Atmospheric and soil degradation of aliphatic-aromatic polyester films

The degradation of an aliphatic-aromatic biodegradable polyester film was studied under conditions of solar exposure and soil burial in a tropical area. Film samples were evaluated for changes over 40 weeks by visual examination, scanning electronic microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, mechanical properties, molecular weight, gel content, and thermal properties. Photodegradation played a major role in the atmospheric degradation of the film, causing it to lose integrity and mechanical properties after week 8 due to main chain scission and crosslinking. SEM micrographs and FTIR spectra indicated that photodegradation started at the exposed side of the film and propagated through the polymer matrix after week 8. FTIR spectra also indicated that subsequent photooxidation processes took place. The reduction of molecular weight of the soil burial samples was much slower than that of the non-crosslinked portion of solar exposed film samples. The reduction of number average molecular weight of the non-crosslinked solar exposed samples followed a first order reaction, whereas the soil burial samples show a surface erosion biodegradation behavior. The relationship among total solar radiation, gel content and number average molecular weight indicated that an accumulated total solar radiation of 800 MJ/m², reached in approximately 7 weeks at the exposure site, is required for PBAT mulch film integrity loss.     

Surface changes during polypropylene photo-oxidation: A study by infrared spectroscopy and electron microscopy

The surface oxidation of polypropylene films which occurs during ultraviolet irradiation in air was found to result in extensive surface restructuring. This restructuring was detected by changes in surface infrared spectra, as measured by attenuated total reflection spectroscopy, and by electron microscopy. The 997 cm^?1/974 cm^?1 absorbance ratio of the film surfaces increased steadily during ultraviolet degradation and was interpreted as an increase in helical ordering which resulted from backbone scission during irradiation. This scission probably also results in the increase in crystallinity detected by density changes. Electron microscopy of direct surface replicas and replicas of material detached from the oxidized film surfaces showed that surface cracking resulted during photo-oxidation, and that this oxidation penetrated selectively into the polymer structure. The replicas of detached, oxidized material showed periodic structures related to the interior morphology of the films. The observed restructuring is believed to be entirely responsible for the decrease in percentage elongation at break which results from photodegradation.     

Controlled degradation of polyhydroxybutyrate via alcoholysis with ethylene glycol or glycerol

It was shown that controlled degradation of poly-[(R)-3-hydroxybutyrate] (PHB) can be achieved by alcoholysis with two types of alcohol in the presence of a catalyst. PHB oligomers terminated with free hydroxyl groups were prepared in this way. Molecular weight of the prepared samples was studied with three methods: SEC analysis with polystyrene calibration, SEC analysis using universal calibration, and viscometry. The data lead to the conclusion that SEC analysis using polystyrene calibration is a suitable method for monitoring degradation. The degradation proceeds by random chain scission and the molecular weight was decreased by almost two orders of magnitude depending on the alcoholysis conditions. The crystallinity and melting temperature, T_m, of PHB after alcoholysis, investigated by differential scanning calorimetry (DSC) show the independence of crystallinity on molecular weight and a decrease in T_m with decreased molecular weight. Time dependence of mechanical properties of selected samples (mechanical ageing) reveals that mechanical properties change with time for degraded samples in a similar way as for the parent polymer.     

Photodegradation of PEEK sheets under tensile stress

The photochemical reaction of poly(ether ether ketone) (PEEK) sheets under tensile loads has been investigated. Two types of UV irradiation tests were carried out in a vacuum environment: with and without a cooling apparatus. Chemical structures, thermal properties, and mechanical properties were measured to clarify photo-deterioration. Chemical analysis based on Fourier Transform Infrared Spectrometry (FT-IR) and X-ray Photoelectron Spectroscopy (XPS) showed photochemical scission caused by UV exposure. Thermal properties, measured by Differential Scanning Calorimetry (DSC), indicated that a crosslinking reaction occurred during the radiation tests. Tensile properties of PEEK sheets after UV radiation clearly showed a tendency to embrittlement affected not only by crosslinking but also by the orientation of molecular chains resulting from the temperature rise of the specimens. Furthermore, applied tensile stress during exposure accelerated molecular scission and disturbed the crosslinking effects of the tensile properties.     

UV stability of HMS-PP (high melt strength polypropylene) obtained by radiation process

HMS-PP in grains was synthesized by the gamma irradiation of PP under a crosslinking atmosphere of acetylene, followed by thermal treatment for radical recombination and thermal treatment for annihilation of the remaining radicals. The UV stability of the material was evaluated in pellet form. The accelerated weathering test of HMS-PP samples were performed under artificial ultra-violet light and in a condensation chamber Comexim (C-UV type) apparatus with UV exposure for 120 and 240 h. The results were compared to those from ageing caused by sunlight and dew under natural exposition. This work investigated changes in mechanical proprieties (elongation and rupture strength), Fourier transform infrared spectroscopy (FTIR), optical microscopy (MO), scanning electron microscopy (SEM) and rheological properties of HMS-PP after the UV ageing. We find that the HMS-PP has more degradation than regular PP and undergoes predominate chain scission in aggressive UV ageing conditions.     

Contribution of carbonyl photochemistry to aging of atmospheric secondary organic aerosol

The photodegradation of secondary organic aerosol (SOA) material by actinic UV radiation was investigated. SOA was generated via the dark reaction of ozone and d-limonene, collected onto quartz-fiber filters, and exposed to wavelength-tunable radiation. Photochemical production of CO was monitored in situ by infrared cavity ring-down spectroscopy. A number of additional gas-phase products of SOA photodegradation were observed by gas chromatography, including methane, ethene, acetaldehyde, acetone, methanol, and 1-butene. The absorption spectrum of SOA material collected onto CaF2 windows was measured and compared with the photolysis action spectrum for the release of CO, a marker for Norrish type-I photocleavage of carbonyls. Both spectra had a band at approximately 300 nm corresponding to the overlapping n --> pi* transitions in nonconjugated carbonyls. The effective extinction coefficient of freshly prepared SOA was estimated to be on the order of 15 L mol(-1) cm(-1) at 300 nm, implying one carbonyl group in every SOA constituent. The absorption by the SOA material slowly increased in the visible and near-UV during storage of SOA in open air in the dark, presumably as a result of condensation reactions that increased the degree of conjugation in the SOA constituents. These observations suggest that photolysis of carbonyl functional groups represents a significant sink for monoterpene SOA compounds in the troposphere, with an estimated lifetime of several hours over the continental United States.     

Photochemistry of ring-substituted polystyrenes. II. Photolyses of poly(p-fluoro-, p-chloro-, and p-bromostyrene)s

The photodegradation of thin films of p-fluoro (PPFS), p-chloro (PPCS), and p-bromo (PPBS) styrenes brought about by exposure to 254-nm radiation under high vacuum was studied. Mass spectroscopic measurements indicated that hydrogen and hydrogen halides were the only gaseous products because yields of H₂ and HF from poly(p-fluorostyrene) were much smaller than the corresponding yields of chloro- and bromo-substituted polymers. UV and visible spectra of degraded films indicated the presence of unsaturated species, for the initial rates of formation were comparable in PPFS and PS but considerably greater in PPCS and PPBS. Solubility and molecular weight data indicated simultaneous crosslinking and chain scission; both PPCS and PPBS showed an inordinately high susceptibility to crosslinking. These observations can be rationalized in terms of the energetics of abstraction reactions by H and halogen atoms and in terms of scission of the Ph–Br and Ph–Cl bonds which lead to the participation of radicals in the para position in crosslinking. Some qualitative correspondence between the Hammett parameters of the p-substituents and rates of H₂ formation in the substituted polymers was observed. Quantum yields of gaseous product formation and probabilities of crosslinking and chain scission were also determined for the three polymers. Mechanisms of the various reactions are discussed.     

Stability of a salicylate-based poly(anhydride-ester) to electron beam and gamma radiation

The effect of electron beam and gamma radiation on the physicochemical properties of a salicylate-based poly(anhydride-ester) was studied by exposing polymers to 0 (control), 25 and 50 kGy. After radiation exposure, salicylic acid release in vitro was monitored to assess any changes in drug release profiles. Molecular weight, glass transition temperature and decomposition temperature were evaluated for polymer chain scission and/or crosslinking as well as changes in thermal properties. Proton nuclear magnetic resonance and infrared spectroscopies were also used to determine polymer degradation and/or chain scission. In vitro cell studies were performed to identify cytocompatibility following radiation exposure. These studies demonstrate that the physicochemical properties of the polymer are not substantially affected by exposure to electron beam and gamma radiation.     

The bifunctionality of poly[(R)-3-hydroxybutyrate] in self-reinforced composite materials

The poly[(R)-3-hydroxybutyrate] (PHB) is a highly crystalline, biosourced polymer. The advantages of the PHB are its biodegradability and biocompatibility; however, the brittleness caused by its high crystallinity decreases the application ability of the PHB in comparison with the polyolefins. Excellent results were observed for the reactive extrusion of PHB in the presence of peroxides in many investigations of the modifications of PHB mechanical properties. The disadvantage must be considered to be the thermal degradation of PHB during extended extrusion and its limitation in natural composite preparation. The peroxides are highly reactive with natural fillers, and this causes a decrease of the filler's mechanical properties. Consequently, the reactive extrusion may be a useful tool for the production of additives only. The results we present of this investigation is based on a different material preparation strategy. The two-stage method incorporated additives preparation via reactive extrusion of PHB and the blending of the obtained product with neat PHB. Theself-reinforced composite material obtained in this way revealed significantly higher values of stress and strain compared to neat PHB. The thermal degradation of the PHB matrix was retarded and total crystallinity of the composite was decreased. The materials were characterized using DSC, SEM and SEC techniques. The samples were also investigated employing tensile and impact strength tests.     

The photodegradation of poly(p-ethyl styrene)

The photodegradation of thin films of poly(p-ethyl styrene) induced by exposure to 254 nm radiation under high vacuum at 25°C has been studied. The principal low molecular weight product was hydrogen and smaller amounts of methane and ethane were also formed. The degraded films showed new absorbances in the 240, and 290 nm regions, and a broad band extending into the visible region appeared. This was associated with the yellow colouration. The intensity of excimer fluorescence also decreases, and this has been attributed in part to the effects of unsaturated groups which are responsible for the new UV absorbances.Solubility analyses indicate simultaneous crosslinking and chain scission, and the higher rate of crosslinking relative to poly(styrene) indicated the participation of the p-ethyl group in these reactions. Quantum yields for gaseous products and estimates of these for crosslinking and chain scission were determined. It would appear that the p-ethyl group participates directly in some photo-reactions and also indirectly by virtue of the inductive (+I) effect. A mechanism is proposed to account for the observed data.     

甲基异丙烯基酮在烷烴中的聚合反应及以其聚合物为基础的远紫外抗蚀剂

采用AIBN引发剂,在C₆-C₁₂烷烃中研究了甲基异丙烯基酮(MIPK)的聚合反应规律,结果表明MIPK的聚合反应速率,随着烷烃分子中碳原子数的增加而增加,但对聚合物的M_η无显著影响。测定了PMIPK及增敏后聚合体的UV光谱、热稳定性以及光降解前和用氢灯辐照40、160分钟后的IR谱图。表明除了聚合物主链断裂之外,还有由于降解而产生的单体。用含有不同增敏剂的PMIPK制成了可以与不同波长光源的光谱主峰相匹配的远紫外抗蚀剂。以增敏的PMIPK涂在镀铬玻璃基片上,通过软接触分辨率板作远紫外曝光、显影、化学蚀刻,得到0.4μ的清晰线条。     

Mechanical properties and heat shrinkability of electron beam crosslinked polyethylene–octene copolymer

The mechanical properties and heat shrinkability of electron beam crosslinked polyethylene–octene copolymer were studied. It was found that gel content increases with increased radiation dose. The analysis of results by the Charlesby–Pinner equation revealed that crosslinking was dominant over chain scission upon irradiation. Formation of a crosslinked structure in the electron beam irradiated sample was confirmed by the presence of a plateau of dynamic storage modulus above the melting point of the polymer. Wide-angle X-ray diffraction revealed that there was little change in crystallinity for the irradiated samples, indicating that radiation crosslinking occurs in the amorphous region of the polymer. The tensile modulus increases, whereas the elongation at break decreases with increased radiation dose. The heat shrinkability of the material increased with an increased radiation dose because the radiation-induced crosslinks serve as memory points during the shrinking process.     

Effects of different sterilization processes on the properties of a novel 3D‐printed polycaprolactone stent

Bioresorbable stents (BRS) offer the potential to improve long‐term patency rates by providing support just long enough for the artery to heal itself. While manufacturing methods to produce BRS using the appropriate architecture, material and mechanical studies, etc., have received much attention, the effects subsequent sterilization methods have on BRS properties are overlooked. Sterilization process can change a device's properties. This work presents the effects ethanol, ultraviolet light (UV), and antibiotic sterilization processes at 0.5, 1, 2, 4, 8, and 16 hours have on a novel 3D‐printed polycaprolactone stent. The stents were analysed using sterility tests, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, mass spectrometry, for molecular weight, and degradation tests. Results have shown ethanol to be an effective sterilization treatment as it barely affected the material's properties. On the other hand, UV had a considerable influence (mainly produced by the photodegradation of UV irradiation) on crystallinity and molecular weight. Lastly, while antibiotic sterilization did not affect crystallinity to the same degree, it did substantially reduce the molecular weight of the samples. Ethanol results in being the best sterilization method for the high material requirements that medical devices such as stents have.     

Effect of UV radiation on photolysis of epoxy maleate of bisphenol A

The behavior of unsaturated polyesteric resin epoxy maleate of bisphenol A (EMBA) to UV was investigated using both infrared (IR) and optical microscopy (OM) techniques. The UV radiation produces important modifications of the EMBA sample. A photodegradation process takes place by a free radical mechanism and involves both photolysis and photodegradation reactions. In the early stage of photolysis, the excitation of the double bonds of EMBA sample takes place with formation of radicals. The radicals, by combination, form some cross-linked structures. These structures undergo secondary reactions with hydroperoxide formation. The splitting of the EMBA chains initiated by hydroperoxide compounds leads to new aromatic and etheric structures, with elimination of both CO and CO₂.     

Effect of light intensity and wavelengths on photodegradation reactions of riboflavin in aqueous solution

A study of the effect of light intensity and wavelengths on photodegradation reactions of riboflavin (RF) solutions in the presence of phosphate buffer using three UV and visible radiation sources has been made. The rates and magnitude of the two major photodegradation reactions of riboflavin in phosphate buffer (i.e., photoaddition and photoreduction) depend on light intensity as well as the wavelengths of irradiation. Photoaddition is facilitated by UV radiation and yields cyclodehydroriboflavin (CDRF) whereas photoreduction results from normal photolysis yielding lumichrome (LC) and lumiflavin (LF). The ratios of the photoproducts of the two reactions at 2.0 M phosphate concentration, CDRF/RF (0.09-0.22) and CDRF/LC (0.54-1.75), vary with the radiation source and are higher with UV radiation than those of the visible radiation. On the contrary, the ratios of LF/LC (0.15-0.25) increase on changing the radiation source from UV to visible. The rate is much faster with UV radiation causing 25% degradation of a 10(-5) M riboflavin solution in 7.5 min compared to that of visible radiations in 150-330 min.     

Degradation of pre-aged polymers exposed to simulated recycling: Properties and thermal stability

Accelerated thermal and photo-aging of four homopolymers, low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP) and high-impact polystyrene (HIPS), was performed and the impact of subsequent reprocessing conditions on their properties studied. Polymer samples oven-aged at 100 °C for varying periods of time or UV irradiated in a Weather-o-meter (WOM) at λ = 340 nm were reprocessed in a Brabender plasticorder at 190 °C/60 rpm for 10 min. Chemical changes and the evolution of rheological and mechanical properties accompanying the gradual degradation of the individual polymers were monitored and evaluated (DSC, FTIR, colorimetric method, MFI, tensile impact strength). LDPE and HIPS were found to be more susceptible to thermo-oxidation than HDPE and PP, whereas HDPE and PP were affected to a greater extent by UV exposure; the crucial role here is being played by the stabilization of the studied resins. In HDPE the scission and crosslinking reactions competed both in thermo-and photo-degradation. In the case of LDPE, scission prevailed over branching during thermo-oxidation, whereas photo-oxidation of the same sample led predominantly to crosslinking. Abrupt deterioration of the LDPE rheological properties after one week of thermal exposure was suppressed by re-stabilization. The scission reaction was also predominant for PP during thermo-oxidation, and it took place even faster during UV exposure. In the case of HIPS a slight photo-degradation of PS matrix is accompanied by simultaneous crosslinking of the polybutadiene component.     

Photodegradation Behavior of Polycaprolactone-Poly(ethylene glycol) Block Copolymer

Polycaprolactone-poly(ethyleneglycol)(PCE)blockcopolymerisabiodegradablepolymer.ThebiodegradationcharacterisationinvitFoandinvivoofthePCEwasreported"'.ItwasfoundthatthedegradationrateofthePCEwasincreasedwithincreasingpoly(ethyleneglycol)content,temperature,acidityandalkalinityanditwasacceleratedbythepresenceofenzyme.Thefastestdegradationratewasobservedinthephysiologicalconditionofthesamplebeingimplantedinthebodyofanimals.SoPCEcopolymerpossessesagoodprospecttobebio-medicalmaterials3.Mostp…     

Photodegradation of ethylene–octene copolymers with different octene contents

The influence of the octene content on the photodegradation behaviour of ethylene–octene copolymers (EOCs) was revealed by investigating the photooxidation of low density polyethylene (LDPE) and EOCs with different octene contents through a series of characterisation methods. LDPE was very sensitive to ultraviolet light and the photostabilities of EOCs decreased with increasing octene concentration. The photodegradation of all samples produced hydroxyl, carbonyl and vinyl groups. The ease of chain crosslinking and scission was increased as the octene content rose. Crosslinking predominated in late irradiation period of LDPE while chain scission was dominant in that of EOCs. Annealing and chain scission promoted the secondary crystallisation of the crystallisable chain segments. Chain scission enhanced the crystallisation ability of the irradiated EOCs while it decreased that of the weathered LDPE. The photostabilities of crystals could be ranked as follows: the chain-folded lamellar crystals > the bundled crystals > the fringed micellar crystals. The thermal stabilities and mechanical properties of samples decreased with increasing irradiation time and the decreasing extent was correlated with the comonomer content.     

Degradation of agar films in a humid tropical climate: Thermal, mechanical, morphological and structural changes

Agar films were subjected to natural weathering exposure in a humid tropical climate for 90 days to determine their biodegradation behavior and functionality. Exposed samples were taken at 15, 30, 45, 60 and 90 days. Mechanical, thermal, structural and morphological properties were determined using tensile test, differential scanning calorimetry (DSC), attenuated reflectance infrared spectroscopy (ATR-FTIR), X-ray diffraction and environmental scanning electron microscopy (ESEM). The photodegradation process and temperature-relative humidity fluctuations promoted a decrease in agar mechanical properties in early exposure stages (30-45 days) caused by a reduction in agar molecular size and a decrease in the number of sulfate groups. These changes alter agar crystallinity, causing contraction that leads to formation of micro-fractures and embrittlement, and promote microbial attack. Accelerated weathering exposure of agar films showed that outdoor climate parameters play an important role in their degradation. These results will aid in further research to determine the potential use of agar as an environmentally friendly solution to the problem of biodegradable composites disposal.     

Mechanical properties,surface chemistry,and barrier characteristics of electron beam irradiated‐annealed LDPE/PA6/LDPE multi‐layer films at N2

The effects of electron beam irradiation in the nitrogen environment, on chain scission, crosslinking, crystallinity, mechanical performance, and barrier properties of LDPE/PA6/LDPE multi‐layer films were studied. The evaluation of radiation‐induced crosslinking effect by the gel content measurement and Charlesby–Pinner plot suggested more of crosslinking over chain scission, in all the layers, which was more pronounced in polyethylene phase. The FTIR analysis results showed good agreement with those observed by the gel content measurements. It is believed that the crosslinking reaction had occurred through the C? N bonds in polyamide‐6, and vinyl group in polyethylene layers. The evaluation of radiation effect on the crystallinity and crosslinking of films by FTIR technique showed that by increasing the applied doses, the crystallinity in all the layers was decreased and the crosslinking was increased. The differential scanning calorimetry of irradiated samples revealed that due to the crosslinking reaction, the crystallinity was decreased by the applied dose. The tensile strength of the films was increased and the percent elongation at break was decreased, by increasing the applied doses. This study was also indicated that the radiation‐induced crosslinking effect on the tensile properties was dominantly observed up to 50 kGy. The surface free energy analysis of the films using the contact angle measurement and geometric mean equation indicated that the surface polarity was decreased by increasing the absorbed doses. It was found that due to the decline in the surface polarity and the simultaneously formation of crosslinked network in these films, both water vapor transmission rate and oxygen permeability were significantly decreased. Copyright © 2009 John Wiley & Sons, Ltd.