Accelerated weathering of unbleached and bleached Kraft wood fibre reinforced polypropylene composites

In this paper, combined moisture/ultraviolet (UV) weathering performance of unbleached and bleached Kraft wood fibre reinforced polypropylene (PP) composites was studied. Composites containing 40 wt% fibre with 3 wt% of a maleated polypropylene (MAPP) coupling agent were fabricated using extrusion followed by injection moulding. Composite mechanical properties were evaluated, before and after accelerated weathering for 1000 h, by tensile and impact testing. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were also carried out to assess the changes occurring during accelerated weathering. Bleached fibre composites initially showed higher tensile and impact strengths, as well as higher thermal stability and greater crystallinity. During accelerated weathering, both unbleached and bleached fibre composites reduced tensile strength (TS) and Young's modulus (YM), with the extent of the reduction found to be similar for both unbleached and bleached fibre composites. Evidence supported that the reduction of TS and YM was due to PP chain scission, degradation of lignin and reduced fibre-matrix interfacial bonding.     

Accelerated weathering of polypropylene/wood flour composites

Wood-plastic composites (WPCs) have received increasing attention during the last decades, because of many advantages related to their use. Some of their main applications are represented by outdoor furnishing and decking; therefore, it is important to assess their behaviour under UV exposure. In this work, polypropylene/wood flour composites were prepared and their resistance to photooxidation investigated. The composites were prepared by extrusion and compression moulding, and were subjected to mechanical tests, FTIR analysis and molecular weight measurements. The results showed that the composites retained a higher fraction of the original mechanical properties after accelerated weathering; the wood flour did not significantly degrade throughout the irradiation time slot of the investigation and the composites kept a higher percentage of the original molecular weight.     

Outdoor and accelerated weathering studies of bisphenol A polycarbonate

The influence of outdoor weathering on the degradation rate of unstabilized bisphenol A polycarbonate (BPA-PC) films is investigated and compared to the results found for indoor accelerated weathering conditions, using UV and IR spectroscopy. At the same dosage, changes in UV and IR were larger for the accelerated than for the outdoor weathered samples, this could be explained by the lower degradation temperature during outdoor exposures. The difference between outdoor and accelerated weathering is according to the IR measurement larger than according to the UV measurement. This difference is ascribed to difference in wavelength distribution between the spectra of the light emitted in the accelerated test and from the terrestrial sunlight. The larger difference for the IR results than for the UV results suggests a difference in ratio between photo-Fries rearrangements and photo-oxidation reaction between both exposures.     

Multivariate correlation analysis of outdoor weathering behavior of polypropylene under diverse climate scenarios

A full understanding on the relationships between weathering factors and deteriorations in the physical or mechanical properties of polymeric materials as well as their intercorrelations is critically important to forecast the durability of materials. In this work, the outdoor weathering behaviors of isotactic polypropylene (iPP) across a 1.5-year period under six typical climate scenarios in China are investigated. A wide sets of natural exposure conditions and test methods allow the establishment of the substantial correlations between chemical/physical structures and appearance/mechanical properties under simultaneous effects of multiple weathering factors (such as light, heat, oxygen etc.). The results under diverse natural environments suggest that the crystallinity and crack development depend largely on the molecular weight while the yellowing index correlates directly with the carbonyl index irrespective of the exposure conditions. The relationship between tensile strength and molecular weight is found to be in accord with an empirical linear model. Subsequently, using principal component analysis (PCA), a data reduction and visualization method, the degradation risk map of PP materials in China is established and the relative importance of relevant weathering factors is evaluated. Temperature is found to be the most dominant weathering factor on iPP aging under the climate scenarios investigated in the present work.     

Modification of the resistance of two epoxy resins to accelerated weathering using calcium sulfate as a photostabilizer

Epoxy-timber composites have received increasing attention during the last decades because there are many advantages related to their uses as construction materials in applications such as timber bridges. However, the durability of epoxy-timber composites under outdoor conditions has become a concern for many epoxy resins. This study evaluated the chemical, thermal, and mechanical properties of two cured epoxies, the product of the diglycidyl ether of bisphenol A with 2,4-trimethyl-1,6-hexanediamine (DGEBA-TMDA) and the analogous resin prepared with the hydrogenated diglycidyl ether of bisphenol A (HDGEBA-TMDA), each mixed with 2?wt. % calcium sulfate (CS). We hypothesized that the use of CS, as an inorganic UV absorber, could decrease undesirable effects arising from exposure to UV light, moisture, and extreme temperatures.

An accelerated aging chamber simulated natural weathering for 1, 2, 3, 4, and 6?months. Chemical changes in cured epoxy systems over time in the presence and absence of CS fillers were determined using Fourier transform infrared spectroscopy (FT-IR). Thermal degradation profiles before and after exposure to accelerated weathering were followed by thermogravimetric analysis (TGA). The glass transition temperatures (T_g) before and after accelerated weathering were measured, and the effect of accelerated weathering on the surface morphology of the epoxy systems was investigated by scanning electron microscopy (SEM). In the presence of CS, after 6?months accelerated weathering the tensile strength of DGEBA-TMDA reduced by 23.8?±?2.4%, compared to 46.5?±?5.5% in its absence, while the corresponding values for HDGEBA-TMDA were 21.4?±?2.1% and 28.7?±?1.8%.     

A study of surface changes of wood-polypropylene composites as the result of exterior weathering

Outdoor applications of composites raised questions about their durability. In this study, the effects of outdoor weathering on the properties of wood-polypropylene composites with and without pigments were examined. The composites were placed outdoors for one year, and their colour changes were evaluated after 1, 3, 6, 9 and 12 months of weathering. The weathering resulted in considerable colour fading of the composites. Composites containing darker colour pigments had better colour stability. Scanning electron microscopy analysis revealed that surface cracks caused by weathering in a wood-polypropylene composite having a higher polypropylene content were less abundant, and the deterioration of the surface layer was lower compared to composites containing less polymer. Measurements of melting temperatures by differential scanning calorimetry gave a consistent picture of polypropylene degradation in the surface layer. After weathering, a decrease in Charpy impact strength was found for composites characterised by higher moisture absorption.     

Wood plastic composites weathering: Visual appearance and chemical changes

The effects of outside and accelerated (xenon-arc and UVA) weathering on the visual appearance and chemical changes of wood plastic composite (WPC) formulations based on high density polyethylene (HDPE) and polypropylene (PP) were investigated. Colorimetry, scanning electron microscopy, Fourier transform infrared spectroscopy (FT-IR), and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) were employed in this study. The study showed that for both outside and accelerated weathering, longer exposure time increased the degree of color change (and lightness), carbonyl concentrations, and wood loss on weathered WPC surfaces. HDPE-based WPC exhibited decreased lightening, carbonyl concentrations, and wood content loss when compared to PP-based WPC. From this study, relationships between chemical and color changes that occurred during exterior weathering of HDPE-based WPC were established. Oxidation and degradation of wood lignin influenced WPC color changes (lightening) during weathering.     

Outdoor and accelerated weathering of acrylonitrile-butadiene-styrene: A correlation study

The influence of outdoor and accelerated weathering conditions on the photo-oxidative degradation of stabilized acrylonitrile-butadiene-styrene (ABS) was investigated, aiming to establish a correlation between both weathering types.     

Mechanical and thermal properties of polylactide/talc microcomposites: before and after accelerated weathering

The purpose of the first part of this study was to investigate effects of micron‐sized talc content on the properties of polylactide (PLA). PLA/talc microcomposites were compounded by melt‐mixing method via twin‐screw extruder, while specimens for testing and analyses were shaped by injection molding. It was observed that, because of the effective stiffening, strengthening, toughening mechanisms of talc, and also their nucleation agent effects for higher crystallinity, many mechanical and thermal properties were improved. In the second part of the study, effects of accelerated weathering on the behavior of PLA microcomposites with 5 wt% talc were investigated by applying ultra violet irradiation and humidity steps according to Cycle‐C of International Organization for Standardization 4892‐3 standards for durations of 100, 200, and 300 hr. Various analyses revealed that, because of the degradation mechanisms of photolysis and hydrolysis during each weathering periods, molecular weight of PLA reduced drastically, that is, mechanical properties almost vanished. Copyright © 2015 John Wiley & Sons, Ltd.     

Molecular orientation,crystallinity, and flexural modulus correlations in injection molded polypropylene/talc composites

In order to promote better understanding of the structure‐mechanical properties relationships of filled thermoplastic compounds, the molecular orientation and the degree of crystallinity of injection molded talc‐filled isotactic polypropylene (PP) composites were investigated by X‐ray pole figures and wide‐angle X‐ray diffraction (WAXD). The usual orientation of the filler particles, where the plate planes of talc particles are oriented parallel to the surface of injection molding and influence the orientation of the α‐PP crystallites was observed. The PP crystallites show bimodal orientation in which the c‐ and a*‐axes are mixed oriented to the longitudinal direction (LD) and the b‐axis is oriented to the normal direction (ND). It was found that the preferential b‐axis orientation of PP crystallites increases significantly in the presence of talc particles up to 20 wt% in the composites and then levels‐off at higher filler content. WAXD measurements of the degree of crystallinity through the thickness of injection molded PP/talc composites indicated an increasing gradient of PP matrix crystallinity content from the core to the skin layers of the molded plaques. Also, the bulk PP crystallinity content of the composites, as determined by DSC measurements, increased with talc filler concentration. The bulk crystallinity content of PP matrix and the orientation behavior of the matrix PP crystallites and that of the talc particles in composites are influenced by the presence of the filler content and these three composite's microstructure modification factors influence significantly the flexural moduli and the mechanical stiffness anisotropy data (E_LD/E_TD) of the analyzed PP/talc composites. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface degradation of ethylene-propylene-diene monomer (EPDM) containing 5-ethylidene-2-norbornene (ENB) as diene in artificial weathering environment

Ethylene-propylene-diene monomer (EPDM) containing 5-ethylidene-2-norbornene (ENB) as diene was exposed to an artificial weathering environment produced by a xenon lamp light exposure and weathering equipment for different time periods. The surface chemical changes were detected by Specular Reflection Fourier Transform Infrared (SR-FTIR) spectroscopy, Raman spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The change in surface color, contact angle and morphology was monitored by spectrophotometer, optical contact angle measuring device and Scanning Electron Microscope (SEM). Furthermore, surface energy was calculated through contact angles of water and formamide. The results showed that hydroxyl, carbonyl and ester groups were formed during exposure to this artificial weathering environment. EPDM surface became redder, yellower and lighter in the first stage of aging and then remained almost unchanged. The contact angles of water and formamide decreased to a minimum and then increased slowly. The surface degradation is a zero order reaction. In addition, the plausible degradation mechanism was proposed.     

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.     

New PP/PLA/cellulose composites: effect of cellulose functionalization on accelerated weathering behavior (accelerated weathering behavior of new PP/PLA/cellulose composites)

Polylactic acid (PLA) was used as partial replacement for conventional thermoplastic matrix, new composites comprising cellulose, polypropylene (PP), and PLA being realized. In order to obtain a compatible interface between cellulosic pulp and polymeric matrix, two chemical modifications of cellulose with stearoyl chloride and toluene di‐isocyanate (TDI) were performed, structural changes being evidenced by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The composite materials were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, dynamic scanning calorimetry, impact, tensile and melt rheological tests, surface tension, and dynamic vapor sorption. Because promising results for impact strength and Young modulus were recorded when replacing 15% of PP with PLA in blends of PP with the same cellulosic pulp load, the aim of our study was to assess the behavior to accelerate weathering of composites comprising PP, cellulosic pulp, and PLA. Although the slight decrease in the mechanical properties was recorded after accelerated weathering, the use of functionalized cellulose successfully prevented the deterioration of surface materials, especially for composite comprising stearoyl chloride treated cellulose pulp. Copyright © 2015 John Wiley & Sons, Ltd.     

Optimization of mechanical properties of polypropylene/talc/graphene composites using response surface methodology

This paper investigated the reinforcing effects of a hybrid filler, including talc and exfoliated graphene nanoplatelets (xGnPs), in polypropylene (PP) composites. In order to increase the interphase adhesion, maleic anhydride grafted polypropylene (MAPP) was added as a compatibilizing agent to the PP/talc/xGnP composites. The experiments were designed according to response surface methodology (RSM) to optimize the effects of three variable parameters, namely talc, MAPP and xGnP, on the mechanical properties. In the sample preparation, three levels of filler loading were used for talc (0, 15, 30 wt%), xGnP (0, 0.75, 1.5 wt%) and MAPP (0, 2, 4 wt%). From the analysis of variance (ANOVA), it was found that the talc and xGnP play a significant role in the mechanical properties and morphology of the composites, as proven by scanning electron microscopy (SEM) and differential scanning calorimeter (DSC). In order to simultaneously maximize these mechanical properties, the desirable values of the additives were predicted to be 30 wt% for talc, 4 wt% for MAPP and 0.69 wt% for xGnP. The obtained normal probability plots indicated good agreement between the experimental results and those predicted by the RSM models.     

Mechanical behaviour of a poydimethylsiloxane elastomer after outdoor weathering in two different weathering locations

The degradation of maxillofacial prosthetic elastomers that occur during physical weathering is usually responsible for the replacement of the prosthesis. In this study the mechanical behaviour of a polydimethylsiloxane (PDMS) elastomer was investigated, after 1 year outdoor weathering in two different weathering locations in Greece (Thessaloniki, Athens). The hypothesis investigated was that irradiation time did not affect the measured properties. Specimens (Elastomer 42) were prepared according to manufacturer’s instructions and exposed to solar radiation for 1 year. Compression, tensile and nanoindentation tests were performed before and after the exposure. Compression and tensile data were also subjected to analysis of variance (ANOVA) and Tukey Post hoc tests at a level of α = .05. These properties were selected due to their clinical significance for fabrication and maintenance of a facial prosthesis. According to statistical analysis all the measured properties changed significantly after outdoor weathering. More specifically, most of the properties presented significant changes after six months of weathering. The observed changes also depended on the weathering locations. The hypothesis investigated was rejected. Material A became harder and the observed differences in the mechanical behaviour resulted from photo-degradation and hydrolysis that might occur due to weathering. The study also provides new information about maxillofacial prosthetics serviceability obtained from nanoindentation tests.     

Comparison of the effect of mica and talc and chemical coupling on the rheology,morphology, and mechanical properties of polypropylene composites

The effect of filler types of mica and talc on the oscillatory shear rheological properties, mechanical performance, and morphology of the chemically coupled polypropylene composites is studied in this work. The Maleic Anhydride grafted Polypropylene (MAPP) was used as an adhesion promoter for coupling mineral particles with the polypropylene matrix. The samples were prepared by a co‐rotating, L/D = 40, 25 mm twin screw extruder. The tensile tests carried out on the injection molded samples showed a reinforcing effect of talc up to 20 wt% on the Polypropylene (PP). The tensile strength of PP‐mica composites showed a slight decrease at all percentages of mica. The effect of chemical coupling by using MAPP on the tensile strength was more pronounced in increasing the tensile strength for PP‐mica than PP‐talc composites. The complex viscosity curve of pure PP and the composites, showed a Newtonian plateau (η₀) up to 30 wt% at low frequency terminal zone. By increasing the filler content to 40 and 50 wt%, the complex viscosity at very low shear rates sharply increased and showed yield behavior that can be due to the formation of filler particles networks in the melt. At the optimum amount of coupling agent, a minimum in cross over frequency curve against MAPP content is observed. The optimum amount of coupling agent for PP‐talc composites is about 1.5%, and about 3% for PP‐mica formulations. The analysis of viscosity behavior at power‐law high region, revealed the more shear thinning effect of mica than talc on the PP matrix resin. Copyright © 2009 John Wiley & Sons, Ltd.     

聚丙烯/纳米级金红石型二氧化钛/聚烯烃弹性体复合材料的抗老化性能研究

采用TEM和UV-Vis等测试手段表征了金红石型纳米级TiO2和体相TiO2的性能特征;通过熔融共混法分别制备了PP/纳米级TiO2/POE和PP/体相TiO2/POE复合材料,采用GB/T16422·2-1999所述的塑料实验室光源暴露实验方法,用氙灯气候试验机对纯PP和复合材料进行28天人工加速老化.结果表明,二氧化钛粒子在PP/POE基体中分散性良好,而纳米粒子对PP/POE基体具有增韧作用;改性后的两类复合材料均具有优异的抗老化性能,而PP/(1·0wt%)纳米级TiO2/POE复合材料的抗老化性能更加优异,其加速老化28天后的无缺口冲击强度达到80·45kJ·m-2,比纯PP提高4倍多,而同期加速老化28天后的PP/(1·0wt%)体相TiO2/POE复合材料的无缺口冲击强度只有47·88kJ·m-2;对纯PP老化过程中的羰基指数和冲击性能的变化情况进行了分析,发现二者近似成线性关系,其相关系数r在0·9以上.     

Effects of temperature on the weathering of engineering thermoplastics

We have determined the activation energies (E_a) of yellowing and gloss loss for a large number of engineering thermoplastics and blends under accelerated weathering conditions. The E_a often depend on the property measured and exposure conditions, although they vary over a fairly small range. Under the CIRA/sodalime-filtered xenon arc conditions most likely to be representative of outdoor exposure, the E_a for gloss loss was ≤5 kcal/mol for all samples tested. The E_a for yellowing was also ≤5 kcal/mol except for SAN and ABS. Evidently the color bodies formed from photo-oxidation of SAN are more sensitive to temperature. A reaction with an E_a of 5 kcal/mol will increase its rate by about 33% for each 10 °C increase in temperature near room temperature. Temperature is an important, but not overwhelming, variable in the weathering of most engineering thermoplastics.     

Influence of weathering on the leaching behaviour of zinc and PAH from synthetic sports surfaces

Synthetic materials used for outdoor sports grounds consist of a mix of inorganic, organic and polymeric compounds that show ageing due to weathering and a complex leaching behaviour by percolation of rainwater, which can limit its lifetime. Additionally, weathering exposure induces degradation processes in the polymers, which leads to the formation of new surfaces allowing water to access additional reservoirs of leachable compounds. A laboratory test comprising artificial weathering, ozonisation and subsequent leaching was developed to investigate this behaviour in a reproducible and controllable way. The experiments showed a general decline of Zn, polycyclic aromatic hydrocarbons (PAH) and total organic carbon (TOC) concentrations after an initial increase. Within this general trend, the course of concentration over exposure duration is very specific for individual sample materials and the analyte under investigation. The results indicate that weathering and degradation behaviour cannot be predicted from initial material conditions. Thus, weathering experiments are recommended to fill this gap of knowledge.     

Perylene-based profluorescent nitroxides for the rapid monitoring of polyester degradation upon weathering: An assessment

A profluorescent nitroxide possessing an isoindoline nitroxide moiety linked to a perylene fluorophore was developed to monitor radical mediated degradation of melamine-formaldehyde crosslinked polyester coil coatings in an industry standard accelerated weathering tester. Trapping of polyester-derived radicals (most likely C-radicals) that are generated during polymer degradation leads to fluorescent closed-shell alkoxy amines, which was used to obtain time-dependent degradation profiles to assess the relative stability of different polyesters towards weathering. The nitroxide probe couples excellent thermal stability and satisfactory photostability with high sensitivity and enables detection of free radical damage in polyesters under conditions that mimic exposure to the environment on a time scale of hours rather than months or years required by other testing methods. There are indications that the profluorescent nitroxide undergoes partial photo-degradation in the absence of polymer-derived radicals. Unexpectedly, it was also found that UV-induced fragmentation of the NO–C bond in closed-shell alkoxy amines leads to regeneration of the profluorescent nitroxide and the respective C-radical. The maximum fluorescence intensity that could be achieved with a given probe concentration is therefore not only determined by the amount of polyester radicals formed during accelerated weathering, but also by the light-driven side reactions of the profluorescent nitroxide and the corresponding alkoxy amine radical trapping products. Studies to determine the optimum probe concentration in the polymer matrix revealed that aggregation and re-absorption effects lowered the fluorescence intensity at higher concentrations of the profluorescent nitroxide, but too low probe concentrations, where these effects would be avoided, were not sufficient to trap the amount of polyester radicals formed upon weathering. The optimized experimental conditions were used to assess the impact of temperature and UV irradiance on polymer degradation during accelerated weathering.