J. Saurina

FTIR and DSC study of HDPE structural changes and mechanical properties variation when exposed to weathering aging during canadian winter

The aging of high-density polyethylene (HDPE) when exposed to drastic climatic conditions (Canadian winter, characterized by low temperature and abrupt temperature variations between the night and the day) was studied. The importance of degradation was determined by evaluating the microstructural changes in HDPE (i.e., oxidations, ramifications, and polymeric chain breaking) by means of FTIR spectrophotometry. The crystallinity variation in HDPE by FTIR and DSC was also studied. Both techniques led to coherent results: there was a loss of crystallinity due to weathering degradation. This crystallinity reduction produced a drastic decrease in impact energy. However, the other properties evaluated were not significantly affected.

Properties of PMMA artificially aged

Abstract We report the effects of artificial aging poly(methyl methacrylate) (PMMA). The aging of samples was performed using a xenon-arc lamp to simulate solar radiation. The maximum time of artificial aging was 1570 h, equivalent to 750 days of solar exposure. The purpose of this work is to study the properties of PMMA and their change with aging time. Analysis of chemical modification and structural change were performed by means of Fourier transformed infrared spectrophotometry (FTIR). The spectra confirmed that the aging process is initially promoted by hydrogen abstraction producing chain breaking and formation of the carbon–carbon non-saturated bonds and shorter macromolecular chains, such as vinyl, vinylidene and methyl. Calorimetric measurements of samples by differential scanning calorimetry (DSC) detected changes of glass transition temperatures. Finally, the fracture toughness was measured by tensile test measurements. The toughness decreased ∼40% after 1570 h.

Comparison of the thermal behavior of three cellulose fibers mercerized or submitted to solar degradation

Comparison of Lyocell, modal and viscose fibers was performed by means of differential scanning calorimetry, thermogravimetry and scanning electron microscopy. Thermal analysis was performed in air atmosphere. Samples were mercerized (21.3 g 100 mL-1) or submitted to solar radiation (seven months). Solar degraded samples presents a higher thermal stability and are initially less degraded. Furthermore, Lyocell fiber is the most stable under thermal degradation conditions. Heating produces a reduction of the fiber diameter (about 50%).

How long does it take to boil an egg? A simple approach to the energy transfer equation

The heating of simple geometric objects immersed in an isothermal bath is analysed qualitatively through Fouriers law. The approximate temperature evolution is compared with the exact solution obtained by solving the transport differential equation, the discrepancies being smaller than 20%. Our method succeeds in giving the solution as a function of the Fourier modulus so that the scale laws hold. It is shown that the time needed to homogenize temperature variations that extend over mean distances xm is approximately xm2/, where is the thermal diffusivity. This general relationship also applies to atomic diffusion. Within the approach presented there is no need to write down any differential equation. As an example, the analysis is applied to the process of boiling an egg.

DSC Study of the Effects of High Pressure and Spray-Drying Treatment on Porcine Plasma

One use of blood generated in abattoirs is to obtain dehydrated plasma which can be used as a functional ingredient in the preparation of foods. High hydrostatic pressure is a new technique for improvement of the sanitary quality of food products or their ingredients. The changes caused in the proteins by treatment can affect their functional properties, and differential scanning calorimetry DSC was therefore applied to detect possible conformational changes in the plasma proteins. The DSC results in the present study show that spray-drying does not appreciably affect the protein structure, but high-pressure treatment seems to have a denaturing effect.

Thermal analysis of two Fe-X-B (X=Nb, ZrNi) alloys prepared by mechanical alloying

The alloys, Fe60Ni14Zr6B20 and Fe85Nb9B6, were produced by mechanical alloying. The formation of the nanocrystallites (about 40 nm) was detected by X-ray diffraction. Furthermore, a slight oxygen presence (<3 at.%) was found by induced-coupled plasma and EDX microanalysis. After milling, calorimetry scans show low temperature recovery process and several crystallization processes related with the crystal growth and reordering of the crystalline phases. The apparent activation energies, 360 and 290 kJ mol-1, were determined by the Kissinger method. A mass increase (about 1 mass%) was detected by thermogravimetry.

Thermal analysis of aged hdpe based composites

HDPE based composites were produced with 10-20-30 and 40% composite mass of wood fiber. The coupling agents were epolene and silane. The thermal behavior of composite samples was analyzed as a function of the coupling agent content, the exposure time and the wood fibers content by means of differential scanning calorimetry. Calorimetric curves of all samples of first and second heating shows a similar behavior. Some significant relation has been observed between the exposure time and the degree of crystallinity for the same percentage of fiber samples. A linear relation between the melting enthalpy average vs. content in cellulosic fibers is detected. Nevertheless, the fibers non-pretreated with coupling agent show a lower loss of crystallinity of the HDPE matrix at low wood fiber content (10%). A slight diminution of the melting peak temperature is detected as increasing the exposure time.

Thermal and Structural Analysis of Mn49.3Ni43.7Sn7.0 Heusler Alloy Ribbons

The martensitic transformation and the solidification structures of Mn49.3Ni43.7Sn7.0 alloy ribbons prepared by melt-spinning were investigated by means of scanning electron microscopy, X-ray diffraction and differential scanning calorimetry. In those experiments special attention was given to melt spinning processing parameters such as the linear surface speed of the copper wheel rotating, the injection overpressure and the distance between wheel and injection quartz tube. Transformation entropy was found higher when increasing linear surface speed or the distance from injection point to wheel. The resulting samples showed chemical compositions close to the nominal ones and, at room temperature, crystallized in a monoclinic single-phase martensite with 14M modulation (without a significant variation in the cell parameters). Strong dependence of ribbon thickness on processing parameters was found. The average grain size varied between 1.6 and 6.6 μm, while the start temperature of the martensitic temperature varied from 394 to 430 K.

Thermal Analysis of a Polyethylene Glycol (PEG 4000): T-CR-T Diagram Construction

A modified isoconversional method is applied to perform the kinetic analysis of non-isothermal processes. The solidification process of a polyethylene glycol with a mean molecular of 4000 (PEG 4000) was here analyzed. It was stated that the Avrami model provides a good description of the solidification process.Temperature-cooling rate-transformation diagrams were constructed and there was a good agreement between experimental data and the calculated T-CR-T curves. Moreover, morphological qualitative analysis has been performed by means of scanning electron microscopy.

A Modified Method for T-CR-T Diagram Construction Application to Polyethylene Glycol

The analysis of DSC experimental data from solidification is improved, thanks to a modified isoconversional method. The validity of the proposed method is tested for a polyethylene glycol with a mean molecular weight of 6000. The temperature-cooling rate-transformation diagrams reveal good agreement between the experimental and calculated data.