPE) were prepared using nano polyethylene oxide PEO doped with Magnesium (Mg) salts. Gamma irradiation was utilized to improve the PEO‐Mg salts particle sizes. Consequently, Magnesium Oxide (MgO) nanoparticles were prepared by green synthesis and incorporated into PEO‐Mg salts to improve their properties toward magnesium battery electrolyte applications. The prepared samples were examined before and after exposures to the radiation doses. Dynamic light scattering (DLS) indicated the particles size of the synthesized nano polymer‐Mg salts and MgO nanoparticles. Fourier transform infra‐red (FTIR) spectroscopic measurements, transmission electron microscopy (TEM), electrical conductivity, electrochemical properties, and thermal stability of the samples were determined. FTIR indicated the interaction between PEO with Mg salts and MgO nanoparticles which confirmed the structure. The TEM results showed a spherical nanoparticles of MgO and a good dispersion of MgO in PEO matrix. It was found that the irradiation dose 70 kGy gave the best results for the nano polymer‐Mg salts (13 nm). The electrical conductivity (σ) evaluated for NCPE, was more than three orders of magnitude of pure PEO. The liquid NCPE of 20 mL MgO NPs at 100 kGy exhibited a maximum conductivity of 3.63 × 10^–3 Scm^?1 at room temperature. The increase in temperature caused a slight effect on conductivity, 4.85 × 10^–3 Scm^?1 at temperature 250°C, at the same concentration. While un‐irradiated sample of 30 mL MgO NPs (σ) reached to 3.8 × 10^?3 Scm^?1 then became 5.03 × 10^?3 Scm^?1 by increasing temperature. From the cyclic voltammetry results, the polymer electrolytes containing MgO filler, 20 and 30 mL, for irradiated and un‐irradiated samples, respectively exhibited wider electrochemical stability window than the others due to the appearance of Mg deposition/desolution peak in CV curve showed that magnesium effectively migrating through electrolytes. Thermogravimetric analysis (TGA) was enhanced by adding Mg salts electrolyte and also MgO nanoparticles to PEO. J. VINYL ADDIT. TECHNOL., 25:243–254, 2019. © 2018 Society of Plastics Engineers     

Effect of clay dispersion on the cell structure of LDPE/clay nanocomposite foams

In this study, the effect of clay and its dispersion state on the cell morphology and foaming behavior of chemically crosslinked polyethylene (PE) foams were examined. In addition, the effect of foaming process on the clay morphology was also considered. It was shown that the morphology of the clay before the foaming process and its compatibility with PE matrix play a major role in determining the final foam properties. A PE‐g‐MA compatibilizer was used to increase the melt intercalation of PE onto the clay galleries and to improve clay dispersion in the PE matrix. The uniform dispersion of clay provided greater and well‐ dispersed nucleation sites. This led to smaller cell size, narrower cell size distribution, and higher cell density, and lower foam density. During the foaming process, intercalated clays were delaminated due to the rapid polymer melt expansion that inhibited gas release and increased foam expansion ratio. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Characterization of Mechanical and Thermal Properties of Vinyl-ester/TiO2 Nanocomposites Exposured to Electron Beam

The effect of electron beam irradiation (EBI) on the properties of vinyl-ester/TiO₂ nanocomposites has been studied in the present paper. The nanoparticles (1, 3 and 5 wt%) in the matrix are dispersed by high shear matrix characterized by transition electron microscopy. Neat polymer and nanocomposites were exposed to EBI in 100, 500 and 1,000 kGy doses. The mechanical, thermal behaviors of nanocomposites were studied by tensile and flexural tests and thermo-gravimetric analysis. The results showed that irradiation improved the properties of neat resin and nanocomposies. Fourier transform spectroscopy spectra showed that VE and nanocomposite are stable against of irradiation of EBI up to 1,000 kGy.     

Investigation of the nanocellular foaming of polystyrene in supercritical CO2 by adding a CO2‐philic perfluorinated block copolymer

Nanocellular foaming of polystyrene (PS) and a polystyrene copolymer (PS‐b‐PFDA) with fluorinated block (1,1,2,2‐tetrahydroperfluorodecyl acrylate block, PFDA) was studied in supercritical CO₂ (scCO₂) via a one‐step foaming batch process. Atom Transfer Radical Polymerization (ATRP) was used to synthesize all the polymers. Neat PS and PS‐b‐PFDA copolymer samples were produced by extrusion and solid thick plaques were shaped in a hot‐press, and then subsequently foamed in a single‐step foaming process using scCO₂ to analyze the effect of the addition of the fluorinated block copolymer in the foaming behaviour of neat PS. Samples were saturated under high pressures of CO₂ (30 MPa) at low temperatures (e.g., 0°C) followed by a depressurization at a rate of 5 MPa/min. Foamed materials of neat PS and PS‐b‐PFDA copolymer were produced in the same conditions showing that the presence of high CO₂‐philic perfluoro blocks, in the form of submicrometric separated domains in the PS matrix, acts as nucleating agents during the foaming process. The preponderance of the fluorinated blocks in the foaming behavior is evidenced, leading to PS‐b‐PFDA nanocellular foams with cell sizes in the order of 100 nm, and bulk densities about 0.7 g/cm³. The use of fluorinated blocks improve drastically the foam morphology, leading to ultramicro cellular and possibly nanocellular foams with a great homogeneity of the porous structure directly related to the dispersion of highly CO₂‐philic fluorinated blocks in the PS matrix. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The preparation and thermomechanical properties of high-temperature foams based on thermoplastic poly(phthalazinone ether ketone)

Poly(phthalazinone ether ketone) (PPEK) is an amorphous thermoplastic polymer with a high glass transition temperature (T_g) exceeding 250°C. We describe the preparation of foams from PPEK and characterize their properties. PPEK foams were prepared using dichloromethane as a foaming agent. The foaming agent was swollen into discs of the PPEK, which were then foamed by heating. Foams could be prepared at temperatures far below the T_g of the PPEK due to plasticization of the polymer by the foaming agent. Foams with densities ranging from 0.1 to 0.65 g/cm³ were prepared. Their thermal conductivity and modulus (measured approximately by indentation tests) were found to decrease with density, and the trends were similar to those expected from existing models. The foams could be annealed at 200°C without collapse suggesting that they may be useful in structural or insulation applications where stability at high temperature is essential.     

Synthesis and in situ foaming of biodegradable malonic acid ESO polymers

In this study, biodegradable rigid cellular materials were synthesized from the reaction of malonic acid with epoxidized soybean oil. Malonic acid reacts with two epoxy groups to give a network polymer. In the course of this reaction, initially formed malonic acid monoester (MAME) can decarboxylate and produce CO₂, which acts as the blowing agent leading to in situ foaming of the polymer. Epoxide addition and decarboxylation reactions of MAME occur competitively and simultaneously and by controlling their relative rates, foams of controlled density were produced. ¹H NMR spectrum of the synthesized foams showed that increasing the temperature increases the rate of decarboxylation reaction of MAME and decreases crosslink density leading to softer and lower density foams. Addition of 1,4‐diazabicyclo[2.2.2]octane (DABCO) as a catalyst also increases the rate of decarboxylation. Load deflection curves of the cellular materials showed that decreasing the temperature and addition of DABCO increase compressive modulus of samples. Cell morphology was studied by microscopic images of foam samples that showed that foam samples have a closed cell structure and a wide distribution of cell volume. Soil burial test was done to determine rate of biodegradation of foam samples. A half‐life of 815 days showed that foam samples are highly biodegradable. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of microcellular poly(ethylene‐co‐octene) rubber foam with supercritical carbon dioxide

In the past 3 decades, there has been great advancement in the preparation of microcellular thermoplastic polymer foams. However, little attention has been paid to thermoplastic elastomers. In this study, microcellular poly(ethylene‐co‐octene) (PEOc) rubber foams with a cell density of 2.9 × 10¹⁰ cells/cm³ and a cell size of 1.9 μm were successfully prepared with carbon dioxide as the physical blowing agent with a batch foaming process. The microcellular PEOc foams exhibited a well‐defined, closed‐cell structure, a uniform cell size distribution, and the formation of unfoamed skin at low foaming temperatures. Their difference from thermoplastic foam was from obvious volume recovery in the atmosphere because of the elasticity of the polymer matrix. We investigated the effect of the molecular weight on the cell growth process by changing the foaming conditions, and two important effect factors on the cell growth, that is, the polymer matrix modulus/melt viscoelastic properties and gas diffusion coefficient, were assessed. With increasing molecular weight, the matrix modulus and melt viscosity tended to increase, whereas the gas solubility and diffusion coefficient decreased. The increase in the matrix modulus and melt viscosity tended to decrease the cell size and stabilize the cell structure at high foaming temperatures, whereas the increase in the gas diffusion coefficient facilitated cell growth at the beginning and limited cell growth because most of the gas diffused out of the polymer matrix during the long foaming times or at high foaming temperatures. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Structural alterations of polycarbonate/PBT by gamma irradiation for high technology applications

In this work, polycarbonate/polybutylene terephthalate (PC/PBT) was irradiated with different gamma doses ranging from 200 kGy to 1950 kGy. Structural alterations of irradiated PC/PBT polymer blend have been studied using UV–vis spectroscopy, X-ray diffraction, and Fourier transform infrared (FTIR), as well as surface wettability. The results of UV–vis spectra showed that gamma irradiation induced an increase in the optical absorption with an increase in the gamma doses with shift in the optical absorption edge in the irradiated samples toward the higher wavelength. This shift is correlated with the decrease in optical band gap energy. Optical band gap decreases up to 12 and 20% with respect to pristine sample for direct and indirect transition, respectively. The number of carbon atoms per conjugated length has been estimated. The α phase and β phase of the crystalline PBT structure were observed. The α phase reflections are slightly increased due to the irradiation but the accompanying α to β transformation alters the results. FTIR investigation showed slight variation in the absorption spectrum specially in the range from 1300 to 1001 cm^?1 which are related to the O–C–O arrangements that is found to be the most affected part of the molecule by irradiation. A remarkable increase was observed in the wettability, surface free energy, and adhesion work of irradiated samples with an increase in the gamma doses.