聚碳酸酯在不同湿热自然环境下的老化行为

对聚碳酸酯(PC)在我国海南琼海及三亚2个典型湿热地区的自然曝露试验结果进行了研究,并利用红外特征指数对PC的老化机理进行了探讨。结果表明:在琼海湿热内陆地区曝晒的PC试样同时发生了氟利斯重排反应和光氧化反应,而在三亚湿热沿海地区曝晒的试样则可能发生了光氧化反应和盐致水解反应。     

聚碳酸酯在自然暴露下的红外特征指数研究

对聚碳酸酯在我国海南琼海、若羌以及海拉尔三个自然环境暴露试验站暴露1年的色差及拉伸强度数据进行测试,并利用红外图谱计算了不同暴露阶段的红外特征指数。根据红外特征指数推断了PC在不同地区暴露的老化机理,并研究了性能与红外特征指数的皮尔逊相关关系。结果表明,暴露的PC样品在琼海地区同时发生氟利斯重排反应和偕二甲基的光氧化反应,在若羌和海拉尔地区主要发生偕二甲基的光氧化反应。两种反应机理都会导致PC样品色差产生变化,在琼海地区主要由氟利斯重排反应导致,而在若羌和海拉尔地区由偕二甲基的光氧化反应导致,但拉伸强度下降的主导反应机理均为氟利斯重排反应。     

热氧老化对聚碳酸酯结构和性能的影响

分别在90～120℃环境下,对聚碳酸酯(PC)进行人工热氧加速老化实验.研究PC老化后的结构性能变化和热氧老化机理.结果表明:在低于120℃温度条件下,老化120 h后,PC仍显示强而韧的性能,但断裂伸长减小;在120℃温度条件下,老化24 h后,PC拉伸断裂伸长消失;PC的热氧降解过程主要是以热诱导氧化降解反应,降解反应引起端基、侧基从主链断裂脱落,导致内部缺陷,力学性能随之下降.     

聚合物材料表层的老化过程

本文用不稳态动力学理论并考虑到老化过程是从材料表面向内部扩展,对材料在紫外光和扩散氧同时作用下而产生的聚合物老化过程进行了理论分析。假设聚合物吸收了其特征吸收带附近的紫外光而使聚合物分子活化,产生解聚和光氧化反应而导致老化并以光化学方式进行下去。研究表明,在一定条件下,老化深度的增长约与曝露时间的平方根成正比。这种t~1/2(抛物线)规律在以前研究混凝土的中性化和金属的氧化过程时也观察到。该理论研究指出,抛物线规律应该也适用于聚合物材料的老化。许多聚合物材料在老化过程表现出与曝露时间成指数规律(t~n,n=0.5～1.0),这种与理论的差别在于复杂的老化机理,包括了解聚和光氧化反应。聚合物材料抗弯强度随时间而降低可解释为受破坏的表面层使材料强度降低。     

汽车内饰用聚丙烯材料老化性能分析

通过人工加速老化试验研究并分析了典型汽车内饰用聚丙烯(PP)材料老化后的力学性能、热性能与流动性能变化规律以及红外光谱(FTIR)。结果表明:随着老化时间的增加,PP材料的拉伸强度及弯曲强度均先提升后降低,分别在老化920和680 h时达到峰值;悬臂梁缺口冲击强度则逐步下降。材料老化后其熔体流动性能比老化前均有所下降,但下降程度与老化时间的关系不明显,其中老化480 h的材料流动性能下降幅度最小。当老化时间为720～1 400 h时,材料的流动性能随老化时间的增加而提升。FTIR分析结果显示,材料老化后聚合碳链氧化断裂,产生羧酸类降解产物。     

酸性溶液对聚碳酸酯结构和性能的影响

研究了聚碳酸酯经过酸性溶液老化后结构和性能的变化,力学性能测试,结果表明:酸性溶液老化后,冲击强度下降,拉伸强度先上升后下降,弯曲强度没有明显的变化;扫描电镜(SEM)断口形貌分析显示老化后PC以剪切屈服破坏机理为主;差示扫描量热分析(DSC)显示老化后玻璃化转变温度向高温区偏移;傅里叶变换红外光谱(FTIR)分析显示老化后PC的基本结构没有变化。     

酸溶液老化对食品级聚碳酸酯性能的影响

研究了聚碳酸酯(PC)在酸溶液中的老化行为。通过体式显微镜、力学性能测试、红外光谱分析(FTIR)、差示扫描量热分析(DSC)等对酸溶液老化前后PC进行表征。结果表明,酸溶液老化后PC的力学性能整体呈下降趋势;酸溶液老化后PC发生了降解反应,并且随着老化时间延长降解程度增大。     

聚碳酸酯自然老化的红外光谱研究

选取3个不同地区(北京、三亚、若羌)分别对聚碳酸酯(PC)进行自然暴晒试验,利用傅立叶变换红外光谱(FTIR)技术研究分子构型(反式-反式或反式-顺式)、羟基指数、羰基指数、氧气浓度及太阳辐照波长对PC户外自然老化机理的影响.结果表明,PC在户外自然老化过程中,PC以光氧老化途径为主,以光-弗里斯重排途径为辅.     

抗氧剂对无规共聚聚丙烯抗紫外光老化性能的影响

研究了4种抗氧剂对无规共聚聚丙烯(PPR)紫外光加速老化条件下耐老化性能的影响。结果表明:PPR在紫外光加速老化条件下,大分子链会发生断裂,产生大量羰基;在紫外加速老化初期,由于分子链断裂,分子链运动和重排更容易,材料结晶度明显提高,致使材料拉伸强度在紫外老化初期出现一定程度的增加;随着紫外光辐照时间的延长,材料断裂伸长率逐渐下降;4种抗氧剂中,0.4%亚磷酸酯类改善PPR抗紫外光老化性能的效果最佳。     

老化试验中PE-HD的结构与力学性能研究

研究了高密度聚乙烯在海南自然曝露和氙灯人工老化后的结构和力学性能变化。结果表明：相比于自然曝露，高密度聚乙烯主要力学性能的氙灯人工老化加速倍率大约为4；老化期间，高密度聚乙烯分子间存在着交联和降解二种竞争反应，老化早期以交联为主，后期以降解为主；氙灯老化试验相比于自然曝露，老化主要集中在材料表层。     

Effects of two staining methods on color stability of wood flour/polypropylene composites during accelerated UV weathering

Two staining methods of wood flour/polypropylene composites in an attempt to improve the color stability of wood‐plastic composites (WPCs) were investigated. The first was to dye wood flour (WF) before compounding with polypropylene (PP) to make stained composites. The second method involved mixing pigments directly with WF and PP. Nine groups of composites were weathered in a QUV accelerated weathering tester for 960 h. Their surface color, surface gloss, washing resistance, and flexural properties were tested during weathering. Additionally, the weathered surface was characterized by SEM and ATR‐FTIR. The results revealed that (1) the washing resistance of composites were improved after staining treatments; (2) composites made of dyed WF showed higher surface gloss values and less cracks on weathered surface at the early stage of weathering; while composites containing pigments displayed brighter color, less color change, and less loss of flexural properties during weathering; and (3) weathering resulted in the protrusion of WF and photodegraded lignin on exposed surface. Adding pigments was proven to be more effective staining method for improving composite color stability during weathering. POLYM. COMPOS., 38:1194–1205, 2017. © 2015 Society of Plastics Engineers     

Effect of accelerated weathering on discoloration and roughness of finished ash wood surfaces in comparison with red oak and hard maple

This study investigated the discoloration and roughening of finish and unfinished ash (Fraxinus americana), red oak (Quercus rubra), and hard maple (Acer nigrum) wood surfaces exposed to artificial weathering, with the aim of assessing the potential for ash wood for interior and exterior applications. Ash wood surfaces were treated with several coats of satin and high gloss polyurethane finishes in order to evaluate their potential for value added products from waste ash wood generated from an exotic insect (emerald ash borer) infestation. Red oak and red maple wood specimens were included in the study for comparison purposes. The weathering experiment was performed by cycles of UV light irradiation with and without water. Surface discoloration was measured according to ISO 2470 standard with a micro flash reflectometer in the CIELAB system. The surface roughness was measured with a surface profilometer and a roughening profile developed for each weathered surface. Results obtained showed that ash wood exposed to a combination of UV light and water spray had a color change pattern very similar to that of maple, and both species had a faster and higher levels of discoloration compared to red oak. However, when exposed to continuous UV radiation without water, ash had a higher level of discoloration than maple and red oak. Evaluation of changes in the roughness showed that maple had the lowest roughness after weathering, but finished ash surfaces also showed roughness characteristics similar to that of maple after 450 h exposure.     

Effect of weathering cycle and manufacturing method on performance of wood flour and high‐density polyethylene composites

Wood–plastic lumber is promoted as a low‐maintenance high‐durability product. When exposed to accelerated weathering, however, wood–plastic composites may experience a color change and loss in mechanical properties. Differences in weathering cycle and composite surface characteristics can affect the rate and amount of change caused by weathering. In this study, 50% wood flour filled high‐density polyethylene composite samples were injection molded, extruded, or extruded and then planed to remove the manufacturing surface characteristics. Composites were exposed to two accelerated weathering cycles in a xenon arc weathering apparatus. This apparatus exposed the samples to xenon arc radiation, which is a combination of UV, visible, and IR radiation that is similar to solar radiation. Composites were exposed to radiation with or without water spray. After exposure to radiation and water spray, composites with more wood component at the surface (i.e., planed samples) experienced a larger percentage of total loss in flexural modulus of elasticity and strength after weathering compared with the other composites. Composites exposed to radiation only did not experience as much change in properties as those exposed to radiation with water spray. The results of this study demonstrate that exposing wood–plastic composites to water spray in combination with radiation is more severe than exposing wood–plastic composites to radiation only. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3131–3140, 2006     

ESCA study of oxidized wood surfaces

Results of a preliminary study of the surface of wood exposed to outdoor weathering as well as to UV irradiation showed that ESCA provides valuable information and insight into the manifestation of weathering and photooxidation. From the ESCA spectra, the increase in signal intensities of carbon–oxygen bonds and oxygen–carbon–oxygen bonds (or unsaturated carbon oxygen bond) and oxygen-to-carbon ratio, and the decrease in carbon–carbon and carbon–hydrogen bonds of weathered and UV-irradiated wood surfaces suggested that wood surface was oxidized. Nevertheless, it was a superficial effect. Only a slow oxidation was observed at 100 μm under the exposed wood surfaces. From the oxygen-to-carbon ratio data, it revealed that weathered wood surface was rich in cellulose, poor in lignin. The leached-away degradation products from weathered wood surface accounted for the discrepancy between the ESCA line shapes of UV-irradiated and weathered wood surfaces.     

Antiweathering effects of vitamin E on wood flour/polypropylene composites

The purpose of this research was to investigate the influence of vitamin E (Ve) with different loading levels (0.1, 0.2, 0.4, and 1.2 %wt) on the photodegradation of wood flour/polypropylene composites. Five groups of composites were exposed in a QUV‐accelerated weathering tester for 960 h and then the surface color and the flexural properties were tested. Besides, the surface morphology and chemical changes of the composites during weathering were analyzed by scanning electron microscopy, attenuated total reflectance fourier transform infrared spectroscopy, and X‐ray photoelectron spectroscopy. The results revealed that (1) the addition of Ve had a positive effect on hindering the photooxidation process of the composites; (2) composites with higher Ve loading levels (0.4 and 1.2 %wt) showed better flexural properties, less color fading, cracks, and disclosure of wood fibers on surface after weathering; (3) Ve alleviated the chain scission of PP and the formation of carbonyl groups by reacting with free radicals that generated from photodegradation during weathering. Therefore, it could be an effective antiphotodegradation agent for the composites. POLYM. COMPOS., 35:2085–2093, 2014. © 2014 Society of Plastics Engineers     

Natural weathering of spruce wood chemically modified by re-used ε-caprolactone solution

Increasing environmental pressures over the last few years have led to attention for non-biocide treatments in the wood protection field. The ε-caprolactone modification of wood by substitution or blocking of hydroxyl groups with hydrophobic poly(ε-caprolactone) (PCL) is one of the novel modification methods developed in recent years. In this study, ring-opening polymerisation of ε-caprolactone in wood cell walls was evaluated by the third and sixth re-use of recovered monomer and by oven-curing method. Spruce samples were modified by re-used ε-caprolactone and exposed to the natural weathering agents for 12 months. After weathering, the colour change, surface roughness measurements, and macroscopic and ultra-microscopic observations revealed that the modified wood had better surface properties than reference wood. Fourier-transform infrared (FTIR) analysis proved that PCL could be found on the weathered surface up to the sixth month, but very little amount was detected on the surfaces with a longer weathering period. The results clearly showed that the efficiency of PCL modification with re-use of the monomer solution was sufficient during the initial weathering periods, but efficiency was reduced after a prolonged exposure period.     

Effect of biological degradation by termites on the flexural properties of pinewood residue/recycled high‐density polyethylene composites

Wood–plastic composites (WPCs) are considered to be highly durable materials and immune to any type of biological attack. However, when one of these composites is exposed to accelerated weathering, its surface is affected by the appearance of cracks, which constitute an ideal access route for biotic agents. Although the destruction of wood caused by termites is recognized worldwide, information on their effects on WPC‐based products is scarce. Thus, in this study, we aimed to examine the effects of termite attacks on weathered and nonweathered pinewood residue/recycled high‐density polyethylene composites. In this study, WPCs with 40 wt % wood were prepared. Test samples obtained by compression molding and profile extrusion were subjected to weathering cycles for 1000 and 2000 h with a UV‐type accelerated tester equipped with UVA‐340 fluorescent lamps. Afterward, specimens were exposed to the attack of higher termites (Nasutitermes nigriceps) native to the Yucatan Peninsula. Subsequently, flexural mechanical essays, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) analyses were performed. FTIR spectroscopy and DSC showed that the surfaces of the compression‐molded specimens were degraded to a higher extent because of the accelerated weathering. The microscopy results revealed that severe damage was caused by the termites on the surface of the compression‐molded samples. Statistical analysis of the mechanical test results showed that biotic attack produced significant changes in the samples previously exposed to accelerated weathering. The results show that the processing method directly affected the sample performance because of differences in the surface composition. The profile‐extruded composites seemed to better resist termite attack. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Weathering of polypropylene composites containing weldlines

Abstract

This work deals with the weathering behaviour of polypropylene composites containing fillers with various aspect ratios (glass fibre, talc, and calcium carbonate). Single and double end gated injection moulded bars were exposed outdoors in Campina Grande (Brazil) for periods up to 45 weeks and then characterised using infrared spectroscopy, tensile testing, and surface fractography. The unfilled polymer displayed the highest level of mechanical deterioration, followed by polypropylene containing glass fibre, whereas compounds with talc and calcium carbonate were the most resistant to photodegradation. These results are partially a consequence of the screening effect caused by talc and calcium carbonate at the exposed surface. The results indicated that weldlines make the parts weaker, although the strength loss caused by weathering of double end gated samples was similar to that observed with mouldings produced by single gated injection. It was also observed that the adhesion between glass fibre and the polymer matrix was much reduced after weathering, probably as a result of diffusion of water to the interface.     

An investigation of the effect of pigment on the degradation of a naturally weathered polyester coating

A series of coil coatings based on a polyester/melamine resin formulation, incorporating different pigment systems, were naturally weathered after being exposed to the elements in Hainan, PRC, for 2 years. The surface chemistry and morphology, before and after weathering, was investigated using both traditional (i.e., gloss retention, color change) and novel (i.e., X-ray photoelectron spectroscopy [XPS], atomic force microscopy [AFM], and scanning electron microscopy [SEM]) methods. Chemical changes occurring in the coating bulk were investigated using step-scan photoacoustic Fourier transform infrared spectroscopy (SSPA-FTIR). It was found that the coating surface morphology, surface chemistry, and bulk chemistry, both before and after weathering, were all affected by the type and concentration of the pigments included in the coating formulation. Moreover, it was found that different types of pigment catalyze different coating degradation mechanisms.