Effect of plasticizer and storage conditions on thermomechanical properties of albumen/tragacanth based bioplastics

The effects of composition of the plasticizer fraction and storage conditions on the physical and thermomechanical properties of egg albumen/tragacanth gum based bioplastics were studied. Thus, glycerol (G) and water (W) were used as plasticizers at different G/W ratios (1:0, 3:1, 1:1, 1:3, 0:1), keeping the biopolymer fraction always at 60% (w/w). Tragacanth gum was included in the formulation for its well-known hydrophilic character, as possible future applications of these bioplastics may be moisture dependent (e.g. modified atmosphere packaging). Moreover, properties of bioplastics stored at room temperature under no control of relative humidity were different of those obtained when bioplastics were equilibrated a 53% relative humidity (RH) atmosphere. This is reflected in the DMTA and tensile tests results, for which water loss in the samples with the highest water contents (1:3, 0:1) involves very significant increases in viscoelastic moduli and tensile strength when equilibrated at 53% RH. Glycerol presence when no RH control was taken promotes water uptake, probably due to an interaction between both plasticizers, which eventually lead to a greater plastic region in the tensile tests.     

Releasing Fat in Whole Milk Powder during Fluidized Bed Drying

Spray-dried whole milk powders have been produced to a high bulk-to-surface-free-fat ratio due to the susceptibility to oxidation of surface free fat. Processing spray-dried whole milk powders in a fluidized-bed crystallizer by hot and high humidity air can cause the release of bulk fat and increase both inner free and surface free fat. This research investigates the fat release and its migration to particle surfaces by two different mechanisms: a) fat melting due to high temperature processing in a fluidized -bed crystallizer so that liquid fat can diffuse outwards to the particle surfaces; b) fat release from the matrix due to lactose crystallization, causing component segregation and releasing molecular bonds.

More free fat is preferable in some dairy-based processing, such as chocolate making, where cocoa butter could be substituted by milk fat to adjust the viscosity of chocolate paste and formulate good chocolate taste. This research shows the possibility of releasing more than 90% of the bulk fat to increase free fat (inner and surface) in 15 minutes processing time. Different temperatures and humidities (45°C and 78% RH) have been found to provide suitable conditions to release the bulk fat by crystallizing lactose in higher amount, as a form of inner free fat (preferentially) which is ready for further use, such as in chocolate industries. Meanwhile the released fat, as inner free fat, has less contact with oxygen than surface free fat and maintains the powder quality better. The changes in particle structure and fat release processes have also been studied during fluidized-bed drying of spray-dried whole milk powders that could improve the control and design of the drying process for milk powders.     

Morphological and mechanical properties of dried skimmed milk and wheat flour mixtures during storage

Five mixtures of dried skimmed milk (DSM) and wheat flour (WF) were prepared and stored for 45 days at 20 °C and various relative humidities (RH) from 0% to 85%. Morphological properties, particle size distributions and mechanical properties were studied before and during storage. Scanning electronic microscopy (SEM) showed that samples stored at high RH (59-85%) agglomerated and formed a compact mass of powder due to caking phenomenon. The caking intensity increased with storage relative humidity and was expressed as the maximum force (F_max.) calculated from force/compression curves. DSM powders showed stick-slip behaviour during deformation and, moreover, this phenomenon increased with the DSM ratio in the mixture (up to 20 ± 1 N for 100% DSM) and disappeared with storage relative humidity.     

Thermal degradation and physical aging of poly(lactic acid) and its blends with starch

Poly(lactic acid) (PLA) and its blends with starch and methylenediphenyl diisocyanate (MDI) were extruded in a twin‐screw extruder and compress‐molded in a dog‐bone shaped tensile bars to form test specimens. The thermalgravimetric profile and thermal endurance of these samples were characterized. The effect of physical aging on mechanical and thermal properties of these samples was evaluated. For the aging study, samples were stored at 25°C and relative humidity fluctuating between 90 and 30%, from 2 to 180 days, with or without a polyethylene bag as a moisture barrier. Physical aging of pure PLA samples stored in a controlled environment from 2 to 360 days was also evaluated. The presence of MDI in the PLA/starch composite did not affect the thermal decomposition profile. The PLA showed the highest Arrhenius activation energy and strongest thermal endurance of all samples, followed by PLA/starch/MDI and PLA/starch. Exposure of the samples to storage conditions with fluctuating relative humidity (RH) significantly affects thermal‐mechanical performance of PLA and its composites. But, the samples stored in plastic bags can minimize such effects. Mechanical properties of PLA and PLA/starch‐based composites sealed in plastic bags had no significant change during 30‐day storage in fluctuating humidity conditions (30–90% RH). POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Microencapsulation of fish oil with n‐octenylsuccinate‐derivatised starch: Flow properties and oxidative stability

Fish oil with 33% long‐chain polyunsaturated fatty acids was microencapsulated in a matrix of n‐octenylsuccinate‐derivatised starch and glucose syrup and stored at varying temperatures (5, 20 and 40 °C) and relative humidities (11, 33, 48–59 and 75%). Development of lipid oxidation parameters upon storage depended to a certain extent on temperature, but to a much greater extent on relative humidity. Temperature had no significant effect on the development of lipid oxidation parameters when samples were stored at 11 or 33% relative humidity. Hydroperoxide concentration doubled over the storage period and reached from 88 to 146 mmol/kg oil in the samples stored at 11 and 33% relative humidity, respectively. An increase in hydroperoxide concentration with increasing storage temperature was observed at 48–59% relative humidity. In all samples, the increase in the lipid oxidation parameters was not linear or exponential and significantly differed from the course as it is described in the literature for bulk oils and emulsions. Based on data for colour measurement, moisture sorption and extractable fat, the course of lipid oxidation is discussed. Finally, the use of silica derivatives and tricalciumphosphate efficiently improved the flowing properties of microencapsulated fish oil without affecting the oxidative stability of the products.     

Comparing the caking behaviours of skim milk powder, amorphous maltodextrin and crystalline common salt

This work examined and compared the caking behaviour of three physically and chemically different food powders. The food powders studied were maltodextrin DE21 which is an amorphous powder, common salt which consists of crystalline NaCl, and skim milk powder (SMP) which contains a mixture of components including 51% lactose. The three powders were all exposed to high relative humidities (76% or 100%) over a 1-week period and to a humidity cycle to investigate their caking behaviour and interpret their caking mechanisms. The humidity cycle consisted of 2-day exposure to a high relative humidity (RH) followed by 2-day exposure to low RH of 11% and finally 2-day exposure to the original high RH. At the end of each day, cake strength was measured using a force displacement tester and cake water content was also measured. All three powders sorbed much water when exposed to high relative humidities; however, their cake strengths were very different. Cake strength was influenced by glass transition and the ability of the powders to form sinter bridges. All three powders had similar water content profiles during the humidity cycle with water gain at high RH and loss at low RH. The cake strength profile of the amorphous maltodextrin powder and amorphous SMP were different even though the maltodextrin and lactose glass transition temperatures were reduced below the powder temperature during exposure to high RH. The cake strength of maltodextrin decreased during low RH exposure while it increased for SMP. The cake strength profile of the SMP was similar to the crystalline NaCl. The paper presents an interpretation of the caking mechanisms behind the caking behaviour of each powder.     

Mechanical and physical properties of protein-starch based plastics produced by extrusion and injection molding

Processing conditions, ingredient ratio, and moisture content were optimized for making soy protein/starch based plastics using a twin-screw extruder and an injection molding machine. A metering pump and a high speed mixer were used for ingredient mixing. The optimal processing temperature for injection molding was 130°C, and the moisture content of extruded pellets was 10–14%. Processing effects were investigated by measuring the tensile properties and water resistance of specimens. Reduction of water and glycerol in mixtures increased the barrel pressure of the extruder. Mold release was improved by incorporating 0.25 parts tallow per 100 parts of solid material (soy protein and starch). The water absorption of the specimens was reduced by adding acids to adjust the pH to the isoelectric point of soy proteins (pH 4.5). Effects of storage at different relative humidities were studied. The processibility of pellets was stable after a 4-wk-storage period, despite some moisture loss. Injection-molded specimens, after being stored for up to 6 mon at dry conditions [50 and 11% relative humidity (RH)] at room temperature and for 4 wk in a 50°C oven, showed no surface crack. However, humid (93% RH) storage at room temperature promoted fungal growth after storage for 3 mon, indicating that preservatives such as potassium sorbate and propionic acid were needed.     

Controlled relative humidity storage for high toughness and strength of binderless green pellets

An equation was developed to predict fracture toughness of green powder compacts. The model combines crack tip toughness predicted by Kendall's model with crack tip shielding due to bridging of moisture meniscuses across the crack. The model predicts that crack tip shielding due to moisture should be dominant. Fracture tests on ceria green pellets verified that storing pellets at a high relative humidity (98% RH) for an extended period of time led to fracture strength more than double those stored at lower RH. However, at lower RH there is no significant increase in fracture strength with increased RH as predicted by the model. The lower strength at low RH is due to insufficient capillary and surface forces but may also be related to the lack of sufficient adsorbed moisture to form bridging meniscuses. The high green strengths achieved by storing pellets at a high RH suggest a method of strengthening green parts without adding binder.     

Crystallization and Drying of Milk Powder in a Multiple-Stage Fluidized Bed Dryer

The rationale of this study has been to use fluidized beds to crystallize amorphous spray-dried skim milk powders with multiple stages of processing at different temperatures and humidities with the aim of rapidly making mostly crystalline powders. This paper discusses the performance of a multiple-stage fluidized bed dryer, and a combination of crystallization of lactose in spray drying at high humidity (lactose nuclei formation) and subsequent fluidized bed drying. Two different combinations of spray dryer and multi-stage fluidized-bed dryer have been suggested to crystallize lactose in skim milk powder. The results show significant improvements in the crystallinity of the powders. Moisture sorption test and X-ray diffraction analysis were used to assess the crystallinity of the powders. The processed powders that were crystallized in a humid-loop spray drying combined with a two-stage fluidized-bed dryer/crystallizer showed 92% improvement in lower amorphicity by processing at different stages of 70°C, 50% RH and 80°C, 50% RH for 15 minutes. The conventionally spray-dried powders that were crystallized in a three-stage fluidized-bed dryer/crystallizer showed 87% improvement in lower amorphicity (less moisture sorption) by processing at different stages of 60°C, 50% RH; 70°C, 40% RH; and 80°C, 40% RH for 20 minutes. The multiple-stage fluidized bed system showed distinctive potential to crystallize lactose significantly in skim milk powder using an industrial-feasible process.     

复合吸附剂MWCNT/MgCl2的水蒸气吸附性能

通过研磨将多壁碳纳米管分别与质量分数为30%、40%和50%的无水氯化镁复合,制备了3种不同配比的复合吸附剂MWCNT/MgCl₂。采用数字化扫描电子显微镜（SEM）观察复合吸附剂表面材质的结构样貌,通过Hot Disk热常数分析仪测得复合吸附剂的热导率,使用恒温恒湿箱选取具有代表性的温湿度,测试复合吸附剂在不同工况下的水蒸气吸附性能,并采用准二级动力学模型对25℃、50% RH工况下的实验数据进行拟合,应用Autosorb-IQ全自动气体分析仪测试了三种样品在25℃下的等温吸湿曲线。实验结果表明,相同温湿度工况下,随着氯化镁含量增加,复合吸附剂的吸附量提高,25℃、50% RH下氯化镁含量为30%、40%和50%的复合吸附剂M1、M2和M3的吸附量分别为0.62、0.79和0.94 g/g;恒定湿度为50% RH,温度变化为15~35℃时,复合吸附剂吸附量受温度和饱和水蒸气分压力的双重影响,表现为先增加后减小;温度固定为25℃,相对湿度从50% RH增加到80% RH时,复合吸附剂吸附量均大大提升;复合吸附剂在35℃、25% RH中高温、低湿条件下仍表现出较好的吸附能力;在相对压力P/P₀为0.3时,M1、M2和M3的吸附量分别为0.24、0.25和0.30 g/g,随着吸附压力的增加,复合吸附剂的吸附量也不断提升,最大吸附量分别达到3.54、3.75和4.42 g/g。复合吸附剂MWCNT/MgCl₂的制备研究,为吸附剂的性能研究提供了基础,对太阳能吸附式空气取水的研究具有潜在意义。     

Moisture Proofing of Spray Dried Particles Comprising Ammonium Nitrate/Potassium Nitrate/Polymer

The aim of this study was to fabricate moisture‐proof, phase‐stabilized, ammonium nitrate/potassium nitrate (AN/PN) particles, with a polymer used as the moisture‐proofing agent. The particles were prepared with a spray drying technique. Water solutions (or water dispersions) containing AN/PN and one of five different types of polymer were spray‐dried, which produced white powders with particle diameters of approximately 20–40 μm. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy indicated that each component was homogeneously distributed throughout the particles. The particles exhibited little aggregation compared to the reagent AN, even when left for 7 d or more. In addition, the moisture absorption of the particles at less than 40 % relative humidity (RH) was lower than that of the polymer‐free particles. Even under high‐moisture conditions (83 % RH), the particles did not deliquesce immediately, and they retained their original shape for 30–60 min, whereas the polymer‐free particles were transformed into droplets within 5 min.     

Effects of antioxidants and humidity on the oxidative stability of microencapsulated fish oil

The effects of various antioxidants and RH on the oxidative stability of microencapsulated fish oil powder were investigated using PV and thiobarbituric acid tests. The micorencapsulation process provided high encapsulation efficiency (≥88% of extractable fish oil). Without antioxidants, the encapsulated fat was 10 times more stable against oxidation than the surface fat, as determined by PV. α-Tocopherol, which is a lipophilic antioxidant, showed a greater antioxidative effect in both surface and encapsulated fats than ascorbyl palmitate, which is an amphiphilic antioxidant. According to TBARS values, the longest lag period was observed at 0% RH. Addition of >200 ppm α-tocopherol in a 10–30% RH range prolonged the oxidative stability of the microencapsulated fish oil powder.     

Effect of moisture on pure mode I and II fracture behaviour of composite bonded joints

The effect of moisture on the fracture properties of composite bonded joints under pure mode I and pure mode II was analysed in this work. The double cantilever beam and end notched flexure tests were used for mode I and mode II fracture characterisation, respectively. Three different moisture conditions (55% and 75% of relative humidity (RH) and immersion in distilled water (IW)) were tested to assess its influence on the fracture behaviour under both pure loading modes. It was verified that fracture energy is drastically affected for the immersion in water in both loading modes. A cohesive zone model was also used to estimate the influence of RH on the cohesive parameters defining the law that mimics accurately the fracture process for each case. It was concluded that alterations on the cohesive laws reflect an increase of material brittle behaviour with the increase of the moisture uptake.     

Novel conductive adhesives for surface mount applications

Electrically conductive adhesives (ECAs) have been explored as a tin/lead (Sn/Pb) solder alternative for attaching encapsulated surface mount components on rigid and flexible printed circuits. However, limited practical use of conductive adhesives in surface mount applications is found because of the limitations and concerns of current commercial ECAs. One critical limitation is the significant increase of joint resistance with Sn/Pb finished components under 85°C/85% relative humidity (RH) aging. Conductive adhesives with stable joint resistance are especially desirable. In this study, a novel conductive adhesive system that is based on epoxy resins has been developed. Conductive adhesives from this system show very stable joint resistance with Sn/Pb‐finished components during 85°C/85% RH aging. One ECA selected from this system has been tested here and compared with two popular commercial surface mount conductive adhesives. ECA properties studied included cure profile, glass transition temperature (T_g), bulk resistivity, moisture absorption, die shear adhesion strength, and shift of joint resistance with Sn/Pb metallization under 85°C/85% RH aging. It was found that, compared to the commercial conductive adhesives, our in‐house conductive adhesive had higher T_g, comparable bulk resistivity, lower moisture absorption, comparable adhesion strength, and most importantly, much more stable joint resistance. Therefore, this conductive adhesive system should have better performance for surface mount applications than current commercial surface mount conductive adhesives. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 399–406, 1999     

Effect of surface esterification with octenyl succinic anhydride on hydrophilicity of corn starch films

Surface of corn starch films was modified through esterification using octenyl succinic anhydride as reactant. Physical properties of the films, moisture absorption, and water contact angle were measured to characterize the effect of the surface esterification modification. The influences of the concentration of alkaline aqueous solution for activating starch, reaction temperature, and time were investigated. It was found that the pretreatments with 1.0% or 2.0% NaOH aqueous solution and reacting at 35°C for 6 h gave rise to films possessing higher water contact angle, lower equilibrium moisture content, and moisture absorption rate at 95% relative humidity (RH). After the surface esterification modification, the equilibrium moisture content of the starch film decreased up to 29% at 95% RH and the surface water contact angle of the film increased up to 83%. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fat encapsulation in spray-dried food powders

The surface composition of spray-dried sodium caseinate/lactose emulsions having different oil phases were estimated using electron spectroscopy for chemical analysis (ESCA), and the particle structure was studied using scanning electron microscopy (SEM) both before and after storage under humid conditions. After spray-drying, powders in which the oil phases consisting of fats with intermediate melting points, such as hardened coconut oil and butter fat, had the highest surface coverage of fat, approximately 34%. The powder with soybean oil as the oil phase had a surface coverage of fat of approximately 15%. The high-melting hardened rapeseed oil was almost completely encapsulated after spray-drying. After storage in a humid atmosphere, fat was released onto all the powder surfaces (surface fat after storage, between 50–65%) except for those with hardened rapeseed oil in which the fat remained encapsulated. These observations are consistent with the powder structure observed by SEM. The surface composition estimated by ESCA for spray-dried sodium caseinate/lactose-containing emulsions with different amounts of soybean oil and a constant lactose/sodium caseinate ratio showed an almost completely encapsulated oil-phase after drying. Storage of these powders in a humid atmosphere leads to a release of fat onto the powder surface even if the soybean oil content is low (1% of the dry weight). Powders made from soybean oil emulsions with sodium caseinate alone exhibit a much lower degree of encapsulation than in the system where lactose is present.     

The effect of humidity and oxygen partial pressure on degradation of Pt/C catalyst in PEM fuel cell

Durability of Pt/C oxygen reduction reaction (ORR) catalyst remains one of the primary limitations for practical application of proton exchange membrane (PEM) fuel cells. In this work, the effects of relative humidity and oxygen partial pressure on platinum catalyst degradation were explored under potential cycling. At 60 °C, the loss rates of Pt mass and catalyst active surface area were reduced by about three and two times respectively when the relative humidity was lowered from 100% to 50%. The effects of oxygen partial pressure on cathode degradation were found to be insignificant. Cyclic voltammetry studies showed a slight increase in Pt electrochemical oxidation by water when the humidity increased from 50% RH to 100% RH. The rates of Pt dissolution were only slightly affected by change in humidity, and the accelerated catalyst degradation was ascribed to the increased Pt ion transport in the more abundant and larger water channel networks within the polymer electrolyte. Based on the parametric study results from our previous cathode degradation model, it was estimated that the diffusivity of Pt ions at fully humidified conditions was three times that of the value at 50% RH and 60 °C.     

Encapsulation of sea buckthorn kernel oil in modified starches

Encapsulation of CO₂-extracted sea buckthorn kernel oil and the stability of the products were investigated. Maltodextrin and an emulsifying starch derivative were used for encapsulation by spray drying. Both shell materials significantly increased the storage stability of sea buckthorn kernel oil, even though in maltodextrin capsules 10% of the total oil was extractable from the surface of the capsule. The cornstarch sodiium octenyl succinate derivative capsules contained essentially no surface oil. After 9 wk storage at controlled conditions (20°C, RH 50%), PV of the unencapsulated oil was above 90 meq/kg, whereas in the encapsulated oils, the PV was still around 20 meq/kg. The PV of the encapsulated oil was dependent on the storage conditions. A small increase in temperature (from 20 to 25–30°C) and a significant increase in humidity (from RH 50 to RH 50–70%) decreased the stability of capsules. This was associated with the physical state of the microcapsule matrix and may be linked with glass transition of the wall polymers.     

空气相对湿度对喷雾干燥生产的影响

我国南北方相对湿度差别较大。相对湿度大会给喷雾干燥生产带来不利影响,如生产时进风温度偏低、塔壁挂粉严重、产品水分含量超标、生产效率降低等。相对湿度是设计喷雾干燥系统的重要参数。设计喷雾干燥系统应对不同地区环境的相对湿度情况区别对待。以RGYP01-500型立式压力喷雾干燥塔生产奶粉为例,对喷雾干燥系统的设计进行阐述。