Automated differential scanning calorimetry at low temperatures

A Perkin-Elmer DSC-2 scanning calorimeter was operated by means of a PDP-11/34 computer with time-shared scanner and voltmeter. Special attention was paid to the problems of measurement below room temperature down to the low-temperature limit. It was found that Ne, rather than He, should be used as a purge gas, that scans should always be started at a standardized liquid nitrogen level, and that gas flow to the dry box should be stopped during measurements. Results on benzoic acid were then accurate to 0.6 % from 120 to 300 K. The specific heat of antimony was measured in the temperature interval 120–720 K.     

Recent advances in polymers and polymer composites for food packaging

The growing world population, evolving urbanization, and globalization have created more demand for food, which has increased challenges in food safety. Development and innovations in food packaging, one of the most important components in the food industry, is of key importance as food safety issues have gathered tremendous attention of the world. Food packaging is mainly intended to prevent a deterioration in quality of foods and beverages during distribution, sales, and consumption. Polymeric materials have been widely used as packaging materials due to their advantageous characteristics, including excellent mechanical, thermal, and corrosion-resistant properties, a lightweight nature, and ease in production. Polymer composites refer to polymers impregnated with nanomaterials and organic or inorganic compounds. Polymer composites have been applied in the packaging industry to enhance or bestow additional properties to packaging materials. This review summarizes the recent advances in polymer and polymer composites used in food packaging applications. First, progress in the polymers utilized for food packaging, with a focus on biodegradable polymers, will be introduced. Subsequently, the utilities of polymer composites in advanced food packaging will be highlighted and categorized into three classifications of packaging: improved, active, and intelligent packaging. Next, concerns on the relevant safety issues and regulations will be briefly discussed. Finally, an outlook on the future research directions of polymer and polymer composites for food packaging will be provided.     

The possibility of high-temperature heat capacity measurements by differential scanning calorimetry

We have been conducting series of heat capacity measurements by differential scanning calorimetry (DSC) on various latent thermal storage materials such as NaOH-NaNO₃. Our concern is now shifting to higher temperature applications of latent thermal storage: space solar dynamic power systems (solar thermal electric power generation systems in space) and so on. Such applications require storage materials which can be operated above 1000 K. Needs for heat-capacity measurements at higher temperatures are increasing. In the present paper, some results of our heat capacity measurements by DSC at intermediate temperatures are presented. Several items which should be considered in order to realize the heat capacity measurements above 1000 K by DSC are discussed.Paper presented at the Second U.S.-Japan Joint Seminar on Thermophysical Properties, June 23, 1988, Gaithersburg, Maryland, U.S.A.     

Quantifying low amorphous or crystalline amounts of alpha-lactose-monohydrate using X-ray powder diffraction, near-infrared spectroscopy, and differential scanning calorimetry

Efficient and accurate quantification of low amorphous and crystalline contents within pharmaceutical materials still remains a challenging task in the pharmaceutical industry. Since X-ray powder diffraction (XRPD) equipment has improved in recent years, our aim was 1) to investigate the possibility of substantially lowering the detection limits of amorphous or crystalline material to about 1% or 0.5% w/w respectively by applying conventional Bragg Brentano optics, combined with a fast and simple evaluation technique; 2) to perform these measurements within a short time to make it suitable for routine analysis; and 3) to subject the same data sets to a partial least squares regression (PLSR) in order to investigate whether it is possible to improve accuracy and precision compared to the standard integration method. Near-infrared spectroscopy (NIRS) and differential scanning calorimetry (DSC) were chosen as reference method. As model substance, alpha lactose monohydrate was chosen to create calibration curves based on predetermined mixtures of highly crystalline and amorphous substance. In contrast to DSC, XRPD and NIRS revealed an excellent linearity, precision, and accuracy with the percent of crystalline amount and a detectability down to about 0.5% w/w. Chemometric evaluation (partial least squares regression) applied to the XRPD data further improved the quality of our calibration.     

Prediction of the self-accelerating decomposition temperature (SADT) for liquid organic peroxides from differential scanning calorimetry (DSC) measurements

We present a prediction (estimation, calculation, screening) method for the estimation of the self-accelerating decomposition temperature (SADT) for liquid organic peroxides from differential scanning calorimetry (DSC) measurements based on the concepts of thermal explosion theory originally introduced by Semonov which are adopted to our problem assuming nth-order reaction kinetics. For the peroxides under investigation, we demonstrate good agreement with the experimental SADT. This method can be used as a quick and easy applicable method for the estimation of the critical temperatures.     

Cure rate of DGEBA/MDA/GN/HQ system by differential scanning calorimetry analysis

To compare investigations of the cure kinetics of DGEBA/MDA/GN/HQ system by different methods, the fractional life method, Kissinger equation, Barrett method and integral method were used. From the fractional life method, reaction orders were between 0.77 and 0.93 but had no correlation with cure temperature, and from the Kissinger equation, the activation energy was 11.08 kcal mol⁻¹ and pre-exponential factor was 2.78×10³ s⁻¹. For the second-order reaction by the Barrett method and integral method, the activation energy was 20 kcal mol⁻¹ and the pre-exponential factor was 8.5×10⁸ s⁻¹. By comparison of the Barrett model with experimental data, it was found that the Barrett model was useful for predicting the cure time at a given temperature.     

Thermal behavior and phase identification of Valsartan by standard and temperature-modulated differential scanning calorimetry

Thermal behavior of angiotensin II type 1 (AT₁) receptor antagonist, Valsartan (VAL), was examined employing thermogravimetric analysis (TGA), standard differential scanning calorimetry (DSC) and temperature-modulated differential scanning calorimetry (TMDSC). The stability of VAL was measured by TGA from 25 to 600°C. Decomposition of Valsartan starts around 160°C. The DSC curve shows two endotherms, occurring around 80°C and 100°C, related to evaporation of water and enthalpy relaxation, respectively. Valsartan was identified by DSC as an amorphous material and it was confirmed by X-ray powder diffraction. The glass transition of fresh Valsartan appears around 76°C (fictive temperature). TMDSC allows separation of the total heat flow rate into reversing and nonreversing parts. The nonreversing curve corresponds to the enthalpy relaxation and the reversing curve shows changes of heat capacity around 94°C. In the second run, TMDSC curve shows the glass transition process occurring at around 74°C. Results from standard DSC and TMDSC of Valsartan were compared over the whole range of temperature.     

A simplified environmental evaluation tool for food packaging to support decision-making in packaging development

Packaging developers in the food industry must consider several, sometimes conflicting, environmental requirements on packaging along with an already complex combination of marketing, logistics and production requirements. Existing methods for the environmental evaluation of packaging either focus on a limited amount of environmental packaging criteria (such as recyclability or renewable content) or rely on life cycle assessment methodology requiring expert competence. To support the food industry in their efforts toward developing product and packaging combinations that reduce the total environmental impact in food supply chains, this article presents a simplified environmental evaluation tool for food packaging. The presented tool was developed through an iterative process in a collaborative research project with the food industry. It evaluates packaging systems based on packaging criteria sorted into four areas that represent the life-cycle steps packaging material production, transport, household and end-of-life. A comparison of the tool results and screening LCA results for three packaging cases showed no major differences. From the practitioners' perspective, the main advantages of the suggested tool are that it does not require LCA-competence, that the required input data is commonly available in packaging development projects and that its overall structure invites several functions of the company to participate. The theoretical benefits of the suggested tool are that it allows for a parallel assessment of eco-efficiency and eco-effectiveness criteria in a life cycle perspective and that it considers littering risk as well as the influence of packaging on food waste in households     

Differential scanning calorimetry study of constrained groove pressed low carbon steel: recovery,recrystallisation and ferrite to austenite phase transformation

Abstract

Low carbon steel sheets are subjected to severe plastic deformation (SPD) via constrained groove pressing (CGP) up to five passes. As a result of this process, strain magnitude up to 5·8 is imposed to the sheets, which leads to grain size of 225 nm. These nanostructured steel sheets, due to their high dislocation density and ultrafine microstructure, are very sensitive to heating. In the present study, recovery, recrystallisation and ferrite to austenite phase transformation phenomena for the SPD steel are investigated using differential scanning calorimetry method. The results show that with increasing the strain in steel sheets, the deformed stored energy (released through recovery and recrystallisation) and enthalpy of ferrite to austenite phase transformation are significantly increased and varied in 38·5–85·8 and 109–156·1 MJ m^?3 ranges respectively. In addition, transformation temperature is decreased from 761 to 750°C after five CGP passes. However, recovery stored energy, recovery and recrystallisation peak temperatures are not changed, considerably. Experimental data show that with increasing the hardness, the stored energy is increased. One empirical equation is developed for relationship between hardness and stored energy of severely deformed low carbon steel. In addition, using the dislocation model, this mentioned relationship is justified.     

Permeability of naphthalene in different types of polymeric food packaging materials

The relative permeabilities of naphthalene through different types of common polymeric food packaging materials were determined by migration studies in a controlled environment. The results illustrate that polyolefins, such as low density polyethylene (LDPE), have a higher relative permeability than other polymers, such as polyethylene terephthalate (PET) or polyvinylchloride co-polymer (PVC). This was explained by the correlation between the permeability of the migrant and the glass transition temperature (Tg) of the different polymers, as well as their polarity.     

Identification of problems arising during manual handling of food packaging by older consumers in Poland

The ageing population all over the world requires much greater attention than it receives from many businesses, including packaging industry. Therefore, it is essential to investigate the specific needs, requirements, and expectations of older consumers, particularly those related to the labelling and ergonomics, so as to shape the food packaging characteristics. In this way, consumers' satisfaction and hence the brand loyalty can be built. The aim of the study was to analyse the needs of older consumers related to food packaging handling and other corresponding issues, as well as to develop guidelines for food producers. The research consisted of two stages: a survey that covered a group of 600 consumers aged 60 and older in southern Poland and individual in‐depth interviews (IDIs) carried out among 60 people over the age of 60 in southern Poland. The outcomes of this consumer research indicated the need for changes in food packaging designed for older consumers, especially in consideration of the physical limitations for its handling before and after the product purchase. Food producers should also pay particular attention to the problems connected with packaging as a source of information. Moreover, they should make modifications in packaging ergonomics, especially in terms of size, shape, and opening and closing features. According to respondents, packaging material should be safe for health but not necessarily environmentally friendly.     

Special features characteristic of the use of differential scanning calorimetry for the investigation of the kinetics of thermal decomposition of energetic materials

The results of analysis of mathematical models of “ideal” differential scanning calorimeter are used for determining the experimental conditions which provide for the minimal level of errors of determination of the kinetic constants of exothermal reactions of thermal decomposition of energetic materials under conditions of constant-rate heating of samples and in the isothermal mode. The predicted estimates of admissible values of the basic parameters of models (mass of samples, rate of heating, temperature range of investigations, and so on) are based on the experimental data largely obtained in the investigation of cyclotetramethylenetetranitramine (HMX).     

Component migration from adhesives used in paper and paperboard packaging for foodstuffs

This paper presents the first results of research on the migration of adhesive components in the paper and paperboard packaging sector. It examines components that can migrate from a variety of commonly used adhesives in the framework of a ‘worst case’ scenario in respect of the contents. The report also explains the methodology used to analyse extraction and migration and the model used for calculating the transfers. Copyright © 1999 John Wiley & Sons, Ltd.     

Coupling of conductivity to the relaxation process in polymer electrolytes

Conductivity relaxation using modulus formalism has been used to explore the coupling of ionic conductivity to dielectric relaxation in polymer electrolyte based on polyethylene oxide complexed with various content of LiAsF₆. The temperature dependence of conductivity followed the VTF behavior suggesting close correlation between conductivity and the segmental relaxation process in polymer electrolytes. The coupling of conductivity to the segmental process has been discussed in terms of coupling index. For all compositions studied, the coupling index was within the range of 1–11 in the temperature range of investigation, which was in agreement with the coupled systems.     

Shelf life extension of fresh asparagus using modified atmosphere packaging and vacuum skin packaging in microwavable tray systems

Asparagus (Asparagus officinalis L.) is one of the most popular vegetables because it contains a wealth of fiber and several essential nutrients. It is a very perishable commodity due to its very high respiration rate. To maintain product quality and to satisfy consumer demand as a convenient food, modified atmosphere packaging (MAP), vacuum skin packaging (VSP), and microwaveable containers were used to extend the shelf life of fresh-cut asparagus as a ready-to-eat food product. The objective of this study was to determine the shelf life of fresh-cut asparagus packed in MAP and VSP microwaveable tray systems at commercial storage conditions, 4°C, 80% RH. Weight loss, moisture content, O₂/CO₂ concentration in the package headspace, product pH, microbial growth, and sensory evaluation were used to determine the product quality and shelf life. Moreover, the preference of product appearance and the quality of the cooked asparagus in both microwaveable tray systems at different cooking times and microwave power levels was also sensorially evaluated. During storage for 21 days, there was no significant difference (p > 0.05) in weight loss, moisture content, and pH. Sanitation and packaging techniques also helped to retard the microbial growth. Both techniques, combined with refrigeration, help to maintain the freshness and product shelf life up to 21 days for MAP and 18 days for VSP. On the basis of hedonic scale results, consumers preferred the appearance of both packaging types. Both microwavable tray systems, thus, can help to prolong the shelf life of fresh-cut asparagus and can be eaten directly from the package.     

Nature and density of lattice defects in ball milled nanostructured copper

Copper powder of 99.9% purity with particle size in the micrometer range was subjected to high energy ball milling by milling times between 2 and 24 h applying stearic acid as surfactant. The nature and density of lattice defects were determined using differential scanning calorimetry (DSC) and X-ray line profile analysis (XPA). The DSC measurements exhibit a considerable drop of the total stored energy with increasing ball milling time indicating a surprising decrease of lattice defect concentrations by more than one order of magnitude. The results from XPA, however, show that neither the dislocation density, nor the crystallite size can account for this behavior. Rather it is to be attributed to a high concentration of deformation induced vacancy type defects, with their density gradually decreasing during ongoing milling.     

Synthesis of nanocrystalline yttria doped ceria powder by urea-formaldehyde polymer gel auto-combustion process

Nanocrystalline yttria doped ceria powder has been prepared by auto-combustion of a transparent gel formed by heating an aqueous acidic solution containing methylol urea, urea, cerium(III) nitrate and yttrium(III) nitrate. The TGA and DSC studies showed the combustion reaction of the gel initiated at 225 °C and completed within a short period of time. XRD spectrum of the combustion product reveals the formation of phase pure cubic yttria doped ceria during the combustion process. Loose agglomerate of yttria doped ceria particle obtained by the combustion reaction could be easily deagglomerated by planetary ball milling and the powder obtained contains particles in the size range of 0.05-3.3 μm with D₅₀ value of 0.13 μm. The powder particles are aggregate of nanocrystallites with a wide size range of 14-105 nm. Pellets prepared by pressing the yttria doped ceria powder sintered to 95.2% TD at 1400 °C.     

Evaluation of measures to mitigate mineral oil migration from recycled paper in food packaging

The presence of mineral oil saturated hydrocarbons (MOSH) and aromatic hydrocarbons (MOAH) in food is a safety concern. Migration to food from recycled paper and board is a relevant source of MOSH and MOAH, and the potential of several technologies to reduce it was explored. These technologies were assessed for food safety (people), environment (planet) and economy (profit) in an integrated way, using a framework developed to compare the effect of the technologies with the current state of the art. Two mature technologies were evaluated (MB12 and flotation), two in development (supercritical CO₂ and thermal treatment), and two as a concept (anionic trash catchers and functionalized clays). The use of mineral-oil-free inks for printing newspapers was also evaluated. It was concluded that, although it is desirable to apply mineral-oil-free inks, in the short-term reduction technologies have more impact. All technologies of which the effectiveness could be investigated (MB12, flotation, supercritical CO₂ and thermal treatment) are able to reduce the potential migration of mineral oils by >70%, but none score optimally on all indicators. The MB12 technology shows the best overall performance and is ready for implementation, provided its patent will be available to more parties. Supercritical CO₂ performs best on food safety, but environmental and economic performance has to be improved. The developed assessment framework yields a clear overview of the advantages and disadvantages of the technologies. Based on the assessment, recommendations are made to stakeholders, including the recycling industry, the ink and printing industry, the food industry and research institutes.     

紫外光分光光度法测定食品包装纸用天然色素虎杖黄酮含量的研究

研究了紫外光分光光度法测定食品包装纸用色素虎杖黄酮含量的方法,以芦丁为参照品,测量波长为359nm,平均回收率为99.96%,精密度为1.34%,说明紫外分光光度法是一种较理想的测定方法.     

Generalized numerical modelling of unsteady heat transfer during cooling and freezing using an improved enthalpy method and quasi-one-dimensional formulation

A numerical solution of a generalized Stefan problem is presented. It covers a great variety of unsteady heat conduction cases accompanied by phase transformations. A mathematical model is developed for determination of the unsteady-state temperature and enthalpy fields (as well as the space-time evolution of the phase content) and of the cooling and freezing (heating and thawing) times of food materials and other bodies of various configuration (representing multicomponent two-phase systems having one freezable component). An improved enthalpy method is proposed by which all non-linearities, caused by the temperature dependence of the thermophysical coefficients, are introduced in a functional relationship between the volumetric specific enthalpy and the Kirchhoff function. Thus the non-linearities are eliminated as a factor making the solution difficult. The applied approach possesses great adaptivity and flexibility in solving complicated moving boundary problems: it is suitable for both isothermal and non-isothermal phase change, reaches a high degree of correspondence between the real physical phenomenon and its mathematical formalization, uses uniform and easy fixed-grid computational techniques, makes it possible to avoid complications and to eliminate possible errors caused by ‘jumping’ of the equivalent specific heat capacity peak at the maximum of the latent heat effect, etc. Efficient procedures and algorithms for computer simulation of complex refrigerating technological processes are created. Experimental verification demonstrating the applicability and accuracy of the model is carried out.