Thermoluminescence characterization of functionalized grafted polymers and its application for radiation dosimetry at low doses

Functionalized polymers were prepared by radiation-induced graft copolymerization of binary monomer system acrylic acid/acrylamide (AAc/AAm) onto low-density polyethylene (LDPE) and polypropylene (PP) films using direct radiation-grafting technique. Sulfonation was carried out for the prepared grafted copolymers using concentrated sulfuric acid (97%) at 60 ^°C for 15 min. The grafted and sulfonated grafted films found to have good properties such as thermal stability and hydrophilic properties. The sulfonated grafted films found to have a better hydrophilic character than the grafted ones due to ionic character resulted by this conversion. The thermoluminescence (TL) characteristics of a set of grafted and sulfonated films have been studied with regard to their use as off-line dosimeters in radiotherapy. The structural characterization has been performed by means of infrared spectroscopy. Their TL responses have been tested with radiotherapy beams of ⁶⁰Co photons in the dose range 0.1–7 Gy. The dosimetric characterization has yielded a very good reproducibility and is independent of the radiation energy. The TL signal is not influenced by the dose rate and exhibits a very low thermal fading. Moreover, the sensitivity of the samples compares favorably with that of the standard TLD100 dosimeters. Finally, at the same dose, the TL response for LDPE-g-P (AAm/AAc) films is higher than the PP-$g$-P(AAm$/$AAc), and the sulfonated grafted films are more sensitive to radiation than the grafted ones.     

Radiation synthesis of acrylamide/N,N-(dimethylamino) ethyl methacrylate grafted onto low density polyethylene films

Radiation-induced graft copolymerization of acrylamide/N,N-(dimethylamino) ethyl methacrylate (AAm/DMAEMA) onto low density polyethylene films was carried out. The effect of grafting conditions such as solvent type and comonomer composition were studied. Characterization of the prepared films was investigated by Fourier transform infrared. Some selected properties such as thermal stability and swelling behavior were determined. It was found that grafting efficiency, swelling behavior and thermal stability increased with increasing DMAEMA content. Scanning electron microscopy was used for predicting the change in surface morphology via the grafted films. The improvement in properties of the prepared films make it possible to use them in some practical applications.     

Thermo-oxidative degradation kinetics of grafted polypropylene films

The thermo-oxidative stability and degradation behavior of polypropylene (PP) and grafted PP have been investigated using thermogravimetric analysis. Three multiple heating rate methods, namely Kissinger, Kim–Park and Flynn–Wall have been used to calculate the activation energy as a function of the extent of degradation. The four different heating rates (5, 10, 15 and 20°C/min) were maintained in the temperature range of 30–550°C during the analysis. Fourier transform infrared spectroscopy has confirmed the presence of carboxylic group on the surface of grafted PP films. Differential scanning calorimetry has shown that the crystallinity decreased with the increase in grafting. In the air atmosphere, the thermo-oxidative degradation occurs via a pathway that involves decomposition of polymer peroxide. Thermo-oxidative stability of grafted PP films is found to increase with an increase in the degree of grafting (DG). The degradation kinetic parameters were used to predict the lifetime of PP and grafted PP films. The activation energy and lifetime of grafted PP films increased with an increase in the DG. The lifetime of PP and grafted PP decreased with an increase in degradation temperature.     

Chemically induced graft copolymerization of 2-hydroxyethyl methacrylate onto polyurethane surface for improving blood compatibility

To improve hydrophilicity and blood compatibility properties of polyurethane (PU) film, we chemically induced graft copolymerization of 2-hydroxyethyl methacrylate (HEMA) onto the surface of polyurethane film using benzoyl peroxide as an initiator. The effects of grafting temperature, grafting time, monomer and initiator concentrations on the grafting yields were studied. The maximum grafting yield value was obtained 0.0275 g/cm² for HEMA. Characterization of the films was carried out by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), water contact angle measurements. ATR-FTIR data showed that HEMA was successfully grafted onto the PU films surface. Water contact angle measurement demonstrated the grafted films possessed a relatively hydrophilic surface. The blood compatibility of the grafted films was preliminarily evaluated by a platelet-rich plasma adhesion test and hemolysis test. The results of platelet adhesion experiment showed that polyurethane grafted polymerization with monomer of 2-hydroxyethyl methacrylate had good blood compatibility featured by the low platelet adhesion. Hemolysis rate of the PU-g-PHEMA films was dramatically decreased than the ungrafted PU films. This kind of new biomaterials grafted with HEMA monomers might have a potential usage for biomedical applications.     

Impact of γ-rays on constructional,optical and thermal behavior of alkaline and non alkaline low density polyethylene

ABSTRACT

In this study, we investigated the graft copolymerization of methyl methacrylate (MMA) onto low-density polyethylene (LDPE) in the presence of aniline as an inhibitor by gamma radiation. An alkaline treatment was carried out for the prepared graft copolymer. The structural properties of the prepared samples were examined via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD peaks were slightly shifted, indicating an interaction between MMA and the polyethylene matrix. The morphology of the samples confirmed the homogenous grafted phase scattered onto the LDPE surface. Analysis of the absorption spectra indicated an allowed indirect transition mechanism. The Urbach energy (E_U) results showed that the value of the E_U for grafted LDPE was found to be higher than that of pure LDPE—up to 15?kGy irradiation dose, although this value decreases upon grafting. However, the value of the E_U for alkaline-treated grafted films decreases systematically by increasing the degree of grafting. The thermogravimetric analysis (TGA) of the sample indicated that the thermal stability of LDPE samples is significantly changed by grafting MMA onto it. Horowitz and Metzger's models were utilized to measure the activation energy of the thermal decomposition of all samples.     

Polarized Raman study of random copolymers of propylene with olefins

The polarized Raman spectroscopy is employed in the study of structural modifications in the films of isotactic polypropylene (PP) whose chain contains ethylene, 1-butene, 1-hexene, 1-octene, and 4-metyl-pentene-1, which represents an isomer of 1-hexene. It is demonstrated that the phase and conformational compositions of copolymer molecules depend on the comonomer content and the side-chain length of the second monomer. The content of the PP molecules in the helical conformation in the crystalline and amorphous phases of the copolymers monotonically decreases with increasing content of the second monomer. The decrease in the content of helical macromolecules in the crystalline phase is faster than the decrease in the amorphous phase. At a certain content of comonomers, the total content of the helical fragments decreases with increasing length of the side chain of the second monomer. The structures and Raman spectra of the copolymers of propylene with 1-hexene and 4-methyl-1-pentene are similar.     

Modification of Low Density Polyethylene with 2-Hydroxyethyl Acrylate by a Swollen-Phase Grafting Method

Low-density polyethylene (LDPE) was modified with 2-hydroxyethyl acrylate (HEA) by a swollen phase grafting method with azobisiso-butyronitrile (AIBN) as initiator and xylene as a swelling agent. Fourier transform infrared spectroscopy (FTIR) and ¹H-nuclear magnetic resonance (¹H-NMR) showed that the HEA was grafted onto the PE molecular chains and the copolymer (LDPE-g-PHEA) was formed. The rheological data illustrated that the content of long chain branches (LCB) in LDPE-g-PHEA was higher than in LDPE. Melt flow index (MFI) measurements indicated that the LDPE backbone was degraded slightly when the HEA content was small in the process of grafting. X-ray diffraction (XRD) and water contact angle measurements demo-nstrated that the grafting degree had an influence on the crystallinity and polarity of the graft polymer. A staining analysis indicated that the dyeing of the product was improved continuously with increasing of the grafting degree. Polyvinylpyrrolidone (PVP), NaCl, and ultrasound were shown to contribute to the staining, with ultrasound being the most productive. The probable grafting reaction mechanism is pro-posed. The results of the influence of monomer concentration on the grafting reaction revealed that the grafting ratio and gel content of the product increased with increasing of HEA amount.     

Surface modification of polyethylene film by acrylamide graft and alcoholysis for improvement of antithrombogenicity

To improve antithrombogenicity of polyethylene (PE) films, the films pretreated by Ar plasma were radiated by ultraviolet light to initiate grafting polymerization with acrylamide (AAm) in absence of photo-initiator, then the AAm-grafted PE films (PE-g-AAm) were alcoholized with octadecyl alcohol. Effects of Ar plasma composite parameter (W/FM), pretreated time, AAm monomer concentration, and UV irradiation time on grafting rate were investigated systematically. AAm-grafted PE film and alcoholized PE film (PE-g-SAAm) were characterized by contact angle, X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transfer infrared (ATR-FT-IR) spectroscopy and atomic force microscope (AFM), respectively. The results indicated that the moieties of AAm and stearyl were successively immobilized onto the PE surface. The platelet adhesion experiment showed that antithrombogenicity of the modified PE films was improved in comparison with PE films. The change in antithrombogenicity is attributed to the surface of the modified film in presence of tail-like structure which consists of polyacrylamide as spacer and stearyl as end groups.     

Raman study of ethylene-propylene copolymers and polyethylene-polypropylene reactor blends

The Raman spectra of the ethylene-propylene copolymers (EPC) synthesized using new metallocene catalytic systems and the polypropylene/polyethylene/diblockcopolymer of propylene and ethylene (PP/PE/DBC) blends obtained using the sequential polymerization are studied. The copolymer and reactor blend spectra are analyzed using the Raman spectra of a series of liquid n-alkanes. Significant monotonic changes are observed in the spectra of EPC and the PP/PE/DBC blends when the ethylene content increases. Substantial differences between the series of samples of blends and copolymers are revealed. In contrast to the EPC spectra, the spectra of the PP/PE/DBC reactor blends are represented as an exact superposition of the homopolymer spectra with the weight coefficients proportional to the contents of the blend components. A monotonic blue shift of the line that corresponds to the symmetric stretching mode of the CH₂ groups is observed in the EPC Raman spectra when the ethylene content increases. It is demonstrated that, for this line, the peak position only depends on the relative content of comonomers and does not depend on the contents of the PP and PE crystalline phases. The intensity ratio of two fundamental vibrations of PE and PP with frequencies of 1295 and 1330 cm^?1 can be used to determine the relative contents of the PE molecules in the trans-conformation and PP macromolecules in the helical conformation in the PP/PE blends. It is demonstrated that variations in the Raman spectra of n-alkanes, EPC, and PP/PE/DBC reactor blends related to variations in the relative contents of various chemical groups are reliably traced in the spectra of all of the materials under study.     

Pre-irradiation-induced graft reaction of maleic anhydride onto polypropylene

The radiation induced graft polymerization is a well-known method to obtain new materials. Until recently, only conventional radiation sources, such as Co-60 and electron beams, were used. Moreover, part of the damage induced in polymers by heavy ions can produce active sites (peroxides and hydroperoxides) that are useful to initiate grafting reactions. Maleic anhydride (MAH) was grafted onto polypropylene (PP) wax with a number-average molecular weight (Mn) of 8000 by gamma pre-irradiation technique. Effects of total dose, monomer concentration, reaction time, and temperature on percentage of grafting are studied in detail. It is shown that the optimum conditions for grafting are temperature of 70 ^°C and total dose of 14.4 kGy. PP-g-MAH is characterized by infrared spectrum. Differential scanning calorimetry shows that the compatibility of PP-g-MAH is better than that of PP.     

Effects of electron-beam irradiation on surface oxidation of polymer composites

The aim of this article was to show the effects of an electron radiation dose and presence of a compatibilizer on the oxidation of composites made of blends of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), and poly(ethylene terephthalate) (PET) as well as of blends of LDPE, HDPE, and PP. As the compatibilizers, the styrene-ethylene/butylene-styrene elastomer grafted with maleic anhydride (SEBS-g-MA) and trimethylol propane trimethylacrylate (TMPTA) were used; they were added in the amounts of 5, 10, and 15 wt% and 1, 2, and 3 wt%, respectively. The oxidation of the surface layer (SL) was investigated by the X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). It was found that the extent of the composite oxidation increased with the increasing dose of the electron radiation. The addition of the compatibilizers enhanced the oxidation of the SL but hindered the oxidation of the bulk of the material.     

Polypropylene modified with 2-hydroxyethyl acrylate-g-2-methacryloyloxyethyl phosphorycholine and its hemocompatibility

Polypropylene (PP) was modified with 2-hydroxyethyl acrylate (HEA) by solution radical grafting to introduce active hydroxyl groups on polypropylene backbone (PP-g-HEA). Then the biomimic monomer, 2-methacryloyloxyethyl phosphorycholine (MPC), was grafted onto the surface of PP-g-HEA film (PP-g-HEA-g-MPC) by redox graft polymerizations with ceric(IV) ammonium nitrate as an initiator. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) showed that the HEA and MPC were introduced onto PP molecular chains and the copolymer, PP-g-HEA-g-MPC were formed. The water contact angle measurements demonstrated that the final modified PP film exhibited a better hydrophilic surface compared to the neat PP film. The platelets adhesion on the neat PP, PP-g-HEA and PP-g-HEA-g-MPC film was examined by scanning electron microscopy (SEM). It was found that a large number of platelets were adhered and activated on the surface of neat PP and PP-g-HEA films, while the number of platelets on PP-g-HEA-g-MPC surface was decreased remarkably. The result revealed that the introduction of poly(MPC) onto the PP surface improved the hemocompatibility of PP substantially.     

Solution Grafting of Maleic Anhydride on Low-Density Polyethylene: Effect on Crystallization Behavior

Maleic anhydride (MAH) was grafted onto low-density polyethylene (LDPE) by a solution approach with dicumyl peroxide (DCP) as initiator and xylene as solvent. The effects of various experimental conditions on the grafting degree (GD, wt%), such as DCP concentration (A), MAH concentration (B), reaction time (C), reaction temperature (D) and the time for initiator addition (E), were investigated by an orthogonal experiment. The results demonstrated that the DCP concentration had the greatest influence on GD, while the reaction temperature had a minimal influence on GD. A copolymer with high GD (up to 4%) was obtained under the optimum conditions. It was proven that MAH was grafted onto the LDPE successfully by FT-IR. The crystallization behavior of the grafted LDPE was studied by differential scanning calorimetry (DSC) and X-ray diffraction (XRD), and the crystallization kinetic parameters of the grafted LDPE were obtained. Compounds of paraffin and grafted LDPE were investigated by XRD. The results demonstrated that a small amount of LDPE-g-MAH could affect the crystallization behavior of paraffin. This suggested that the grafted LDPE has a potential application as a pour point depressant (PPD) for heavy oil.     

Relationship between Peroxide Initiators and Properties of Styrene Grafted Polypropylene via Reactive Extrusion

To understand the relationship between the initiators and the properties of grafted polypropylene (PP), and provide guidance for designing polymers with different performance through selecting appropriate initiators, a series of styrene (St) grafted PP was prepared by modifying commercial linear PP via reactive extrusion using two different peroxide initiators, dicumyl peroxide (DCP) and benzoyl peroxide (BPO). Fourier transform infrared spectra indicated that the use of DCP led to a higher St grafting degree compared to the system using BPO. The melt flow index and rheological characteristics suggested the existence of short chain branching (SCB) structures in the St grafted PP using DCP, and long chain branching (LCB) structures in the St grafted PP using BPO. Differential scanning calorimetry and polarized optical microscopy results showed that the degradation of the PP chains and the introduction of SCB structures hindered the crystallization process of the St grafted PP using DCP, and the existence of the LCB structures accelerated the crystallization process of the St grafted PP using BPO. We suggest this research can contribute to the understanding of methods to prepare grafted PP with special properties via reactive extrusion by using proper initiators.     

Characterization and application of radiation grafted membranes in waste treatment

Ionic membranes were prepared by radiation-induced grafting of acrylic acid onto low density polyethylene films. To elucidate the possibility of practical use, a study has been made for the characterization of the grafted and chemically treated membranes. The selectivity of such prepared membranes towards the chelation or complexation of different alkali metals was investigated, to find that the higher affinity is observed for K⁺, Na⁺ and Li⁺ ions compared to other alkali metals used. The metal uptake percent was determined using different techniques: flame photometer and X-ray fluorescence (XRF). The uptake of metal from its feed solution by the grafted membrane increased as the degree of grafting increased, i.e., it is directly proportional to the content of functional carboxylic acid groups in the graft copolymer. As a consequence, the electrical conductivity of metal feed solution decreased during such process of metal chelation by the membrane. The higher the grafting degree of membrane, the lower the electrical conductivity of metal feed solutions observed. The changes in thermal properties of the prepared membranes were investigated and characterized using differential scanning calorimeter (DSC), and thermal gravimetric analysis (TGA). The thermal stability of these membranes increased with a degree of grafting due to the formation of crosslinked network structure via hydrogen bonding. Furthermore, such stability is enhanced for the alkali-treated membranes even at high elevated temperatures. The prepared membranes showed a great promise for possible use in the recovery of uranium from zirconium in their wastes.     

Thermal Behavior of Polypropylene-g-glycidyl Methacrylate Prepared by Melt Grafting

The thermal behaviors of glycidyl methacrylate (GMA)-grafted polypropylene (PP) (PP-g-GMA) with two different grafting degrees, namely, GPP1 and GPP2, were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray diffraction (WAXD), dynamic mechanical analysis (DMA), and thermogravimetrical analysis (TGA). DSC results suggested that the GMA grafted PP exhibited higher crystallization temperature T_c, higher melting temperature T_m, and higher crystallinity compared with the neat PP. The isothermal crystallization kinetics was analyzed with the Avrami equation and the total crystallization activation energy was calculated. It was concluded that the crystallization processes of PP and the grafted PP were controlled by nucleation and the values of the crystallization activation energy of PP and the grafted PP were almost identical. POM results suggested that the GMA grafted PP exhibited smaller spherulites size compared with the neat PP. WAXD patterns indicated that the neat PP encouraged the formation of γ phase, compared with the grafted PP, during the crystallization process. DMA results showed that melt grafting did not induce a clear effect on the γ-transition and β-transition of the amorphous phase but resulted in a decrease in mobility of the PP chains in the crystals. TGA curves suggested that the melt grafting slightly improved the thermal stability of PP.     

Mechanical Properties and Morphology of LDPE/PP Blends

Two types of polypropylene (PP) with different molecular structure, namely, homogeneous PP (PPH) and PP block‐copolymer (PPC), were blended with a long chain, branched, low density polyethylene (LDPE) in a twin screw extruder and then injection moulded into test specimens; the mechanical properties and morphology of the blends are reported. The tensile strength, elastic modulus, flexural strength, and flexural modulus of the blends increased monotonically with increasing PP content, although exhibiting a slightly negative deviation from the rules of mixtures due to the relatively poor compatibility of the components, which caused the blends to separate into individual phases. Comparatively, these mechanical properties of the LDPE/PPH blend were much higher than that of the LDPE/PPC blend, which was attributable mainly to the fact that the mechanical properties of neat PPH are stronger than that of neat PPC. With respect to the impact strength of the blends, a maximum value appeared in LDPE/PPH blends when PPH content was about 20% and also in LDPE/PPC blends when PPC content was about 40%.     

Porous structure, permeability, and mechanical properties of polyolefin microporous films

Microporous films of polyolefins, namely, polyethylene and polypropylene, have been prepared using the process based on the extrusion of the melt with the subsequent annealing, uniaxial extension, and thermal fixation. The influence of the conditions used for preparation of the films on their morphology, porosity, number and sizes of through-flow channels, and mechanical properties has been investigated. It has been found that a significant influence on the characteristics of the porous structure of the films is exerted by the degree of orientation of the melt at extrusion, the annealing temperature, and the degree of uniaxial extension of the films. The threshold values of these parameters, at which through-flow channels are formed in the films, have been determined. It has been shown using filtration porosimetry that polyethylene films have a higher permeability to liquids as compared to the polypropylene samples (240 and 180 L/(m² h atm), respectively). The porous structure of the polyethylene films is characterized by larger sizes of through pores than those of the polypropylene samples (the average pore sizes are 210 and 160 nm, respectively), whereas the polypropylene films contain a larger number of through-flow channels.     

A Novel Strategy for Achieving High Melt Strength Polypropylene and an Investigation of Its Foamability

A novel and feasible strategy for preparing high melt strength polypropylene (HMSPP) was developed by a melt grafting reaction in the presence of macro-monomer vinyl polydimethylsiloxane (VS), co-monomer styrene (St), and initiator benzoyl peroxide through a one-step reactive extrusion. The rheological behaviors, melt strength, and foaming ability of HMSPP were studied. The results showed that VS and St were successfully grafted onto polypropylene (PP), and the weight average molecular weight, molecular weight distribution, and melt strength of HMSPP were dramatically increased compared with those of the virgin isotactic polypropylene (iPP). Especially, the melt strength of HMSPP increased from 0.022 N for the virgin iPP to 0.29 N, which made the foamability of HMSPP significantly improved when supercritical carbon dioxide was used as the blowing agent. The foaming condition was optimized to 160°C and 14 MPa, for which HMSPP foams with a high expansion ratio of 66 times and a high cell density of about 5.8×10⁷ cell/cm³ were obtained, while the virgin iPP did not yield foams with good cell structure. Moreover, the resultant HMSPP could be foamed in a remarkably wide temperature range from 145°C to 165°C, which would be of great significance for industrial application.     

Polypropylene surface modification by entrapment of polypropylene-graft-poly(butyl methacrylate)

Surface modification of polypropylene was carried out by entraping a copolymer of polypropylene grafted poly(butyl methacrylate) into polypropylene. The effects of structure of copolymers, contact die and content of modifiers on their surface enrichment were studied by attenuated total reflection infrared spectroscopy (ATR-FTIR), contact angle measurements and scanning electron microscopy (SEM). The results indicated that PPw-g-PBMA could diffuse preferably onto the surface and effectively increase the hydrophilicity of PP. Lower content and higher surface energy die were in favor of the copolymer to enrich on the PP surface. PPw-g-PBMA with low PBMA contents, short length of PBMA distributed in PP with smaller phase domains and favored its selective enrichment on the surface of PP, especially at lower loadings in blends. The modified material exhibited excellent solvent-resistance.