Practical Processing Conditions Research Articles

A Computational Study on the Influence of the Rheological Behavior of Polystyrene and its Blends on their Thermoforming Ability

The present work aims at understanding the relationship between heating conditions, rheological behavior and thickness distribution that lead to the optimization of the latter in thermoforming. The materials used in this study were polystyrene, PS, high-impact polystyrene, HIPS, and a 50/50 w/w % blend of the two. The study was done by investigating computationally the influence of the material thermo-rheological properties on sheet temperature and final thickness distribution of a vacuum-produced part and relating the sheet heating conditions with the forming stage. When sheet temperature is uniform, the degree of strain hardening and the failure behavior in extension are the most important parameters in controlling the kinetics of the process and the thickness profile. In the case of nonuniform sheet temperature, the results show that an increased degree of strain-hardening is more relevant to the dynamics of the process than relatively small differences in sheet temperature. However, the solution of the inverse thermoforming problem (determining the heater temperature that induces a certain thickness distribution) showed that under practical processing conditions the effect of differences in thermal properties are predominant over the rheological ones.

Effect of sidewall roughness on the bottom etch properties of an SiO2 trench produced in a CF4 plasma

The effect of sidewall roughness on the bottom etch profile and the etch rate of an SiO2 trench produced in a CF4 plasma were examined using a specially designed apparatus that involved a Faraday cage, which permits the observation of microfeatures on an enlarged scale under practical processing conditions. A microtrench was produced on the bottom of a trench-shaped structure with a low aspect ratio when its sidewalls were smooth because ions reflected from the sidewall enhanced the bottom etch rate near the sidewall. However, the microtrench was not produced in a trench-shaped structure with a high aspect ratio and smooth sidewalls because the effects of ions reflected from two sidewalls were overlapped, nor in step-shaped and trench-shaped structures with rough sidewalls because the contribution of reflected ions to the bottom etch rate was negligible. The overlap in ion reflection effects in a trench having a high aspect ratio and smooth sidewalls was responsible for the inverse reactive ion etching lag phenomenon observed in this study.

Biodegradable Plastics from Cellulose

Brief history of the attempts trying to develop biodegradable plastics from cellulose acetates were reviewed in the first part. Then, two kinds of authors' trials were introduced. One of them is a plasticization trial for cellulose acetates (CAs) that is based on the reaction with dibasic acid anhydrides and monoepoxides during melt processing under practical process conditions. This reactive melt-processing method allowed the preparation of biodegradable cellulosic plastics with enough thermoplasticity and moldability. The biggest problem was the occurrence of external plasticizer's bleeding, which was found to be prevented by effective yield of grafting. Higher biodegradabilities have been found for the grafted CAs compared to the unmodified CAs. From the above trial, the amounts of grafting and the graft efficiency were intended to increase. As one of its extensions, a plasticization method for CA based on selective grafting of ϵ -caprolactone (CL) and lactide (LACD) has been developed. The selective-grafted products could be prepared by ring-opening polymerization in the melt state. By using adequate reaction conditions, the grafting reaction proceeded and completed rapidly (within 10–30 min). Transparent amorphous molding were obtainable. The fact that the formed graft side-chains contain a large amount of randomly polymerized parts explains the high thermoplasicity and amorphous nature of the grafted products.

Plasticization of cellulose derivatives by reactive plasticizers II: characterization of plasticized cellulose acetates and their biodegradability

A plasticization method for cellulose acetates (CAs) has been developed that is based on the reaction with dibasic acid anhydrides and monoepoxides during the melting processing. As a continuation of the discussion in the previous report, additional evidence is presented for the role of grafting oligoesters onto cellulose acetates to prevent the bleeding of homo-oligoesters from the inside of molded articles to their surface. Based on these results, a method for enhancing the amount of grafting has been pursued by varying the combination of dibasic acid anhydrides and monoepoxides. The resulting reactive meltprocessing method allows preparation of biodegradable cellulosic plastics using practical process conditions. Higher biodegradability has been found for the oligoester-grafted CAs than for the unmodified parent CAs.

Studies on melt flow properties of low density and linear low density polyethylene blends in capillary extrusion

Two linear low density polyethylenes (LLDPE) with a different melt flow index (MI) are selected to blend with a low density polyethylene (LDPE) in molten state by means of a screw extruder. The flow behaviour of the blend melts is studied by using capillary rheometry under rear practical processing conditions. The results indicate that with addition of the weight percentage content ( φ LD ) of LDPE the end pressure losses decrease for the blends with low MI LLDPE and increase for the blends with high MI LLDPE. These are similar to the case of apparent shear viscosity ( η a ) of the blend melts. The dependence of η a on temperature can be described by the Arrhenius equation. The relationship between η a and component viscosity accords with the logarithmic mixing rule, and the shear flow of the blend melts basically obeys the index law.

Crystallization kinetics in poly(butylene terephthalate)/copolycarbonate blend

In the practical processing conditions of poly(butylene terephthalate)/copolycarbonate (PBT/cPC) blends, crystallization starts from a partially demixed melt. To understand the crystallization mechanism in commercially important blends, we carried out time-resolved light scattering, transmission electron microscopy and small-angle X-ray scattering studies of crystallization in blends with various compositions at various crystallization temperatures. Even after crystallization, memory of demixing via the spinodal decomposition remained and crystallization seems to proceed in the PBT-rich region. PBT crystal lamellae were visualized by electron microscopy and the thickness and spacing were measured by X-ray scattering analysis. Kinetic analysis by light scattering showed a regime transition from regime II to regime I. The kinetic results were successfully interpreted by the modified Hoffman—Lauritzen theory involving a two-step diffusion mechanism characteristic of crystallization of a polymer blend, i.e. mutual diffusion for the formation of the first stem at the crystal surface and self-diffusion for the attachment of following stems in the chain.

Xylanases in bleaching: From an idea to the industry

The utilization of hemicellulases in bleaching of kraft (sulphate) pulp is considered as one of the most important new large-scale industrial applications of enzymes. This is partly due to the great potential of an environmentally safe method. This method has in a short period also proven to be economically realistic. The main enzymes needed in the enzyme-aided bleaching have been shown to belong to the group of endo-/gb-xylanases. Xylanases act mainly on the relocated, reprecipitated xylan on the surface of the pulp fibres. Enzymatic hydrolysis of this specific type of xylan renders the structure of the fibres more permeable. The hydrolysis of xylan or mannan in the inner fibre layers may also enhance the bleachability. In practical process conditions, properties of the enzymes such as substrate specificity and the pH and temperature optima are of utmost importance. The benefits obtained by enzymes are dependent on the chemical bleaching sequence used as well as on the residual lignin content of pulp. The main goals in the enzyme-aided bleaching of kraft pulps have been the reduction of consumption of chlorine chemicals in the bleaching process and consequently lowering the AOX of the effluents. Enzymes have been applied as a pretreatment both in conventional (C/D)EDED and in ECF (elementary chlorine-free) bleaching sequences. In the production of TCF (totally chlorine-free) pulps, enzymes have also been successfully used for increasing the brightness of pulp.

Inhibiton of browning by sulfur amino acids. 2. Fruit juices and protein-containing foods

Enzymatic and nonenzymatic browning reactions may adversely affect the quality, nutritional value, and safety of foods. A need therefore exists to develop methods to control such reactions in a variety of foods. Reflectance measurements were used to compare the relative effectiveness of a series of compounds in inhibiting browning in freshly prepared and commercial fruit juices including apple, grape, grapefruit, orange, and pineapple juices. The potential inhibitors tested include ascorbic acid, a commercial formulation called Sporix, sodium sulfite, N-acetyl-L-cysteine, L-cysteine, and reduced glutathione. For comparison, related studies were also carried out with several protein-containing foods such as casein, barley flour, soy flour, nonfat dry milk, and the commercial infant formula Isomil. The results revealed that under certain conditions SH-containing N-acetyl-L-cysteine and the tripeptide reduced glutathione may be as effective as sodium sulfite in preventing both enzymatic and nonenzymatic browning. The unique electronic and nucleophilic properties of sulfhydryl compounds that enable them to act as inhibitors of both enzymatic and nonenzymatic browning are discussed. These sulfur amino acids merit further study to assess their potential for preventing long-term food browning under practical storage and processing conditions.

The Use of Disperse Dyes Containing Diester Groups to Produce Discharge Effects on Fully Dyed Lightweight Polyester Fabrics

The chemistry of a range of disperse dyes containing diester groups of carboxylic acids (Dispersol PC dyes) are briefly described. The development of a ‘discharge–resist’ printing method and a true resist technique on 100% polyester using these disperse dyes is then outlined. The introduction of two new auxiliary products (Matexil PN–AD and PN–DG) has now led to the use of these Dispersol PC dyes in a process for the discharge printing of fully dyed lightweight polyester fabrics (generally defined as those fabrics having a weight of 80 g/m2 or less and a yarn count per filament of less than 3 dtex). Emphasis is placed on the practical processing conditions necessary to produce these discharge styles and in particular on a new approach to the print thickening system that will enable extremely fine line definition to be achieved.

On the conversion factors in thermal processes

SummaryConverting experimental or assumed heating parameters of one container size to another using the so‐called conversion factor, CF, is an important practical step in the initial design of thermal processes. However, the current prevailing approach for conversion is limited to cans where the two containers are of metal and are processed essentially in the same heating medium. The present study develops the theoretical equations, verified experimentally, for the conversion factors in a broader spectrum of containers (e.g., glass jars to metal cans and vice versa) and different processing media (e.g., water to steam and vice versa). The developed relationships enable the thermal process engineer to use conversion factors in a simple manner for most practical processing conditions.

Chemical and biological properties related to toxicity of heated fats.

Heating of fats brings about measurable changes in their chemical and physical characteristics. Heat is applied in processing for food manufacture, such as during hydrogenation of oils with a catalyst, and in frying for meal preparation. Partially hydrogenated products generally contain substantial quantities of geometric and positional isomers of the original unsaturated fatty acids. During deep-fat frying, when the fat is used repeatedly, oxidative and thermal effects result in the formation of many volatile and nonvolatile products, some of which are potentially toxic, depending on the level of intake. Because of concern about the types of changes that take place in fats during oxidative and thermal deterioration and the effects the derivatives could have on the consumer, many chemical and biological studies have been carried out. Experimental findings indicate that any potential danger to the consumer is relative to the severity of the overall treatment of the fat. In some studies we evaluated biological effects on rats of trans fatty acid in the diet and of concentrates of fatty acid derivatives produced in thermally oxidized fats. trans-Octadecenoic acid changed the concentrations of the phospholipid classes in the liver lipids, and interfered with conversion of the essential n - 6 series of fatty acids to higher members. Compared to oleic acid, elaidic acid was preferentially incorporated into the phospholipids instead of the triacylglycerols and was also concentrated in the lipoprotein fractions. Administration of non-urea-adductable concentrates from thermally oxidized fats produced cellular damage in hearts, livers, and kidneys of the animals. Since even practical processing and frying conditions can produce some nutritionally undesirable products, a concerted effort should be made to minimize substantial accumulation of these in our dietary fats.

Practical Process Conditions for the Use of Immobilized Glucose Isomerase

AbstractThe present world‐wide rush into the production of high fructose corn syrups has increased the demand for the enzym glucose isomerase for the isomerization process. Economics have forced producers of these sweeteners to use the immobilized enzyme in a continuous process. The most suitable way of performing continuous isomerization turned out to be a process in a fixed‐bed column. However, a downflow mode of the substrate through the enzyme bed required special properties of the beads, especially when using very high enzyme beds.Practical process conditions are described for the use of immobilized Maxazyme glucose isomerase in a continuous fixed‐bed column operation procedure, e. g. pH, temperature, concentration of activators, quality of the substrate and enzyme bed dimensions. Special attention is paid to compressibility of the enzyme particles and the characteristical pressure drop of this product. Improvements are described for the production of this immobilized enzyme, which make it possible to use Maxazyme Gl‐Immob in columns up to 5 m bed height.

DEHYDRIDING OF Ti–6AI–2Sn–4Zr–6Mo HYDRIDE POWDER

AbstractA systematic investigation of temperature/pressure/time variables for dehydriding titanium alloy (Ti–6AI–2Sn–4Zr–6Mo) powder was made to determine practical processing conditions for reducing the hydrogen content of the powder to levels below 100 ppm. Studies made between 650·C (1200·F) and 871·C (1600·F) established the following conditions for obtaining the desired hydrogen contents:Analyses of the experimental results of tests made between 650°C (1200°F) and 816°C (1500°F) indicate that at 1–0·088 μm partial pressure of hydrogen the dehydriding process is controlled by the second order reaction: 2H (gas)= H2 (gas) with an activation energy of 21 760 ± 1840 cal. At <0·088 μm partial pressure of hydrogen the process appears to be controlled by the rate of removal of H2 molecules clinging to the powder surfaces. The type of vacuum system used for dehydriding is believed to be the major factor governing removal of these molecules.