玻璃纤维/环氧乙烯基酯树脂复合材料的湿热老化力学性能

为掌握玻璃纤维/环氧乙烯基酯树脂复合材料经湿热老化后的力学性能,采用真空辅助注射成型技术,制作玻璃纤维/环氧乙烯基酯树脂复合材料层合板,并根据复合材料压力容器在服役过程中的受力特点,利用水切割技术将层合板制成弯曲和剪切试样。考虑到压力容器的使用工况,对试样进行浸泡加速老化试验,分析了在不同温度和周期下复合材料的质量和力学性能变化。结果表明,随着浸泡时间的增加,复合材料的弯曲和剪切性能逐渐降低。相比于浸泡时间的影响,温度对复合材料性能的影响更显著,如在90℃水中浸泡6周后,复合材料的剪切强度、弯曲强度以及弯曲模量降为初始值的1/2。     

红外光谱研究Fenton试剂对多壁碳纳米管表面的影响

碳纳米管经焙烧和稀硝酸纯化处理后,在不同实验条件下采用Fenton试剂对多壁碳纳米管进行化学改性,红外光谱(FTIR)结果表明,Fenton试剂化学处理后能够在碳纳米管表面引入羟基和羰基,且羰基峰的吸收强度随着反应时间的增加而增加;碳纳米管的化学处理条件即过氧化氢与亚铁离子物质的量之比、pH值和反应时间等因素能够影响碳纳米管的改性效果;过氧化氢与亚铁离子物质的量之比控制在10左右,pH保持在3,反应10h即能在碳纳米管表面产生较多的羰基.此外,根据Fenton试剂产生羟基自由基的机理和碳纳米管改性前后的FTIR变化,初步分析了Fenton试剂与碳纳米管作用的可能机理.机理分析表明,羟基和羰基的产生是由亲电性的HO·对碳纳米管上的不饱和键进行加成氧化引起的.     

ATR-FTIR研究超支化聚酯对PEG型聚氨酯弹性体的力学性能及形态的影响

为改善聚乙二醇(PEG)型聚氨酯弹性体的力学性能,将改性超支化聚酯(HBP)引入形成共混体系,利用衰减全反射傅里叶变换红外光谱(ATR-FTIR)研究了聚氨酯胶片的化学结构.结果表明,超支化聚酯对PEG型聚氨酯弹性体具有较好的增强增韧作用,当加入0.4%的第三代超支化聚酯时,聚氨酯弹性体的拉伸强度比空白胶片提高了2.5...     

丙烯酸酯乳液文物保护材料耐老化性能评价

水溶性的丙烯酸酯乳液是文物领域常用的保护材料,多用于壁画、彩画、骨质文物、漆木器文物的加固和粘接。使用最广泛的丙烯酸酯乳液类文物保护材料是由原罗门哈斯公司生产的Primal系列。商品材料如PrimalAC33、 SF016、 B60A、 WS24和MC76等在国内外的文物保护修复实践中应用较多,但文献报道大多数是直接购买使用的修复案例,缺乏较为系统科学的性能评价研究。针对5种常用的Primal系列丙烯酸酯乳液文物保护材料的湿热老化性能和光老化性能开展研究,通过微观形貌、色差和光泽度等分析比较其耐老化性能,采用红外光谱追踪光老化过程中的分子结构变化和吸收峰强度,阐释其降解机理。实验结果表明,WS24和B60A的耐湿热性能较好,SF016耐湿热性能最差;AC33的颜色和失光率变化最明显。光老化测试发现,紫外光照射过程中所有的材料均发生了断链反应,另外AC33与MC76有内酯生成。经过4 200 h光老化后,AC33、 SF016、 B60A和MC76的羰基指数(CI)均有不同程度的增大,羰基吸收峰强度(D_t)降低了10%～15%。WS24的羰基指数下降非常迅速,羰基吸...     

壳聚糖基聚合物点荧光材料的合成及其对纸张的抗紫外老化性能

以壳聚糖、柠檬酸、N-(2-羟乙基)乙二胺为原料,通过水热法合成了壳聚糖基聚合点(P(CS-g-CA)Ds)荧光材料,发现柠檬酸的接枝可明显提高壳聚糖聚合物点的量子产率。对P(CS-g-CA)Ds进行了红外光谱、紫外光谱、光电子能谱、透射电镜、热分解性能及光致发光光谱表征,测试了不同p H值下的荧光强度。结果表明,P(CS-g-CA)Ds在p H=4~12范围内有良好的稳定性。通过测试紫外老化前后宣纸的羰基指数和乙烯基指数研究了P(CS-g-CA)Ds在宣纸中的应用,结果表明其具有良好的抗紫外老化性能。     

Paraloid文物保护材料光老化的红外光谱研究

Paraloid(乳胶粘合剂)是一系列丙烯酸树脂的商品名称,是文物保护领域中最常用的保护材料之一,主要用于文物的加固、封护和粘接,适用文物材质范围非常广泛。其中以Paraloid B-72最具代表性,在国内外的文物保护中被大量使用,相关的应用案例、性能评价及其老化机理研究都有较多报道,而Paraloid系列的其他产品却鲜有关注,在国内应用较少,老化性能研究尚未开展工作。该研究系统评价了Paraloid B-72, Paraloid B-44, Paraloid B-48N和Paraloid B-67的光老化性能,采用红外光谱跟踪紫外辐照3 864 h过程中Paraloid材料分子结构变化,对光老化机理进行了深入解析和半定量评测。结果显示,4种Paraloid系列丙烯酸树脂材料中,B-72老化前后颜色和光泽度均没有发生明显变化,B-48N和B-67老化前后色差较大,B-44光泽度降低最多。丙烯酸树脂老化过程中高分子材料内部发生断链反应以及一定程度的交联反应,表现在主要官能团吸收的减弱和羰基指数(CI)的增加。根据主要官能团吸收峰CO相对强度的半定量分析结果反映出,B-72的光稳定性最好,...     

废水处理过程中色氨酸荧光特性研究

色氨酸是废水中一种常见的标志性污染物。采用荧光光谱法对浓度效应、pH值以及离子强度与色氨酸的荧光光谱特性之间的关系进行了相关研究。研究结果表明:(1)色氨酸在低浓度范围(0.01~3 mg.L-1)呈现出良好线性关系,相关系数达到0.995 88,在高浓度范围内(3~30 mg.L-1)线性关系稍差,相关系数0.912 47;(2)在酸性条件下,其荧光相对强度随着pH值的升高而增强,6.5pH7.5的范围内荧光相对强度比较稳定,在pH值接近12时,荧光相对强度急剧下降;(3)随着离子强度的增强,其荧光相对强度有所降低,当硝酸根的浓度达到一定量后,出现了红移现象。     

泡沫硅橡胶拉伸压缩过程的扫描电镜原位观察

泡沫硅橡胶具有成孔容易、相对密度低、比模量和比强度优良等许多独特的力学特性，因而广泛用于重要设备的防护及内部结构的填充等方面。相关研究表明，泡沫硅橡胶力学性能在很大程度上取决于其泡孔结构。但是，泡孔结构对泡沫硅橡胶力学性能的影响从根本上来说仍然取决于其内部泡孔在拉伸或压缩过程中的破坏模式或失效机制。因此，研究泡沫硅橡胶材料的在拉伸或压缩过程中泡孔结构的变化对正确评价其力学性能及对其配方和工艺改进等都具有指导意义。     

XRD与NMR的热处理竹材结晶性能研究

木质纤维素的结晶度研究方法较多,但目前观点不一。采用三种不同的热处理方法(稀酸,碱及甘油高温处理)并基于X射线衍射(XRD)和固体核磁共振技术(CP/MAS 13 NMR),综合研究竹材结晶度变化规律,通过X射线衍射参数及高斯函数曲线分析结晶纤维素C-4区域的信号面积分析,获得不同的化学热处理介入下竹材化学成分及结晶度变化机理。结果表明:经过化学热处理后,竹材的结晶度指数总体增加,碱处理002峰尖锐程度增大,并向大角度方向偏移明显,002晶面宽度变大,结晶区层间距尺度变小。CP/MAS 13 NMR与XRD结果基本一致,但是计算值偏小。未处理竹材在84.6ppm信号处分裂成两个峰顶,88.7和83.1ppm,,表明C-4在热处理过程中发生了从纤维素Ⅰ~Ⅱ的化学转换,从化学结构变化的角度证明了碱处理可以有效破坏竹子纤维之间的内结合阻力,并产生高度活性纤维素,对于实现木质纤维素原料的高效生物转化利用提供指导。     

γ射线辐照处理竹材的X射线光谱研究

利用X射线衍射仪,对γ射线辐照处理前后的竹材进行X射线光谱分析,得出竹材结晶度和微纤丝角在辐照过程中的变化规律。随着辐照剂量的增加,竹材纤维素结晶度呈现先升高后降低的趋势,微纤丝角变化不明显,表明微纤丝角不是影响辐照过程中竹材物理、力学性能变化的主要因子。     

The Enhanced Melt Intercalation of Polyethylene Using Exothermal Montmorillonite

Exothermal montmorillonite (EMMT) was prepared and used in the preparation of HDPE composites in which the EMMT was intercalated. Compared with the ODA modified montmorillonite (OMMT), EMMT exhibited better intercalation behavior during melt compounding, resulting in similar tensile modulus and better tensile strength and elongation at break of the corresponding composites. The crystallization of the polymeric matrix and the dispersion of MMT were systemically investigated; their relationship with the mechanical properties of the composites are discussed as well.     

Influence of Carbon Nanotubes on the Crystallization and Directional Tensile Behavior of High-Density Polyethylene Prepared by Dynamic-Packing Injection Molding

The influence of multi-walled carbon nanotubes (MWCNTs) on the crystallization and directional tensile properties of high-density polyethylene (HDPE) was studied for samples prepared by dynamic-packing injection molding (DPIM). Oscillatory shear was imposed on the gradually cooled melt during the packing solidification stage of DPIM. For the oriented composites containing 1.8 wt% MWCNTs, the tensile fracture behavior showed typical brittle features along the flow direction (FD) and perpendicular direction (PD), which were almost the same as those that occurred in oriented pure HDPE. The elongation at break along both directions decreased due to the incorporation of MWNCTs in the oriented composites compared with the oriented pure HDPE. However, the tensile strength of the oriented HDPE/MWCNT composites was greatly improved along the FD due to the presence of carbon nanotubes; meanwhile, it was not weakened along the PD. In scanning electron microscopy observations, it was found that there were some oriented hybrid shish-kebab structures in a nanometre scale in the oriented HDPE/MWCNT composites, but not in its isotropic composites. This suggests that MWCNTs were involved in the shear-induced crystallization of HDPE. Differential scanning calorimetry measurements confirmed that the crystallinity of oriented HDPE composites with 1.8 wt% MWCNTs was higher than those of isotropic HDPE and isotropic composites, but was not obviously higher than that of oriented pure HDPE. These findings demonstrate that MWCNTs indeed affected the formation of crystalline structures, but did not greatly influence the crystallinity of HDPE under shear flow. The transition of crystalline morphology might be the reason for change in tensile behavior for the oriented HDPE/MWCNT composites compared with the oriented pure HDPE.     

Morphology and mechanical properties of PP/HMWPE blends

Mechanical properties and morphology of blends of polypropylene (PP) with high molecular weight polyethylene (HMWPE) prepared by coprecipitation from xylene solution are investigated. Compared to blends of PP with commercial high-density polyethylene (HDPE), the mechanical properties of the blends of PP/HMWPE are much superior to those of PP/HDPE blends. Not only is the tensile strength stronger, but also the elongation at break is much higher than that of the PP/HDPE blends of the same composition. These differences increase with increasing HMWPE and HDPE content. Scanning electron microscopy of the fracture surface resulting from the tensile tests shows that the compatibility in PP/ HMWPE blends is much better than that in PP/HDPE blends. This is most likely attributable to the enhanced chain entanglement of HMWPE with the PP in the amorphous phase due to the lower crystallinity, owing to the high molecular weight of the HMWPE, and a much more flexible chain. The thermal behavior and spherulite morphology of both blends are also investigated.     

A general scheme derived from video-controlled stretching tests and WAXS for describing tensile deformations of polyethylenes

When polyethylene (PE) is deformed to large strains, the stress originates from both the viscous forces associated with the plastic deformation of the crystallites by slip and fragmentation processes and the entropic elastic forces arising from the stretching of the entangled amorphous regions. The dependencies of the relative weights of these processes on crystallinity were analyzed in a comprehensive study of A series of samples: high-density polyethylene (HDPE), low-density polyethylene (LDPE), and ethylene-vinylacetate copolymers. The comparison was based on measured true stress-strain curves at constant strain rates, on the recovery properties of the samples studied in tensile tests with included unloading-reloading loops, and on wide-angle X-ray spectroscopy (WAXS) measurements carried out to determine the related texture changes. It was found that, in spite of the large changes in the gross mechanical properties from solid-like to rubberlike behavior, there always exist four characteristic points at which the deformation behavior changes. These may be associated with (1) the onset of isolated slip processes, (2) a change into a collective activity of the slips, (3) the beginning of crystallite fragmentation, and (4) chain disentanglement. Increasing crystallinity leads to increasing stresses at these points: the related strains, however, remain essentially constant. The crystal texture is a function of the imposed strain only. Experiments support the novel picture of a granular substructure of the crystalline lamellae as a basic structural feature.     

Extrinsic fluorescence as a sensitive method for studying photo-degradation of high density polyethylene part I

Artificial ageing of high density polyethylene (HDPE) exposed to ultra-violet irradiation has been investigated by fluorescence spectroscopy. In the case of HDPE, fluorescence spectroscopy requires the addition of fluorophore, (rhodamine 101 laser dye). The spectral features of fluorescence are very sensitive to the interaction between the exited molecules and the polymer matrix. Under wavelength close to 254 nm, the diffusion of oxygen can introduce groups such as CO, CO and C(O)O into the molecular chains. Thus entail structural and chemical modifications such as polymeric chain breaking, cross linking and oxidation. In the present work, we clearly illustrate the fact that fluorescence spectroscopy is very worthwhile in particular to follow the early stages of photo-degradation.     

Kinetics of ozone oxidation of oriented polypropylene and high-density polyethylene

The interrelation between the rate of ozone oxidation of oriented samples of PP and HDPE and the structural processes in the region of relaxation transitions at 50–70°C in PP and 40–60°C in HDPE was found. Within the studied temperature range, the annealing results in significant structural changes accompanied by the emergence of breaks in the temperature dependence of the rate of ozone oxidation. The chemical and temperature preannealing decreases the oxidation rate. After the chemical annealing at 96°C, the Arrhenius temperature dependence of the oxidation rate was observed.     

On the method for determining the true strength of inorganic glasses

The possibility of determining the true structural strength of glass by bending of glass fibers with a defect-free surface is considered. Two methods are compared, viz., the method of transverse three-point bending in which the breaking stress (strength) is determined, and the method of two-point bending in which the breaking strain is determined. In the latter case, the dependence of the elastic modulus on strain is required for determining the breaking stress (strength). The strength measured in three-point bending is compared with the strength calculated from the breaking strain measured in two-point bending. It is shown that the measurements based on these two methods give close values of strength for defect-free silica fibers used as optical waveguides. The observed difference of ～12% in the values of strength is explained by the difference in the loading rates obtained using these two methods. The advantages and disadvantages of these two techniques are analyzed.     

Impact on textile properties of polyester with laser

Modification of the textile properties of polyester due to laser irradiation were studied and these properties included fibre weight and diameter, tensile strength and elongation, yarn abrasion, bending, surface lustre, wetting, air permeability as well as crystallinity. Properties such as wettability and air permeability were positively affected while properties of fibre weight and diameter, tensile strength, yarn abrasion and bending were adversely affected. In this study, laser irradiation used was not found to affect the bulk properties of polymer due to its low penetration depth, and hence, the effect of laser irradiation on bulk and structural properties was limited. However, the performance and comfort properties of the laser-irradiated polyester could be significantly affected by laser irradiation.     

显微红外光谱法研究聚乙烯复合材料光氧化的深度分布

采用显微红外光谱法结合表面形貌分析研究了分别填充碳酸钙、绢英粉、云母、高岭土和硅藻土的高密度聚乙烯(HDPE)的自然光氧化随深度的分布。研究结果表明无机填料对HDPE光氧化的深度分布有很大的影响。填充碳酸钙的HDPE从表面到内部都没有明显氧化发生。而填充绢英粉、云母、高岭土和硅藻土的HDPE从表面到内部羰基指数逐渐减小,氧化深度都在150 μm以上。HDPE复合材料沿深度方向的氧化情况与其断面裂纹的产生情况吻合。结合无机填料的紫外吸收特性讨论了它们对HDPE光氧化的影响机理。     

Preparation and Mechanical and Tribological Properties of High-Density Polyethylene/Hydroxyapatite Nanocomposites

High-density polyethylene (HDPE) nanocomposites reinforced with hydroxyapatite nanorods (nHA) were fabricated by means of extrusion and injection molding. The thermal, mechanical, and dry sliding wear properties of HDPE-based nanocomposites filled with nHA loadings up to 20 wt% were investigated. The results of mechanical property characterization showed that nHA additions improved the hardness, elastic modulus, and yield strength of HDPE at the expense of its tensile ductility and impact strength. Thermogravimetric analysis and heat deflection temperature measurements revealed that nHA fillers are very effective to enhance the thermal stability of HDPE. The wear behavior of HDPE/nHA nanocomposites was studied using a pin-on-disk tribometer. nHA fillers of a large aspect ratio improved the wear resistance of HDPE substantially because of their load-bearing effect and the formation of a continuous transfer film on the steel counterface.