Strategies to Cope with Inferior Long-Term Photostability of Bentonite Polyolefin Nanocomposites.

This study provides insight into the causes of inferior long-term stability of nanocomposites based on organic layered silicates (OLSs) used for cable mantles. A hierarchy was established by analyzing bentonite products and their respective polyolefin nanocomposites. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), gas adsorption, energy-dispersive spectroscopy (SEM-EDX), and infrared spectroscopy (IR) provided evidence for the adsorption of stabilizers onto the filler surface and thus their reduction in activity, promoting polymer oxidation. This behavior corresponds to the specific surface area of the incorporated OLS. Therefore, it can be stated that gas adsorption and XRD are especially useful for the evaluation of long-term photostability. It was revealed that photocatalytically active iron is of secondary importance since iron-rich bentonites still formed the most stable nanocomposite. This also applies to the Hofmann elimination products of the modifying agent, where higher contents do not accelerate the degradation process. No elimination products could be traced within the composites. Due to the polymer-filler interface being essential for long-term photostability, prior analysis of the filler surface properties can be used to estimate the stability of the respective nanocomposite as a rationale for product selection in the early stages of development. The reasons identified in this work for decreasing the long-term photostability of OLS nanocomposites compared with unfilled formulations is an important step toward increasing their stability.

Quality comparison of plastic packaging waste from different separation systems: Result enhancement with non-negative matrix factorization of FTIR spectra.

Whether plastic packaging waste is disposed of in different bins (source separation, S) or in a single bin (post source separation, P) is generally assumed to impact the waste stream's quality. To elucidate this question, we evaluated the quality of LDPE, HDPE, and PP plastic waste from both separation systems (S and P) through a concise analytical strategy. The materials received similar treatment after collection (e.g., washing, NIR-sorting). A multivariate approach to ATR-FTIR spectroscopy was developed to assess their material composition and the effect of washing. Results were complemented by TGA, DSC, and py-GC/MS analysis. The material performance was investigated by a lab-scale extrusion and granulation, followed by an assessment of the mechanical properties and the melt volume rate. Our study reveals the HDPE materials to be of good quality, regardless of their source. For LDPE and PP, the P-materials are fractionally more contaminated after washing. Both PP-materials display poor material performance with highly fluctuating elongations-at-break (between 30% and 380%). S-LDPE was found to contain more polymeric impurities than P-LDPE. We conclude that the quality depends strongly on the material type and on the treatment after collection (washing, sorting). The multivariate approach to FTIR data evaluation we propose aims at simplifying the quality evaluation of polyolefin waste plastics and may serve as a basis for future work in this field.

Unraveling the comonomer distribution in ethylene - vinyl ester terpolymers through liquid chromatography with infrared detection.

Polyolefins are the most commercially relevant polymers by volume. A readily available feedstock and their tailor-made microstructure allow to adapt polyolefins to many fields of application. Important molecular design features of olefin copolymers are the molar mass distribution (MMD) with the corresponding average values, comonomer type, chemical composition distribution (CCD) with the corresponding average and the tacticity distribution (TD). Advanced separation techniques i.e., high-temperature gel permeation chromatography (HT-GPC) as well as its hyphenation with high-temperature high performance liquid chromatography (HT-HPLC) in the form of high-temperature two-dimensional liquid chromatography (HT 2D-LC) have been successfully applied in this work. This allowed to deeply analyze the molecular heterogeneities of complex polyolefin terpolymers consisting of ethylene, vinyl acetate and branched vinyl ester monomers. By using filter-based infrared detection, the capabilities of HT-GPC are further extended so that the distribution of methyl- and carbonyl groups could be obtained along the molar mass axis. Using porous graphitic carbon (PGC) as a stationary phase for HT-HPLC separation provided information about the CCD of these complex polyolefins from experimental data as part of the hyphenated approach of HT 2D-LC. The latter revealed the full MMD x CCD distribution function, which is the key for a comprehensive analysis of the bivariate molecular structure of the polyolefin terpolymers.

Accurate determination of the layer thickness of a multilayer polymer film by non-invasive multivariate confocal Raman microscopy.

Plastic films of multiple layers are widely used in packaging. While a detailed spatially resolving analysis is highly relevant, the currently used approaches are either tedious or lack spatial resolution. An advanced method of confocal Raman microscopy was therefore developed in this work, using a water immersion objective combined with multivariate data analysis and ray tracing models for analysing a commercial-grade five-layer plastic film. The water immersion objective and ray tracing models are able to reduce the refraction induced artefacts in depth profiling and ensure a correct and accurate interpretation of each layer thickness. The multivariate data analysis can distinguish each layer without prior knowledge of the sample and unique markers of each composition. Finally, the resulting thicknesses of the film layers could be successfully compared to complementary experimental results. In conclusion, each layer thickness of a multilayer polymer film and its chemical composition could be measured accurately and non-invasively without sample preparation.