稀土La2O3改性脲醛树脂的黏度特性研究

脲醛树脂(UF树脂)胶黏剂具有胶合强度高、制作简单、成本低廉、原料来源丰富等一系列特点,成为我国人造板生产的主要胶种,是市场上需求量最大的胶黏剂之一。但由于在固化时会放出刺激性的甲醛,游离甲醛高,在使用时严重危害人的健康。近年来,随着人们环保意识的提高,生产和使用低毒UF树脂胶势在必行。本文介绍了稀土氧化镧对脲醛树脂的改性过程并对改性后脲醛树脂胶的各项性能进行了测试。本实验通过在不同反应阶段加入稀土氧化镧,分别探讨它们对脲醛树脂胶黏剂性能影响。实验表明:在脲醛树脂胶中加入稀土氧化镧可以增加黏度、固化时间、固含量,并可以减少游离甲醛释放量。     

催化共振光散射法测定空气中痕量甲醛的研究

吖啶橙分子聚集体微粒可在513nm波长处出现最大的共振光散射强度(RLS)。在稀硫酸介质中,甲醛能催化溴酸钾氧化吖啶橙的反应,促使其RLS强度减弱。在最佳实验条件下,甲醛质量浓度ρ在0.020～0.25μg/mL的范围内与△I值呈良好的线性关系,线性回归方程为△I=1113.99ρ+49.23,线性相关系数r为0.9986。本法与国标法进行对照,在置信度等于95%时,用Cochran检验,两种方法间不存在显著性差异,方法操作简单、灵敏度高,用于室内外空气中甲醛测定,结果满意。     

Formaldehyde as a Chemical Defence Agent of Fruiting Bodies of Mycena rosea and its Role in the Generation of the Alkaloid Mycenarubin C

Mycenarubin C, a previously unknown red pyrroloquinoline alkaloid, was isolated from fruiting bodies of the mushroom Mycena rosea and its structure was elucidated mainly by NMR spectroscopy and mass spectrometry. Unlike mycenarubin A, the major pyrroloquinoline alkaloid in fruiting bodies of M. rosea, mycenarubin C, contains an eight-membered ring with an additional C₁ unit that is hitherto unprecedented for pyrroloquinoline alkaloids known in nature. Incubation of mycenarubin A with an excess of formaldehyde revealed that mycenarubin C was generated nearly quantitatively from mycenarubin A. An investigation into the formaldehyde content of fresh fruiting bodies of M. rosea showed the presence of considerable amounts of formaldehyde, with values of 5 μg per gram of fresh weight in fresh fruiting bodies. Although mycenarubin C did not show bioactivity against selected bacteria and fungi, formaldehyde inhibits the growth of the mycoparasite Spinellus fusiger at concentrations present in fruiting bodies of M. rosea. Therefore, formaldehyde might play an ecological role in the chemical defence of M. rosea against S. fusiger. In turn, S. fusiger produces gallic acid—presumably to detoxify formaldehyde by reaction of this aldehyde with amino acids and gallic acid to Mannich adducts.     

Performance of a CO2 sorbent for indoor air cleaning applications: Effects of environmental conditions,sorbent aging,and adsorption of co-occurring formaldehyde

Indoor air cleaning systems that incorporate CO₂ sorbent materials enable HVAC load shifting and efficiency improvements. This study developed a bench-scale experimental system to evaluate the performance of a sorbent under controlled operation conditions. A thermostatic holder containing 3.15 g sorbent was connected to a manifold that delivered CO₂-enriched air at a known temperature and relative humidity (RH). The air stream was also enriched with 0.8-2.1 ppm formaldehyde. The CO₂ concentration was monitored in real-time upstream and downstream of the sorbent, and integrated formaldehyde samples were collected at different times using DNPH-coated silica cartridges. Sorbent regeneration was carried out by circulating clean air in countercurrent. Almost 200 loading/regeneration cycles were performed in the span of 17 months, from which 104 were carried out at reference test conditions defined by loading with air at 25°C, 38% RH, and 1000 ppm CO₂, and regenerating with air at 80°C, 3% RH and 400 ppm CO₂. The working capacity decreased slightly from 43-44 mg CO₂ per g sorbent to 39-40 mg per g over the 17 months. The capacity increased with lower loading temperature (in the range 15-35°C) and higher regeneration temperature, between 40 and 80°C. The CO₂ capacity was not sensitive to the moisture content in the range 6-9 g/m³, and decreased slightly when dry air was used. Loading isothermal breakthrough curves were fitted to three simple adsorption models, verifying that pseudo-first-order kinetics appropriately describes the adsorption process. The model predicted that equilibrium capacities decreased with increasing temperature from 15 to 35°C, while adsorption rate constants slightly increased. The formaldehyde adsorption efficiency was 80%-99% in different cycles, corresponding to an average capacity of 86 ± 36 µg/g. Formaldehyde was not quantitatively released during regeneration, but its accumulation on the sorbent did not affect CO₂ adsorption.     

Occupational exposure and health risks of volatile organic compounds of hotel housekeepers: Field measurements of exposure and health risks

Hotel housekeepers represent a large, low-income, predominantly minority, and high-risk workforce. Little is known about their exposure to chemicals, including volatile organic compounds (VOCs). This study evaluates VOC exposures of housekeepers, sources and factors affecting VOC levels, and provides preliminary estimates of VOC-related health risks. We utilized indoor and personal sampling at two hotels, assessed ventilation, and characterized the VOC composition of cleaning agents. Personal sampling of hotel staff showed a total target VOC concentration of 57 ± 36 µg/m³ (mean ± SD), about twice that of indoor samples. VOCs of greatest health significance included chloroform and formaldehyde. Several workers had exposure to alkanes that could cause non-cancer effects. VOC levels were negatively correlated with estimated air change rates. The composition and concentrations of the tested products and air samples helped identify possible emission sources, which included building sources (for formaldehyde), disinfection by-products in the laundry room, and cleaning products. VOC levels and the derived health risks in this study were at the lower range found in the US buildings. The excess lifetime cancer risk (average of 4.1 × 10⁻⁵) still indicates a need to lower exposure by reducing or removing toxic constituents, especially formaldehyde, or by increasing ventilation rates.     

Surface sedimentation and adherence of Nano‐SiO2 to improve thermal stability and flame resistance of melamine‐formaldehyde foam via sol‐gel method

Melamine‐formaldehyde foam possesses intrinsic flame retardance; however, relative poor thermal stability and a certain amount of heat release rate restrict its applications in heated environment to a degree. In the present research, sol‐gel method has been adopted to precipitate nano‐SiO₂ particles on the surface of the melamine‐formaldehyde foam's fibers to construct a protective inorganic gel layer. Taking advantages of the shielding effects of the gel layer, the thermal‐oxygen degradation of the foam can be greatly retarded during heating; hence, the thermal stability is remarkably improved, and the flame retardance is further enhanced. In addition, introducing a small amount of membrane‐forming agent in the sol‐gel system can make the depositional nano‐SiO₂ particles well adhered to avoid dusting.     

Intercalation structure and toughening mechanism of graphene/urea‐formaldehyde nanocomposites prepared via in situ polymerization

Based on the industrialized graphene (GN) product, a series of graphene/urea‐formaldehyde nanocomposites were synthesized via in situ polymerization by incorporation of silicon coupling agent with terminal amino groups (SA) as the compatibilizer. The results showed that addition of SA coupling agent led to much more efficient grafting of UF molecules on the GN surface with high layer thickness by formation of hydrogen bonding, and thus complete exfoliation and uniform dispersion of GN were achieved for the composites. Compared with neat UF, the addition of 1.0 wt% GN resulted in a roughly 25% increase in tensile strength and 12% increase in impact strength; meanwhile the impact fracture surfaces of the composite showed obvious ductile fracture characteristics, indicating the reinforcing and toughening effect of GN on the UF matrix. With increasing GN content, the storage modulus, glass transition temperature and crosslinking density of UF increased, while the tan δ_max decreased, suggesting that a double crosslinking network structure with GN centered crosslinking point and chemical crosslinking point of UF molecular chains formed, leading to improvement in the stiffness of the composites. The present work showed promising potential for developing high performance UF resin on an industrial scale. © 2017 Society of Chemical Industry     

Density of solutions of formaldehyde in water and alcohols

Formaldehyde is an important chemical that is mostly handled in aqueous solutions, which generally also contain methanol; furthermore, also solutions of formaldehyde in other alcohols are used. The density of these solutions is an important thermophysical property. The available models of the density of formaldehyde-containing solutions, however, all have shortcomings, such as a poor accuracy or a limited range of applicability. Therefore, in the present work, a new model of the density in systems of the type (formaldehyde + water + alcohol) was developed. The alcohols that are presently included in the new model are methanol, 1-propanol, and isoprenol; an extension to other alcohols is straightforward. The model was developed using literature data and extensive new density data measured in this work covering binary, ternary, and quarternary solutions of formaldehyde in water, methanol, 1-propanol, and isoprenol at temperatures of $283-333$ K and formaldehyde concentrations of 0.06 − 0.30 g g⁻¹.     

大气压介质阻挡放电降低纯棉织物中甲醛污染

如何降低纯棉织物中的甲醛污染已成为当前的重大研究课题.目前使用的甲醛清除剂虽然对降低纯棉织物中甲醛污染有一定的效果,但都存在各自的缺陷,如使纺织品耐久定型性下降,染色织物经处理后褪色严重等等.为了解决这一问题,寻找一种更加理想的手段,开展了利用大气压下介质阻挡放电技术降低纯棉织物中甲醛污染的研究.通过采取不同的工艺参数,研究了大气压介质阻挡放电技术对纯棉织物中甲醛污染降低的效果;大气压下介质阻挡放电技术降低甲醛污染的物理化学过程.检测方法采取GB/T2912.1-1998<纺织品中甲醛的测定第一部分:游离水解的甲醛(液相萃取法)>.通过实验可以确定,大气压下介质阻挡放电对降低纯棉织物中的甲醛污染有一定的效果.     

光催化型过滤器分解有机化合物的实验研究

以TVOC及甲醛为测试对象对光催化型过滤器分解VOCs的性能进行了实验测试。结果显示:光催化型空调过滤器能有效分解VOCs,能在较短的时间内(12h)使室内VOCs的浓度达到GB/T-18883-2002的要求;其平均反应速率及分解效率随着过滤器层数的增加而增加,并且其分解效率随面风速的增加而略有降低(当面风速从0.42m/s增加至0.8m/s时,在第3小时,分解效率下降了约5%);对于室内VOCs浓度较低的民用建筑,光催化分解过程中的反应速率与反应浓度成正比。