Non-isothermal crystallization process of polyoxymethylene studied by two-dimensional correlation infrared spectroscopy

CH4 and CH2O Oxidation in Lean Gas Engine Exhaust Using Fe2O3 Catalysts

A systematic series of commercial α-Fe2O3 catalysts was investigated with respect to the after-treatment of the lean exhaust emissions of gas engines. The samples were physico-chemically characterized by X-ray diffraction, Laser Raman spectroscopy, N2 physisorption, temperature-programmed reduction with CO and the temperature-programmed desorption of CO2, whereas the catalytic efficiency was evaluated using a model exhaust gas. Structure–activity correlations showed that for the oxidation of CH4 the number of active Fe sites and the availability of surface and subsurface oxygen are crucial properties of the catalysts. By contrast, the conversion of CH2O is driven by the CO2 adsorption capacity and the amount of OH surface species, in line with the mechanistic understanding gained by step function experiments and diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS). The in-situ DRIFTS studies suggested that the CH2O oxidation follows a Cannizzaro-type mechanism including the reaction of two CH2O molecules with a surface OH site to form CH3OH and formate species. The subsequent conversion of the formate moieties with H2O results in the reconstruction of the OH groups and the release of formic acid. The latter is assumed to decompose into CO2 and H2 which finally oxidizes to H2O. The best iron oxide catalyst was upscaled to the level of a real catalytic converter, which was tested in the lean exhaust gas of a 600 kW biomethane engine. As a result, the catalyst demonstrated high activity with regard to CH2O and CO removal above 300 and 500 °C, respectively, while only negligible conversion of CH4 occurred.

Use of synthetic wollastonite nanofibers in enhancing mechanical, thermal, and flammability properties of polyoxymethylene nanocomposites

This study investigates the mechanical, thermal, and flammability properties of synthetic wollastonite nanofibers (SWN) reinforced polyoxymethylene (POM) nanocomposites. SWN has been added into the POM nanocomposites in the range of 0.5–3 phr via melt blending. The mechanical properties were investigated through tensile and impact tests with scanning electron microscopy and energy dispersive X‐ray analysis. The thermal characterization was performed by thermogravimetry analysis and differential scanning calorimetry. Flame retardancy of nanocomposites was studied through cone calorimetry analysis and limiting oxygen index test. The tensile strength of nanocomposites improved by 5.88% at 1 phr SWN content, whereas Young's modulus increased with increasing content. The thermal stability of nanocomposites was enhanced as indicated by the higher initial degradation temperature, which rose about 22°C at 1 phr SWN content. The POM/SWN nanocomposites exhibited better mechanical strength despite their lower crystallinity due to the substantial reinforcing effect of SWN. The flame retardancy of nanocomposites improved, as indicated by the reduction of peak heat release rate from the cone calorimetry test. This study shows that SWN has simultaneously enhanced the mechanical strength, thermal stability, and flame retardancy of POM nanocomposites and has the potential in automotive applications.

Influence of early thermal-oxidative ageing on the structure and properties of polyoxymethylene copolymer

Thermal-oxidative ageing of polyoxymethylene (POM) copolymer in the oven at 100°C for 1, 2, 3, 5, 7, 10, 14 and 21 days and the influence of early thermal-oxidative ageing on POM structure and properties were studied by means of wide-angle X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry and tensile test. Based on the results, we found that the early thermal-oxidative ageing of POM copolymer can be divided into three regions. The region I is the initial 3 days. In this region, some molecular chains rearranged, resulting in internal stress relaxation, increase of crystallinity degree and grain size due to the perfection of crystal structure; both extended chain crystal (ECC) and folded chain crystal (FCC) increased and ECC grew faster than FCC. The region II is from 3 days to 10 days, and in this region, chain scission took place in amorphous region and led to chemi-crystallization. The region III is after 10 days. In this region, the structure and performance of POM copolymer reached a stable situation at this stage. In this work, the difference between skin and core were also analysed.

What Can You Learn about Apparent Surface Free Energy from the Hysteresis Approach?

The apparent surface free energy is one of the most important quantities in determining the surface properties of solids. So far, no method of measuring this energy has been found. The essence of contact angle measurements is problematic. Contact angles should be measured as proposed by Young, i.e., in equilibrium with the liquid vapors. This type of measurement is not possible because within a short time, the droplet in the closed chamber reaches equilibrium not only with vapors but also with the liquid film adsorbed on the tested surface. In this study, the surface free energy was determined for the plasma-activated polyoxymethylene (POM) polymer. Activation of the polymer with plasma leads to an increase in the value of the total apparent surface free energy. When using the energy calculations from the hysteresis based approach (CAH), it should be noted that the energy changes significantly when it is calculated from the contact angles of a polar liquid, whereas being calculated from the angles of a non-polar liquid, the surface activation with plasma changes its value slightly.

Thermal Stabilization of Polyoxymethylene by PEG-Functionalized Hydroxyapatite: Examining the Effects of Reduced Formaldehyde Release and Enhanced Bioactivity

Nanostructured hydroxyapatite (HA) functionalized with poly(ethylene glycol) (HA-g-PEG) of different molar mass was used as a thermal stabilizer to prepare polyoxymethylene (POM) composites by a melt processing method. The chemical and crystalline structure of (HA-g-PEG) and POM/HA-g-PEG composites was investigated by means of FTIR and XRD. The thermal properties, degree of crystallinity, and melting behaviour of POM-based composites were analysed with TG, DSC, and TOPEM DSC methods. The tensile strength, Young’s modulus, toughness, and wettability of POM were investigated as well. A preliminary assessment of bioactivity, in vitro chemical stability, and formaldehyde release from POM/HA-g-PEG composites by Schiff’s test was also performed. An SEM/EDX method was used to observe the morphology of POM/HA-g-PEG composites. The results indicate that the addition of 1% HA-g-PEG slightly increases the melting temperature and degree of crystallinity. In small amounts, HA-g-PEG particles probably act as nucleating agents for the POM crystallization process. Incorporation of 5% HA-g-PEG to POM caused a decrease in the crystallinity of the polymer matrix, as a result, some mechanical properties of POM/HA-g-PEG composites also decreased. The thermal stability of POM/HA-g-PEG composites improved significantly from 309°C for unmodified POM to 342°C for POM/10.0% HA-g-PEG 600. The most effective thermal stabilizer was synthesized with the lowest mass-average molar mass PEG. The in vitro bioactivity test confirmed that, as the average molar mass of PEG in HA-g-PEG hybrids increased, POM-based composites indicated higher bioactivity. The in vitro chemical stability analysis results showed that both the POM matrix and the HA-g-PEG additive remain stable during the whole incubation time. Importantly, after seven days of dynamic incubation, no formaldehyde was detected in all filtrates, which is crucial in biomedical applications, among others.

Understanding the crystallization behavior of polyamide 6/polyamide 66 alloys from the perspective of hydrogen bonds: projection moving-window 2D correlation FTIR spectroscopy and the enthalpy

In this study, the crystallization behavior of PA6/PA66 alloys was studied using in situ FTIR spectroscopy, combined with Proj-MW2D correlation analysis and Van't Hoff analysis.

Cross-linking process of cis-polybutadiene rubber with peroxides studied by two-dimensional infrared correlation spectroscopy: a detailed tracking

Detailed mechanism of cis-BR cross-linking with peroxides was studied using PCMD2D and 2D correlation FTIR, and a 5-step process was determined.

Separation of the molecular motion from different components or phases using projection moving-window 2D correlation FTIR spectroscopy for multiphase and multicomponent polymers

This study developed a new analytical method called projection moving-window 2D correlation FTIR spectroscopy to separate the molecular motion of groups generated from different components or phases for multiphase and multicomponent polymers.

Hydrogen bond breaking of TPU upon heating: understanding from the viewpoints of molecular movements and enthalpy

Hydrogen bond breaking of TPU based on 4,4′-methylenediphenyl diisocyanate (MDI)/1,4-butanediol (BDO) upon heating was studied and elucidated from molecular movements and enthalpy.