Characterization to the weathering extent of LLDPE/LDPE thin film

A kind of LLDPE (linear low density polyethylene)/LDPE (low density polyethylene) thin film for farm applications was subjected to accelerated and natural weathering. Carbonyl group, melting point, tensile elastic modulus, and high‐temperature shearing modulus of weathered films were investigated as function of weathering time. Two kinds of carbonyl index, I₁ and I₂, which result from infrared spectroscopy (IR) spectra of the weathered films, were defined to characterize the weathering extent of the LLDPE/LDPE thin film. Based on I₁ and I₂, a correlation is made between the artificial and natural weathering of the film: 1 h of the artificial weathering is equivalent to about 10.73 h of the natural weathering. The difference between the accelerated weathering and the natural weathering was also discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 12–16, 2003     

Characterization of fluorinated polyethylene surfaces

Polyethylene foils, used as greenhouse foils stabilized with various types of sterically hindered amine light stabilizers (HALS), showed an extraordinary prolonged lifetime on exposure to natural or artificial weathering if a gas-phase fluorination under low-pressure conditions was applied. The fluorination was performed using F₂/N₂ mixtures and provided ca. 50 F/100 C (fluorination degree ≈25%). The lifetimes of fluorinated PE foils on exposure to artificial or natural weathering were increased at least by a factor of 2-4 as measured in terms of tensile strength and elongation at break.     

The oxidative degradation of styrenic copolymers: A comparison of photoproducts formation under natural and accelerated conditions

Natural and accelerated weathering of polystyrene and high‐impact polystyrene were carried out in the present investigation. The structural changes in the polymer samples were characterized by using FTIR spectroscopy, tensile strength testing, and SEM spectroscopy. The natural exposure was conducted throughout the year. Rates of photooxidation were determined by measuring the evaluation in hydroxyl and carbonyl regions. The surface deterioration was revealed from SEM micrographs. The drop in tensile strength was also monitored. A correlation between natural and artificial weathering was considered for lifetime prediction in a short exposure time. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1676–1682, 2002     

The Effect of Accelerated Weathering on the Mechanical Properties of Alkali Treated Hemp Fibre/Epoxy Composites

In this study, 65 wt% aligned untreated long hemp fibre/epoxy (AUL) and aligned alkali treated long hemp fibre/epoxy (AAL) composites cured at 70°C using compression moulding were subjected to accelerated weathering using an accelerated weathering chamber with UV-irradiation and water spray at 50°C for four different time periods (250, 500, 750 and 1000 h). After accelerated weathering, tensile strength (TS), flexural strength, Young's modulus (YM), flexural modulus and fracture toughness (K _Ic) were found to decrease and impact energy (IE) was found to increase for both AUL and AAL composites. AUL composite had greater overall reduction in mechanical properties than that for AAL composite upon exposure to accelerated weathering environment. FTIR, TGA and WAXRD analyses of the accelerated weathered composites support the results of the deterioration of mechanical properties upon exposure to accelerated weathering environment.     

高分子材料的气候老化实验技术

分析了影响高分子材料老化性能的气候因素，介绍了自然气候老化、人工气候加速老化等实验技术，并探讨了加速试验的相关性。     

Natural and artificial aging of polypropylene–polyethylene copolymers

The degradation of polypropylene–polyethylene copolymers (which were used to make the seats for the Olympic stadium in Barcelona, Spain), in response to natural aging for 2.5 years and artificial aging for 5000 h in a xenon lamp chamber, was studied. The extent of the various photoreactions, including the formation of carbonyl groups, the scission of hydrocarbonated chains, the formation of free radicals in tertiary carbons, and the formation of nonsaturated bonds followed by branching and crosslinking, was analyzed by Fourier transform infrared spectrophotometry. Melting and thermal decomposition were studied by differential scanning calorimetry. In all cases, aging led to a loss of crystallinity. By scanning electron microscopy, it was possible to detect the formation of a porous material after melting crystallization, as well as the presence of micelle orientation. Finally, a comparison between natural and artificial aging effects showed differences, the samples exposed to weathering being modified to a greater extent than the artificially aged ones. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1685–1692, 2003     

Degradation studies of plasticized PVC. I. Multiple internal reflection infrared spectroscopy

Multiple internal reflection infrared spectroscopy (MIR) was used to study surface degradation in commercial and laboratory prepared plasticized PVC samples. Samples were subjected to accelerated (UV exposure) and natural weathering. Ultraviolet-exposed samples show peak formation at 3200 cm^?1 (OH), and 1400cm^?1(CH bend), as well as increased absorption at 1720 cm^?1 (CO). Outdoor-exposed samples show essentially similar changes, but the variation in peak ratio shows large variations of a random nature; it has been proposed that rainfall has a major influence on surface plasticizer concentration.     

Durability of the flame retardance of ethylene-vinyl acetate copolymer cables: Comparing different flame retardants exposed to different weathering conditions

Scientific publications addressing the durability of the flame retardance of cables during their long-term application are rare and our understanding lacks. Three commercial flame retardants, aluminum hydroxide, aluminum diethyl phosphinate (AlPi-Et), and intumescent flame retardant based on ammonium polyphosphate, applied in ethylene-vinyl acetate copolymer (EVA) model cables, are investigated. Different artificial aging scenarios were applied: accelerated weathering (UV-irradiation/temperature/rain phases), humidity exposure (elevated temperature/humidity), and salt spray exposure. The deterioration of cables' surface and flame retardancy were monitored through imaging, color measurements, attenuated total reflectance Fourier transform infrared spectroscopy, and cone calorimeter investigations. Significant degradation of the materials' surface occurred. The flame retardant EVA cables are most sensitive to humidity exposure; the cable with AlPi-Et is the most sensitive to the artificial aging scenarios. Nevertheless, substantial flame retardance persisted after being subjected for 2000 h, which indicates that the equivalent influence of natural exposure is limited for several years, but less so for long-term use. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47548.     

Microstructural investigations of naturally and artificially weathered autoclaved aerated concrete

The microstructural changes in autoclaved aerated concrete (AAC), particularly due to chemical degradation, have been investigated. The carbonation process has been studied on naturally and artificially weathered AAC by spectrographic and microscopic analysis. Visual inspections of unexposed and aged AAC were made by means of light optical microscopy and scanning electron microscopy (SEM), while chemical and structural analysis were based on X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). The results obtained from two different experimental exposure set-ups, i.e., natural and artificial weathering, are presented. Thin-section images clearly indicate leaching out of the surface layer resulting in open larger air voids. Both naturally and artificially weathered samples displayed similar ageing characteristics in terms of mineralogical changes. The XRD patterns confirm that tobermorite were gradually transforming into calcium carbonate with exposure time. Calcite and gypsum were the two main crystal structures growing during weathering as detected in the SEM+EDS examinations.     

农用棚膜人工加速老化试验与大气曝露试验相关性探讨

介绍农膜大气曝露试验与人工加速老化试验的结果,寻求农膜老化性能的变化规律,并探讨农膜大气曝露与人工加速老化试验之间性能变化的相关性。     

Molecular relaxation phenomena during accelerated weathering of a polyurethane coating

Results from a polyester-urethane (PU) coating system under accelerated weathering showed that crosslink density, obtained from high-temperature modulus data, diminished due to chain scission. However, T _g and room-temperature tensile modulus both increased with weathering. Molecular relaxation phenomena in polymers have long been investigated to explore changes occurring in a polymer at temperatures below its glass transition and were explored for an explanation to supplement chemical degradation for these observations. Relaxation was quantified using “enthalpy recovery” which first increased with exposure, then diminished. The concurrent physical and chemical aging effects were characterized by tracking nonexponentiality in the spectrum of relaxation times, and the size of “co-operatively relaxing regions” deduced from relaxation around the glass transition. Mechanical relaxation in this coating extended longer than cycle periods typical of accelerated weathering, suggesting that frequency effects might be important when comparing accelerated to natural weathering. This paper was awarded Third Place in the John A. Gordon Best Paper competition, presented as part of 2006 FutureCoat! Conference, sponsored by Federation of Societies for Coatings Technology, November 1–3, 2006, in New Orleans, LA.     

Accelerated weathering performance of Scots pine preimpregnated with copper‐based chemicals before varnish coating Part:1 coated with cellulosic and polyurethane varnishes

This study aimed to determine the effect of accelerated weathering on gloss, surface hardness and colour changes of Scots pine (Pinus sylvestris L.). Test samples were impregnated with Adolit KD‐5, Wolmanit CX‐8 and Celcure AC‐500 covered with cellulosic and polyurethane varnishes. The results showed that the values of surface hardness and gloss increased after accelerated weathering. While the surface hardness of Scots pine was increased for impregnated and polyurethane‐coated varnish, it decreased for impregnated and cellulosic varnish‐coated Scots pine after 1000 hours of accelerated weathering exposure. Copper‐based chemical impregnation and varnish coating developed the gloss of Scots pine specimens relative to the surface characteristics observed in single‐coated Scots pine specimens. While the most appropriate chemical was Celcure AC‐500 for surface hardness, it was Adolit KD‐5 for the gloss of Scots pine after 1000 hours of accelerated weathering exposure. Wood specimens impregnated prior to the application of varnish were more effective in stabilising the colour of Scots pine than Scots pine only coated with varnish. Polyurethane varnish‐treated Scots pine showed better colour stability for each partial and total accelerated weathering exposure period. The total colour changes were lowest for polyurethane varnish‐coated Scots pine impregnated with Celcure AC‐500 after 1000 hours of accelerated weathering exposure.     

Surface properties of tannin-impregnated and varnished beech wood after exposure to accelerated weathering

The aim of this study was to determine selected surface properties of varnished beech wood impregnated with natural extracts after exposure to accelerated weathering. Beech wood samples were impregnated with aqueous solutions of 5 and 10% mimosa (Acacia mollissima) and quebracho (Shinopsis lorentzii) tannins. After weathering, colour changes (ΔL*, Δa*, Δb*, and ΔE*) in addition to scratch resistance and surface hardness values were calculated and evaluated. As a result of the weathering process, greater colour changes (ΔE*) were detected in the beech wood samples impregnated with tannins compared with the unimpregnated control samples. The least colour change occurred in the Tanalith-E-impregnated samples. Total colour change was adversely affected with tannin impregnation after the weathering processes. In terms of surface hardness and scratch resistance, the highest values were observed in the mimosa-solution-impregnated and control samples. Furthermore, it was found that scratch resistance and hardness values tended to increase during the first period of weathering and decreased thereafter. Regarding surface properties, the best results were obtained when polyurethane varnish was employed compared with the other varnish types.     

Studying the effects of the chemical structure of an automotive clearcoat on its biological degradation caused by tree gums

The effects of artificial and natural tree gums on the mechanical, chemical, and aesthetic performances of two automotive acrylic/melamine clearcoats were studied. To this end, two clearcoats with different acrylic/melamine ratios were investigated. Biological experiments were performed under post-aging conditions using an accelerated weathering test. Analytical techniques including optical microscopy, scanning electron microscopy (SEM), gloss measurement, FTIR, and DMTA analyses were utilized to reveal the responses of the coating system upon exposure to the aforementioned biological materials. Contact angle measurements were also conducted to estimate the surface energy of the coatings. Greater crosslinking density, together with a higher T _g and damping behavior of the clearcoat, indicative of a greater degree of cure, were obtained as the ratio of melamine crosslinker increased. It was shown that both Arabic and natural tree gums could strongly attach to the clearcoats’ surface, imposing a significant stress during the drying process, thereby leading to a physical failure. In addition, the acidic nature of these biological materials leads to a chemical alteration in the clearcoats’ structure. The greater crosslinking density and lower hydrophilicity of the clearcoats containing higher melamine crosslinker were responsible for the weaker interaction of gums with the surface. This showed a greater capability for stress damping. Small surface cracks with fracture morphology on the coatings exposed to biological materials at higher exposure times (in the xenon test) were also observed. This is discussed based on the adhesion of the coatings to gums at longer exposure times, because of significant stress.     

Determination of PVC cable insulation degradation

Assessing the degradation of electrical cable insulation is an important feature in extending plant life. The older generating stations are extensively wired with PVC insulated cables, and procedures have been developed to assess degradation using micro specimens in a manner that does not destroy the function of the cable. Material degradation of accelerated aged specimens was systematically monitored by measuring melting or glass transition temperatures ( Tg ), gel content, infrared peroxide absorbance, relative hardness, and plasticizer loss. The shift in the Tg or the characteristic melting peak predicted the maximum exposure temperature of the PVC. The peroxide absorbance and gel content measurements were sensitive indicators of degradation. The relative hardness as measured by thermo-mechanical analyzer (TMA) penetration distance and plasticizer content decreased as the material aged. The results obtained on micro specimens were related to the ultimate elongation values, which have been the traditional measure of degradation.     

Natural and artificial weathering of low-density polyethylene (LDPE): Calorimetric analysis

Studies of the thermal and photodegradation of two commercial polymers, stabilized and unstabilized low-density polyethylene (LDPE), show the effects of weathering in differential scanning calorimetry (DSC) curves. The shape and the size of the melting peak vary significantly in thermal aging and in accelerated photoirradiation, but no change was observed in natural weathering implying that the crystallinity remains steady in outdoor exposures. The melting temperatures remain steady for all exposure tests. The fall of mechanical properties and the evolution of chemical structure, followed by IR spectroscopy especially near the carbonyl regions, was also performed. The resistance to UV light irradiation as probed by deformation at break was superior in stabilized LDPE compared to unstabilized LDPE. Simple correlations were not observed between the fall of mechanical properties, the rate of oxidation, and the morphology.     

Effects of Natural Weathering on Properties of Recycled Newspaper-filled Polypropylene (PP)/Natural Rubber (NR) Composites

Natural weathering has been applied to investigate the properties of recycled newspaper (RNP)-filled polypropylene (PP)/natural rubber (NR) composites. Three sizes of RNP (11 mm, 23 mm, and 53 mm) were used in this study. These composites were subjected to natural weathering conditions; i.e, tropical climate in Penang, Malaysia, for 3 and 6 months. Different techniques including mechanical tests, Fourier transform infrared spectrometry (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) were used in order to obtain a comprehensive view of degradation occurring during the natural weathering of the composites. Results of mechanical tests show that an increasing content of RNP in composites decreased the tensile strength and elongation at break (EB), while increasing the Young's modulus after exposure of 3 and 6 months. Scanning electron microscopy on surfaces after weathering shows that the filler was poorly wetted by the matrix. This explains the reduction in tensile strength and elongation at break after weathering. The Fourier transform infrared spectrometry results on the composites after exposure to natural weathering indicate the presence of carbonyl, vinyl, and hydroxyl groups, which formed from various chemical reactions taking place during weathering.     

Photodegradation of talc-filled polypropylene

Injection-molded talc-filled polypropylene (PP) composites have been exposed to ultraviolet (UV) radiation in the laboratory for periods up to 26 weeks. The extent of chemical degradation has been assessed by means of Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC), and the results correlated with the mechanical properties. In the early stages of exposure, the photo-oxidation is faster in the talc-filled composites than in the unfilled polymer, but this trend is reversed for exposures longer than ∼12 weeks. Scanning electron microscopy (SEM) inspection has revealed that surface cracks caused by photodegradation in the filled PP occur in the surface exposed to the UV source only, resulting in much less deterioration in tensile properties when compared with the unfilled polymer which degrades significantly at the unexposed surface also. Measurements of melting temperatures by differential scanning calorimetry (DSC) gave a consistent picture of degradation with that obtained by FTIR and GPC studies. DSC analyses have also shown that an increase in the melting enthalpy for both the unfilled and filled grades occurs during exposure.     

Thermal and UV degradation of polypropylene with pro‐oxidant. Abiotic characterization

The oxodegradation of an injection molding grade polypropylene (PP), formulated with 0%, 1.5%, and 3% w/w of a pro‐oxidant additive, was studied. The degradation was conducted in a weathering tester at 60 °C for 40 h. The process was monitored by Fourier transform infrared spectroscopy, standard differential scanning calorimetry, and successive self‐nucleation and annealing. Neat PP samples did not exhibit significant changes during the exposure time employed. PP samples with oxo‐additive presented similar changes independently of the amount of oxo‐degradative additive employed; however, the changes manifested more rapidly in the formulation with higher pro‐oxidant content. Fourier transform infrared spectroscopy studies revealed the presence of hydroxyl and carbonyl functional groups whereas differential scanning calorimetry tests showed the decrease in the melting and crystallization temperatures as a consequence of the chain scission and oxidation reactions taking place during exposure. In addition, the induction time (t_id) of the oxo‐degradative process was determined for each technique employed and successive self‐nucleation and annealing was found to be the most sensitive characterization technique to reveal structural modifications in PP samples. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46088.     

Natural and artificial weathering of low-density polyethylene (LDPE): Calorimetric analysis

Studies of the thermal and photodegradation of two commercial polymers, stabilized and unstabilized low-density polyethylene, show the effects of weathering on differential scanning calorimetry (DSC) curves. The shape and the size of the melting peak vary significantly in thermal aging and in accelerated photoirradiation, but no change was observed in natural weathering, implying that the crystallinity remains steady in outdoor exposures. The melting temperatures remain steady for all exposure tests. The fall of mechanical properties and the evolution of chemical structure, followed by IR spectroscopy results, especially near the carbonyl regions, were also observed. The resistance to UV light irradiation as probed by deformation at break was superior in stabilized LDPE compared to unstabilized LDPE. Simple correlations observed between the fall of mechanical properties, the rate of oxidation, and morphology. © 1993 John Wiley & Sons, Inc.