可微波春卷系列研究之一微波春卷"浸湿"原因的探讨

研究了春卷水分的活度，水分含量，感官评定值和最大抗剪切强度的关系，确定了春卷皮的临界水分活度为０．４５，并对冷冻的预油炸春卷在微波重制时产生浸湿现象的原因进行了探讨。     

纤维间剪切结合强度的一种测量方法

以PAGE方程为基础,结合光散射系数测量技术,提出了一种测量纤维间剪切结合强度的新方法,并以针叶木为原料,研究了打浆和湿压对纤维剪切结合强度和结合面积的影响。实验结果表明,打浆对纤维键合结合强度没有影响,提高湿压对剪切结合强度有增大作用;提高打浆度和增大湿压对纸页抗张强度的提高主要是纤维相对结合面积增大的结果。     

机械木浆纤维形变性表征及其对纤维间结合性能的影响

针对不同木素含量的纤维原料,采用不同评价方法对其形变性能进行表征,包括纤维柔软性(F)、纤维横截面纵横比(AR)和纤维压溃指数(CI);同时围绕纤维形变性对纤维间结合性能以及手抄片物理强度的影响进行分析。结果表明,F、AR和CI都可以用来表征纤维的形变性,其中,当木素含量从24.28%减少到2.67%时,F表征的相对形变量为956.5%,数倍于其他两者,说明F这一指标表征的更为全面;随着F从0.516×10~(12)N~(-1)·m~(-2)增加到5.454×10~(12)N~(-1)·m~(-2),纸张中纤维间的相对结合面积(RBA)和剪切结合强度(b)增大,Page结合强度指数从3.60 N·m/g线性增加到84.07 N·m/g;在纸张成形过程中,可以通过改变纤维形变性能调节纸张强度和松厚度之间的对立关系。     

微波春卷“浸湿”原因的探讨

研究了春卷皮水分活度、水分含量、感官评定值和最大抗剪切强度的关系 ,确定了春卷皮的临界水分活度为 0 45 ,并对冷冻的预油炸春卷在微波炉重制时产生浸湿现象的原因进行了探讨     

水分含量对即食酥脆鲫鱼质构及色泽的影响

采用两段式脱水烤制方式开发即食酥脆鲫鱼,以质构和色泽为指标,结合感官评定,探讨了烤前水分含量(70%降至45%)及最终水分含量(11%降至3%)对酥脆鲫鱼质构和色泽的影响。结果表明:随着烤前水分含量的降低,硬度、咀嚼性、剪切力增大,但从70%降至55%变化不显著,进一步降低之后显著增大(p0.05),L*值减小,a*、b*值增大,从60%降至55%产品a*、b*值增加较显著(p0.05);随着最终水分含量的降低,硬度、剪切力增大,咀嚼性先增大后略微减小,弹性、内聚性及回复性减小,3%~5%变化不明显,L*值增大,a*、b*值减小,5%~9%之间差别不显著(p0.05)。结合感官评定确定烤前水分含量在55%,二次干燥之后最终水分含量为5%时产品品质最佳。     

水分对碱面条品质的影响

以武汉热干面(碱面条)为研究对象,研究不同水分添加量对碱面条品质的影响。采用流变仪和差示扫描量热仪研究面团的流变性质和热力学性质,同时对碱面条的剪切性质、拉伸性质以及吸水率进行测定。结果表明,随着水分添加量增大(20%～38%),碱面团的弹性下降,且吸热峰值逐渐向高温移动,焓值增加。同时,碱面条的硬度、拉伸强度、拉伸距离出现先增加后减小的现象。当水分添加量为30%时,其硬度、拉伸强度、弹性达到最大值,分别为730、73g和63 mm。此外,面条的吸水率随着面条中加水量的增大而增加。     

油莎豆的剪切力学特性

为选择适宜的油莎豆破碎设备,探究了脱皮前后油莎豆剪切力学特性变化。以油莎豆为试验原料,利用物性分析仪,在初步考察脱皮对油莎豆剪切特性影响基础上,分别探讨了水分含量、加载速率、加载方位和粒径等级对未脱皮和脱皮油莎豆破坏力、硬度和破坏能的影响。结果表明：脱皮对油莎豆的剪切特性存在影响;水分含量、加载速率、加载方位和粒径等级均对未脱皮和脱皮油莎豆的破坏力、硬度和破坏能具有显著影响。未脱皮和脱皮油莎豆的破坏力、硬度和破坏能随油莎豆水分含量增大以及粒径的减小而降低,随加载速率增加呈先增大后降低的趋势,并在加载速率为0.3 mm/s时获得较大值。在抗剪切能力上脱皮油莎豆X轴最大,Z轴次之,Y轴最小,未脱皮油莎豆Z轴最大,X轴次之,Y轴最小。此外,在相同的剪切条件下,脱皮油莎豆的破坏力、硬度和破坏能均远低于未脱皮油莎豆的。研究结果可为油莎豆加工机械改进和工艺条件制订提供必要的理论依据。     

纤维素纳米纤丝对电容器纸性能的影响

以未漂硫酸盐针叶木浆为电容器纸主要原料，研究了添加纤维素纳米纤丝（CNF）对电容器纸强度等性能的影响，并在Page方程的基础上进一步研究了添加CNF和提高打浆度对相对结合面积（RBA）的影响，最后研究了CNF对电容器纸电气性能的影响。结果表明，CNF对电容器纸的紧度、透气度、抗张指数均有明显影响，但随着打浆度提高，CNF对紧度提高、透气度降低、抗张指数增大的贡献逐渐减小；在Page方程的基础上研究得出，提高打浆度和添加少量CNF可以增大纸张的RBA。综合考虑电容器纸高紧度、低透气度的要求，以及打浆节能和CNF成本因素，适宜的打浆度为80°SR，CNF的添加量为2%(相对于绝干浆质量)，在此条件下纸张抗张指数达76.0 N?m/g，紧度为0.80 g/cm³，透气度为0.233 μm/（Pa?s）；工频下电容器纸的介电常数为1.21，介质损耗为0.037，击穿场强为15.13 kV/mm。     

低聚木糖对蒸制过程中馒头坯水分变化的影响

通过比较零添加和添加2.0%低聚木糖馒头坯在蒸制过程中水分含量、水分活度和水分分布的变化规律,研究低聚木糖对蒸制过程中馒头坯水分变化的影响。结果表明:在蒸制过程中,添加2.0%低聚木糖的馒头坯相较于零添加馒头坯,水分含量增大更快,水分活度减小;低聚木糖的添加使更多的自由水转化成弱结合水,部分结合程度低的弱结合水转化为与蛋白质淀粉分子紧密结合的强结合水时间更快。     

油炸温度与时间对白公干鱼传质特性及品质的影响

以白公干鱼为研究对象,探究不同油炸温度(160,180,200℃)和油炸时间(0,20,40,60,80,100,120,150,180s)对白公干鱼水分损失和吸油率的影响,采用特定指数方程对油炸过程中的传质动力学进行曲线拟合;测定油炸后白公干鱼水分活度,建立水分活度与水分含量的关系;测定油炸后白公干鱼色泽、硬度、咀嚼性、表层硬度、韧性,并进行感官品质分析。结果表明:油炸温度的升高可显著增大白公干鱼的水分损失速率和吸油速率,且拟合曲线均符合特定指数方程;白公干鱼水分含量和水分活度呈正相关性,并分为两个区域:水分含量<22%时水分活度随水分含量的增加而快速增大,水分含量>22%时水分活度随水分含量的增加而趋于平缓;结合企业生产经验和感官品质分析,油炸后白公干鱼水分含量控制在22%~26%为宜,达到此水分含量且吸油率最低的加工条件为180℃油炸180s。     

Untersuchungen zum Einfluss der Holzfeuchte auf ausgewählte Eigenschaften von Spanplatten und MDF

On industrially produced particle boards and MDF, the influence of wood moisture on bending MOE, bending strength and shear modulus G_zx and G_zy was determined. The equilibrium moisture content and the differential swelling of thickness proved to be smaller for MDF than for particle boards. Tensile strength and tensile MOE, shear modulus and bending strength decrease likewise with increasing wood moisture content. Furthermore the Poisson ratio μ₁₂ decreases with increasing wood moisture content.     

Determination of the internal bond of particleboard and fibreboard

Tensile strength perpendicular to the surface is generally used as a measure of the internal bond of particleboard and fibreboard. This strength property cannot be used in structural strength calculations. Besides, determining the tensile strength perpendicular to the surface is troublesome. The object of this research was to find correlations between the tensile strength perpendicular to the surface and other strength properties and to detect a more easily determinable strength property for describing the internal bond of boards. The test material comprised 124 particleboards and 95 fibreboards from the standard production of Finnish factories. The following board properties were determined: density, moisture content during the tests, tensile strength perpendicular to the surface, shear strength, tension-shear strength, torsion-shear strength, torsion strength, and modulus of rigidity. The results show that torsion strength and torsion-shear strength correlate most strongly with the tensile strength perpendicular to the surface. Further investigations must thus be concentrated on developing a suitable method of determination for these strength properties.     

Influence of processing parameters and wood properties on the edge gluing of green <Emphasis Type="Italic">Eucalyptus grandis</Emphasis> with a one-component PUR adhesive

The predominant plantation hardwood species in South Africa Eucalyptus grandis is, despite relatively good strength and stiffness properties, seldom used for lumber production due to low dimensional stability, splitting, and cracking of the wood. As critical defects often develop or aggravate during the drying process, the edge gluing of Eucalyptus grandis lumber in its wet state, before kiln-drying, was considered a potential inhibiting factor for this behaviour. The objective of this study was to determine how certain material and processing variables influence the bond quality of unseasoned, edge-glued, Eucalyptus grandis, using a moisture-curing one-component polyurethane adhesive. The study considered the effect of four parameters, namely wood density, moisture content, adhesive spread rate and pressure, on the shear strength of bondlines. Micro computed tomography scanning was used to observe adhesive penetration behaviour. Overall, the bonding quality was satisfactory proving the feasibility of edge gluing of this wood in the wet state. Multiple ANOVA showed that generally better results were obtained for samples with a higher moisture content of roughly 60% compared to specimens with lower moisture content around fibre saturation point. Results indicated that the lower spread rate tested (150 g m^?2) should be preferred to the higher one (250 g m^?2), since it will likely give more stable shear strength results and it would be preferable from an economic point of view. Increasing pressure did not increase the shear strength significantly.     

Effect of layers relative moisture content on the IB strength of pine tannin bonded particleboard

Relative percentage of moisture content of surface and core layers in pine tannin-bonded particleboard influences markedly the internal bond (IB) strength of the board. This is due to the differential compression exercised on the layers related to their moisture content. The moisture content differential between surface and core layers in particleboard during pressing is a determining parameter for the internal bond (IB) strength of particleboard. In the case of tannin adhesives where these differences can be more pronounced than for synthetic adhesive the effect is more easily observable.     

Effect of overdrying of yellow-poplar veneer on physical properties and bonding

The intent of this study was to follow the changes of various wood physical properties as the wood was overdried at high temperature and to determine if these changes correlated with the ability of the wood to bond with phenolic resins. Yellow-poplar (Liriodendron tulipifera L.) was dried from a water-soaked state at 170°C, 195°C, and 220°C for various lengths of time. Light reflectance, wettability, equilibrium moisture content (EMC), loss of wood substance, and compression shear bond strength were measured. Wettability was severely affected over time and was very quickly affected at high temperatures. The bulk properties, EMC and loss of wood substance, were slightly affected by drying for 224 min at 170°C but were more affected at the higher temperatures with time. The results for these bulk properties correlated well with light reflectance measurements regardless of temperature level. However, compression shear bond strength remained high and was unresponsive to either drying time or drying temperature. After these laboratory samples were analyzed, yellow-poplar plywood samples produced by an industrial manufacturer were tested for bond quality. One sample was composed of regularly dried veneer, and one sample was overdried.     

Cold tack of urea formaldehyde resins as an important factor in plywood production

The ability of urea formaldehyde (UF) resins to develop cold tack is needed in plywood production during pre-pressing in a cold press to ensure that the veneers stick together, can be transported, and fit into a multi-daylight hot press. The influence of defined factors on the cold tack was analyzed by determining the tensile shear strength of uncured birch veneers bonded with UF resin, and the statistically significant impact factors were determined. The factors tested were lay-up time, resin amount, resin age, moisture content, veneer temperature and pre-press time. Moisture content and veneer temperature had the highest impact on the cold tack of UF resins. A negative impact of high moisture content on the tensile shear strength and therefore on the cold tack of UF resins was proven as well as a positive impact of a comparably high (30 °C) veneer temperature. Lay-up time and pre-press time showed a minor impact on the tensile shear strength. Models were created using Design-Expert software to calculate the optimum operation conditions for cold tack.     

纳米SiO_2改性金刚石柔性磨轮磨削性能的研究

文章通过依次研究超声分散时间、纳米添加量对丙烯酸树脂力学性能的影响规律,确定当纳米S iO2含量为3%,超声分散时间为15m in时树脂胶粘剂具有最佳抗拉伸强度和较高拉伸剪切强度,都较未超声分散时提高近21%;当超声分散15m in,纳米S iO2添加量为3%时,具有最佳抗拉强度和拉伸剪切强度,较未添加纳米S iO2时分别提高4%和7%;以胶料比为2∶1加入w 40金刚石后,经3%纳米S iO2改性胶粘剂抗拉伸强度提高40%,拉伸剪切强度提高36%;采用3%纳米S iO2改性后的丙烯酸树脂胶粘剂配制的金刚石柔性磨轮较未改性金刚石柔性磨轮磨削性能有大大提高,同时证明了胶粘剂力学性能与金刚石柔性磨轮磨削性能的相对应性。     

亚麻籽剪切力学性能试验

对亚麻籽进行干燥处理,采用食品物性分析仪研究含水率、加载速率对亚麻籽剪切力学的影响。结果表明:建立干燥时间与含水率关系曲线,亚麻籽最大剪切力在10.465~12.692N,剪切功在2.277~3.677mJ,同一加载速率下,不同含水率亚麻籽的剪切力和剪切功存在差异。方差分析表明含水率对剪切力和剪切功影响显著(P0.05),加载速率对剪切力和剪切功影响不显著(P0.05)。