elastic–plastic materials displaying mixed hardening.
International Journal for Numerical Methods in Engineering
Vol. 14 (1979) 211–225.
Chaboche, J. L.: A review of some plasticity and viscoplasticity constitutive theories
Authors:Daniela Schlemmer, E. de Oliveira and M. Araújo Sales
Conventional plastics has a
large impact in increasing the environment’s pollution. That’s
why the interest has turned towards novel partially and completely biodegradable
polymers. In this work, blends of polystyrene and thermoplastic starch with
glycerol and Buriti (Mauritia flexuosa
L.) oil as plasticizers were prepared. Samples were analyzed using TG/DTG
and DSC techniques. The TG results indicated that the blends with Buriti oil
are thermally more stable than those with glycerol. The DSC analysis that
Buriti oil provides a higher degree of plasticization of PS, compared to the
blends plasticized using glycerol under the studied conditions.
Authors:D. Nomura, S. Mateus, M. Saiki and P. Bode
Plastic products may contain high levels of trace elements, which, upon final incineration, may affect the environment. In the case of packing material, may affect food quality. In this work, instrumental neutron activation analysis was applied to the determination of As, Ba, Br, Cd, Co, Cr, Fe, Sb, Sc, Se, Ti and Zn in plastic materials originated from household and hospital wastes. Toxic elements such as Cd and Sb were found at the levels of mg·kg–1 in some food containers and also high levels of Ti were found in opaque packages. The accuracy and the precision of results were also evaluated by interlaboratory comparison.
Studies have shown that plots of the log of the distribution ratio versus pH for the distribution of uranium(VI) between non-plasticized and TBP-plasticized dibenzoylmethane-loaded polyurethane foams and dilute aqueous uranium(VI) solutions have a limiting slope of 0.6 at equilibrium pH values 4 and reach a maximum distribution constant at about pH 6.0. The results indicate that the extracted complex is a simple chelate, UO2Me2, where HMe denotes dibenzoylmethane. Plasticization of the foam with TBP has been found to significantly enhance the rate of extraction.
Liquid scintillation counting is widely used to measure radioactivity, but it generates radioactive organic liquid waste.
Not to generate the liquid waste using a liquid scintillation counter, novel counting method with a plastic scintillation
vial was designed. The counting efficiency for 32P was 10–40% and that for 125I was 4–8%. The efficiency depended on the sample volume. The color quenching effect was negligible. No radioactive liquid
waste was generated by this method. In addition, you can reuse the measured sample.
Volume reduction studies were carried out on low level radioactive plastic wastes containing polyethylene, PVC and neoprene
by melt densification. The optimized temperature for melting of plastics was between 170 and 180 °C. Based on laboratory scale
studies. Plant scale studies were planned and conducted. The volume reduction factors obtained were around 30, which was 6-10
times higher than that of the conventional compaction process. Thermogravimetry and infrared spectroscopy were used to investigate
the thermal and structural properties of the given materials. The effect of the presence of salts like potassium permanganate
and hydrazine sulphate on the thermal properties of the materials was also evaluated. Leaching studies were also performed
on melt-densified specimens in the laboratory. The average leach index was observed to be around 9, which was higher than
the minimum stipulated value.
Authors:Y. H. Roos, K. Jouppila and Bettina Zielasko
An exotherm, observed in differential scanning calorimetry (DSC) scans of amorphous food materials above their glass transition temperature,Tg, may occur due to sugar crystallization, nonenzymatic browning, or both. In the present study, this exothermal phenomenon in initially anhydrous skim milk and lactose-hydrolyzed skim milk was considered to occur due to browning during isothermal holding at various temperatures above the initialTg. The nonenzymatic, Maillard browning reaction produces water that in amorphous foods, may plasticize the material and reduceTg. The assumption was that quantification of formation of water from theTg depression, which should not be observed as a result of crystallization under anhydrous conditions, can be used to determine kinetics of the nonenzymatic browning reaction. The formation of water was found to be substantial, and the amount formed could be quantified from theTg measured after isothermal treatment at various temperatures using DSC. The rate of water formation followed zero-order kinetics, and its temperature dependence well aboveTg was Arrhenius-type. Although water plasticization of the material occurred during the reaction, and there was a dynamic change in the temperature differenceT−Tg, the browning reaction was probably diffusioncontrolled in anhydrous skim milk in the vicinity of theTg of lactose. This could be observed from a significant increase in activation energy. The kinetics and temperature dependence of the Maillard reaction in skim milk and lactose-hydrolyzed skim milk were of similar type well above the initialTg. The difference in temperature dependence in theTg region of lactose, but above that of lactose-hydrolyzed skim milk, became significant, as the rate in skim milk, but not in lactose-hydrolyzed skim milk, became diffusion-controlled. The results showed that rates of diffusion-controlled reactions may follow the Williams-Landel-Ferry (WLF) equation, as kinetic restrictions become apparent within amorphous materials in reactions exhibiting high rates at the same temperature under non-diffusion-controlled conditions.
Authors:F. Wilmet, N. Sbirrazzuoli, Y. Girault and L. Elegant
The kinetic parameters of solid-plastic transitions on alcohols derived from neopentane were determined using differential scanning calorimetry (DSC) by a single or multiple scan analysis. The methods studied (Borchard-Daniels, Ellerstein, Multilinear law, Freeman-Carroll, Ozawa, Kissinger), never used before for that kind of transition, imply a single Arrhenius behaviour. These methods werre applied to 2,2-dimethyl 1-propanol (DP), 2,2-dimethyl 1,3-propanediol or neopentylglycol (NPG), 2-hydroxymethyl 2-methyl 1,3-propanediol or pentaglycerine (PG), and 2,2-dihydroxymethyl 1,3-propanediol or pentaerythritol (PE). A simple isothermal test is recommended to check the validity of activation energies experimentally obtained and Arrhenius frequency factors. Taking some restrictions on the heating rate for the heat evolution methods, the results are in agreement with the data obtained by isothermal tests. We have noted a linear dependence of the activation energy values on the number of hydroxyl groups with the exception of pentaerythritol. Isothermal simulations of the solid-plastic transition are an example of industrial applications.
Authors:J. Ely, K. Anderson, D. Bates, R. Kouzes, C. Lo Presti, R. Runkle, E. Siciliano and D. Weier
Plastic scintillator material is often used for gamma-ray detection in many applications due to its relatively good sensitivity
and cost-effectiveness compared to other detection materials. However, due to the dominant Compton scattering interaction
mechanism, full energy peaks are not observed in plastic scintillator spectra and isotopic identification is impossible. Typically
plastic scintillator detectors are solely gross count detectors. In some safeguards and security applications, such as radiation
portal monitors for vehicle screening, naturally-occurring radioactive material (NORM) often triggers radiation alarms and
results in innocent or nuisance alarms. The limited energy information from plastic scintillator material can be used to discriminate
the NORM from targeted materials and reduce the nuisance alarm rate. An overview of the utilization of the energy information
from plastic scintillator material will be presented, with emphasis on the detection capabilities and potential limitations
for safeguards and security applications.