Effect of Acidic and Basic Solutions on Electron Beam Irradiated Epoxy Nanocomposites Containing Nanoclay,CaCO3 and TiO2 Nanoparticles

High chemical resistance is the main prerequisites for materials that are intended to be utilized in usages such as chemicals storage containers production. Nanocomposites of epoxy resin containing nanoclay, CaCO₃ and TiO₂ nanoparticles were prepared and their chemical resistance was studied. Moreover, the effect of electron beam irradiation was explored. TEM micrographs proved the dispersion of nano-size particles in the polymeric matrix. XRD patterns showed an exfoliated structure for nanocomposite containing 1 % nanoclay and intercalated structures for nanocomposites with higher nanoclay contents. SEM showed the pits that appeared in epoxy/nanoclay structure due to chemical corrosion. Weight loss measurements revealed that an addition of 1 % nanoclay to the epoxy matrix is effective for improving the chemical properties of the polymer. Desirable effect of 100 kGy irradiation on chemical resistance properties of the samples was also observed in both acidic and basic environments.     

Preparation and Electron Beam Irradiation of PVC/ENR/CNTs Nanocomposites

Poly (vinyl chloride), PVC/epoxidized natural rubber blend, ENR/carbon nanotubes, CNTs nanocomposites were prepared using melt intercalation and solution blending methods. In both preparation methods PVC: ENR: CNTs ratios were fixed at 50:50:2, while the 50/50 PVC/ENR blend without the addition of CNTs was used as control. The PVC/ENR/CNTs nanocomposites were exposed to electron beam (EB) irradiation at doses ranging from 0–200 kGy. The effects of two different preparation methods on the tensile properties, gel fraction and morphology of the PVC/ENR/CNTs nanocomposites were studied. Prior to EB irradiation, the addition of 2 phr of CNTs caused a drop in the tensile strength (Ts) of the 50/50 PVC/ENR blend, implying poor distribution of CNTs in the PVC/ENR blend matrix. However upon EB irradiation, the nanocomposites prepared by the melt blending method exhibited higher values of Ts as compared to the neat PVC/ENR blend due to occurrence of radiation-induced cross-linking in the PVC/ENR blend matrix. Transmission electron microscopy (TEM) images proved that a better dispersion of CNTs in PVC/ENR blend matrix can be achieved by melt intercalation compared to solution blending and the dispersion of CNTs was improved by irradiation. Scanning electron microscopy (SEM) results showed a distinct failure surface with formation of rough structure for the irradiated nanocomposites, which explains the higher values of tensile properties compared to the non-irradiated nanocomposites.     

Mechanical and physicochemical properties of electron beam irradiated rubber/clay nanocomposites

Effect of electron beam irradiation on the mechanical and physicochemical properties of both styrene butadiene rubber (SBR)/clay and ethylene propylene diene monomer (EPDM)/clay nanocomposites containing clay contents from 3 to 10 phr prepared by melt blending method has been investigated. The prepared composites were subjected to electron beam irradiation doses of up to 150 kGy to induce radiation curing, whereas the mechanical properties in terms of tensile strength (TS), tear strength (Ts), and elongation at break (E_b) were studied as a function of irradiation dose and clay content. TS and Ts increased with increasing irradiation dose up to 100 kGy, they were decreased with further increase in dose. An increase in TS and Ts for SBR and EPDM nanocomposites containing various organomodified montmorillonite (OMMT) contents (3–5 phr) was noticed, whereas a decrement behavior was observed at higher OMMT content. The elongation at break decreased continuously with both irradiation dose and OMMT content. The crosslink density for either EPDM or SBR samples increases with increasing irradiation dose up to 150 kGy and by increasing clay content up to 5 phr, whereas it decreases at higher clay content (7–10 phr). At 5 phr OMMT and 100 kGy irradiation, SBR nanocomposites showed higher TS and Ts than EPDM nanocomposites, while the crosslink density of SBR is lower. POLYM. COMPOS., 34:1600–1610, 2013. © 2013 Society of Plastics Engineers     

Chitosan/CNTs nanocomposite as green carrier material for pesticides controlled release

Chitosan-based nanocomposites containing gamma-treated carbon nanotubes (CNTs) were developed for controlled release of pesticide. The CNTs were irradiated under gamma irradiation in air at different doses. The transmission electron microscopic images of gamma-treated CNTs showed disentanglement of the tubes without distorting their tubular structure which effectively increased the dispersion properties of CNTs in nanocomposites. X-ray diffraction analysis of CNTs showed some structural changes, and an irradiation dose of 150 kGy is the most effective. Azinphos methyl (AZM) was selected as a model drug, and its release was studied using HPLC technique. Controlled release response of CNTs-based nanocomposites opens a new avenue for pesticides applications because it requires less quantity of pesticides. As a result, the side effects of pesticide in our environment are minimized.     

Mechanical,Thermal and Electrical Properties of Ethylene Vinyl Acetate Irradiated by an Electron-Beam

The effects of electron beam irradiation of (ethylene vinyl acetate) EVA containing 18% vinyl acetate was studied. The EVA sample was then irradiated by using 3 MeV electron beam machine at doses ranging from 120 to 360 kGy in air at room temperature and analyzed for mechanical, thermal and electrical properties. It was revealed by DSC analysis that the crystallinity of the electron-beam radiated EVA decreased slightly as verified by a marginal reduction in the densities and heats of melting. Thermal degradation of EVA occurred through two steps as shown by the thermogravimetric curve with maximum rates of 350 and 450°C, respectively. The results obtained from both gel content and hot set tests showed that under the irradiation conditions employed, the EVA sample cross-linked by the electron beam irradiation, and the degree of cross-linking in the amorphous regions was dependent on the irradiation dose. A significant improvement in the tensile strength of the neat EVA samples was obtained upon electron-beam radiation up to 210 kGy with a concomitant decline in elongation of break. Various electrical properties of EVA such as surface and volume resistance, breakdown voltage and dielectric constant were studied as a function of radiation dose. It was revealed that the surface resistance and volume resistivity of the EVA reaches a maximum at a 190 kGy dose of radiation. No considerable change of breakdown voltage and dielectric constant was observed with increasing irradiation dose. These studies suggest that radiation-cured EVA is more thermally and mechanically stable than pure EVA. Similarly, the results from the electrical properties revealed that surface and volume resistance are higher than pure EVA.     

Effect of Electron Beam Irradiation,EPDM and Azodicarbonamide on the Foam Properties of LDPE Sheet

The effect of electron beam irradiation, EPDM blending, and Azodicarbonamide (ACA) concentration on the foaming properties of LDPE sheet was investigated. The studied properties are foaming degree, cell densities, mechanical properties and thermal decomposition properties. The data showed that the increasing of foaming agent (ACA) concentration reduces the mechanical properties and increases the gel content. Also, electron beam irradiation has a clear effect on increasing the cell density, mechanical properties gel content and thermal properties of irradiated samples when compared with unirradiated samples. EPDM blending with LDPE at a concentration of 20% reduces the doses required to obtain the foaming degree (71.4%) from 50 kGy in LDPE to 5 kGy in LDPE/EPDM (80/20%). This effect may be attributed to enhancement of radiation cross-linking for LDPE by blending with the amorphous polymer (EPDM).     

Nanocomposites of polypropylene/titanate nanotubes: morphology,nucleation effects of nanoparticles and properties

High-quality titanate nanotubes (TiNT) were mixed with modified polypropylene (PP*) by a batch melt-mixing procedure. To improve compatibility between the nanofiller and the matrix, polypropylene (PP) was modified by electron beam irradiation. Effects of TiNT nanoparticles on crystallization, mechanical, thermal and rheological properties of the modified polypropylene were studied and compared with the analogous systems filled with commercial micro- (mTiO₂) and nano- (nTiO₂) titanium dioxide particles. Nucleation effects of the TiO₂-based fillers on PP* crystallization were investigated in detail. The microstructure of the PP*/TiNT nanocomposites shows well-dispersed TiNT sparse aggregates (clouds), penetrated by the polymer. A large-scale structure in the nanocomposite melts confirmed also rheology. In comparison to the matrix characteristics, the stiffness and microhardness of the TiNT nanocomposites increase by 27 and 33 %, respectively. The enhancement in mechanical properties demonstrates that the quality titanate nanotubes can be used as an efficient filler in non-polar polymers using the polymers modified by irradiation. In the case of the nanocomposites containing nTiO₂-anatase particles, the increase in these mechanical characteristics is lower. The investigated changes in the rate of crystallization indicate a marked nucleation effect of the nanotubes. The crystallization kinetics data, processed by the Avrami equation, suggest 3-dimensional crystal growth in the polypropylene matrix. The observed improvement in mechanical properties of the TiNT nanocomposites is induced not only by the nanofiller reinforcement but also by the changes of supermolecular structure of the polymer matrix due to nucleated crystallization.     

Polyurethane/clay nanocomposites reinforced with carbon and glass fibres: study of mechanical and thermal properties,and the effect of electron beam irradiation

Polyurethane (PU) nanocomposites with 0, 1, 3, 5, and 7?wt-% nanoclay contents were prepared. X-ray diffraction patterns, transmission electron microscopy images, tensile test, and thermogravimetric analysis were utilised to reveal the morphological, mechanical, and thermal-resistant properties of the prepared nanocomposites. The exfoliated structure was obtained for nanoclay contents up to 3?wt-%. Incorporation of nanoclay to the PU matrix prompted the thermal stability of the polymer. A nanocomposite filled with 3?wt-% nanoclay showed the best tensile strength in the prepared nanocomposites. Subsequently, the nanocomposite with the 3?wt-% nanoclay was reinforced with carbon and glass fibres. Reinforcement of the PU/nanoclay matrix with carbon and glass fibres significantly ameliorated the tensile properties. Finally, the effects of the electron beam irradiation on the nanocomposites and fibre-reinforced composites were studied. Irradiation with the doses up to 500?kGy enhanced the mechanical and thermal properties. However, further irradiation deteriorated the mechanical and thermal-resistant properties.     

Effect of electron beam irradiation on the properties of ethylene‐(vinyl acetate) copolymer/natural rubber/organoclay nanocomposites

The effects of electron beam (EB) irradiation on the morphology, crosslink density, and tensile properties of EVA/SMR L (Standard Malaysian Rubber)/organoclay nanocomposites prepared by a melt‐blending technique were investigated. All the samples were irradiated by using a 3.0‐MeV EB apparatus with doses ranging from 50 to 200 kGy. Organoclay loading was varied from 0 to 10 phr (parts by weight per hundred parts of resin). X‐ray diffraction results and transmission electron microscopy images proved that the dispersion of organoclay in the nanocomposites was slightly improved by EB irradiation. The gel fraction yield for the nanocomposites increased with irradiation dose but decreased with organoclay loading. However, at 200 kGy, the gel fraction yield was almost the same at all organoclay loadings. Tensile strength and stress at 100% elongation increased proportionally with the irradiation dose. Elongation at break of the nanocomposites increased up to 100 kGy but then decreased at higher irradiation doses. The intercalation and exfoliation of the organoclay, the barrier effect, and the Hofmann degradation of the modification agent are the three major factors leading to the improvement of the properties of the irradiated nanocomposites. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Electron beam synthesis and characterization of poly(vinyl alcohol)/montmorillonite nanocomposites

Poly(vinyl alcohol) (PVA)/montmorillonite clay (MMT) nanocomposites in the form of films were prepared under the effect of electron beam irradiation. The PVA/MMT nanocomposites gels were characterized by X‐ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and mechanical measurements. The study showed that the appropriate dose of electron beam irradiation to achieve homogeneous nanocomposites films and highest gel formation was 20 kGy. The introduction of MMT (up to 4 wt %) results in improvement in tensile strength, elongation at break, and thermal stability of the PVA matrix. In addition, the intercalation of PVA with the MMT clay leads to an impressive improved water resistance, indicating that the clay is well dispersed within the polymer matrix. Meanwhile, it was proved that the intercalation has no effect on the metal uptake capability of PVA as determined by a method based on the color measurements. XRD patterns and SEM micrographs suggest the coexistence of exfoliated intercalated MMT layers over the studied MMT contents. The DSC thermograms showed clearly that the intercalation of PVA polymer with these levels of MMT has no influence on the melting transitions; however, the glass transition temperature (T_g) for PVA was completely disappeared, even at low levels of MMT clay. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1129–1138, 2006     

The comparison of the behaviors of polymer/clay nanocomposites based on high density polyethylene and polypropylene in exposure of electron‐irradiation

The effect of irradiation on thermal and mechanical properties of high density polyethylene (HDPE) and polypropylene (PP)/clay nanocomposites in the presence of polyethylene glycol (PEG) and polypropylene glycol (PPG) for enhancing the clay dispersion into the polymer matrices is considered. The morphology studies show that clay layers satisfactorily expand in the presence of compatibilizers. The irradiation improves the mechanical properties of HDPE nanocomposites at 500 kGy, but it decreases the tensile strength of PP nanocomposites. The addition of PEG markedly ameliorates the mechanical properties of HDPE nanocomposites at 500 kGy, while this improvement is not deduced for PP nanocomposites. The thermogravimetric analysis data show that the irradiation increases the thermal stability of HDPE nanocomposites at the clay content of 5 wt% with and without compatibilizer. The thermal stability of PP nanocomposites descends with the irradiation dose, and the presence of PPG into the PP matrix intensifies this reduction. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Thermal,mechanical, and corrosion resistance properties of vinyl ester/clay nanocomposites for the matrix of carbon fiber‐reinforced composites exposed to electron beam

Vinyl ester/clay nanocomposites with 1, 3, and 5% nanoclay contents were prepared. X‐ray diffractography patterns and Scanning Electron micrographs showed that nanocomposites with the exfoliated structure were formed. Thermogravimetric analysis, water absorption test, and Tafel polarization method, respectively, revealed the improvements in thermal resistance, water barrier properties, and corrosion resistance properties of the samples with an increase in the amount of the incorporated nanoclay. Tensile tests showed that nanoclay also enhanced the mechanical properties of the polymer, so that the tensile strength of the samples with 5% nanoclay was more than 3 times higher than tensile strength of pure vinyl ester samples. Overall, the best properties were observed for the samples containing 5% nanoclay. Pure vinyl ester and nanocomposite with 5% nanoclay content were exposed to the electron beam radiation and their mechanical properties improved up to 500 kGy irradiation dose. Finally, pure vinyl ester and vinyl ester/nanoclay (5%) matrixes were reinforced with carbon fiber and the effect of electron beam irradiation on their mechanical properties was examined. The tensile strength and the modulus of the samples initially increased after exposure to the radiation doses up to 500 kGy and then a decrease was observed as the irradiation dose rose to 1000 kGy. Moreover, nanoclay moderated the effect of the irradiation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42393.     

Influence of sepiolite and electron beam irradiation on the structural and physicochemical properties of polyethylene/starch nanocomposites

This study presents the influence of functionalized sepiolite and electron beam irradiation on the structural and physicochemical properties of high density polyethylene (HDPE)/starch blends. HDPE/Starch blends containing varying amounts of sepiolite [from 2 to 6 parts per hundred (phr) resins] were prepared in an internal mixer and subjected to electron beam irradiation. The structural analysis of nanocomposites revealed an interaction among the incorporated components. The morphological analysis depicted the void‐free dispersion of additives in the nanocomposites as well as an improvement in the compatibility between the matrix and additives. The sepiolite served as a heat barrier and improved the thermal stability of blend upto a maximum of 45°C. The ultimate tensile strength and Young's modulus (E) of blend was slightly improved with the incorporation of sepiolite and radiation. On the contrary, the E of nanocomposites was significantly improved with radiation dose. The sample containing 6 phr sepiolite and irradiated at 100 kGy showed 61% increase in E when compared with its unirradiated counterpart. Likewise, the thermal distortion temperature and Vicat softening temperature of the blend was slightly changed with the incorporation of sepiolite and radiation dose; however, increased with radiation dose in the nanocomposites. The improvements in the properties of nanocomposites with radiation dose were assigned to the formation of radiation‐induced crosslinked network as revealed by gel content analysis. The results presented here revealed substantial improvements in the properties of nanocomposites with irradiation, which pave way for their potential applications in various sectors including packaging materials for radiation sterilizable products. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Sound isolation properties of polycarbonate/clay and polycarbonate/silica nanocomposites

The soundproofing properties of polycarbonate (PC)/nanoclay and PC/nanosilica nanocomposites were studied through testing and theoretical analysis. Nanocomposite sheets with a 3 mm thickness were fabricated by direct hot-compression molding process. The nanoclay and nanosilica particles were incorporated into the PC matrix by a twin-screw extruder. The dispersion efficiency of 1, 3 and 5 wt% nanoclay and nanosilica in the PC matrix was investigated by transmission electron microscopy. Dynamic mechanical analysis was performed for evaluation of mechanical properties of nanocomposites. Sound transmission loss (STL) was measured by an impedance tube over the frequency range of 1600–6300 Hz, and further employed in sound proofing characterizations of nanocomposites. A new finite element model was developed to model the sound transmission loss in impedance tube test. The results showed that the PC/3 wt% nanoclay and 3 wt% nanosilica nanocomposites had an average maximum increase of 5.5 and 6 dB in STL values in the stiffness control region (1600–3600 Hz), respectively. On the other hand, the PC/3 wt% nanoclay and PC/3 wt% nanosilica nanocomposites showed the same sound isolation characteristics in the frequency range of 1600–3600 Hz. In addition, the finite element model developed for modeling the sound transmission loss in the impedance tube demonstrated a good correlation between the theoretical curves and the experimental results in the stiffness control region for both nanocomposites.     

Characterization and electrical conductivity of poly(ethylene glycol)/polyacrylonitrile/multiwalled carbon nanotube composites

Poly(Lactic acid) (PLA)‐layered silicate nanocomposite films were prepared by solvent casting method. The films were irradiated with Co⁶⁰ radiation facility at dose of 30 kGy. The effect of γ irradiation on mechanical properties of the neat PLA and nanocomposites was evaluated by data obtained from tensile testing measurements. The tensile strength of the irradiated PLA films increased with addition of 1 wt % triallyl cyanurate indicating crosslink formation. Significant ductile behavior was observed in the PLA nanocomposites containing 4 pph of nanoclay. Incorporation of nanoclay particles in the PLA matrix stimulated crystal growth as it was studied by differential scanning calorimetry. The morphology of the nanocomposites characterized by transmission electron microscopy and X‐ray diffraction revealed an exfoliated morphology in the PLA nanocomposite films containing 4 pph of nanoclay. Only very small changes were observed in the chemical structure of the irradiated samples as it was investigated by Fourier transform infrared spectroscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Irradiation Modification of PVC/NBR Blend

Electron beam initiated cross-linking on the 50/50 poly(vinyl chloride), PVC/acrylonitrile butadiene rubber, NBR blend was studied in the absence and presence of 4 phr trimethylolpropane triacrylate (TMPTA). The 50/50 NBR/PVC blend was prepared by mixing in a Brabender Plasticoder at 170°C. The blend was then irradiated by using a 3.0 MeV electron beam machine at doses ranging from 0 to 200 kGy in air and room temperature. The changes in gel fraction, tensile strength, hardness, impact strength, scanning electron micrographs and dynamic mechanical properties of the samples were investigated. The gel fraction results indicate that under the irradiation conditions employed, the PVC/NBR blend cross-linked by electron beam irradiation. The addition of TMPTA was found to be effective in the acceleration of the radiation-induced cross-linking. Gradual increases in mechanical properties with irradiation dose were observed before exhibiting a decline due to embrittlement as a consequence of excessive cross-linking at higher irradiation doses. The gradual changeover from ductile to brittle fracture due to the irradiation-induced cross-linking was evident from the SEM examination The increase in the storage modulus and T_g as well as the reduction in the damping peak with the increase in irradiation dose reveal that the enhancement in mechanical properties of NBR/PVC blends upon irradiation is due to the irradiation-induced cross-linking, as well as the improved interaction between NBR and PVC.     

Development and characterization of surface-modified mullite reinforced BMI-toughened epoxy nanocomposites

High-performance diglycidyl ether of bisphenol-A (DGEBA) epoxy-based composite systems with improved thermal stability for advanced structural applications were developed, using bismaleimide (BMI) as toughening agent and surface-modified mullite as reinforcing agent. The nanocomposites developed in the present study are referred to as M/DGEBA–BMI. 95 % by wt. of DGEBA was toughened with 5 % by wt. of BMI and further reinforced with varying weight percentages of (0.5, 1.0 and 1.5 wt%) glycidyl-functionalized mullite to obtain M/DGEBA–BMI nanocomposites. The formation of nanocomposites was ascertained using Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The mechanical and dielectric properties of nanocomposites were investigated by analytical techniques. The thermal behaviour of nanocomposites was characterized using thermogravimetric analyzer and differential scanning calorimeter. Contact angle, surface free energy and percentage water absorption were also studied and reported. Studies suggest that the properties of M/DGEBA–BMI nanocomposites viz; mechanical, dielectric, surface energy and thermal properties improved to an appreciable extent, when compared to those of neat epoxy matrix.     

Preparation and Performance of High-Barrier Low Density Polyethylene/Organic Montmorillonite Nanocomposite

Montmorillonite (MMT) was first modified with dodecyl dimethylbenzyl ammonium (DDA) salt and octadecyl trimethyl ammonium (OTA) salt. Then low density polyethylene (LDPE)/organic montmorillonite (OMMT) nanocomposites were prepared by twin-screw extruder and hot-press. Transmission electron microscopy (TEM) results showed that OMMT layers were homogeneously intercalated into the LDPE matrix. In terms of MMT, the modification effect of OTA is superior to that of DDA. CO₂ and O₂ barrier properties of nanocomposites were increased by 7 times and 4 times with 0.5 wt.% OTA-MMT loading, respectively. At 2 wt% OTA-MMT loading, water vapor permeability of LDPE has also decreased about 2.5 times. Compared with pure PE film, 49.5% and 178% improvement of tensile strength of nanocomposites films were obtained by addition of only 4 wt.% DDA-MMT and OTA-MMT, respectively. In addition, with only 0.5 wt.% OMMT loading, the onset degradation temperature of nanocomposites increases by 23°C and 26°C for LDPE/DDA-MMT and LDPE/OTA-MMT, respectively.     

Electron Beam Irradiation to Recrosslink Devulcanized Sulfur Cured Rubber Blended Polypropylene

This study aims to investigate the effect electron beam (EB) irradiation on the polypropylene/devulcanized sulfur cured rubber (PP‐DVC) compound. The PP‐DVC compounds were compounded using twin‐screw extruder and then compression molded into required shapes before irradiation begins. The gel content of all irradiated PP‐DVC compounds gradually increased with higher irradiation dose indicated that the presence of DVC plays an important role in crosslinking enhancement. The mechanical properties of PP‐DVC compounds were observed marginally higher at low irradiation dosages (≤50 kGy). However, higher irradiation dosages up to 200 kGy cause adverse effect to the PP‐DVC compounds. In addition, the application of low irradiation dosage could enhance the dispersion of DVC particles at 20 phr composition in PP matrix. This also found that the scanning electron microscopy (SEM) observation where the DVC particles dispersed better in PP matrix compared to that of nonirradiated samples. Further increment in irradiation dosages up to 200 kGy reduced the crystallinity caused by chain scissoring process could rupture the crystalline structure in PP matrix. It was also found that the wavenumber of the C? H and CH₂ groups for irradiated samples reduced at high irradiation dosages due to the formation of carbonyl group. POLYM. ENG. SCI., 59:1017–1027, 2019. © 2019 Society of Plastics Engineers     

Synthesis of PLGA using a <Emphasis Type="Italic">C</Emphasis><Subscript>3</Subscript>-symmetric Zr (IV) amine tris(phenolate) alkoxide initiator and the effects of gamma radiation on its properties

In this paper, we report the preparation and characterisation of poly(lactic-co-glycolic) acid (PLGA) using a C ₃-symmetric Zr (IV) amine tris(phenolate) alkoxide initiator. Although the zirconium alkoxide initiator is slower than the most commonly used Sn(Oct)₂, relatively high molecular weights were obtained at a temperature of 130 °C, for a monomer to initiator ratio of 1000/1 (24 h) and 5000/1 (48 h). The degree of racemisation also depends on the initiator used. The reactions performed with the zirconium initiator showed a higher degree of racemisation when compared to those performed with Sn(Oct)₂. A slight increase in the racemisation with time was also observed. The effects of gamma radiation on PLGA were also studied. Doses commonly applied to sterilise materials for biomedical applications were employed—10, 18, 25 and 50 kGy. The molecular weight of all samples irradiated decreased in a dose-dependent fashion—up to 56 % loss for 10 kGy and 72 % for 50 kGy—but were less pronounced for higher doses. Changes in thermal properties, such as melting point, glass transition temperature and enthalpy of crystallisation and fusion, were also observed after irradiation.