Gamma irradiation degradation/modification of 5-ethylidene 2-norbornene (ENB)-based ethylene propylene diene rubber (EPDM) depending on ENB content of EPDM and type/content of peroxides used in vulcanization

In this study, the radiation degradation/modification of the vulcanized EPDM and the effects of dose rate, peroxide type/content in vulcanization system and ENB content of EPDM were studied to investigate the change in the extend of the modification/degradation of the mechanical properties of vulcanized EPDM via gamma irradiation. In addition, thermal, dynamic mechanical, ATR-FTIR, TGA, TGA-FTIR tests were carried out to understand the change of properties of vulcanized EPDM via irradiation. Samples were irradiated with two different dose rates of 1280 and 64.6 Gy/h. Total dose of irradiation was up to 184 kGy. The FTIR spectral analysis showed structural changes of EPDM via irradiation. It was observed that the dose rate changed the mechanical properties with different extends. The change of ENB content of EPDM and peroxide type and content in vulcanization system affect extend of the modification/degradation of the EPDM's properties

Monte Carlo simulations of radioactive waste embedded into polymer

Radioactive waste is generated from the nuclear applications and it should properly be managed according to the regulations set by the regulatory authority. Poly(carbonate urethane) and poly (bisphenol a-co-epichlorohydrin) are radiation-resistant polymers and they are possible candidate materials that can be used in the radioactive waste management. In this study, maximum allowable waste activity that can be embedded into these polymers and dose rate distribution of the waste drum (containing waste and the polymer matrix) were found via Monte Carlo simulations. The change of mechanical properties of above-mentioned polymers was simulated and their variations within the waste drum were determined for 15, 30 and 300 years after embedding

Use of poly(methyl methacrylate) in radioactive waste management: II. Monte Carlo simulations

Radioactive waste is generated from the nuclear applications and it should properly be managed in a radioactive waste management system. Different methods are available for treatment and conditioning of radioactive waste. Polymers can be used in the radioactive waste management as an embedding matrix. Poly(methyl methacrylate (PMMA) is a possible candidate material that can be used in the low level radioactive waste management. In this study, based on total resistible dose for PMMA, maximum waste activity that can be embedded into a waste drum was found via Monte Carlo simulations. In addition, Monte Carlo simulations for radioactive waste embedded into above mentioned polymer was performed and the dose rate distribution in the polymer matrix was determined for the initial and different periods of 15.1, 30.2 and 302 years after embedding of waste. Changes of mechanical properties in the polymer embedded waste drum was simulated for PMMA embedded waste matrices based on experimental data

Degradation of poly(bisphenol-a-epichlorohydrin) by gamma irradiation

In this study, radiation stability of poly(bisphenol-a-epichloroliydrin) (PBEH) was studied via gamma irradiations at two different dose rates of 1540 and 82.8 Gy/h, in order to understand the possible use of PBEH in radioactive waste management as a solidifying agent. The total dose of irradiation was up to 2150kGy. Degradation nature was tested by studying the changes in mechanical and thermal properties with the change of dose rate and total dose of irradiation. Tensile strength at yield was increased first then decreased when irradiated, while toughness decreased. The half value dose (HVD) of elongation was found as 29 kGy at dose rate of 1540 Gy/h. The non-irradiated PBEH was transparent, and the color changed to yellow with irradiation. Mechanical tests showed that PBEH has high radiation stability although there were some structural changes. It was seen that PBEH is a candidate polymer to be used in the immobilization of radioactive waste regarding radiation stability

Solid State Polymerization of N-vinylcaprolactam via Gamma Irradiation and Characterization

In this study, N-vinylcaprolactam was polymerized via gamma irradiation in the solid state. The polymerization was carried out at room temperature both under vacuum and open to atmosphere. The polymerization mechanism showed auto acceleration and the rate of polymerization was higher in the presence of oxygen. Complete conversion was obtained under vacuum conditions and 90% conversion was obtained in the case of polymerization open to atmosphere. The polymers were characterized by FTIR, NMR, DSC, TGA, GPC, X-ray diffraction and mass spectrometry tests. FTIR and NMR results showed that polymerization proceeded through the vinyl groups and caprolactam is pendant group. DSC results showed that the polymer obtained could be polymerized further or crosslinked by heat treatment. The Tg value for the polymer obtained from radiation induced polymerization was about 135C and increased to 174.6C after thermal treatment. Molecular weights of some polymer samples were measured by GPC. X-ray diffraction studies showed that the monomer structure was retained up to about 86% conversion of monomer to polymer. The chain structure of the polymer was confirmed by mass spectroscopy results

Polymerization of N-Vinylcaprolactam and Characterization of Poly(N-Vinylcaprolactam)

Poly(N-vinylcaprolactam), PNVCL, is a nonionic, nontoxic, water soluble, thermally sensitive and biocompatible polymer. It contains hydrophilic carboxylic and amide groups with hydrophobic carbon-carbon backbone suitable for biomedical applications. In this study, N-vinylcaprolactam was polymerized by free radical polymerization at 50, 60 and 70 degrees C. The synthesized polymers were white powder, soluble in water and common organic solvents. The percent conversion vs. time plot is almost linear up to about 60% conversion without induction period. The activation energy of polymerization was calculated as 108.4 kJ/mol from the Arrhenius plot. FTIR and NMR results showed that polymerization takes place by opening of carbon-carbon double bond without any change in the caprolactam ring. Polymer was characterized by FTIR, 1H-NMR and 13C -NMR, DSC, TGA and XRD techniques. The DSC thermogram of monomer has shown a melting point at 37.3 degrees C. The polymer has Tg value at 1.8 degrees C and softening temperature at 68.8 degrees C. It was determined from the X-Ray powder pattern that the polymerization proceed in the b-crystallographic axis direction

Mechanical, Vulcametric, and Thermal Properties of the Different 5-ethylidene 2-norbornene Content of Ethylene-Propylene-Diene-Monomer Vulcanized with Different Types and Compositions of Peroxides

Ethylene-propylene-diene-monomer (EPDM) rubber is an important commercial polymer. The vulcanization process significantly changes its thermal, mechanical, and vulcametric properties. This study was carried out to find optimum formulation of EPDM composite for a better application in automotive industry. Sixteen EPDM polymer samples having different 5-ethylidene 2-norbornene (ENB) and ethylene contents were vulcanized with different types and compositions of pet-oxide and coagents. The mechanical and vulcametric properties of these samples were measured and compared. The type of peroxide, coagent, and EPDM grade affected the mechanical, thermal, and vulcametric properties of the EPDM rubber to some extend. Use of aromatic peroxide and coagent increased the thermal stability slightly. Mechanical properties were changed very slightly with the change of peroxide type for the same content of peroxide and coagent. Scorch time and cure time decreased with initial increase of the peroxide content. EPDM compound vulcanized with BBPIB peroxide and TAC/S coagent has higher cure time than EPDM compound vulcanized with DMBPHa peroxide and TMPTMA coagent. Coran method was used for the modeling of experimental data. Velocity constant for the formation of peroxide radical and polymer radical were found for each case. (C) 2009 Wiley Periodicals, Inc. Appl Polym Sci 112:1891-1896, 200

Comparative Study of the Mechanical Properties of Fiber-Reinforced Denture Base Resin

Poly(methyl methacrylate) (PMMA) is used for removable prostheses. However, PMMA denture base resin does not meet all the mechanical requirements of prostheses. The aim of this in vitro study was to compare the transverse strength, modulus of elasticity, and impact strength values of nonreinforced heat-polymerized and microwave-polymerized denture base resin with those of denture base resin reinforced with continuous unidirectional E-glass, woven E-glass, and ultrahigh-molecular-weight polyethylene fibers. The mechanical properties of polymer reinforced with polyethylene fibers showed no significant increase in flexural properties. However, reinforcement with Stick fiber improved the mechanical properties. The test specimens that expressed low fracture strength values showed void spaces inside the test specimens. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 716-720, 200

Effect of thermocycling and treatment with monomer on mechanical properties of soft denture liner Molloplast B

Bonding between soft liner (Molloplast B) and denture base resins (poly(methyl methacrylate)) is a significant problem. Surface treatment with some adhesives of denture base resins increase bonding between these two materials. The purpose of this study was to investigate the effect of thermocycling and of surface treatment with MMA monomer on the mechanical properties of the silicone-based soft liner. A silicone soft lining material (heat-polymerized silicone rubber) and heat-polymerized denture base resin, PMMA, were chosen for this investigation. Transient mechanical and dynamic mechanical properties changed with monomer treatment and/or thermocycling

Possible use of EPDM in radioactive waste disposal: Long term low dose rate and short term high dose rate irradiation in aquatic and atmospheric environment

In this study, changes in the properties of ethylene propylene diene terpolymer (EPDM) irradiated with different dose rates in ambient atmosphere and aqueous environment were investigated. Irradiations were carried out both with low dose and high dose rate irradiation sources. EPDM samples which were differentiated from each other by peroxide type and 5-ethylidene 2-norbornene (ENB) contents were used. Long term low dose rate irradiations were carried out for the duration of up to 2.5 years (total dose of 1178 kGy) in two different irradiation environments. Dose rates (both high and low), irradiation environments (in aquatic and open to atmosphere), and peroxide types (aliphatic or aromatic) were the parameters studied. Characterization of irradiated EPDM samples were performed by hardness, compression, tensile, dynamic mechanical analysis (DMA), TGA-FTIR, ATR-FTIR, XRD and SEM tests. It was observed that the irradiation in water environment led to a lower degree of degradation when compared to that of irradiation open to atmosphere for the same irradiation dose. In addition, irradiation environment, peroxide type and dose rate had effects on the extent of change in the properties of EPDM. It was observed that EPDM is relatively radiation resistant and a candidate polymer for usage in radioactive waste management