Effect of a Nanoclay on the Mechanical,Thermal and Flame Retardant Properties of Rigid Polyurethane Foam

Water blown rigid polyurethane foams (PUF) with organoclay/organically modified nanoclay (ONC) were prepared and their properties such as density, mechanical, morphological, insulation, thermal and flame retardant properties were studied. In this investigation, the ONC content was varied from 1 to 10 parts per hundred of polyol (php) by weight. It was observed that the compressive strength of ONC filled PUF increased up to 3 php of ONC loading and then it decreased. Wide angle X-ray diffraction and transmission electron microscopy studies indicated the exfoliated dispersion of ONC in PUF. The thermal conductivity of ONC filled PUF decreases up to 5 php and then increases. The glass transition temperature (Tg) of PUF decreases on loading of ONC. The TGA analysis shows that there is slight increase in degradation temperature with increase in ONC loading. The flame retardant properties (LOI and flame spread rate) are improved slightly on addition (3 php) of ONC filled PUF.     

Effect of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of intumescent flame retardant ethylene-vinyl acetate copolymer

Ethylene vinyl acetate copolymer (EVA) flame retarded by ammonium polyphosphate (APP) and pentaerythritol (PER) was cross-linked by electron beam irradiation. The effects of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of EVA composites were investigated. The volatilized products of EVA/APP/PER composites were characterized by thermogravimetric analysis/infrared spectrometry. As VA content increased, the volatilized products increased in the second decomposition step, but decreased in the third decomposition step. For all samples, the increase of irradiation dose could improve both the gel content and the Limit Oxygen Index (LOI, the minimum oxygen concentration by volume for maintaining the burning of a material) values of irradiated composites. The mechanical and thermal properties of the irradiated EVA composites were also evidently improved at appropriate irradiation dose as compared with those of unirradiated EVA composites, whereas these properties decrease at higher irradiation dose because of the electron beam irradiation-induced oxidative degradation or chain scission.     

Differential scanning calorimetry of irradiated polymers

DSC was used to study the influence of fast electron irradiation on the molecular mobility and melting of semicrystalline polymers and copolymers of ethylene and of fluorocopolymer. The heat capacity-temperature dependences obtained in the range from 100 K to 500 K revealed the specific features of the irradiation effect on four relaxational transitions associated with the appearance of segmental motion in different molecular elements of the disordered regions in the polymer. The pronounced dependence of the radiation stability of crystallites on the thermal prehistory of the object under study was found. The results were interpreted on the basis of the decisive role of the molecular mobility and free volume for the predominance of the radiation cross-linking of the molecules. Correlations were established between the characteristics of the thermal transitions and the mechanical properties of the irradiated polymers.     

Effect of organoclay loading and electron beam irradiation on the physico‐mechanical properties of low‐density polyethylene/ethylene‐vinyl acetate blend

The influence of electron beam (EB) irradiation and organoclay (OC) loading on the properties of low‐density polyethylene (LDPE)/ethylene‐vinyl acetate (EVA) blends was investigated. The samples were subjected to the EB irradiation with the dose values of 50 and 250 kGy. X‐ray diffraction (XRD), gel content, mechanical, thermal, and electrical properties were utilized to analyze the characteristics of the LDPE/EVA blends with and without OC at different irradiation dosages. Gel content analysis showed that the OC promotes considerably the insoluble part so that the LDPE/EVA blends filled with OC become fully crosslinked at 250 kGy; possibly through the formation of further crosslinks between OC and polymer chains. The samples irradiated by EB showed enhanced mechanical properties due to the formation of three‐dimensional networks. In addition, thermogravimetric analysis indicated that combined OC loading and radiation‐induced crosslinking improved thermal stability of LDPE/EVA blends considerably. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

Phenol‐urea‐formaldehyde cocondensed resol resins: Their synthesis,curing kinetics,and network properties

Several phenol‐urea‐formaldehyde (PUF) cocondensed resol resins were synthesized by different procedures. The curing kinetics and network properties of these PUF resins were examined by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). A kinetic study indicated that the activation energy values of PUF resins are generally higher than those of phenol‐formaldehyde (PF) resins during curing processes, but the curing rates of PUF resins are faster than those of PF resins. The pH values of PUF systems have a significant influence on the rate constants, although they affect the activation energy very slightly. Moreover, the dependence of activation energy on the conversion showed that there are more individual reactions with different activation energies occurring during the curing processes in PUF resins than in PF resins. The decomposition of methylene ether bridges to form methylene bridges probably occurs at high temperature in PUF resins. DMTA data indicated that the network rigidity of PUF resins is slightly lower than that of PF resin. The gel point and T_{tan δ2} transition measured by DMTA were consistent with the kinetic results obtained from the DSC data, but they were also related to the physical and mechanical properties of the network, especially with regard to the T_{tan δ2} transition. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1929–1938, 2003     

Effects of gamma irradiation on the properties of flame-retardant EVM/magnesium hydroxide blends

The ethylene vinyl-acetate copolymer (EVM) rubber/magnesium hydroxide (MH) blend was crosslinked by ⁶⁰Co irradiation in the presence of trimethylolpropane triacrylate. And the effects of gamma irradiation on the properties of irradiated EVM/MH blend were investigated through the measurements of the gel content, Vicat point, limiting oxygen index, UL-94, tensile properties, X-ray diffraction and thermogravimetric analysis. The test results show that the thermal, mechanical and flame-retardant properties of the EVM/MH blend all are markedly improved by ⁶⁰Co irradiation.     

Degradation behavior of poly (l-lactide-co-glycolide) films through gamma-ray irradiation

Gamma-ray irradiation is a very useful tool to improve the physicochemical properties of various biodegradable polymers without the use of a heating and crosslinking agent. The purpose of this study was to investigate the degradation behavior of poly (l-lactide-co-glycolide) (PLGA) depending on the applied gamma-ray irradiation doses. PLGA films prepared through a solvent casting method were irradiated with gamma radiation at various irradiation doses. The irradiation was performed using 60Co gamma-ray doses of 25–500 kGy at a dose rate of 10 kGy/h.The degradation of irradiated films was observed through the main chain scission. Exposure to gamma radiation dropped the average molecular weight (M_n and M_w), and weakened the mechanical strength. Thermograms of irradiated film show various changes of thermal properties in accordance with gamma-ray irradiation doses. Gamma-ray irradiation changes the morphology of the surface, and improves the wettability. In conclusion, gamma-ray irradiation will be a useful tool to control the rate of hydrolytic degradation of these PLGA films.     

Development of a novel self-healing dental nanocomposite containing PUF nanocapsules and nanoclay

The aims of this research were to develop the first self-healing dental nanocomposite and to evaluate mechanical properties (compressive and flexural strength), crack-healing, and self-healing longevity after 90 days of water aging. The principal reasons for failure are microcracks formed by polymerization shrinkage, recurrent dynamic mechanical stress, water sorption, and thermal fatigue. N, N-dihydroxyethyl p-toluidine and triethylene glycol dimethacrylate (DEPT-TEGDMA) nanocapsules were synthesized as they have been proven previously to be biocompatible for dental materials. Nanoclay was used as a filler to improve the mechanical properties of self-healing tooth nanocomposites. Nanocapsules were prepared by in situ emulsion polymerization of poly urea-formaldehyde (PUF) shells. The synthesized PUF shells were characterized by FTIR, SEM, and DLS analyses. The results showed that incorporating nanocapsules at a 7.5% mass fraction into the nanocomposite increased the mechanical properties. A good self-healing efficiency ranging from 54.06 to 58% recovery was obtained. The 90 days of water-aging compared to 1 day did not reduce the self-healing efficiency (p > 0.1), showing water-aging did not damage the nanocapsules.     

Thermal degradation and flame retardancy of rigid polyurethane foams containing a novel intumescent flame retardant

A novel cheap macromolecular intumescent flame retardants (MIFR) was synthesized, and its structure was a macromolecule containing phosphorus characterized by IR. Rigid polyurethane foam (PUF) filled with MIFR as fire retardant additive was prepared. The effects of MIFR on properties such as density, compressive strength, flame-retardant behavior, thermal stability, and morphology of char were studied. The compressive strength of the MIFR-filled PUF increased initially and then decreased with further increase of MIFR content while its density straightly increased. Its flammability and burning behavior were characterized by UL 94 and limiting oxygen index (LOI). Twenty five percent of MIFR was doped into PUF to get 24.5 of LOI and UL 94 V-0. Activation energy for the decomposition of samples was obtained using Kissinger equation. The resultant data show that for PUF containing MIFR, compared with PUF, the mass loss, thermal stability, and the decomposition activation energy decreased, the char yield increased, which shows that MIFR can catalyze decomposition and carbonization of PUF to form an effective charring layer to protect the underlying substrate.     

Influence of gamma irradiation on the ageing characteristics of poly(ethylene-co-vinyl acetate) and poly(ethylene-co-vinyl acetate)/carbon black mixture

In this comparative study, the effect of gamma rays on the ageing characteristics of poly(ethylene-co-vinyl acetate) (EVA) and poly(ethylene-co-vinyl acetate)/carbon black mixture (EVA/CB) was investigated in terms of thermal stability. EVA, containing 13% vinyl acetate (VA), and EVA/CB, containing 13% VA and 1% carbon black (CB), were aged at 85°C in air up to 30 weeks for thermal ageing. Same substances were aged by means of UV light with a wavelength in the vicinity of 259 nm, in air, up to 400 h for UV ageing. Same substances were also irradiated with gamma rays at ambient conditions up to 400 kGy. Following these experiments, samples which had been irradiated with gamma rays, were subjected to thermal and UV ageing under the same conditions as for unirradiated samples. Dynamic thermogravimetry studies were performed for determination of the thermal stabilities of the samples. 10 and 50% mass losses were calculated for the samples from their respective curves. As a result of thermal analysis experiments, it was found that CB dramatically loses its protective property against thermal ageing of EVA after gamma irradiation. On the other hand, gamma irradiation does not have any significant effect on the UV ageing characteristics of EVA and EVA/CB in terms of thermal stability.     

Halogen-free flame retardant PUF: Effect of melamine compounds on mechanical, thermal and flame retardant properties

Water blown rigid polyurethane foam (PUF) was prepared with melamine polyphosphate (MPP) and melamine cyanurate (MC) as fire retardant (FR) additives. The effect of these additives on the properties of rigid PUF such as physico-mechanical, morphological, thermo-oxidative stability, flame retardancy and smoke density properties were studied. The mechanical and thermo-oxidative stability of PUF filled with MC was found to be better than those of MPP filled PUF. The insulation property of both MPP and MC filled PUF was improved with respect to the neat PUF. The FR properties of these filled PUF were evaluated by cone calorimeter, limiting oxygen index (LOI), smoke density, rate of burning and char residue estimation. The FR property of MPP filled PUF was better than that of the MC filled PUF.     

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.     

Grafting of styrene into pre-irradiated fluoropolymer films: Influence of base material and irradiation temperature

In this study, the influence of irradiation temperature on mechanical properties of three fluoropolymers and on grafting of styrene into the polymers by the pre-irradiation method was investigated. Electron paramagnetic resonance spectroscopy and infrared spectroscopy were used to characterize the irradiated polymers regarding trapped radical species and changes in the chemical structure, respectively. For poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) the irradiation temperature was found to be an important factor for tensile strength and elongation at break of the pre-irradiated film. No strong effect of irradiation temperature on the mechanical properties was noticed for poly(tetrafluoroethylene-co-ethylene) (ETFE); however the yield of grafting drops at high irradiation temperatures. Finally, mechanical properties of poly(tetrafluoroethylene) (PTFE) were found to be dramatically altered, even if the film was irradiated at elevated temperature.     

Fabrication of nano-crystalline cellulose with phosphoric acid and its full application in a modified polyurethane foam

Nano-crystalline cellulose was fabricated in an anhydrous phosphoric acid system with medical absorbent cotton as its raw material. After ammonia neutralization, the whole system with produced phosphates and hydrolyzed saccharides was used as a modifier for preparing polyurethane foam (PUF). The NCC worked as a reinforce material, the phosphates served as flame-retardants, and the hydrolyzed saccharides partly replaced polyol. The addition of the modifier significantly improved mechanical property and flame-retardancy without an inferior thermal conductivity. When the dosage of modifier was 6% of the whole polyol, compressive strength increased 4.29 times, heat release rate dropped to 50.7%, and time to ignition extended to 2.6 times of those of the neat PUF. XRD and TEM analyses proved that the NCC in the modifier was rod-shape cellulose Ⅱ with diameter of 10 nm or so. FTIR analysis confirmed that the modifier well reacted with isocyanate, and SEM results revealed that the flame-retardant PUF had more uniform cells and more regular skeleton structure than the neat PUF.     

Effect of gamma radiation on the physico mechanical properties of recycled HDPE/modified sugarcane bagasse composite

In this work, the sugarcane bagasse (SCB) fibers were used as reinforcing filler for recycled high density polyethylene (rHDPE) to form eco-friendly composite. The SCB surface was chemically modified to improve the compatibility with rHDPE matrix. The SCB fibers were alkali modified using 10% sodium hydroxide (SCBm) and acetylated using acetic anhydride (SCBac). The chemically modified SCB fibers were characterized using Fourier transform infrared (FTIR) and scanning electronic microscopy (SEM). The composites were prepared by mixing of rHDPE with 15 phr (parts per hundred parts rHDPE) of different SCB samples. Neat rHDPE and its composites with SCB were irradiated by gamma radiation dose of 50–250 kGy. The Effect of gamma radiation on the water up-take, mechanical properties and the thermal stability of (rHDPE) and its composites was studied. The effect of gamma radiation on the compatibility between rHDPE and SCB was also investigated. The results showed that the combination between the chemical modification of fibers and the irradiation of polymer composites were more effective in compatibility improvement than chemical modification alone. The irradiated (at 100 kGy) composite containing of SCBac gave the best mechanical properties, lowest water up-take and the highest thermal stability.     

Effect of gamma-ray irradiation on the mechanical strength of polystyrene-ferrocene composite

Thin films of polystyrene-ferrocene (PS---Fe) composite were irradiated with various doses of gamma irradiation ranging from 4·1 to 25·3 Mrad. The Vickers hardness number (H_v) was calculated for pure and irradiated specimens. It was used to analyse mechanical strength at a saturation load of 100 g. The mechanical strength was found to increase with irradiation dose up to 12 Mrad. Brittleness of the composite PS-Fe was found to occur at a higher dose of 25 Mrad as compared to 15 Mrad for polystyrene. Further, fracture toughness, brittleness index and yield strength were calculated for various irradiated specimens consequent to crack propagation in the specimens.     

Temperature influence on the stability and chemical composition of electron beam‐irradiated polytetrafluoroethylene

Polytetrafluoroethylene powder (PTFE) was exposed to electron beam radiation in presence of air. The irradiation mainly resulted in chain scission and induction of oxygenated groups and radicals as well as unsaturation. The thermal behavior of the irradiated PTFE and the fate of the radicals were studied comprehensively. Apart from fluorine, saturated and unsaturated fluorocarbons and oxygen‐containing groups were released during heating. Furthermore, irradiation‐generated peroxy radicals were transformed into alkyl radicals in a partly reversible process. A proposal for the complex reaction mechanisms of irradiated PTFE is given. The thermal stability of irradiated PTFE was improved by annealing. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2404–2411, 1999     

Gamma radiation for preservation of biologically damaged paper

Samples of nine different papers in use in the library, including two mould-contaminated papers, were irradiated with 14.4 kGy in a Co-60 facility. Five of the samples were subsequently subjected to an accelerated UV-ageing process. mechanical (tensile energy absorption and stretch) and optical properties were measured on control and irradiated samples, before and after ageing.

For most samples, the effect of ageing on mechanical properties turned out to be larger than that of irradiation. Irradiated and control samples were similarly affected by the accelerated ageing. Mould contaminated samples were still in acceptable conditions of use after irradiation. No discoloration effect was observed after irradiation and/or ageing.     

Gamma Irradiation Effects on Mechanical and Thermal Properties and Biodegradation of Poly(3-hydroxybutyrate) Based Films

Summary: Their biodegradable properties make polyhydroxyalkanoates (PHAs) ideal candidates for innovative applications. Many studies have been primarily oriented to poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-valerate) (PHBV) and afterwards to blends of PHAs with synthetic biodegradable polymers, such as poly(ε-caprolactone) (PCL). Medical and pharmaceutical devices require sterilization and γ irradiation could provide a proper alternative since it assures storage stability and microbiological safety. This contribution presents the effect of γ irradiation on the mechanical and thermal properties and on the biodegradation of PHB, PHBV and a commercial PHB/PCL blend. Samples, prepared by compression moulding, were irradiated in air at a constant dose rate of 10 kGy/h, from 10 to 179 kGy. Polymer chain scission was assessed by changes in the molecular weight, thermal properties and tensile behaviour. The correlation between absorbed dose and changes in the mechanical properties and biodegradation is discussed in detail. The optimum dose to guarantee microbiological sterilization without damage of the structure or meaningful loss of the mechanical properties is also reported.