Crystallization of Isotactic Polypropylene Nanocomposites with Fibrillated Poly(tetrafluoroethylene) under Elevated Pressure

Nanocomposites of isotactic polypropylene with 1–5 wt.% of fibrillated PTFE (PP/T) were prepared, and their crystallization during cooling under elevated pressure, in a wide pressure range, up to 300 MPa, as well as the resulting structure, were examined. The crystallization peak temperatures of PP/T, especially with 3 and 5 wt.% of PTFE, exceeded by up to 13 °C those of neat PP. Moreover, a fine-grain structure was formed in PP/T in the entire pressure range, which proved the ability of the fibrillated PTFE to nucleate crystallization of PP in the γ-form under elevated pressure. This also resulted in a higher crystallinity level developed in the γ-domain, before the temperature range of the α-domain was reached during cooling. Hence, the γ-content increased in comparison to that in neat PP, under the pressure up to 200 MPa, especially under 50–100 MPa.

Physical Properties of Biodegradable Poly(L-lactide) Induced by N, N -Bis(Benzoyl) 1, 3-Cyclohexanedicarboxylic Acid Dihydrazide as Crystallinity Additive

This work is aimed at synthesizing an organic compound N, N -bis(benzoyl) 1,3-cyclohexane-dicarboxylic acid dihydrazide (CABH) to focus on its effect on the non-isothermal crystallization of poly(L-lactide) (PLLA), meanwhile the melting behavior, thermal decomposition process and optical property of PLLA/CABH samples in different CABH concentrations were also investigated. It was found that CABH acted as efficient heterogeneous nucleating agent for inducing PLLA�s crystallization through comparative analysis of melt-crystallization process of the virgin PLLA with PLLA/CABH samples, and a high amount of CABH played a much more significant role in promoting PLLA�s crystallization. Additionally, the melt-crystallization processes also showed that both the cooling rate and the final melting temperature affected the crystallization behavior of PLLA, an increase of cooling rate could weaken the crystallization ability of PLLA/CABH samples, and the final melting temperature of 180�C made PLLA/CABH exhibit the best crystallization ability. For the cold-crystallization process, the cold-crystallization peak became flatter and shifted toward the lower temperature with increasing of CABH concentration, but an increase of heating rate could prevent the cold-crystallization peak from moving to low temperature because of the thermal inertia. The melting behaviors of PLLA/CABH depended on the previous crystallization and heating rate in heating, and the difference in melting behavior of PLLA/CABH samples effectively reflected the nucleation role of CABH, as well as the double melting peaks behavior of PLLA/CABH was thought to due to the melting-recrystallization. The introduction of CABH led to a drop in light transmittance, moreover, this negative effect were more obvious with an increase of CABH loading. In contrast, the fluidity of PLLA was significantly enhanced due to the existence of CABH.

IDENTIFICATION OF BIODEGRADABLE POLYMERS AS CONTAMINANTS IN THE THERMOPLASTICS RECYCLING PROCESS

In this work, the presence of biodegradable polymers in recycled plastic materials was characterized using readily available techniques. Recycled polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET) were studied. The contamination of these plastics with polylactic acid (PLA), polyhydroxybutyrate (PHB) and thermoplastic starch (TPS) was simulated using 10 wt.% of the contaminant. Fourier transform infrared spectrometry (FTIR) and differential scanning calorimetry (DSC) were used as characterization techniques. In addition, the effect of aging on recycled products from PET blends contaminated with TPS and PHB was studied. The results show changes in the intensity of the FTIR spectra bands of the PS and PP blends contaminated with biodegradable polymers. By DSC, changes in the cold crystallization peak of recycled PET are observed when mixed with TPS and PHB. When the contaminant is PLA, the changes are masked due to the thermal characteristics of both materials. In PS, changes in the calorimetric curves are identified by the presence of PLA and PHB. Contamination with PLA, PHB and TPS hinders the processing of recycled PET after one year of storage due to the aging of the material.

Regional zircon U-Pb geochronology for the Maniitsoq region, southwest Greenland

Zircon U-Pb geochronology places high-temperature geological events into temporal context. Here, we present a comprehensive zircon U-Pb geochronology dataset for the Meso- to Neoarchean Maniitsoq region in southwest Greenland, which includes the Akia Terrane, Tuno Terrane, and the intervening Alanngua Complex. The magmatic and metamorphic processes recorded in these terranes straddle a key change-point in early Earth geodynamics. This dataset comprises zircon U-Pb ages for 121 samples, including 46 that are newly dated. A principal crystallization peak occurs across all three terranes at ca. 3000 Ma, with subordinate crystallization age peaks at 3200 Ma (Akia Terrane and Alanngua Complex only), 2720 Ma and 2540 Ma. Metamorphic age peaks occur at 2990 Ma, 2820–2700 Ma, 2670–2600 Ma and 2540 Ma. Except for one sample, all dated metamorphic zircon growth after the Neoarchean occurred in the Alanngua Complex or within 20 km of its boundaries. This U-Pb dataset provides an important resource for addressing Earth Science topics as diverse as crustal evolution, fluid–rock interaction and mineral deposit genesis.

Effect of Cyanuric Acid as an Efficient Nucleating Agent on the Crystallization of Novel Biodegradable Branched Poly(Ethylene Succinate)

Novel biodegradable branched poly(ethylene succinate) (b-PES) composites, i.e., nucleated b-PES samples, were prepared by incorporating low loadings of cyanuric acid (CA) through a solution and casting method to enhance the crystallization rate. As an efficient nucleating agent, CA could remarkably increase the nonisothermal melt crystallization peak temperature, shorten the crystallization half-time, accelerate the overall isothermal melt crystallization, and enhance the nucleation density of b-PES spherulites in the composites. Despite the addition of CA, the crystallization mechanism and crystal structure of b-PES remained unchanged. A possible epitaxial crystallization mechanism may account for the nucleation of b-PES crystals induced by CA.

Crystallization and properties of nucleated poly(l-lactic acid): Effect of cyclopentanecarboxylic acid derivative as a new nucleating agent

In this study, the potential effects of N, N’-dodecanedioic bis(cyclopentanecarboxylic acid) dihydrazide (BCADD) as a new additive in poly(L-lactic acid) (PLLA) was estimated. The comparative study on the melt-crystallization showed that the BCADD as heterogeneous nuclei facilitated crystallization of PLLA in cooling, which indicated by the obvious crystallization exotherms and sharp melt-crystallization peak. Unfortunately, with increasing of BCADD from 0.5 wt% to 3 wt%, it is unexpected that the melt-crystallization peak of the BCADD-nucleated PLLA shifted toward the lower temperature and became flatter, evidencing the importance of BCADD loading for PLLA’s crystallization. Additionally, the cooling rate and the final melting temperature were also proved to be important influence factors during PLLA’s melt-crystallization process, but in contrast with the effect of the final melting temperature on the melt-crystallization, a higher cooling rate could more seriously weaken crystallization ability of the BCADD-nucleated PLLA. The chemical nucleation mechanism was proposed to explain the promoting effect of BCADD on the crystallization of PLLA via the analysis of frontier orbital energy. The melting behaviors after crystallization further confirmed the crystallization accelerating role of BCADD, and the melting behaviors were affected by the heating rate, crystallization temperature and BCADD loading. Although the onset thermal decomposition of the BCADD-nucleated PLLA occurred at lower temperature comparing with the pure PLLA, the intermolecular interaction of PLLA with BCADD attempted to prevent the decrease of thermal stability. Overall, the addition of BCADD resulted in the complicated effect on the tensile modulus and tensile strength of PLLA, but the elongation at break continuously decreased when increasing BCADD loading.

Thermomagnetic Analysis of the Crystallization in Soft Magnetic Nanocrystalline Alloys

In this work, we investigated the dynamics of nanocrystallization from the amorphous state of the Fe72.5Cu1Nb2Mo1.5Si14B9 alloy together with magnetic phase transformations. The thermomagnetic analysis was performed with the simultaneous recording of the temperature inside the core by a thermocouple and the inductance of the winding wound over the core. It was found that the permeability of the core after the crystallization peak first increases rapidly, and then decreases and stabilizes at some level. Permeability growth begins at a temperature that coincides with the Curie point of the Fe80Si20 solid solution. A decrease in permeability was associated with stabilization of the structure of the amorphous and crystalline phases upon cooling. With decreasing temperature, the active redistribution of chemical elements is suppressed, and silicon atoms occupy a stable position in the crystal lattice of iron. Nanocrystalline cores have different Curie temperatures in the state after the peak of crystallization and 300 seconds after the peak. This indicates the continuation of the diffusion of silicon from the amorphous matrix into Fe-Si nanocrystals for some time after the crystallization peak.

Prominent Crystallization Promotion Effect of Montmorillonite on PTT/PC Blends with PTT as the Continuous Phase

To regulate the crystallization of poly(trimethylene terephthalate) (PTT) retarded by melt blending with polycarbonate (PC), the crystallization of the PTT/PC blend was investigated employing nano-montmorillonite (MMT) as a crystallization promoter with PTT as the continuous phase. The results showed that MMT exhibits a significant promoting effect on PTT crystallization; the presence of 1 wt. % MMT shifts the initial and peak crystallization temperatures of the 70/30 PTT/PC blend to ~17 °C and ~32 °C, respectively. Additionally, the full width at half maximum (FWHM) narrows by ~45%, and the ΔHc increases by 3.7 J.g−1. The accelerating effect of MMT is determined by its distribution and dispersion which depends on the shear intensity, mixing mode, and loading. MMT is easier to exfoliate via the two-step method than by the one-step method. The distribution in the PTT phase is enriched along the phase interface forming an MMT layer. This endows sections of the PTT with abundant nuclei and thus crystallization is promoted markedly compared with the one-step method. Moreover, the finer MMT migrates more readily to the interface to cause a much smoother phase interface. However, a secondary crystallization peak appears when the shear force is not sufficient enough to make MMT finely dispersed, in case of the two-step method and the MMT content is increased to 3 wt. %. The mixing temperature shows little effect on the acceleration of MMT on the crystallization of PTT/PC compared with the shear force. Only when MMT did not exfoliate or uncomplete did the presence of epoxy resin help to promote crystallization because of the improved MMT dispersion.

Heterogeneous Nucleation Effect of N, N'-Adipic Bis(4-phenylbutyric Acid) Dihydrazide on Crystallization Process of Poly(L-lactic Acid)

Enhancing crystallization ability is a fundamental challenges in Poly(L-lactic acid) (PLLA) industry, therefore, the goal of this work was to synthesis a new organic nucleating agent N, N'-adipic bis(4-phenylbutyric acid) dihydrazide (APAD), and investigate its effect on non-isothermal crystallization, isothermal crystallization, melting behavior, thermal stability, and optical property of PLLA. Non-isothermal melt crystallization results showed that APAD acted as more effective nucleating and accelerating agent for the crystallization of PLLA, as a result, upon cooling at 1 °C/min, PLLA/0.5 %APAD had the highest onset crystallization temperature 136.4 °C and the crystallization peak temperature 132.0 °C, as well as the largest non-isothermal crystallization enthalpy 48.1 J/g. However, with increasing of APAD concentration from 0.5 wt.% to 3 wt.%, the crystallization peak shifted to the lower temperature. In contrast, for the non-isothermal cold crystallization process, the effect of APAD concentration on the crystallization behavior of PLLA was negligible. Additionally, the non-isothermal crystallization process was also depended on the cooling rates and the final melting temperature. In isothermal crystallization section, to compare with the primary PLLA, the crystallization half-time of PLLA/APAD could decrease from 254.3 s to the minimum value 29.4 s, with 0.5 wt.% APAD contents at 125 °C. Melting behavior of PLLA/APAD samples under different conditions further confirmed the heterogeneous nucleation effect of APAD for PLLA, and the appearance of the double melting peaks was attributed to the melting-recrystallization. Finally, the addition of APAD decreased the thermal stability to some extent, although APAD could not change the thermal decomposition profile of PLLA. And a drop of PLLA/APAD samples in light transmittance resulted from the double influence of the enhancement of crystallization and the opaqueness of APAD.

Fabrication of Ultrafine PPS Fibers with High Strength and Tenacity via Melt Electrospinning

Electrospinning (e-spinning) is an emerging technique to prepare ultrafine fibers. Polyphenylene sulfide (PPS) is a high-performance resin which does not dissolve in any solvent at room temperature. Commercial PPS fibers are produced mainly by meltblown or spunbonded process to give fibers ~20 μm in diameter. In this research, an in-house designed melt electrospinning device was used to fabricate ultrafine PPS fibers, and the e-spinning operation conducted under inert gas to keep PPS fibers from oxidizing. Under the optimum e-spinning conditions (3 mm of nozzle diameter, 30 kV of electrostatic voltage, and 9.5 cm of tip-to-collector distance), the as-spun fibers were less than 8.0 μm in diameter. After characterization, the resultant PPS fibers showed uniform diameter and structural stability. Compared with commercial PPS staple fibers, the obtained fibers had a cold crystallization peak and 10 times higher storage modulus, thereby offering better tensile tenacity and more than 400% elongation at break.