木材变色的研究状况及发展趋势

阐述了木材变色问题的国内外研究状况及发展趋势,并给出了木材防变色方法和对已变色木材的除色方法.     

Encapsulation of PV modules using ethylene vinyl acetate copolymer as a pottant: A critical review

The primary purpose of this work is to review the literature about what is and is not known about using ethylene vinyl acetate (EVA0 copolymer as the encapsulant (or pottant) material in photovoltaic (PV) modules. Secondary purposes include elucidating the complexity of the encapsulation problem, providing an overview about encapsulation of PV cells and modules, providing a historical overview of the relevant research and development on EVA, summarizing performance losses reported for PV systems deployed since ca. 1981, and summarizing the general problems of polymer stability in a solar environment. We also provide a critical review of aspects of reported work for cases that we believe are important.Failure modes resolved in the early work to establish reliability of deployed modules and the purposes and properties of pottants, are summarized. Typical performance losses in large field-deployed, large-scale systems ranging from 1% to 10% per year are given quantitatively, and qualitative reports of EVA discoloration are summarized with respect to ultraviolet (UV), world-wide location and site dependence.The general stability of polymers and their desirable bulk properties for solar utilization are given. The stabilization formulation for EVA, its effectiveness, and changes in it during degradation are discussed. The degradation mechanisms for the base resin, e.g., unstabilized Elvax 150^TM, and stabilized EVA are indicated for literature dating to the early 1950s, and the role played by unsaturated chromophores is indicated. The limited number of studies relating discoloration and PV cell efficiency are summarized.Observed degradation of EVA or the unstabilized base resin in the laboratory and examples used to measure the degradation are summarized in sections entitled: (1) thermally-induced degradation; (2) photodegradation and photothermal degradation of EVA in different temperature regimes; (3) photobleaching and photodegradation of the UV absorber and cross-linking agent; (4) acetic acid and metal and metal-oxide catalyzed oxidative degradation; and (5) discolaration and PV cell efficiency losses.Processing effects/influences on EVA stability are discussed in sections entitled: (1) EVA raw materials and extruded, uncured films; (2) thermal encapsulation processes; (3) effects of lamination, curing, and curing peroxide on gel content and chromophores formed; and (4) incomplete shielding of curing-generated chromophores. A summary is given for the limited number of accelerated lifetime testing efforts and examples of erroneous service lifetime predictions for EVA are discussed. The known factors that effect the discoloration rate of several EVA formulations are discussed in which the reduction in rate by using UV-absorbing superstrates is a prime example. A summary is given of what is and is not known about EVA degradation mechanisms, degradation from exposures in field-deployed modeules and/or laboratory testing, and factors that contribute to EVA stability or degradation. Finally, conclusions about using Elvax 150 in EVA formulations are summarized, and future prospects for developing the next-generation pottant for encapsulating PV modules are discussed.     

Cationic polymerization of hydrogenated bisphenol‐A glycidyl ether with cycloaliphatic epoxy resin and its thermal discoloration

One of the key issues associated with epoxy resin–based LED encapsulant is discoloration under operating conditions that caused a decrease in light output. In this article, thermal cationic polymerization of hydrogenated bisphenol‐A glycidyl ether using 3‐methyl‐2‐butenyltetramethylenesulfonium hexafluoroantimonate and its discoloration are reported. Polymerization was followed by thermal analysis, FT‐IR spectrum, and hardness measurements. Thermal discoloration was measured by yellowness index based on transmittance spectrum. Increased catalyst concentration causes acceleration in polymerization rates, but this also increased discoloration after thermal aging. In low catalyst concentration under 0.3 wt %, the hardness of plaque was low and required a high temperature to complete polymerization and this resulted in a highly colored plaque. Formulation with cycloaliphatic epoxy (3′‐4′‐epoxycyclohexane)methyl 3′‐4′‐epoxycyclohexyl‐carboxylate (CEL2021P) enhanced the polymerization even at low catalyst concentration and reduced thermal discoloration. With addition of di‐t‐butylphenol (BHT) as the oxidation inhibitor, the thermal discoloration was extremely improved but this also caused inhibition of polymerization as seen by thermal analysis. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1395–1400, 2005     

亲水性低黄变氨基改性硅微乳的合成

以D4和改性氨基硅烷偶联剂为原料，采用磺酸类催化剂和非离子型复合乳化剂，通过将预乳液滴入催化剂的水溶液的方法，制成了氨基改性硅微乳。预乳液的滴加速度对产品的透明度有很大影响；硅微乳具有良好的酸、碱、阴离子表面活性剂、离心、热稳定性，并可与荧光增白剂、还原性染料、活性染料同浴使用；用其整理的织物具有良好的亲水性和低黄变性。     

Pressure effects on acid-catalysed autoxidation of oxymyoglobin

 Two opposing factors have been found to affect the rate of autoxidation of the fresh meat pigment oxymyoglobin, MbFe(II)O₂, in air-saturated aqueous acetate buffer with increasing hydrostatic pressure to yield metmyoglobin, MbFe(III): (1) expansion in the transition state, corresponding to a volume of activation of ΔV# = +12.7±0.6 ml mol^–1 (25.0°C, 0.16 M NaCl), in effect decreasing the rate; and (2) an increased specific acid catalysis resulting from a decrease in solution pH and increasing the rate. In the pressure range investigated (up to 250 MPa) and at the pH relevant to traditionally deboned meat (pH = 5.65 at ambient pressure investigated, together with pH = 5.21 in order to obtain mechanistic information), the pressure/pH effect was found almost to negate the kinetic effect of expansion in the transition state. Red-to-brown discoloration during pressure treatment of meat is accordingly expected to be less significant for hot-deboned and other high-pH meats. Received: 7 April 1997 / Revised version: 2 June 1997     

银镀层抗腐蚀变色的测定方法

对银镀层抗腐蚀变色的测定方法做了分析和试验比较,为银镀层抗腐蚀变色的处理工艺、质量判定及相关标准的修订提供了准确可靠、操作性较强的测定方法。     

不可逆温敏变色油墨的显色动力学探究

目的 探究温敏变色油墨对时间、温度的响应情况,以及不同制备配方对其动力学参数的影响。方法 利用光生酸剂的分解反应使结晶隐性紫染料开环显色,以此作为变色体系置于丝网油墨中,制备出可随时间–温度累积进行不可逆变色的智能温敏标签。利用分光密度仪测量标签b*值,以标签b*值变化作为测量指标,将其与变色时间进行拟合,探讨油墨组分对标签变色性能的影响。并探究不同组配方下b*值对温度变化的响应,以及不同配方对反应活化能的影响。结果 随着时间的积累,油墨印刷标签b*值逐渐减少,标签颜色由浅黄色变成深蓝色;同时,当温度升高,标签的变色速率也随之加快,温度越高,标签所测量的b*值越低,呈现出的蓝色越深。相同温度下标签|Δb*|值较高时,标签的活化能较低。结论 该标签对时间、温度的积累均有响应,制备的标签活化能在11.453～27.676kJ/mol波动,具有应用在食品品质智能监控领域的潜力。     

光伏组件用网格玻璃PID测试后变色原因分析

针对光伏组件用网格玻璃经过-1500 V的电势诱导衰减(PID)测试后出现局部变色现象进行了分析,通过对样品进行扫描电子显微镜法(SEM)、能量散射光谱(EDS)及X射线光电子光谱法(XPS)测试,分析元素的含量、结合能等,认为造成发黑的主要原因是Na+的迁移及Ti3+形成使白色TiO2的正四方晶格发生紊乱,导致价带的电子跃迁到导带所需的能量减小,禁带宽度变窄,使原来白色TiO2也可以被能量较小的光子激发,从而吸收部分能量较低的可见光,出现变色。     

不同处理方法对贺兰山紫蘑菇多糖抗氧化活性的影响

采用热水浸提法提取贺兰山紫蘑菇多糖,分别考察真空冷冻干燥法、真空干燥法（丙酮乙醚洗涤、乙醇洗涤）对其抗氧化活性的影响,确定最优干燥方法;干燥后多糖再分别经Sevag法脱蛋白、大孔树脂脱色、双氧水脱色3 种方法进一步处理,采用1,1-二苯基-2-三硝基苯肼法分析不同处理方法对其抗氧化活性的影响。结果表明,真空干燥法（乙醇洗涤）对贺兰山紫蘑菇多糖的抗氧化活性影响最小;大孔树脂脱色效果优于双氧水脱色,Sevag法对该多糖抗氧化活性影响较大,应尽量避免使用。     

鱼腥草多糖活性炭脱色工艺研究

研究了鱼腥草多糖活性炭脱色的工艺。以多糖含量和脱色率为指标,在单因素筛选的基础上,采用正交试验法对脱色工艺进行优选。优化的脱色工艺为:在pH 4.0,20℃的条件下,加入0.4%活性炭,搅拌40 min。该脱色工艺适合工业化应用。