Guillermina Burillo

Polymer recycling: potential application of radiation technology

Abstract Management of solid waste is an important problem, which is becoming progressively worse as a byproduct of continuing economic growth and development. Polymeric materials (plastics and rubbers) comprise a steadily increasing proportion of the municipal and industrial waste going into landfill. Development of technologies for reducing polymeric waste, which are acceptable from the environmental standpoint, and which are cost-effective, has proven to be a difficult challenge due to complexities inherent in the reuse of polymers. Establishing optimal processes for the reuse/recycling of polymeric materials thus remains a worldwide challenge as we enter the new century. Due to the ability of ionizing radiation to alter the structure and properties of bulk polymeric materials, and the fact that it is applicable to essentially all polymer types, irradiation holds promise for impacting the polymer waste problem. The three main possibilities for use of radiation in this application are: (1) enhancing the mechanical properties and performance of recovered materials or material blends, principally through crosslinking, or through surface modification of different phases being combined; (2) treatment causing or enhancing the decomposition of polymers, particularly through chain scission, leading to recovery of either low molecular weight mixtures, or powders, for use as chemical feedstocks or additives; (3) production of advanced polymeric materials designed for environmental compatibility. This paper provides an overview of the polymer recycling problem, describes the major technological obstacles to the implementation of recycling technologies, and outlines some of the approaches being taken. A review of radiation-based recycling research is then provided, followed by a discussion of future directions where irradiation may be relevant to the problems currently inhibiting the widespread recycling of polymeric materials.

Medical devices modified at the surface by γ-ray grafting for drug loading and delivery

Importance of the field: Medical devices with the capability of hosting drugs are being sought for prophylaxis and treatment of inflammatory response and microbial colonization and proliferation that are associated with their use. Areas covered in this review: This review analyzes the interest of γ-ray irradiation for providing medical devices with surfaces able to load drugs and to deliver them in a controlled way. The papers published in the last 20 years on the subject of γ-ray irradiation methods for surface functionalization of polymers and their application for developing medicated medical devices are discussed. What the reader will gain: The information reported may help to gain insight to the state-of-the-art of γ-ray irradiation approaches and their current advantages/limitations for tailoring the surface of medical devices to fit preventive and curative demands. Take home message: Grafting of polymer chains able to establish specific interactions with the drug, grafting of stimuli-responsive networks that regulate drug diffusion through the hydrogel-type surface as a function of the surrounding conditions, and grafting of cyclodextrins that control uptake and delivery through the affinity constant of inclusion complexes have been revealed as efficient approaches for endowing medical devices with the capability of also acting as drug delivery systems.

Polypropylene grafted with smart polymers (PNIPAAm/PAAc) for loading and controlled release of vancomycin

New smart surface-modified polypropylene (PP) was prepared for improving the loading and the sustained delivery of vancomycin and, thus, reducing the risk of biofilm formation when used as component of biomedical devices. Isothermal titration calorimetry (ITC) served for screening the most suitable monomers for grafting; the drug preferentially bonding to ionized acrylic acid (AAc). A net-PP-g-PNIPAAm-inter-net-PAAc was synthesized by first grafting and cross-linking of N-isopropylacrylamide onto PP films and then interpenetrating a second network by redox polymerization and cross-linking of AAc. PP-g-PAAc slabs were prepared by grafting AAc and, optionally, cross-linking. The amount and composition of grafted polymer (FTIR-ATR), morphology (SEM), temperature- and pH-responsiveness (swelling measurements), thermal behavior (DSC), friction coefficient (rheometry), drug loading and release rate, and effect against methicillin-resistant Staphylococcus aureus (MRSA) biofilms (modified robbins device) were evaluated. Grafting of AAc notably decreased the friction coefficient from 0.28+/-0.03 to 0.05+/-0.02 and enhanced the vancomycin loading (up to 2.5mg/cm(2)). Drug-loaded films showed a pH-dependent release rate, sustaining the release in pH 7.4 aqueous media at 37 degrees C for several hours. All drug-loaded films reduced biofilm formation by MRSA; the anti-biofilm effect being statistically significant (91.7% reduction, alpha<0.05) for PP-g-PAAc with the thinnest grafting layer.

Cyclodextrin-functionalized biomaterials loaded with miconazole prevent Candida albicans biofilm formation in vitro.

Polyethylene (PE) and polypropylene (PP) were functionalized at their surfaces with cyclodextrins (CDs) in order to prevent the adhesion and proliferation of Candida albicans on medical devices made from these polymers. The surface functionalization involved the grafting of glycidyl methacrylate (GMA) after oxidative gamma-ray pre-irradiation, followed by the attachment of beta-CD and HP-beta-CD to PE-g-GMA and PP-g-GMA surfaces. The yield of CD functionalization directly depended on the amount of GMA grafted. The presence of CDs on the surface of the polymers did not compromise their cell compatibility, but remarkably changed their protein adsorption profile. In contrast to unmodified PE and PP that adsorb significant amounts of fibrinogen ( approximately 0.047 mg cm(-2)) but not albumin, the CD-modified polyethers promoted the adsorption of albumin (between 0.015 and 0.155 mg cm(-2)) and reduced the adsorption of fibrinogen. Furthermore, functionalization with CDs provided PE and PP with the capability to incorporate the anti-fungal drug miconazole (up to 0.27 mg cm(-2)), leading to reduced biofilm formation by C. albicans in an in vitro biofilm model system. Overall, the results of the work indicate that the novel approach for functionalization of PE and PP is potentially useful to reduce the likelihood of foreign body-related infections.

Changes in poly-vinylidene fluoride produced by electron irradiation

Abstract A study was made of the effects of electron irradiation of poly-vinylidene fluoride, using the DSC, FTIR, and X-ray techniques, as well as determining the percent cross-linking. Changes in crystallinity and melting point of the sample as a function of dose were found, the latter due to competition between cross-linking and crystallinity. The cross-linking was observed to increase with radiation dose. Chemical changes observed include the formation of carbonyl groups and double bonding, associated with the loss of HF.

Radiation crosslinking of highly plasticized PVC

Abstract To improve the physical properties of highly plasticized PVC, the polymer was crosslinked by gamma irradiation using a dose rate of 91 kGy/h. The effect of plasticizer type was studied by using three different plasticizers, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (TXIB), di(2-ethyl hexyl) phthalate (DOP), and di(2-ethylhexyl terephthalate) (DOTP), and varying irradiation doses. Gel content was determined by soxhlet extraction, tensile measurements were made on a universal testing machine and the mechano-dynamic measurements were made in a dynamic rheometer. It was found that a considerable bonding of plasticizer molecules to macromolelcules takes place along with crosslinking, so that the use of the solvent extraction method for measuring the degree of crosslinking can give erroneous information. Radiation-chemical crosslinking yield ( G c ) and molecular weight of interjunctions chains ( M c ), were calculated for different systems studied. Addition of ethylene glycol dimethacrylate (EGDM) as a crosslinking coagent and dioctyl tin oxide (DOTO) as a stabilizer was also studied. Plasticizers extraction resistance was increased by irradiation treatment.

Cyclodextrin-functionalized polyethylene and polypropylene as biocompatible materials for diclofenac delivery

Polyethylene (PE) and polypropylene (PP) were surface functionalized with beta-cyclodextrin (beta-CD) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) with the aim of providing PE and PP with the capability of behaving as drug delivery systems. Functionalization was carried out according to a two-step procedure: (i) glycidyl methacrylate (GMA) was grafted by means of gamma radiation and (ii) the epoxy groups of GMA reacted with the hydroxyl groups of CDs forming ether bonds. For a fix radiation dose and GMA concentration, grafting yield (ranging from 1 to 100 micromol GMA cm(-2)) depended on the time during which the preirradiated PE and PP films and slabs were immersed in the GMA solution. CD grafting (from 0.013 to 0.734 micromol cm(-2)) was confirmed by infrared analysis, DSC and the organic compound approach (using 3-methylbenzoic acid as a probe). Functionalization with CDs rendered as highly cytocompatible materials as the starting ones, did not cause relevant changes in the water contact angle and the friction coefficient of PE and PP, but remarkably improved their capability to uptake diclofenac through formation of inclusion complexes with the CDs. Furthermore, the functionalized materials released the drug for 1 h, which could be useful for management of initial pain, inflammation at the insertion site as well as adhesion of certain microorganisms if these materials are used as medicated medical devices.

Compatibilization of recycled and virgin PET with radiation-oxidized HDPE

Abstract Blends of high-density polyethylene (HDPE), which cross-links on radiation, and both, recycled and pristine polyethylene terephtalate (PET), one of the most radiation-stable polymers, that contain aromatic groups, which are effective at dissipation of the energy of the ionizing radiation, were irradiated with gamma rays, in order to form a copolymer capable of improving the compatibility of the blend HDPE/PET. Due to the low content of the PET in the resulting copolymer, blends PET and radiation-oxidized HDPE, were also studied. The tensile and flexural properties were improved when the PET content was increased and when the HDPE was pre-irradiated; the largest increase in the mechanical properties was observed for PET contents between 10% and 20% (w/w). The improvement in the properties is believed to occur because of a percolation effect of the PET in the HDPE matrix and the radiation-improved compatibility by means of polar groups formed in the polyethylene. However, impact properties were observed to decrease when the PET content increased in spite of the irradiation.

Crosslinking of recycled polyethylene by gamma and electron beam irradiation

Recycling of polymeric materials is usually accompanied by degradation and deleterious properties. Irradiation crosslinking of recycling low density polyethylene by electron beam and gamma rays could be the solution to improve their properties. This paper presents a comparison on the effects of gamma and electron irradiation on virgin and recycled polyethylene. Their mechanical, thermal and chemical properties were analyzed. VPE samples shown higher crosslinking percentages than RPE samples in all range of doses studied, unirradiated RPE samples had higher values on their tensile properties than VPE. Percentage crystallinity was similar in all range of doses studied.

Effect of irradiation dose, storage time and temperature on the ESR signal in irradiated oat, and corn and wheat

Results obtained for electron-irradiated oat, corn and wheat kernels are discussed. The applied irradiation doses were up to 160 kGy. For doses up to approx. 50 kGy the number of free radicals produced by the irradiation is linear with the absorbed dose; moreover, the decay at room temperature in the dark or in the presence of light is quite similar. These facts point to the possible use of these kernels as dosimeters. An analysis of the free radical decay as a function of time and temperature shows the contribution of at least three types of radicals, whose half-lifes, radiochemical yields and activation energies are given.