Evaluation of VOC emission and sorption characteristics of low-VOC adhesive-bonded building materials

To reduce the risk of indoor air pollution caused by synthetic building materials, low-volitile organic compounds (VOC) building materials, including adhesives, are commonly used in building construction. Although adhesives do not directly contact indoor air, they affect VOC mass transfer at the surface of finishing materials by diffusion. This study investigates VOC emission and sorption behaviors of building materials with low-VOC adhesives. Small chamber emission and sorption experiments were designed in parallel to field measurements to examine the onsite VOC emission and sorption rates of adhesive-bonded building materials. It was found that the onsite emission rates from a wallpaper composite (polyvinyl chloride wallpaper?+?paper adhesive?+?gypsum board) were higher than the emission rates detected in the small-scale chamber, which demonstrates the possible sorption effect of the wallpaper composite. The results of the sorption chamber experiment confirm that the wallpaper is a sorptive building material and that the bonding of wallpaper to gypsum board increases the sorption and re-emission rates. These results indicate that even though low-VOC adhesive-bonded materials are used, additional indoor air quality control techniques should be applied to minimize re-emission by sorption processes over long periods of time.     

建材VOC散发过程模拟与传质参数测定新方法

建材中挥发性有机化合物(VOC)的散发是一个复杂传质过程。为准确把握传质特性,首先建立了一套描述干建材散发行为的显性完全解析模型,适用于模拟对人体最不利的无换气情况;代入有关文献中的传质参数预测了环境舱浓度,与文献中对应的实验数据及数值算法预测值吻合良好。然后基于对模型的分析提出一套简便快捷的实验方法,能够利用不同VOC背景值下干建材在密闭舱中散发的平衡浓度或逐时浓度,求取预测散发过程的4个重要的传质参数:可散发浓度C₀、扩散系数D、分配系数K和对流传质系数h_m;实验部分测算了两类密度板中甲醛散发的C₀、D、K、h_m,代入数值算法预测了密闭舱和直流舱的环境舱浓度,与实验数据吻合良好。该套模型和测定方法能够应用于建材散发的模拟研究。     

Measurement of 2-ethyl-1-hexanol emitted from flooring materials and adhesives

It has been reported that 2-ethyl-1-hexanol (2E1H) was emitted through hydrolysis between di-2-ethylhexyl phthalate used as plasticizer in flooring material and moisture generated from a strongly alkaline material such as concrete slab. The purpose of this study was to clarify the relationship between diffusion of 2E1H in flooring material and 2E1H emission rate from floor surface. In this study, we measured 2E1H emitted from floor paper, poly(vinyl chloride) (PVC) tile, cushion floor and carpet for 200,?days and effective diffusion coefficients for 2E1H in various flooring materials were measured. Effective diffusion coefficients of 2E1H for cushion floor and PVC tile were 115?×?10^?9 and 7.8?×?10^?9 m²/s, respectively. Emission rate of 2E1H emitted from flooring material significantly depends on the kind and shape of flooring materials and was influenced by the effective diffusion coefficient for 2E1H of flooring material. Emission rates of 2E1H from floor surface varied with the amount of 2E1H and resin present in the adhesive. When carpet was attached to the flooring material with high water content using adhesive, emission of 2E1H significantly increased. The results show that primary and secondary emissions of 2E1H from the adhesive influence the emission rate of 2E1H for flooring material.     

Influence of VOC and formaldehyde emission from tile adhesives on their indoor concentrations in buildings

Volatile organic compounds (VOC) and formaldehyde emitted from building materials are considered to be one of the main causes of indoor air pollution in buildings. To reduce indoor pollutant concentrations, new installation methods for wall papers and flooring materials have been widely introduced to the construction field, including a nonadhesive floating method. However, adhesives are still widely used to install wall tiles or floor tiles on areas such as kitchens, bathrooms, and showers. The objective of this study was to investigate the influence of tile adhesive emissions on indoor air quality. The VOC and formaldehyde emission rates from two different types of tile adhesives, a conventional adhesive and a low-VOC emission adhesive, were measured using small emission test chambers. Full scale experiments were also carried out in three identical test rooms in a building. One wall of each room was finished with wallpaper in Test Room 1 and with tiles in Test Rooms 2 and 3. The other walls and ceilings were finished with wall papers in all test rooms. Wall tiles of Test Room 2 were installed with the conventional adhesive, while those of Test Room 3 were installed with the low-VOC emission adhesive. The indoor VOC concentrations in Test Room 2 were significantly higher than those in Test Room 3 due to a significantly higher VOC emission from the conventional tile adhesive. Even though the adhesives were applied under the finishing materials, investigation revealed that the adhesives were the most dominant contributor of indoor VOC concentration.     

Influence of water content in sub-flooring materials using adhesive on chemical compounds emission

Indoor air pollution is caused predominantly by emission of primary pollutants from building materials or finishing materials. Recently, there has been increasing interest in the new secondary pollutants caused by chemical reaction of the primary pollutants. In this study, the pollutants emitted from poly(vinyl chloride) (PVC) flooring material were measured, and 2-ethyl-1-hexanol (2E1H) and volatile organic compounds (VOCs) emitted from composite building materials made of PVC flooring material used as a self-leveling flooring were measured to identify the mechanism of emission of 2E1H. The moisture sorption isotherm was measured with a Magnetic Suspension Balance to examine the moisture content of the self-leveling flooring material and its effect on emission of 2E1H. 2E1H was emitted from the PVC flooring material through hydrolysis or oxidation of di-2-ethylhexyl phthalate (DEHP). The composite building material including the self-leveling flooring material emitted more 2E1H through hydrolysis over time. It was determined that liquid prevails in the self-leveling flooring material when the water content is higher than 4% and vapor prevails when the water content is lower than 4%. The prevailing liquid in the flooring material contributes to the increased emission of 2E1H and the prevailing vapor in the material did not cause increase in emission of 2E1H. It is considered that control of water in the self-leveling flooring material or concrete slab is very important in order to inhibit emission of 2E1H through hydrolysis of DEHP on the floor.     

湿建筑材料中VOC释放规律

湿建筑材料中挥发性有机物（volatile organic compound,VOC）释放过程是一个非常复杂的物理过程,其中包括材料本身的干燥过程以及质量传递过程。为探讨湿建筑材料中VOC的释放机理,本文建立了描述湿建筑材料中VOC释放过程的物理模型,模型考虑了湿建筑材料中VOC释放过程中的干燥过程,并用该模型分析了VOC的饱和蒸气压在整个VOC释放过程中的作用机理。把该模型的计算结果与VB模型求解结果、Yang等建立的模型求解结果以及实验结果进行了对比,得出干燥模型计算结果与Yang等建立的模型计算结果以及实验数据吻合较好,较VB模型能更准确地描述VOC的扩散过程。通过不同工况下环境小室的实验数据,对温度与相对湿度对湿建筑材料中VOC释放过程的影响规律进行了分析。     

测定建材散发关键参数的密闭舱C-history方法与其他方法的比较

室内建材中散发的挥发性有机物(VOC)所引起的空气品质问题显著影响着人们的健康、舒适和工作效率。目前有不少测定建材VOC散发3大关键参数(初始可散发浓度、分配系数和扩散系数)的密闭舱方法,本文将最近提出的密闭舱C-history方法与其他密闭舱测定散发关键参数的方法(多次散发回归法、多平衡态回归法及多气固比法)进行了比较研究。结果表明,密闭舱C-history方法与其他测试方法对于所选建材中目标VOC散发关键参数测定的最大偏差均不超过25%。而密闭舱C-history方法只需在密闭舱中对建材执行一次散发过程即可求得上述3大关键参数,通常不超过3d,大大节省了实验时间,因而比其他方法更便于工程应用。     

Study on the characteristics of pollutant emission from floor adhesive formulated using red clay

Development of building materials has been actively underway using natural materials in order to improve indoor air quality. Among such natural materials, red clay has been frequently used for development of building materials. In this study, 138 different environment-friendly adhesives were analyzed, aiming at determining the performance of adhesives prepared using red clay. The emission factors of formaldehyde and total volatile organic compounds (TVOCs) were examined for adhesives that had acquired the environment-friendly building materials certification before comparing with the characteristics of emission from red clay containing adhesives. In order to analyze pollutant reduction performance of the red clay adhesive, we exposed the clays to pollutants of formaldehyde and volatile organic compounds (VOCs), and analyzed the emission reduction performance due to adsorption on the red clay. The analysis results demonstrated the emission reduction performance of formaldehyde. Lastly, we compared the pollutant emission factors from multilayer building materials using red clay adhesive and general materials. The comparison results showed low emission factors for formaldehyde and VOCs. These results can be used as the basic data on performance characteristics of red clay adhesive.     

木家具表面挥发性污染物散发传质特性

木家具表面挥发性污染物的散发是一类污染环境的复杂传质行为。为准确把握传质特性,首先建立了一套更完善的新式完全解析模型,综合考虑了两大传质机理(扩散、对流)、气候箱中污染物阻力、背景浓度和进气浓度,同时适用于无换气或换气条件下的模拟研究;例如,预测气候箱或木家具中污染物浓度变化,评价传质速率或散发量,以及估算室内浓度达标时限。然后通过对模型的分析提出了一套简便快捷的新式实验法,利用木家具在换气箱中散发的逐时浓度,一并求取目标污染物的3个重要传质参数:可散发量ρ₀、扩散系数δ和分配系数β。实验部分使用该换气箱法测算了某密度板家具中甲醛和总挥发性有机化合物的ρ₀、δ和β,与文献中基于密封箱的数据处理方法所得结果的变异系数小于5%,并有效避免了出现负压等密封箱采样可能导致的潜在问题。将传质参数代入数值算法预测了密封箱和换气箱中木家具散发挥发性污染物的浓度变化,与实验测量的数据吻合良好。该模型和方法能够准确预测或测定木家具表面挥发性污染物传质特性。     

直流舱测定材料VOC散发关键参数的浓度轨迹法

室内及车内环境中材料散发的挥发性有机化合物(VOC)是造成空气品质低劣的重要因素之一, 显著影响着人们的舒适度和身体健康。材料VOC散发特性由3个关键参数表征:初始可散发浓度C₀、扩散系数D_m和分配系数K。测定上述散发关键参数是研究材料VOC散发规律进而预测人体暴露和健康风险的基础。基于目前应用最广泛的直流舱中材料VOC的散发过程, 提出了同时测定C₀和D_m的浓度轨迹法。该方法通过预设K值, 然后对环境舱浓度的对数进行线性拟合, 根据斜率和截距获得关键参数C₀和D_m。敏感性分析表明, 不同的K值对测定的C₀和D_m值影响很小。通过对文献中的直流舱散发实验数据进行处理, 结果表明该测定方法具有较高的精度。     

Measurement of constant drying rate of wet material placed in a fluidized bed of inert particles under reduced pressure

The objective of this study is to estimate the drying characteristics of a relatively large material immersed in a fluidized bed under reduced pressure by measuring the constant drying rate. The constant drying-rate period in a fluidized bed under reduced pressure is difficult to measure because it is extremely short. To maintain the constant drying-rate period, distilled water is directly supplied to the drying material. Through our experiment, the heat transfer coefficient of the material surface was also determined. The results were compared with data on hot air drying. The constant drying rate is higher for fluidized bed drying than for hot air drying. It suggests that the heat transfer coefficient on the surface of the drying material is much larger for fluidized bed drying than for hot air drying. For fluidized bed drying, the effect of pressure in the drying chamber on the heat transfer coefficient is slight at the same normalized mass velocity of dry air (G/G_mf). The temperature difference between the inside of the drying chamber and the drying material is much smaller for fluidized bed drying than for hot air drying. The constant drying rate increases as the pressure in the drying chamber decreases.     

Cold weather installation of wood flooring by adhesive bonding and its impact on indoor air quality

This study discusses the effect of installation of wood flooring by adhesive bonding under cold weather conditions on indoor air quality (IAQ) and analyzes an onsite strategy that can ensure the adhesion strength of the wood flooring and improve IAQ. To examine the temperature effects of adhesive bonding on volatile organic compound (VOC) emissions from wood flooring, the emission rates from flooring composites were compared with those from adhesive and plywood flooring as individual materials under temperature variations in a small-scale chamber. In addition, the effect of strategies, including room heating to enhance adhesion performance, and the ventilation on material emissions and indoor concentrations, were examined in onsite apartment units equipped with a radiant floor heating system. The results of the small-scale chamber test showed that VOC emissions increased notably when the temperature was elevated, particularly in the adhesive-bonded plywood flooring compared to plywood flooring alone. The results of the onsite field test showed that the flooring bonded onto the radiant floor heating system, which supplied direct heat to the flooring, caused emission of a large amount of VOCs due to the combined effects of the bonding installation and temperature-dependent characteristics. Overall, the results indicate that heating the room in conjunction with ventilation is an effective strategy to ensure adhesion strength and to improve IAQ under cold weather adhesive bonding conditions when the material temperatures can be properly maintained.     

Modeling volatile organic compounds sorption on dry building materials using double-exponential model

A double-exponential surface sink model for VOCs sorption on building materials is presented. Here, the diffusion of VOCs in the material is neglected and the material is viewed as a surface sink. The VOCs concentration in the air adjacent to the material surface is introduced and assumed to always maintain equilibrium with the materialphase concentration. It is assumed that the sorption can be described by mass transfer between the room air and the air adjacent to the material surface. The mass transfer coefficient is evaluated from the empirical correlation, and the equilibrium constant can be obtained by linear fitting to the experimental data. The present model is validated through experiments in small and large test chambers. The predicted results accord well with the experimental data in both the adsorption stage and desorption stage. The model avoids the ambiguity of model constants found in other surface sink models and is easy to scale up.     

Effect of the radiation surface on temperature and NOx emission in a gas fired furnace

A significant increase in the efficiency of furnaces burning natural gas is achieved by increasing the radiation heat transfer from the flame. In this study, the effect of cylindrically shaped additional radiation surface called, filling material (FM), on emissions and temperature distribution in the combustion chamber (CC) was investigated experimentally. Experiments were carried out on a fire tube water heater described in the standard EN 676 for the firing rates of 58, 87 and 116 kW. Two diameters of the filling materials, 25 and 30 cm, and two lengths of 20 and 40 cm were considered. The flame temperature and nitrogen oxide (NO) emission were measured for different positions and geometries of the filling material in the combustion chamber. The flame temperature and the temperature drop of the flame in the back flow increased with the increasing diameter and length of the filling materials compared to the case without filling material. It was observed that the filling material with the larger diameter increased the heat transfer rate in the back flow compared to the case without filling material. The in-furnace measured NO concentration was in good agreement with NO concentration in the well-mixed flue gas. The 20 cm long filling materials decreased the NO emission. Increased length of the filling material resulted in increased the NO emission.     

木家具中挥发性有机物的散发传质特性

建立了新的木家具挥发物散发完全解析模型,全面考虑了各种传质机理和污染物阻力,同时适用于有无换气的模拟. 经分析模型提出了一套简捷的新实验方法,利用同一家具在密封箱中若干释放周期的稳态和实时浓度,同时求取目标污染物的4个重要传质参数：可散发量C0、扩散系数D、分配系数K和对流传质系数h. 测定了(23±0.5)℃、相对湿度45%±5%下某家具中甲醛和总挥发物的传质参数,甲醛C0=4994 mg/m3, D=4.05′10-10 m2/s, K=499, h=1.4′10-3 m/s;总挥发物C0=19939 mg/m3, D=2.12′10-10 m2/s, K=1001, h=5.0′10-4 m/s,均落于常见范围,与其他方法所得对应参数的变异系数小于0.5%. 将参数代入数值算法预测有无换气条件下气候箱中的散发浓度,与实验值的平均偏差小于3.5%.     

Chemical composition and mass emission factors of candle smoke particles

The aim of this study is to investigate the physical and chemical properties of particle emissions from candle burning in indoor air. Two representative types of tapered candles were studied during steady burn, sooting burn and smouldering (upon extinction) under controlled conditions in a walk-in stainless steel chamber. Steady burn emits relatively high number emissions of ultrafine particles dominated by either phosphates or alkali nitrates. The likely source of these particles is flame retardant additives to the wick. Sooting burn in addition emits larger particles mainly consisting of agglomerated elemental carbon. This burning mode is associated with the highest mass emission factors. Particles emitted during smouldering upon extinction are dominated by organic matter. A mass closure was illustrated for the total mass concentration, the summed mass concentration from chemical analysis and the size-integrated mass concentration assessed from number distribution measurements using empirically determined effective densities for the three particle types.     

Performance Optimization of a Brick Dryer Using Porous Simulation Approach

In the present study, an innovative method for an accurate simulation and design of a chamber dryer used in the brick/ceramic industry has been proposed. A thorough investigation of currently used dryers is conducted and optimization criteria are detected and discussed. Three-dimensional modeling of the chamber dryer has been performed. In the second step, from the result of 3D modeling, the critical values for heat transfer coefficient are obtained. The governing equations for a two-dimensional brick as a porous solid are derived by combining conservation laws and Fourier's law for heat conduction and Darcy's and Fick's laws for mass diffusion in porous material. The set of partial differential equations governing heat and mass transport in a single brick together with the respective temperature and humidity boundary conditions have been solved numerically based on finite difference method. Finally, an efficient scheme for the air circulation devices, inlet air temperature and humidity, burner characteristics, flow rates, and drying process control have been proposed for a typical industrial-scale brick dryer.     

流化床用树脂基球形活性炭及其VOCs吸附性能

以聚苯乙烯树脂为原料,采用水蒸气活化、氯化锌活化及水蒸气?氯化锌协同活化方法制备了3种流化床用树脂基球形活性炭,采用固定床反应器考察了活性炭对乙酸乙酯的动态吸附行为,对比了其传质区长度,并利用Yoon?Nelson模型对实验数据进行了拟合. 结果表明,3种活性炭的摩擦磨损指数均小于0.1%,耐磨性能出色,物理、化学协同活化活性炭比表面积高达1702.49 m2/g,对二甲苯的静态吸附容量达0.86 g/g.     

A unified conjugate mass transfer model of VOC emission

This paper develops a unified conjugate mass transfer model for VOC (Volatile Organic Compound) emission, which implies conjugate boundary condition for mass transfer at the material-air interface. Thus, no special treatment is needed at the material-air interface and numerical methods for conjugate heat transfer problem can be applied directly. The material-air partition coefficient has been taken into account and its effect is the same as specific heat in the energy equation. The equivalent diffusion coefficient in the material K_maD_m instead of D_m characterizes the rate of mass transfer. The ratioK _ma D _m /D _a indicates whether VOC emission is controlled by the internal diffusion or not. The equivalent air-phase initial concentration C₀/K_ma determines the order of maximum concentration in the air. VOC emission contains two stages: the initial stage and the pseudo-steady stage when the emission rate nearly equals mass rate through the outlet of the air. Diffusion coefficient of VOC in the material has a significant effect on VOC emission in the two stages. The effect of partition coefficient on VOC emission depends on the value of K_maD_m/D_a.