Characterization of Tomato Pulp Stickiness during Spray Drying using a Contact Probe Method

A contact probe test was developed to characterize the surface stickiness of a tomato pulp droplet at various moisture contents and temperatures. To provide tomato pulp samples with different moisture contents, tomato powder produced by a laboratory spray dryer was wetted to seven different moisture levels. The instantaneous tensile force curve was recorded during the probe withdrawal from which the maximum tensile force and other useful information were obtained and cross-examined against images of bonding, debonding, and failure of the material. Generally, at higher moisture contents tomato pulp exhibited cohesive failure followed by semi-adhesive failure, but when moisture content decreased to a certain level, a peak tensile pressure was observed and the failure was adhesive. In addition, higher temperatures shifted the points of adhesive failure toward lower moisture content.     

An Advanced Centrifugal Technique to Characterize the Sticking Properties of Tomato Pulp during Drying

An advanced centrifugal technique was developed to characterize the stickiness of tomato pulp at various moisture contents and temperatures. To provide tomato pulp samples with different moisture contents, tomato powder produced by a laboratory spray dryer was wetted to six different moisture levels. By noting the rotational speed for a tomato pulp droplet detachment and weighing the mass of the droplet remaining on the surface it is possible to gauge the approximate attachment forces holding the droplet to the substrate. The effects of droplet mass and centrifugation time after reaching the desired rotor speed on the detachment rate were also studied. The detachment force was found to increase at the beginning and then started decreasing as the moisture content decreased presenting a maximum at moisture content of about 34%. In addition, the higher the droplet temperature, the higher the attachment force.     

An Advanced Centrifugal Technique to Characterize the Sticking Properties of Tomato Pulp during Drying

An advanced centrifugal technique was developed to characterize the stickiness of tomato pulp at various moisture contents and temperatures. To provide tomato pulp samples with different moisture contents, tomato powder produced by a laboratory spray dryer was wetted to six different moisture levels. By noting the rotational speed for a tomato pulp droplet detachment and weighing the mass of the droplet remaining on the surface it is possible to gauge the approximate attachment forces holding the droplet to the substrate. The effects of droplet mass and centrifugation time after reaching the desired rotor speed on the detachment rate were also studied. The detachment force was found to increase at the beginning and then started decreasing as the moisture content decreased presenting a maximum at moisture content of about 34%. In addition, the higher the droplet temperature, the higher the attachment force.     

Retention of Ascorbic Acid during Drying of Tomato Halves and Tomato Pulp

The objective of this study was to determine a mathematical model for the reaction kinetics of ascorbic acid degradation to describe the rate of vitamin C loss in a drying process of tomato halves or tomato pulp. Tomato samples with different moisture contents were heated at specified temperatures for different time periods. The kinetics of ascorbic acid degradation followed a first-order reaction with a reaction rate constant dependent on product moisture content, in addition to temperature. Furthermore, there was a maximum rate constant when the moisture content of tomato samples was between 65 and 70%. These effects were expressed by a linear relationship between temperature, moisture content, and natural logarithm of rate constant. The model was used to simulate the vitamin C loss during drying of tomato halves and two drying processes of tomato pulp—evaporative concentration and spray drying. It was concluded that there was a close agreement between the experimental and predicted values of ascorbic acid loss during the tomato pulp concentration, confirming the validity of the proposed model for this process. However, for the spray-drying process and the tomato halves drying a correction coefficient was introduced in the model due to more intense exposure of the product surface to air.     

Retention of Ascorbic Acid during Drying of Tomato Halves and Tomato Pulp

The objective of this study was to determine a mathematical model for the reaction kinetics of ascorbic acid degradation to describe the rate of vitamin C loss in a drying process of tomato halves or tomato pulp. Tomato samples with different moisture contents were heated at specified temperatures for different time periods. The kinetics of ascorbic acid degradation followed a first-order reaction with a reaction rate constant dependent on product moisture content, in addition to temperature. Furthermore, there was a maximum rate constant when the moisture content of tomato samples was between 65 and 70%. These effects were expressed by a linear relationship between temperature, moisture content, and natural logarithm of rate constant. The model was used to simulate the vitamin C loss during drying of tomato halves and two drying processes of tomato pulp—evaporative concentration and spray drying. It was concluded that there was a close agreement between the experimental and predicted values of ascorbic acid loss during the tomato pulp concentration, confirming the validity of the proposed model for this process. However, for the spray-drying process and the tomato halves drying a correction coefficient was introduced in the model due to more intense exposure of the product surface to air.     

Evaluation of a structural epoxy adhesive for timber-glass bonds under shear loading and different environmental conditions

This article presents a study of timber-glass adhesive joints. It examines the shear specimen and shear tools preparation process and the evaluation of the results backed up with an overview of existing similar studies. The chosen adhesive was a cold-curing two-component structural bonding epoxy resin (Mapei Adesilex PG1). The shear tests were performed under different temperatures and the timber samples had different moisture contents. A simple shear test tool was designed and was clamped into a universal testing machine for the shear test. The force and crosshead displacement values from the universal testing machine were used for evaluating the results. The environmental conditions of 20 °C and 5% timber moisture content resulted in the highest average shear strength obtained from the shear tests of the analysed joints (9.89 MPa), whereas the environmental conditions of 50 °C and 20% timber moisture content resulted in the lowest average shear strength (3.42 MPa). It was found that the joint strength is dependent on the environmental temperature and timber moisture content. Moreover, the shear specimen load-displacement behaviour at the environmental temperature of 50 °C was linear and nonlinear – depending on the timber moisture content. The most frequent failure type was timber failure. Additionally, a nonlinear contact finite element analysis was performed to demonstrate the additional shear specimen rotation due to the clearance between the shear specimen and shear tools. This impact was evaluated regarding the stress distribution in the bond line. The evaluated epoxy resin adhesive was proved to be suitable for timber-glass bonds.     

Change of mechanical properties related to starch gelatinization and moisture content of rice kernel during fluidized bed drying

Rice fissuring during the drying process is a major problem affecting rice quality. To alleviate this critical issue, it is necessary to understand the change of mechanical properties and the drying kinetics of paddy during drying. The objective of this work is therefore to study the drying characteristics and changes of mechanical properties, i.e., breaking force (F), ultimate tensile strength (UTS), and apparent modulus of elasticity (AMOE) during fluidized bed drying. Suphanburi 1 paddy variety with three initial moisture contents (Mi) of 29.5, 30.2, and 42.8% dry basis was used as the raw material, which was dried at drying air temperatures (Ta) of 110, 130, and 150?°C. A three-point bending method was used for testing the mechanical properties with a texture analyzer. The experimental results showed that the breaking force and the ultimate tensile strength of paddy during drying were more strengthened with higher drying temperatures and higher initial moisture content while its apparent modulus of elasticity was changed only with the moisture content. However, both operating parameters positively affected the apparent modulus of elasticity when evaluated at a 16% dry basis. The maximum changes in F, UTS, and AMOE concerning the initial moisture content were 25.1, 25.2, and 19.5%, respectively. Besides, the maximum changes in F, UTS, and AMOE concerning drying temperatures during drying were 14.2, 14.3, and 13.5%, respectively. The improvement of the mechanical properties could be attributed to the starch gelatinization of which the degree was higher in cases of higher initial moisture content and higher drying temperatures. The empirical models of ultimate tensile strength and apparent modulus of elasticity were developed and related to intermediate moisture content and the degree of starch gelatinization.     

硅烷偶联剂及其水解物对环氧树脂拉伸剪切强度的影响

以双酚A和环氧氯丙烷为原料,通过缩聚反应制得环氧树脂;将硅烷偶联剂γ-甲基丙烯酰氧基丙基三甲氧基硅烷(KH-570)在酸催化下水解,得到水解物。探讨了KH-570及其水解物用量对环氧树脂胶黏剂拉伸剪切强度的影响。结果表明,不加KH-570及其水解物时,环氧树脂胶黏剂的拉伸剪切强度最大为2.47 MPa;只加KH-570水解物时,环氧树脂胶黏剂的拉伸剪切强度最大为3.28 MPa;只加入KH-570时,环氧树脂胶黏剂的拉伸剪切强度最大为5.23 MPa。在KH-570水解物与环氧树脂的质量比相同条件下,随着KH-570用量的增大,环氧树脂胶黏剂的剪切强度先增后减,在KH-570的用量为环氧树脂质量的15%时达到最大;相同KH-570用量下,随着KH-570水解物用量的增大,环氧树脂胶黏剂的剪切强度先增后减,在KH-570水解物和环氧树脂的质量比为5∶5时达到最大。当KH-570的用量为环氧树脂质量的15%、KH-570水解物与环氧树脂的质量比为5∶5时,环氧树脂胶黏剂的拉伸剪切强度达到9.36 MPa。     

Effect of moisture content on mechanical properties,thermal and structural stability and extrudate texture of poly(vinyl chloride)/wood sawdust composites

Mechanical properties and thermal and structural changes of poly(vinyl chloride) (PVC)/wood sawdust composites were assessed with respect to the effect of moisture content, varying from 0.33 to 3.00 % by weight in the composite, for three different wood sawdust contents. The swell ratio and texture characteristics of the composite extrudates were also evaluated. Unique explanations were given to describe changes in the composite properties in terms of molecular interactions between PVC, cellulosic sawdust and moisture, such as dipole–dipole interactions, interfacial defects and bonding, fibre swelling, and moisture evaporation. The results suggest that at low moisture content the tensile modulus decreased and elongation at break of the composites increased with moisture content, the effect being reversed for high moisture content. Tensile strength decreased with increasing moisture content up to 1–2 %, and then unexpectedly increased at higher moisture contents. The effect of moisture content on flexural properties of the composite was similar to that on tensile properties. Impact strength of the composites was considerably improved with moisture content at low sawdust contents (16.7 wt%), and was independent of the moisture content at higher sawdust contents (28.6 and 37.5 wt%). A decrease in decomposition temperature with an increase in polyene content was evidenced with increasing moisture content, while the glass transition temperature did not change with varying moisture content. The extrudate swell ratio increased with the shear rate but remained unaffected by moisture content. The bubbling and peeling‐off in the composite extrudate occurred as a result of the evaporation of water molecules and the application of a high shear rate. Copyright © 2004 Society of Chemical Industry     

Morphology and Properties of Waterborne Polyurethane/CNT Nanocomposite Adhesives with Various Carboxyl Acid Salt Groups

Three series of waterborne polyurethane (WBPU)/carbon nanotube (CNT) nanocomposites were prepared, and their morphology and properties with various 2,2-dimethylol propionic acid (DMPA) and CNT contents were investigated. The CNTs were homogeneously dispersed up to the optimum content in WBPU/CNT nanocomposite films. The degree of homogeneous CNT dispersion increased with increasing DMPA content in WBPU/CNT nanocomposite films. The optimum CNT content showed maximum tensile strength, Young's modulus and adhesive strength of WBPU/CNT nanocomposite film. The optimum CNT contents for WBPU/CNT nanocomposite samples containing 3.61, 5.16 and 5.86 wt% DMPA were about 0.50, 1.00 and 1.50 wt%, respectively. The WBPU/CNT nanocomposite adhesive showed higher adhesive strength at moderately high temperatures (40/60/80/100°C) compared to conventional WBPU. The highest adhesive strength at moderately high temperatures was found with 5.86 wt% DMPA and 1.5 wt% CNT content.     

Influence of the filler material on the thermal stability of one‐component moisture‐curing polyurethane adhesives

Filler materials are part and parcel for the adjustment of adhesives, in particular, their rheological and mechanical properties. Furthermore, the thermal stability of adhesives can be positively influenced by the addition of an expedient filler, with inorganic types common practice in most cases. In this study, one‐component moisture‐curing polyurethane adhesives for engineered wood products based on isocyanate prepolymers with different polymer‐filled polyether polyols were investigated with regard to the filler's potential to increase the thermal stability of bonded wood joints. The property changes due to the addition of fillers were determined by means of mechanical tests on bonded wood joints and on pure adhesive films at different temperatures up to 200°C. Additional analyses by atomic force and environmental scanning electron microscopy advanced the understanding of the effects of the filler. The tested organic fillers, styrene acrylonitrile, a polyurea dispersion, and polyamide, caused increases in the cohesive strength and stiffness over the whole temperature range. However, the selected filler type was hardly important with regard to the tensile shear strength of the bonded wood joints at high temperatures, although the tensile strength and Young's modulus of the adhesive films differed over a wide range. Prepolymers with a lower initial strength and stiffness resulted in worse cohesion, in particular, at high temperatures. This disadvantage, however, could be compensated by means of the filler material. Ultimately, the addition of filler material resulted in optimized adhesive properties only in a well‐balanced combination with the prepolymer used. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Hygrothermal Properties of Epoxy Film Adhesives

The hygrothermal response of high performance epoxy film adhesives, in their bulk state, has been characterized over a wide range of temperatures, following exposure to a combination of humidity (95% R.H.) and heat (50°C).

Experimental results have indicated that the testing temperature has a pronounced effect on both tensile modulus and strength of the adhesives, while the effect of moisture content varies with respect to the adhesive type. The moduli of the film adhesives, which have a wide range of glass transition temperatures (T_g), have been related to both moisture level in the adhesive and testing temperature. This has been accomplished by employing a dimensionless temperature, which incorporates the wet and dry T_g and the testing, as well as a reference, temperature. The strength properties have shown a higher degree of scatter using the abovementioned dimensionless temperature.

Scanning electron microscopy of the fracture surfaces have shown a good agreement between the effects of moisture and the mechanical properties. Adhesives which exhibited good moisture resistance, as manifested by the stability in their tensile properties, showed minor changes in their fracture surfaces regardless of moisture conditioning. Distinctively, the effect on strength properties has been correlated with typical moisture-induced fracture mechanisms.     

A Method of Predicting the Stresses in Adhesive Joints after Cyclic Moisture Conditioning

The durability of adhesive joints is of special concern in structural applications and moisture has been identified as one of the major factors affecting joint durability. This is especially important in applications where joints are exposed to varying environmental conditions throughout their life. This paper presents a methodology to predict the stresses in adhesive joints under cyclic moisture conditioning. The single lap joints were manufactured from aluminium alloy 2024 T3 and the FM73®-BR127® adhesive-primer system. Experimental determination of the mechanical properties of the adhesive was carried out to measure the effect of moisture uptake on the strength of the adhesive. The experimental results revealed that the tensile strength of the adhesive decreased with increasing moisture content. The failure strength of the single lap joints also progressively degraded with time when conditioned at 50°C, immersed in water; however, most of the joint strength recovered after drying the joints. A novel finite element based methodology, which incorporated moisture history effects, was adopted to determine the stresses in the single lap joints after curing, conditioning, and tensile testing. A significant amount of thermal residual stress was present in the adhesive layer after curing the joints; however, hygroscopic expansion after the absorption of moisture provided some relief from the curing stresses. The finite element model used moisture history dependent mechanical properties to predict the stresses after application of tensile load on the joints. The maximum stresses were observed in the fillet areas in both the conditioned and the dried joints. Study of the stresses revealed that degradation in the strength of the adhesive was the major contributor in the strength loss of the adhesive joints and adhesive strength recovery also resulted in recovered joint strength. The presented methodology is generic in nature and may be used for various joint configurations as well as for other polymers and polymer matrix composites.     

Effect of Maltodextrin Addition during Spray Drying of Tomato Pulp in Dehumidified Air: II. Powder Properties

This work investigates the effect of maltodextrin addition on the main powder properties during spray drying of tomato pulp in dehumidified air. A pilot-scale spray dryer was employed for the spray-drying process. The modification made to the original design consisted in connecting the spray dryer inlet air intake to an absorption air dryer. 21 DE, 12 DE, and 6 DE maltodextrins were used as drying agents. Tomato pulp was spray dried at inlet air temperatures of 130, 140, and 150°C and (tomato pulp solids)/(maltodextrin solids) ratios of 4.00, 1.00, and 0.25. The tomato powders were analyzed for rheological properties, moisture content, bulk density, solubility, hygroscopicity, and degree of caking. It was found that maltodextrin addition improved powder hygroscopicity, caking, and solubility, whereas it deteriorated slightly its moisture content and density. In addition, analysis of experimental data yielded correlations between powder properties and the above-mentioned variable operating conditions. Regression analysis was used to fit a full second-order polynomial, reduced second-order polynomials, and linear models to the data of each of the properties evaluated. F values for all reduced and linear models with an R ² ≥ 0.70 were calculated to determine if the models could be used in place of full second-order polynomials.     

Spray Drying of Tomato Pulp: Effect of Feed Concentration

The effect of feed concentration on spray drying of tomato pulp preconcentrated to 78, 82, and 86% wet basis is investigated in two spray drying systems: a pilot scale spray dryer (Buchi, B-191) with cocurrent regime and a two-fluid nozzle atomizer, and the same connected with an absorption air dryer (Ultrapac 2000). Data for the residue on the chamber and cyclone walls were gathered and two types of efficiencies were calculated as an indication of the spray dryer performance. Tomato powders were analyzed for moisture, particle size, and bulk density. In both spray drying systems, with increases in tomato pulp concentration overall thermal efficiency, evaporative efficiency, material loss in the cyclone, powder moisture content, and bulk density decreased, whereas powder particle size increased. On the contrary, the effect of feed solids content on residue formation and product recovery was dependent on the drying medium. In the standard dryer, the higher the feed concentration, the higher was the residue accumulation, and the lower the product recovery, whereas in the modified system increases in pulp concentration resulted in lower residue formations and higher product yields.     

温度、接触压力与时间对燃煤飞灰固体桥力的影响规律

在所开发的用于在高温条件下(最高使用温度可达1600℃)测量灰的固体桥力的实验系统上,研究了温度、接触压力及接触时间对燃煤飞灰的固体桥力的影响规律。结果显示,燃煤飞灰的脖颈抗拉强度与温度之间呈现出双峰分布曲线的关系。这是由于随着温度的变化,燃煤飞灰的物相状态发生改变,玻璃体成分的含量也随之变化。在温度不变的情况下,燃煤飞灰的烧结脖颈抗拉强度随接触时间和接触压力的增加而增大。     

Factors Affecting the Processing of Epoxy Film Adhesives II. Moisture Content

Dielectric and thermomechanical analysis, infrared spectroscopy, and mechanical testing were used to study the changes which occur in the cure behavior of a 178°C (350°F) epoxy film adhesive, Hysol EA-9649. The response of the system was compatible with the catalyst type employed. The overall effect of increasing moisture content was an increase in flow accompanied by lower T_g values in the cured film with no loss in ambient temperature tensile lap shear strength. These effects are interpreted in terms of the dicyandiamide portion of the adhesive catalyst system reacting with the absorbed moisture resulting in a cured adhesive of different structure but equivalent in bonded joint strength to those made with low moisture content adhesive.     

Hygrothermal Properties of Epoxy Film Adhesives

The hygrothermal response of high performance epoxy film adhesives, in their bulk state, has been characterized over a wide range of temperatures, following exposure to a combination of humidity (95% R.H.) and heat (50°C).

Experimental results have indicated that the testing temperature has a pronounced effect on both tensile modulus and strength of the adhesives, while the effect of moisture content varies with respect to the adhesive type. The moduli of the film adhesives, which have a wide range of glass transition temperatures (T_g ), have been related to both moisture level in the adhesive and testing temperature. This has been accomplished by employing a dimensionless temperature, which incorporates the wet and dry T_g and the testing, as well as a reference, temperature. The strength properties have shown a higher degree of scatter using the abovementioned dimensionless temperature.

Scanning electron microscopy of the fracture surfaces have shown a good agreement between the effects of moisture and the mechanical properties. Adhesives which exhibited good moisture resistance, as manifested by the stability in their tensile properties, showed minor changes in their fracture surfaces regardless of moisture conditioning. Distinctively, the effect on strength properties has been correlated with typical moisture-induced fracture mechanisms.     

Factors Affecting the Processing of Epoxy Film Adhesives II. Moisture Content

Dielectric and thermomechanical analysis, infrared spectroscopy, and mechanical testing were used to study the changes which occur in the cure behavior of a 178°C (350°F) epoxy film adhesive, Hysol EA-9649. The response of the system was compatible with the catalyst type employed. The overall effect of increasing moisture content was an increase in flow accompanied by lower T_g values in the cured film with no loss in ambient temperature tensile lap shear strength. These effects are interpreted in terms of the dicyandiamide portion of the adhesive catalyst system reacting with the absorbed moisture resulting in a cured adhesive of different structure but equivalent in bonded joint strength to those made with low moisture content adhesive.     

Effect of Maltodextrin Addition during Spray Drying of Tomato Pulp in Dehumidified Air: I. Drying Kinetics and Product Recovery

This work investigates the effect of maltodextrin addition on the drying kinetics and the stickiness during spray drying of tomato pulp in dehumidified air. A pilot-scale spray dryer was employed for the spray-drying process. The modification made to the original design consisted in connecting the spray dryer inlet air intake to an absorption air dryer. Twenty-seven different experiments were conducted varying the dextrose equivalent (DE) of the maltodextrin, the ratio (tomato pulp solids)/(maltodextrin solids), and the inlet air temperature. Data for the residue remaining on the walls were gathered. Furthermore, the effect of maltodextrin addition on the drying kinetics and the stickiness of the product was investigated using a numerical simulation of the spray-drying process modeled with the computational fluid dynamics (CFD) code Fluent. The code was used to determine the droplet moisture content and temperature profiles during the spray-drying experiments conducted in this work. The stickiness was determined by comparing the droplet temperature with its surface layer glass transition temperature (T_g ). The T_g was determined using a weighted mean rule based on the moisture content profiles calculated by the CFD code and the experimental data of T_g , which were obtained for the different tomato pulp and maltodextrin samples and fitted to the Gordon and Taylor model.