Radiation‐induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films. I. Effect of grafting conditions and properties of the grafted films

Radiation‐induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films was studied by a simultaneous irradiation technique. Grafting was carried out using γ‐radiation from a ⁶⁰Co source at dose rates of 1.32–15.0 kGy h⁻¹ at room temperature. The effects of type of diluent, dose rate, irradiation dose, and the initial monomer concentration in the grafting solution on the degree of grafting were investigated. The degree of grafting was found to be strongly dependent upon the grafting conditions. The dependence of the initial rate of grafting on the dose rate and the initial monomer concentration in the grafting solution was found to be in the order of 0.6 and 1.7, respectively. The chemical structure and the crystallinity of the grafted PTFE films were studied by means of Fourier‐transform infrared, (FTIR), electron spectroscopy for chemical analysis (ESCA) and X‐ray diffractometry (XRD). © 2000 Society of Chemical Industry     

Radiation‐induced crosslinking of ultra high molecular weight polyethylene fibers by means of electron beams

Crosslinking of ultra high molecular weight polyethylene fibers (UHMW‐PE fibers) is investigated by means of electron beam irradiation. The structure and mechanical properties of the fibers in different irradiation atmospheres are discussed. The results show that the gel fraction and crosslinking density increase with the increase of absorbed dose. The swelling ratio and average molecular weight of crosslinked net decrease with the increase of absorbed dose. The relation between s + s^?1 of the UHMW‐PE fibers and reciprocal irradiation dose 1/R is obtained. The tensile strength and failure elongation decrease with the increase of absorbed dose, and the tensile modulus increases with the increase of absorbed dose. The samples are irradiated in air, vacuum, and acetylene atmospheres, separately. The radiation effects, such as crosslinking fraction and mechanical properties of UHMW‐PE fibers, are the most significant in acetylene atmosphere in comparison with in air and in vacuum. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1761–1764, 2005     

Modification of properties of CaCO3‐polymerization‐filled polyethylene

CaCO₃–polyethylene (PE) compositions, containing an ultrahigh molecular polyethylene (UHMPE) interlayer between the filler surface and the PE matrix, were synthesized by two‐step polymerization of ethylene on a filler surface activated with a suitable catalyst. The properties of the compositions were studied depending on the molecular weight of the PE matrix and the thickness of the UHMPE intermediate layer at the filler particles. It was shown that the presence of UHMPE as an interlayer in chalk–UHMPE–PE compositions leads to an increase of plastic deformation of the materials as long as the M_w value of the PE matrix is higher than is the brittleness threshold for PE. Chalk–UHMPE–PE compositions exhibit a higher ability for plastic deformation compared to chalk–PE compositions based on a PE matrix of a molecular weight equal to the molecular weight of the total polymer phase (UHMPE–PE) in the first case. There is no improvment of the mechanical properties when the UHMPE is dispersed in the compositions and not as an interlayer between a filler and a matrix. This means that the method of polymerization filling allows one to incorporate the polymer interlayer with a desired nature and properties between a filler surface and polymer matrix in filled polyolefin compositions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 577–583, 2003     

Spinning and drawing properties of ultrahigh‐molecular‐weight polyethylene fibers prepared at varying concentrations and temperatures

The concentrations and temperatures of ultrahigh‐molecular‐weight polyethylene (UHMWPE) gel solutions exhibited a significant influence on their rheological and spinning properties. The shear viscosities of UHMWPE solutions increased consistently with increasing concentrations at a constant temperature above 80°C. Tremendously high shear viscosities of UHMWPE gel solutions were found as the temperatures reached 120–140°C, at which their shear viscosity values approached the maximum. The spinnable solutions are those gel solutions with optimum shear viscosities and relatively good homogeneity in nature. Moreover, the gel solution concentrations and spinning temperatures exhibited a significant influence on the drawability and microstructure of the as‐spun fibers. At each spinning temperature, the achievable draw ratios obtained for as‐spun fibers prepared near the optimum concentration are significantly higher than those of as‐spun fibers prepared at other concentrations. The critical draw ratio of the as‐spun fiber prepared at the optimum concentration approached a maximum value, as the spinning temperature reached the optimum value of 150°C. Further investigations indicated that the best orientation of the precursors of shish‐kebab‐like entities, birefringence, crystallinity, thermal and tensile properties were always accompanied with the as‐spun fiber prepared at the optimum concentration and temperature. Similar to those found for the as‐spun fibers, the birefringence and tensile properties of the draw fibers prepared at the optimum condition were always higher than those of drawn fibers prepared at other conditions but stretched to the same draw ratio. Possible mechanisms accounting for these interesting phenomena are proposed.     

Alanine grafting of ion‐beam‐modified polyethylene

The grafting of a polyethylene (PE) surface layer implanted with 156 keV Xe⁺ ions at fluences of 3.10¹³ to 1.10¹⁵ cm⁻² with alanine was studied with the aim to prepare prospective materials for biological experiments. It was shown by different spectroscopical methods that alanine adds onto double bonds or reacts with radicals created by ion irradiation on the polymer chain. The grafting occurs in the whole ion‐damaged polymer layer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1144–1148, 2000     

Effect of trimethylolpropane triacrylate (TMPTA) on the properties of irradiated epoxidized natural rubber (ENR‐50), ethylene‐(vinyl acetate) copolymer (EVA), and an ENR‐50/EVA blend

The effect of trimethylolpropane triacrylate (TMPTA) monomer on the tensile properties, dynamic mechanical properties, and morphology of irradiated epoxidized natural rubber (ENR‐50), ethylene‐(vinyl acetate) copolymer (EVA), and an ENR‐50/EVA blend was investigated. The ENR‐50, EVA, and ENR‐50/EVA blend were irradiated by using a 3.0‐MeV electron‐beam apparatus at doses ranging from 20 to 100 kGy. The improvement of tensile properties and morphology with irradiation indicated the advantage of having irradiation‐induced crosslinks in these materials. Observation of the properties studied confirmed that TMPTA was efficient in enhancing the irradiation‐induced crosslinking of ENR‐50, EVA, and the ENR‐50/EVA blend. Addition of TMPTA improved the adhesion between the ENR‐50/EVA blend phases by forcing grafting and crosslinking at a higher irradiation dose (100 kGy). J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers.     

SEM study of the morphologic change of high‐density polyethylene surface grafted with glycidyl methacrylate

Scanning electron microscopy (SEM) study of the morphologic change of high‐density polyethylene (HDPE) surface grafted with glycidyl methacrylate (GMA) was reported. Radiation‐induced grafting of GMA onto HDPE was carried out in acetone and dichloromethane solution, respectively. The effects of irradiation dose, atmosphere, and swelling time on grafting were investigated. Generally, the extent of grafting increased with irradiation dose, but for the grafting carried out in acetone solution, the extent of grafting initially increased with irradiation dose and then remained almost constant. The extent of grafting was higher in acetone solution than in dichloromethane solution at the same irradiation dose. The extent of grafting in nitrogen was higher than that in air. The successful grafting of GMA onto HDPE was confirmed by weighing and FTIR analysis. SEM investigations showed that the morphologies of the PE samples grafted in acetone solution were quite different to those grafted in dichloromethane. The grafting of GMA carried out in acetone was mainly on HDPE surface and that carried out in dichloromethane was mainly in the bulk of HDPE. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of gamma‐irradiation on the electret properties of poly(L‐lactide)

Electret stability of poly(L ‐lactide) (PLA) films, gamma‐irradiated up to 100 kGy has been investigated by measuring the surface potential during the storage period. PLA samples—40‐μm thick films—were prepared by the casting method and then irradiated in a ⁶⁰Co radiation facility at a dose rate of 0.25 kGy/h. The structural changes during the irradiation were estimated by viscometric, differential scanning calorimetry and scanning electron microscope measurements. Random chain scission and appearance of end radicals are the most probable results of the irradiation process. After irradiation, the samples were charged in a corona discharge system and surface potential was measured by the method of the vibrating electrode with compensation. The values of the surface potential of the irradiated samples were higher in comparison with the non‐irradiated samples. This effect could be related to the degradation of the macromolecules and changes in the crystal state of PLA during the irradiation. Both of the mentioned factors lead to structural defects that increase the number of discrete trapping levels. The effect of low pressure on the surface potential drop was also investigated. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Melt free‐radical grafting of hindered phenol antioxidant onto polyethylene

A monomeric antioxidant (3) was prepared by reacting 3,5‐di‐tert‐butyl‐4‐hydroxybenzyl alcohol (1) with N‐[4‐(chlorocarbonyl) phenyl] maleimide (2). This reactive antioxidant was grafted onto polyethylene (PE) by melt processing with free‐radical initiators in a mini‐max molder. The IR spectra of the grafted PE showed that the monomeric antioxidant was introduced onto the PE. IR spectroscopic methods and titration were used for the quantitative determination of the extent of grafting of the monomeric antioxidant. Also, the extent of crosslinking was indicated by the gel content. Grafting occurred in the following order: dicumyl peroxide (DCP) > benzoyl peroxide > 2,2′‐azobisisobutyronitrile. The influences of the DCP concentration and monomeric antioxidant on the extent of grafting were studied. The effects of the reaction time and temperature were also determined. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2968–2973, 2000     

Radiation grafting of vinyl monomers onto poly(tetrafluoroethylene) powder produced by γ irradiation and properties of grafted poly(tetrafluoroethylene) filled low density polyethylene

Scrap poly(tetrafluoroethylene) (PTFE) was γ irradiated under an ambient atmosphere in order to produce extensive chain scission and oxidative degradation. After irradiation the PTFE was ground into a fine powder (2°‐PTFE) and grafted with styrene (St), vinyl acetate (VAc), and 4‐vinylpyridine (4‐VP) by using the direct irradiation technique. The grafted PTFE were then blended with low density polyethylene (LDPE). The study covered the characterization of irradiated PTFE and grafted 2°‐PTFE powder with various methods. Mechanical grinding was found to reduce trapped radicals formed during the irradiation process faster than the annealing process. Grafting on 2°‐PTFE was followed by gravimetric analysis, TGA, and the change in the particle size of the samples. Although we reached almost 20% grafting by weight in the St and 4‐VP monomers, VAc grafting was found to be maximum at around 8% by weight at the maximum absorbed dose. The addition of VAc grafted 2°‐PTFE into LDPE produced better final mechanical properties with a fine dispersion. However, as may be expected, the incorporation of the other two 2°‐PTFEs into LDPE showed low film quality and poor mechanical properties. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 816–826, 2001     

Waste‐reducing preparation of PE‐g‐MAH and PE‐g‐DBM via solid phase grafting reaction and their application as compatibilizers

Kinetics for grafting two reactive monomers (dibutyl maleate (DBM) and maleic anhydride (MAH)) on polyethylene (PE) was investigated for the modified PE (PE‐g‐MAH and PE‐g‐DBM) using solid phase grafting process. This process avoided solvent waste produced in solution process and high operation temperature in melt process. In the presence of the radical initiator, coupling reactions, between the PE and product, and macromolecular radicals, routinely form gels and/or increase molecular weight, resulting in a worse rheological behavior for the grafting products. By adding small amount of interface agents, using combined initiators and optimizing reactor design, graft copolymers with controlled grafting degrees and good rheological properties were prepared. The grafting degrees of copolymers were determined by chemical analysis. FTIR, DSC, and pure water contact angle characterized the chemical structure, the thermal property, and the hydrophilic property of the grafting copolymers, respectively. The peel strength of the graft copolymer as powder coating on the stainless steel surface was measured as high as 12–24 kgf/cm. Mechanical strength and toughness of PE/kaolin clay, PVC/CPE, and PVC/CPE/CaCO₃ alloys with small amount of the graft copolymer (～5 wt %) added were improved significantly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3781–3790, 2006     

Temperature Sensitive Behavior of Poly(N‐isopropylacrylamide) Grafted Onto Electron Beam‐Irradiated Poly(propylene)

Summary: N‐Isopropylacrylamide (NIPAAm) was graft‐polymerized from its acetone solution onto poly(propylene) (PP) films, after electron‐beam irradiation in the presence of air oxygen. The effects of pre‐irradiation dose as well as monomer concentration, reaction temperature and reaction time on the grafting efficiency were investigated. Typical conditions for achieving maximum grafting yield were observed for 1 M monomer concentration, after PP pre‐irradiation with a 300 kGy dose and a reaction temperature of 50 °C. The location of the graft polymerization was examined by different methods including measurements of dimensional variations, calorimetry, SEM and AFM. The temperature‐responsive behavior of grafted copolymer was studied by swelling and contact angle measurements at different temperatures.

Temperature dependence of the swelling ratio in water as a function of temperature.     

Radiation processing of ethylene‐propylene rubber

The effects of ionizing radiation on ethylene‐propylene copolymer were evaluated over the range of total γ doses up to 500 kGy. The influence of the irradiation dose was investigated by oxygen uptake and thermal analysis. Four testing temperatures (170, 180, 190, and 200°C) and two heating rates between 2.9 and 5.9 K/min were selected for oxygen uptake measurements and thermal analysis, respectively. The competition between crosslinking and scission was examined on the basis of kinetic parameters of postirradiation oxidation. The influence of the momentary concentration of hydrocarbon free radicals is discussed in regard to the contribution of the antagonistic processes of crosslinking and oxidative degradation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 298–303, 2000     

Radiation‐induced oxygen scavenging activity in EVOH copolymers

Oxygen scavenging capacity has been observed for the first time in an ethylene‐vinyl alcohol (EVOH29, i.e., 29 mol % of ethylene) copolymer as a consequence of electron beam irradiation at doses of 30 and 90 kGy. This oxygen blocking activity is thought to arise from the reaction of oxygen with the free radicals formed during the irradiation process and it has been observed to be dependent of the irradiation dose, i.e., the higher the dose, the longer the time the polymer is able to react with oxygen. The characterization of the irradiated polymeric samples has been carried out through DSC and FT‐IR and the oxygen transmission rate has been measured as a function of time and compared with the properties of the nonirradiated material. A drop in the melting point and in the enthalpy of fusion and broader peaks were observed after irradiation, which indicated changes in the morphology of the copolymer. Through FT‐IR, a slight decrease in the crystallinity of the irradiated EVOH29 was observed at the highest irradiation dose and several bands arise which correspond to the formation of degradation products such as aldehydes and ketones after irradiation. Those radiolysis compounds were identified through gas chromatography coupled to mass spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Graft copolymerization of polyethylene glycol methacrylate onto polyethylene film and its blood compatibility

In an attempt to produce surfaces that show low levels of adsorption of protein and adhesion of platelets, different molecular weights of polyethylene glycol methacrylate (PEG‐MA) were grafted onto polyethylene film by a preirradiation grafting process. The extent of grafting was found to be dependent on the storage condition of the irradiated polyethylene film, the preirradiated dose, reaction time and temperature, molecular weight of PEG‐MA, and the type of solvent. The grafting yield was found to decrease rapidly with storage time for irradiated polyethylene film stored at room temperature. On the other hand, the grafting yield in the irradiated polyethylene stored at −130°C remained nearly constant up to 20 days after irradiation. The grafting yield decreased with an increased PEG‐MA molecular weight. Human plasma protein was adsorbed onto control and PEG‐MA‐grafted polyethylene film surfaces, and the relative adsorbed amount of proteins on the surfaces was evaluated by electron spectroscopy for chemical analysis. The adsorbed protein and platelet adhesion on the polyethylene film surface decreased rapidly with the grafting yield. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 631–641, 1999     

Structure and optical investigation of the effect of electron beam‐irradiation in poly‐allyl‐diglycol‐carbonate

The effect of electron beam irradiation on the structural and optical properties of Poly‐Allyl‐Diglycol‐Carbonate CR‐39 solid state nuclear track detector was investigated. Samples from CR‐39 detector were irradiated with electron beam with doses at levels between 10 and 140 kGy. The structural and optical modifications in the electron beam irradiated CR‐39 samples have been studied as a function of dose using different characterization techniques such as FTIR spectroscopy, Vickers hardness, refractive index and color difference measurements. The electron beam irradiation in the dose range 25–140 kGy led to a more compact structure of CR‐39 polymer, which resulted in an improvement in its hardness with an increase in the refractive index. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical,dynamic mechanical,and thermal characterization of fly ash and nanostructured fly ash‐waste polyethylene/high‐density polyethylene blend composites

Disposal of polyethylene used as carry bags is the greatest challenge increasing day by day. Composite materials were prepared by mixing Fly ash (FA) and nanostructured fly ash (NFA) from thermal power station as filler and blends of Waste polyethylene (WPE)(carry bags) collected from municipal solid waste (MSW) with virgin high‐density polyethylene (HDPE) as matrix. Different modifications were induced to improve the overall properties of these composites. At first, the WPE/HDPE blend matrix was modified by grafting with maleic anhydride (MA) and the composite prepared with FA/NFA. Then, the WPE/HDPE‐FA/NFA composite as a whole was treated with electron beam irradiation at 250 kGy radiation dose and finally the FA/NFA filler was treated with radiation dose of 250 kGy and the composite prepared. Significant enhancement in tensile strength, flexural strength, flexural modulus, and hardness are observed for MA modified and irradiated composites, the increase being more prominent in irradiated composites. Furthermore, an increase in storage/loss moduli with enhanced thermal stability was observed with the addition of FA/NFA and upon modifications. The analysis of the tensile fractured surfaces by scanning electron microscopy was in well correlation with the mechanical properties obtained. In summary, after analyzing the effects of the three different modifications on mechanical, dynamic mechanical and thermal properties, the irradiation on to the WPE/HDPE‐FA/NFA composites investigated was selected as the most appropriate for future applications. POLYM. COMPOS., 37:3256–3268, 2016. © 2015 Society of Plastics Engineers     

Monitoring of the discoloration on γ‐irradiated PE and EVA films to evaluate antioxidant stability

γ‐Irradiated films could provoke unexpected interaction with proteins for instance just after irradiation and not necessarily after 12 months indicating there is no more reactive species. The optical properties of two multilayer films [polyethylene (PE)/ethylene vinyl alcohol (EVOH)/PE and ethylene vinyl acetate (EVA)/EVOH/EVA] after different γ‐irradiation doses is then studied in this work. The investigation on these films, either non‐irradiated or γ‐irradiated (up to 270 kGy), is performed by colorimetry measurement over time (up to 12 months) to assess the generation of new species inside the materials. The color change is directly correlated with absorbed γ‐doses. Over time, the color decreases and goes back to its initial time level. This discoloration evolution could be therefore used as an indication of the completion of the generated species reactions induced by γ‐irradiation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46114.     

Radiation‐induced grafting of pentamethyl hindered amine light stabilizer 1,2,2,6,6‐pentamethyl‐4‐piperidinyl methacrylate onto polypropylene

The γ‐radiation‐induced grafting of 1,2,2,6,6‐pentamethyl‐4‐piperidinyl methacrylate (PMPM) onto polypropylene (PP) was investigated with a simultaneous irradiation technique. The effects of the solvent, dose, monomer concentration, and photoinitiator on the grafting were investigated. The grafting was easier in a benzene solution than in chloroform and acetone solutions. The grafting percentage first increased almost linearly with the irradiation dose until 20 kGy and then increased slowly or remained constant. The grafting percentage increased with the monomer concentration until 1.1 mol/L. The grafting percentage was higher when the proper amount of benzophenone was added. The grafted samples were characterized with Fourier transform infrared spectroscopy and thermogravimetric analysis. Carbonyl groups were found on grafted PP samples, and the carbonyl index increased with the grafting percentage. Thermogravimetric analyses proved the existence of grafted materials on PP, and grafted PMPM thermally decomposed at a lower temperature than PP. The radiation resistance of PP with grafted PMPM was better than that of pristine PP. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2157–2164, 2005     

Radiation‐induced graft polymerization of glycidyl methacrylate onto PE/PP nonwoven fabric and its modification toward enhanced amidoximation

A nonwoven fabric made of polypropylene coated by polyethylene was used as the trunk polymer in the preparation of a highly efficient new adsorbent. Metal ion uptake capacity has been aimed to be increased by introducing double amidoxime groups per repeating unit of the chains grafted to trunk polymer. The base polymer was irradiated by electron beams with a dose of 200 kGy under N₂ atmosphere and glycidyl methacrylate (GMA) was grafted onto irradiated nonwoven fabric. Grafting conditions were optimized, and GMA‐grafted polymer was modified with 3,3′‐iminodipropionitrile in ethanol at 80°C. GMA grafting (150%) was determined to be the optimum degree given that higher extent of grafting rendered the materials brittle. Pendant nitrile groups were then amidoximated by using 6% hydroxylamine in methanol–water mixture (1 : 1). The all‐polymeric structures were characterized by using FTIR, SEM, and thermal analysis methods, confirming the grafting, modification, and amidoximation stages gravimetrically, spectroscopically, and visually. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007