Effects of plasticizers on the properties of oat starch films

Oat starch films were prepared by casting using glycerol, sorbitol, glycerol–sorbitol mixture, urea and sucrose as plasticizers. The effects of these plasticizers on the microstructure, moisture sorption, water vapor permeability (WVP) and mechanical properties were investigated using films stored under a range of relative humidities. The plasticizer type did not affect significantly (p ≤ 0.05) the equilibrium moisture content of films, except at 90% relative humidity (RH). Films without plasticizer adsorbed less water and showed higher WVP than plasticized ones, indicating the antiplasticizing effect observed in this work. In general, a decrease in stress at break and Young's modulus and an increase in strain at break were observed when RH increased in all film formulations. Films without plasticizer showed higher stress at break values than the plasticized ones and presented stable strain at break under a range of RH. Sucrose films were the most fragile at low RH while glycerol films were the most hygroscopic.     

Understanding the drying shrinkage performance of alkali-activated slag mortars

In this work, drying shrinkage of four alkali-activated slag (AAS) mortars, prepared using various types/dosages of activator, was characterized at four different levels of relative humidity (RH) and two drying regimes (i.e. direct and step-wise drying). The results show that drying shrinkage values of AAS are significantly dependent on the drying rate, as AAS shrinks more when the RH is decreased gradually, instead of directly. At high RH, the drying shrinkage of AAS exhibits a considerable visco-elastic/visco-plastic behavior, in comparison to ordinary portland cement (OPC). It is concluded that the cause of high-magnitude shrinkage in AAS mortar is due to the high visco-elastic/visco-plastic compliance (low creep modulus) of its solid skeleton. Furthermore, the activator affects the shrinkage behaviors of AAS by influencing the pore structure and mechanical properties.     

Investigation of the effect of relative humidity on polymers by depth sensing indentation

Stereolithography (SL) resins absorb varying amounts of moisture dependent on the relative humidities, which can significantly affect the mechanical properties. In this work, the influence of relative humidity (RH) on the mechanical behaviour of an SL resin is investigated using depth sensing indentation (DSI). The samples were conditioned by two methods. In the first method, samples were pre-conditioned at 33.5, 53.8, 75.3 and 84.5% RH using saturated salt solutions. These preconditioned samples were tested at 33.5% RH, using a humidity control unit (HCU) to control RH in the DSI system. In the second method, samples were conditioned and tested at 33.5, 53.8, 75.3 and 84.5% RH by regulating humidity in the DSI system using the HCU. Temperature was kept constant at 22.5 °C for the conditioning and DSI testing. It was seen that hardness and modulus decreased with increasing RH and conditioning time but recovered significantly when tested after drying. This study demonstrates that RH needs to be taken into account during the DSI testing of polymers.     

超细球形空心磷铵灭火粉的制备与应用

采用气流和离心两种喷雾干燥方法制备超细球形空心磷酸二氢铵灭火粉,并添加甲基含氢硅油乳液、氟碳表面活性剂FK-510、羧甲基纤维素钠对粉体进行原位改性。结果表明:气流喷雾制备出的颗粒较细但不均匀,而离心喷雾制备出的颗粒均匀却较粗;表面活性剂甲基含氢硅油、FK-510的添加使粉体疏水性得到了很大提高;羧甲基纤维素钠的添加能使提高颗粒的球形度以及表面光滑度;喷雾干燥过程选择温度较低以及空气相对湿度较小的大气条件有利于制备高品质灭火粉。另外灭火实验结果表明:喷雾干燥制备的超细球形空心磷酸二氢铵灭火粉灭火效果明显优于某些市售灭火粉。     

Breath Figures法制备漆酚铜聚合物多孔膜

以漆酚铜聚合物(UCP)有机溶液为铸膜液,采用Breath Figures法制备漆酚铜聚合物多孔膜,探讨了溶剂、环境相对湿度和潮湿气体流速等因素对多孔膜形貌的影响,并使用红外光谱和扫描电镜等进行表征。结果表明,以二硫化碳为溶剂,在静态(潮湿气体流速为0mL/min,湿度为95%)或动态(潮湿气体流速为400mL/min,湿度为85%)时,均可制得孔分布均匀、孔型规整、优良耐热性和耐酸碱性的疏水性UCP多孔膜,其平均孔径分别为1.5和0.85μm。     

聚乙烯醇/海藻酸钠复合膜性能的正交优化

目的提高海藻酸钠/聚乙烯醇复合膜的断裂伸长率。方法利用溶液流延制备系列复合薄膜,采用正交设计方法研究海藻酸钠和聚乙烯醇的质量比、甘油用量和Zn O用量等3个因素对复合膜拉伸强度和断裂伸长率及其他性能的影响。结果甘油用量显著影响海藻酸钠/聚乙烯醇复合膜的断裂伸长率,其影响程度高于其他2个因素;Zn O和甘油的加入使得复合膜的拉伸强度显著降低。结论采用正交设计方法有利于研究各因素对复合膜物理性能的影响,为进一步的复合膜研究提供参考。     

Effects of production process and plasticizers on stability of films and sheets of oat starch

The main disadvantage of biodegradable starch-based films is their hydrophilic character, which leads to low stability when these materials are submitted to different environmental conditions. The higher lipid content (1.36%) of oat starch compared to other traditional starches could impart more hydrophobic characteristics to its films, thereby increasing stability. The objective of this work was to investigate the behavior of oat starch films (produced by casting) and sheets (produced by extrusion), plasticized with urea, glycerol or sorbitol, and conditioned at 11, 57, 76 and 90% relative humidity (RH). In general, the increase of RH results in a decrease of stress and an increase of strain at break, independent of the type of plasticizer. The Tg of materials plasticized with polyols was similar. The extruded sheets were more permeable to water vapor than the casted films. Films containing urea presented a relative crystallinity (5.14%) four times lower when compared with the other films, but the same behavior was not observed for sheets. The lipid content of oat starch was not high enough to avoid altering of mechanical properties as a function of RH. When the two processes (casting and extrusion) applied for materials production were compared, similar trends were observed on the final effects.     

Electrical and morphological characterization of polyaniline/sulfonated poly(arylene ether sulfone) composite films

Electrically conductive polyaniline/sulfonated poly(arylene ether sulfone) (PANI/BPS-35) composites were prepared. The influence of humidity and temperature on electrical conductivity of 20 wt% polyaniline containing composite films was tested. The conductivity increment from 17 mS/cm to 44 mS/cm was observed when the temperature increased from 24 °C to 80 °C at 50% relative humidity (RH). The maximum conductivity was 53 mS/cm at 80 °C and 70% RH. Aluminum (Al) and gold (Au) contacts were deposited onto PANI/BPS composite films and their contact properties have been investigated. While Al contacts behave like Schottky type contact, Au contacts showed nearly ohmic characterization. Scanning electron microscopy technology was used to investigate the morphology of PANI/BPS-35 composite films.     

A surface acoustic wave humidity sensor with high sensitivity based on electrospun MWCNT/Nafion nanofiber films

Humidity detection has been widely used in a variety of fields. A humidity sensor with high sensitivity is reported in this paper. A surface acoustic wave resonator (SAWR) with high resonance frequency was fabricated as a basic sensitive component. Various nanotechnologies were used to improve the sensor's performance. A multi-walled carbon nanotube/Nafion (MWCNT/Nafion) composite material was prepared as humidity-sensitive films, deposited on the surface of an SAWR by the electrospinning method. The electrospun MWCNT/Nafion nanofiber films showed a three-dimensional (3D) porous structure, which was profitable for improving the sensor's performance. The new nano-water-channel model of Nafion was also applied in the humidity sensing process. Compared to other research, the present sensor showed excellent sensitivity (above 400 kHz/% relative humidity (RH) in the range from 10% RH to 80% RH), good linearity (R(2) > 0.98) and a short response time (～3 s@63%).     

乳清蛋白膜对花生氧化酸败抑制效果的研究

采用乳清浓缩蛋白(WPC)膜液对烤花生进行涂膜保藏,经加速酸败试验对比了涂膜花生和未涂膜花生的保鲜效果,考察了蛋白和甘油质量比、环境相对湿度和涂膜厚度对花生保鲜效果的影响。结果表明:乳清蛋白涂膜能够延缓花生的氧化酸败进程,当蛋白和甘油质量比为60∶40时,涂膜液具有更好的阻氧保鲜效果;相对湿度为53%和涂膜厚度为5层时,能够增强花生的保藏效果。     

Effect of different atmospheres on the electrical stabilization of NiO films

Sputtered nickel oxide (NiO) films have a wide range of applications including their use in transparent conductive anodes for organic light-emitting diodes (OLEDs) where stable electrical properties are essential. Unfortunately, NiO films show electrical aging phenomenon in air. In the present experiments, the phenomenon of aging was investigated in different atmospheres including H₂, CO, O₂, CO₂, N₂, and Ar together with varying the humidity. It was found that NiO films were relatively stable in Ar but very unstable in H₂, CO and humid argon atmospheres. The aging rate increased rapidly as the humidity was increased from 2 to 20 relative humidity (RH) and became constant from 20 to 40 RH.     

Influence of curing at different relative humidities upon compound reactions and porosity in Portland cement paste

The reduction in relative humidity within drying concrete depends mainly on the depth from the exposed surface, exposure duration, temperature and environmental humidity; this limits hydration and coarsens pore structure, thus impairing durability. OPC paste, of 0.59 water/cement ratio, was cured for 2 days and then exposed to controlled relative humidity environments. After 14 and 90 days exposure, hydration of the individual compounds was measured using quantitative X-ray diffraction and thermogravimetry. Methanol adsorption was used to monitor porosity and gel formation. Even a small drop in relative humidity below 95% r.h. significantly limited cement hydration. Gel porosity increased with amount of hydration and, for a given level of hydration, decreased with drying. Curing below 80% r.h. produced a coarsened pore structure with a large-diameter porosity three times greater than that obtained with saturated curing.     

How does hydration affect the mechanical properties of wine stoppers?

Data related to the comparison of the mechanical properties of the different stoppers used in the wine industry are scarce. This study aims at comparing the effect of hydration (from 0 to 100 % relative humidity at 25 °C) on the mechanical properties of four widely used types of stoppers: natural corks, agglomerated corks, technical stoppers and synthetic (co-extruded) stoppers. For both natural and agglomerated corks, the Young’s modulus was significantly and similarly affected by hydration, with a constant plateau value up to 50 % relative humidity (RH) and a mean value around 22 and 14 MPa, respectively. For higher RH, the increase in water content leads to a decrease in the material rigidity (Young’s modulus <10 MPa), which is attributed to water clusters formation between polymer chains. Technical stoppers revealed a similar profile, but with a much smaller impact of the water content and with overall lower Young’s moduli values, around 5 MPa, throughout the RH range. The stiffness of synthetic closures was not affected by hydration, in agreement with the hydrophobic behavior of polyethylene. Differential scanning calorimetry and dynamic mechanical thermal analysis allowed us to identify a glass transition temperature (T _g) in cork (around 0 °C), and another one in agglomerated cork and technical stoppers (close to ?45 °C, corresponding to additives). All together, for the first time the data highlight the comparative mechanical properties of such materials of the wine industry, and the progressive loss of the “cork-like” behavior of cork composites when other components are mixed with cork.     

Effect of crystallization on humidity sensing properties of sol-gel derived nanocrystalline TiO2 thin films

In the present work, we describe the effect of crystallization on humidity sensing properties of nanocrystalline TiO₂ thin films prepared by sol-gel techniques. Here, we report an enhancement in the relative humidity (RH) sensitivity just after the crystallization at 375 °C, which is attributed to increased surface activity near crystallization and lower crystallite size. After crystallization, the RH sensitivity was found to decrease with increasing grain size. The complex impedance of the sensor, measured using impedance spectroscopy, fits well with an equivalent circuit consisting of inter-granular resistance and capacitance in parallel. It was found that with the change in RH, only resistance changes significantly, when compared with the capacitance.     

Mucoadhesive Polymeric Hydrogels for Nasal Delivery of Acyclovir

The study evaluated different mucoadhesive polymeric hydrogels for nasal delivery of acyclovir. Gels containing poly-N-vinyl-2-pyrrolidone (PVP) were prepared with crosslinking achieved by irradiation with a radiation dose of 15 kGy being as efficient as 20 kGy. Gels containing chitosan and carbopol were also evaluated. The mucoadhesive properties of gels were measured by a modification of a classical tensile experiment, employing a tensile tester and using freshly excised sheep nasal mucosa. Considering the mucoadhesive force, chitosan gel and gel prepared with 3% PVP in presence of polyethylene glycol (PEG) 600 were the most efficient. The in vitro drug release depended on the gel composition. Higher release rates were obtained from PVP gels compared to chitosan or carbopol gels. The release rate of drug from PVP gels was increased further in presence of PEG or glycerol. Histopathological investigations proved that the PVP was a safe hydrogel to be used for mucosal delivery. The PEG in gel formulations caused less damages to the nasal mucosal compared to formulation containing glycerol.     

Mucoadhesive polymeric hydrogels for nasal delivery of acyclovir

The study evaluated different mucoadhesive polymeric hydrogels for nasal delivery of acyclovir. Gels containing poly-N-vinyl-2-pyrrolidone (PVP) were prepared with crosslinking achieved by irradiation with a radiation dose of 15 kGy being as efficient as 20 kGy. Gels containing chitosan and carbopol were also evaluated. The mucoadhesive properties of gels were measured by a modification of a classical tensile experiment, employing a tensile tester and using freshly excised sheep nasal mucosa. Considering the mucoadhesive force, chitosan gel and gel prepared with 3% PVP in presence of polyethylene glycol (PEG) 600 were the most efficient. The in vitro drug release depended on the gel composition. Higher release rates were obtained from PVP gels compared to chitosan or carbopol gels. The release rate of drug from PVP gels was increased further in presence of PEG or glycerol. Histopathological investigations proved that the PVP was a safe hydrogel to be used for mucosal delivery. The PEG in gel formulations caused less damages to the nasal mucosal compared to formulation containing glycerol.     

The Stability of Theophylline Tablets with a Hydroxypropylcellulose Matrix

The behavior of 40:60 anhydrous theophylline/hydroxypropylcellulose (HPC) direct compression tablets obtained using a variety of hydroxypropylcelluloses with low or medium-high degrees of substitution (L-HPCs and HPCs, respectively) was determined immediately following their preparation and after storage for 6 months at 20°C and a relative humidity (RH) of either 70.4% or 93.9%. The lower relative humidity did not bring about hydration of the active principle in any formulation, but the higher relative humidity totally hydrated the drug in all except one L-HPC formulation, in which hydration remained incomplete. Both relative humidities caused significant tablet swelling, with L-HPC formulations being more affected than HPC formulations. Drug release was slowed by hydration of the active principle, but accelerated with tablet swelling. The lower relative humidity caused significant alteration of drug release characteristics in only two L-HPC formulations, release from which was accelerated, while the higher relative humidities only failed to cause such alterations in two HPC formulations, with release from all except one of the others slowed (in the exceptional formulation, which exhibited incompletely hydrated theophylline and the greatest swelling of all, release was accelerated).     

The stability of theophylline tablets with a hydroxypropylcellulose matrix

The behavior of 40:60 anhydrous theophylline/hydroxypropylcellulose (HPC) direct compression tablets obtained using a variety of hydroxypropylcelluloses with low or medium-high degrees of substitution (L-HPCs and HPCs, respectively) was determined immediately following their preparation and after storage for 6 months at 20°C and a relative humidity (RH) of either 70.4% or 93.9%. The lower relative humidity did not bring about hydration of the active principle in any formulation, but the higher relative humidity totally hydrated the drug in all except one L-HPC formulation, in which hydration remained incomplete. Both relative humidities caused significant tablet swelling, with L-HPC formulations being more affected than HPC formulations. Drug release was slowed by hydration of the active principle, but accelerated with tablet swelling. The lower relative humidity caused significant alteration of drug release characteristics in only two L-HPC formulations, release from which was accelerated, while the higher relative humidities only failed to cause such alterations in two HPC formulations, with release from all except one of the others slowed (in the exceptional formulation, which exhibited incompletely hydrated theophylline and the greatest swelling of all, release was accelerated).     

Effects of humidity changes on damping and stress relaxation in wood

Mechanical damping (tan ) and stress relaxation on pine veneer samples under stepwise humidity changes were investigated. The loss factor shows a transient peak every time the relative humidity (RH) of the surrounding atmosphere is changed. The effect appears to be associated with the diffusion of water molecules into or out of the material, the peaks being observed both when the sample is humidified (5%–85% RH) or subjected to drying. The results are supplemented by stress relaxation data obtained on similar specimens. Also in this case a higher relaxation rate is observed when the RH level around the sample is changed, the total stress decrease after several cycles being significantly larger than the corresponding value observed after the same period at the higher RH level.