Process-induced Degradation Research Articles

Cascadic degradation of selected polyolefin grades in a simulated closed-loop recycling process

Reintroducing recycled plastics into production processes can lead to irreversible degradation and changes in their properties, thereby limiting their recycling potential to a finite number of loops. This study investigates the impact of process-induced degradation resulting from multiple reprocessing cycles on specific material properties and aims to establish structure–property relationships. Four different polyolefins, including two polypropylenes, high-density polyethylene, and low-density polyethylene, were selected for the study. The materials underwent extrusion, pelletizing, injection molding, and milling before being reintroduced into the reprocessing cycle. This sequence of processing steps was repeated six times on each material. Various characterization techniques, including high-temperature gel permeation chromatography, melt mass flow rate, parallel-plate rheology, differential scanning calorimetry, gas chromatography–mass spectrometry, and optical defect control system, were performed to evaluate the molecular structure, rheological behavior, thermal stability, and the resulting contaminants and defects after each reprocessing step. The reprocessing of polypropylene resulted in a gradual decrease in the average molecular weights accompanied by a shift to lower viscosities and higher melt mass flow rates, whereas the polyethylene grades showed the opposite trend with a less pronounced effect in high-density polyethylene. The volatile organic compounds rose in polypropylene and sank in polyethylene after reprocessing. Additionally, all four materials exhibited an increase in degradation-related defects based on optical defect analysis.Graphical abstract

Review on the Degradation of Poly(lactic acid) during Melt Processing.

This review paper presents an overview of the state of the art on process-induced degradation of poly(lactic acid) (PLA) and the relative importance of different processing variables. The sensitivity of PLA to degradation, especially during melt processing, is considered a significant challenge as it may result in deterioration of its properties. The focus of this review is on degradation during melt processing techniques such as injection molding and extrusion, and therefore it does not deal with biodegradation. Firstly, the general processing and fundamental variables that determine the degradation are discussed. Secondly, the material properties (for example rheological, thermal, and mechanical) are presented that can be used to monitor and quantify the degradation. Thirdly, the effects of different processing variables on the extent of degradation are reviewed. Fourthly, additives are discussed for melt stabilization of PLA. Although current literature reports the degradation reactions and clearly indicates the effect of degradation on PLA's properties, there are still knowledge gaps in how to select and predict the processing conditions that minimize process-induced degradation to save raw materials and time during production.

Influence of boron implantation induced defects on solar cells: Modeling the process defects

The effect of process-induced defects on the photo-generated charge-carrier lifetime and solar cell performance is critical, which will help optimize the process recipe. In this work, we attempt to quantify the effects of process-induced defects during boron implantation on the n-type silicon wafer in different annealing ambiences. We have evaluated the role of defects that can be formed during oxygen and inert ambience annealing on n-type bifacial passivated emitter rear totally diffused solar cells using a recombination current prefactor (J0). The numerically calculated J0 is calibrated with the reported experimental J0 values using two different methods: (i) Shockley–Read–Hall lifetime and (ii) effective trap-density method. In the latter method, we used the simulated defect density profiles. Both methods capture the process-induced degradation. We observed that the process-induced defects could deteriorate by almost 1% absolute efficiency for the considered annealing conditions. We found that dislocation loops alone cause an ignorable effect on terminal characteristics, but other process-induced mechanisms could dominantly degrade the cell's performance. To further support, we show that independent defects (apart from coupled defects) other than dislocation loops could explain the experimentally reported boron-implanted diodes’ J–V curves under reverse bias conditions.

Effects of Hydrothermal Processing on Volatile and Fatty Acids Profile of Cowpeas (Vigna unguiculata), Chickpeas (Cicer arietinum) and Kidney Beans (Phaseolus vulgaris)

Legumes are an economical source of protein, starch, dietary fibre, fatty acids, vitamins and minerals. However, they are not as fully utilised, due to volatile compounds contributing to their undesirable odour. The purpose of this work was to understand the processing time's effect on the legumes' volatile profile. Hence, this study investigated the effects of hydrothermal processing times on the volatile and fatty acids profiles of cowpeas, chickpeas and kidney beans. All legumes were pre-soaked (16 h) and then hydrothermally processed at 95 °C for 15 to 120 min, using an open system to approximate standard household cooking practices and a closed system to represent industrial processing. Alcohol, aldehyde, acid and ester volatile compounds showed decreasing trends during processing, which can be associated with enzyme inactivation and process-induced degradation. This work showed that processing at 95 °C for 30 min significantly reduced the number of compounds commonly associated with undesirable odour, but showed no significant change in the fatty acid profile. Other volatiles, such as furanic compounds, pyrans and sulphur compounds, showed an increasing trend during processing, which can be related to the Maillard reactions. This observation contributes to the growing knowledge of legume processing and its impact on volatile flavour. It can advise consumers and the industry on selecting processing intensity to maximise legume utilisation.

Process-Property Relationships for Melt-Spun Poly(lactic acid) Yarn.

Poly(lactic acid) (PLA) is an attractive biomaterial due to its biocompatibility, biodegradability, and fiber-forming ability. However, the polymer is highly susceptible to both hydrolytic and thermal degradation during processing. Melt processing conditions typically involve high temperature and shear, whereas to prevent premature degradation, PLA needs to be processed under the mildest conditions that still yield the desired yarn properties. Thus, there is a need to determine the optimum processing conditions to achieve the desired properties of extruded PLA yarn. This study focuses on the effect of melt-spinning process parameters on the mechanical and physicochemical properties of the resulting PLA yarn and to derive their process–property relationships. The study compares the effect of process parameters like melt temperature, throughput through the spinneret, take-up speed at the wind-up roller, draw ratio, and drawing temperature on the yarn properties such as the yarn size (linear mass density), tenacity, elongation at break, crystallinity, and molecular weight. Depending on the combination of process parameters, the resulting PLA yarn had a yarn size ranging from 6.2 to 101.6 tex, tenacity ranging from 2.5 to 34.1 gf/tex, elongation at break ranging from 4 to 480%, and degree of crystallinity ranging from 14.6 to 62.2%. Certain combinations of processing parameters resulted in higher process-induced degradation, as evident from the reduction in molecular weight, ranging from 7.6% reduction to 20.5% reduction. Findings from this study increase our understanding on how different process parameters can be utilized to achieve the desired properties of the as-spun and drawn PLA yarn while controlling process-induced premature degradation.

Thermo-mechanical degradation of polypropylene (PP) and low-density polyethylene (LDPE) blends exposed to simulated recycling

Polypropylene (PP) and low-density polyethylene (LDPE) are among the most converted resins; as such, they also have the largest share in municipal waste fractions. Currently, there is a great societal and industrial need to recycle these polymers using thermo-mechanical processes. However, process-induced degradation during recycling operations may lead to irreversible changes. In this study, PP was blended with 0 to 10 wt.% of LDPE was subjected to consecutive twin-screw extrusion cycles (0 to 5 times) to mimic thermo-mechanical recycling. The effect of reprocessing on the rheological, thermal, and mechanical properties of PP/LDPE blends was investigated. An increase in MFR and decrease in viscosity was observed for PP and the blends. DSC results showed that the crystal structure of PP was seriously affected and generated more disorder with reprocessing. Although tensile properties were not substantially affected, all properties had a decreasing trend. While successive thermo-mechanical processing caused chain scission of the PP phase of the blend, the overall property of the studied blend composition maintained acceptable properties. Thus, recycling of PP with low PE blend additive is a feasible option not only to reduce plastic waste but also to generate value from an otherwise waste product.

Influence of Tabula Rasa on Process- and Light-Induced Degradation of Solar Cells Fabricated From Czochralski Silicon

Monocrystalline Si solar cells are fabricated from Czochralski (Cz) Si, which contains 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> oxygen atoms. Cz Si undergoes degradation during high-temperature thermal processing steps, such as dopant diffusion to form the p-n junction. This degradation in the bulk minority carrier lifetime can be related to the formation of oxygen precipitates. We found that a high-temperature annealing process known as tabula rasa (TR) not only mitigates process-induced degradation via oxygen precipitate nuclei dissolution, but also modifies subsequent light-induced degradation. We report on the bulk carrier lifetime of n- and p-type Cz Si after TR, which homogenizes the interstitial oxygen in the bulk Si to its monoatomic form in either an N2 or O2 environment. A control sample, which was not subjected to a TR processing step, experienced severe process-induced degradation during a boron emitter thermal budget as oxygen precipitates were formed in the Si bulk. These precipitates could be imaged using photoluminescence. Additionally, samples that underwent a TR processing step prior to the boron emitter thermal budget show efficient gettering of metallic impurities compared to the control sample, which showed a decline in the implied open-circuit voltage after the gettering step. Furthermore, modification of the interstitial oxygen bonding by TR had a strong effect on the light-induced degradation kinetics. Instead of a typically observed monotonic decrease, minority carrier lifetime increases first, followed by a nonmonotonic decrease over a ~20 h period. We conclude that by modifying the interstitial oxygen bonding via TR pretreatment, p-type Cz Si wafers become substantially resistant to harsh solar cell processes and strongly modified light-induced degradation, which would open alternative ways to mitigate this degradation mechanism.

Effect of Powder Recycling in Electron Beam Melting on the Surface Chemistry of Alloy 718 Powder

Process-induced degradation of the powder feedstock in additive manufacturing may have a negative influence on the final properties of built components. Consequently, it may lower the cost-effectiveness of powder bed additive manufacturing, which relies on recycling of the nonconsumed powder. This is especially the case for production of high-performance aero engine components where high material and process reliability is required. This study comprises a detailed investigation on the degradation of Alloy 718 powder during multicycle electron beam melting (EBM). The surface-sensitive analysis methods, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), were combined with scanning electron microscopy (SEM) to depict the differences in surface morphology, and surface composition of powder samples exposed to varying numbers of re-use cycles. The results show a significant change in surface characteristics after exposing the powder to the process and the environment in the build chamber. The virgin powder is covered mainly by a relatively thin and homogeneous oxide layer. The re-used powder, however, has undergone transformation to a heterogeneous oxide layer, rich in thermodynamically stable Al-rich oxide particulates, which started already during the first build cycle. Significant growth of the Al-rich oxide occurs via selective oxidation of Al under the conditions in the build chamber, including both pick-up of oxygen from the process atmosphere and redistribution of initial surface-bound oxygen from less-stable products like Ni-oxide and/or hydroxide.

Correction to: Process-induced degradation of bioresorbable PDLGA in bone tissue scaffold production.

The original version of this article unfortunately contained a mistake. E. Themistou was missing from the author group and so is now included with this erratum.

Process-induced degradation of bioresorbable PDLGA in bone tissue scaffold production.

Process-induced degradation of clinically relevant resorbable polymers was investigated for two thermal techniques, filament extrusion followed by fused deposition modelling (FDM). The aim was to develop a clear understanding of the relationship between temperature, processing time and resultant process-induced degradation. This acts to address the current knowledge gap in studies involving thermal processing of resorbable polymers. Poly(DL-lactide-co-glycolide) (PDLGA) was chosen for its clinically relevant resorption properties. Furthermore, a comparative study of controlled thermal exposure was conducted through compression moulding PDLGA at a selected range of temperatures (150-225 °C) and times (0.5-20 min). Differential scanning calorimetry (DSC) and gel permeation chromatography (GPC) were used to characterise thermally induced degradation behaviour. DSC proved insensitive to degradation effects, whereas GPC demonstrated distinct reductions in molecular weight allowing for the quantification of degradation. A near-exponential pattern of degradation was identified. Through the application of statistical chain scission equations, a predictive plot of theoretical degradation was created. Thermal degradation was found to have a significant effect on the molecular weight with a reduction of up to 96% experienced in the controlled processing study. The proposed empirical model may assist prediction of changes in molecular weight, however, accuracy limitations are highlighted for twin-screw extrusion, accredited to high-shear mixing. The results from this study highlight the process sensitivity of PDLGA and proposes a methodology for quantification and prediction, which contributes to efforts in understanding the influence of manufacture on performance of degradable medical implants.

MALDI-TOF technique to study process-induced degradation of bioabsorbable polymers

Event Abstract Back to Event MALDI-TOF technique to study process-induced degradation of bioabsorbable polymers Chirag R. Gajjar1, Haripriya Ramesh1 and Martin W. King1 1 North Carolina State University, College of Textiles, United States Introduction: Bioabsorbable polymers like poly(lactic acid) (PLA) are attractive biomaterials for regenerative medicine and tissue engineering applications due to their inherent property of in vivo resorption over time. However, the challenge is to be able to better understand and predict the degradation profile and the formation of by-products for bioabsorbable polymers. The problem is further compounded by the fact that these polymers are sensitive to processing conditions, such as temperature and moisture, which cause pre-mature degradation. In order to study process-induced degradation of PLA, we propose the use of Matrix-Assisted Laser Desorption /Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF-MS). MALDI-TOF technique has been widely used for the characterization of proteins and peptides, but recently, the technique has been used for synthetic polymers as well. In this study, PLA fibers were formed using melt-spinning process and the process parameters were varied. The fibers were then characterized using MALDI-TOF technique to study the extent and the by-products of process-induced degradation. Materials and Methods: NatureWorks PLA polymer (6100 HP) was used for the experimental melt-spinning process to form PLA multifilament yarns. The effects of extrusion temperature (220 °C vs. 250 °C), and the residence time in the extruder (3 minutes vs. 6 minutes) were considered for the study. The choice of the matrix, the solvent for the matrix and the analyte and the ratio of the matrix and the analyte are crucial parameters for good-quality and reliable MALDI measurements. We followed the protocol described here. Individual solutions of the analyte (PLA) and the matrix (2,5-dihydroxybenzoic acid (DHB)) were prepared in tetrahydrofuran (THF) at a concentration of 10 g/L. The analyte and the matrix were mixed in the ratio 1:5 (v/v) and the mass spectra were obtained using AB Sciex 5800 MALDI-TOF mass spectrometer. Results: The MALDI spectrum corresponding to 22 repeat units of PLA is shown in Fig. 1 [1]. This is an example that enables the identification of the cyclic and the linear oligomeric species summarized in Table-1 [1]. The predominant species found for PLA were, in order of abundance: (i) cyclic [LAc]n, mainly present as Na+ adducts ([M+Na]+: m/z 1608.3) and in smaller quantities, H+ adducts ([M+H]+: 1585.3 m/z); (ii) linear H-[LAL]n-OH, which bears a hydroxyl and a carbonyl end groups ([M+Na]+: m/z 1626.3 and [M+H]+: m/z 1604.3); and, (iii) linear H-[LAL]n-O-CH3, which has a methoxyl group and a hydroxyl group bearing ([M+Na]+: m/z 1640.3 and [M+H]+: m/z 1618.3), commonly found with PLAs obtained by ring opening polymerization (ROP) due to the use of alkoxydic initiators, which remain in the terminal units[2]. Other low predominant species found that might be formed as by-products at higher processing temperatures were: (iv) linear CH3-O-[LAL]n-CH3, bearing two methoxyl groups ([M+Na]+: m/z 1654.4 and [M+H]+: m/z 1632.4); and (v) linear CH3-CO-O-[LAL]n-H, which has a hydroxyl and a carboxylic methyl ester groups as end units ([M+Na]+: m/z 1668.4 and [M+H]+: m/z 1646.4), that might appear due to esterification reactions from different chain capping routes during polymerization. Different species corresponding to different m/z values would be formed under different processing conditions, which can be used to determine the extent of degradation. Conclusion: Different spectra from PLA samples produced under different processing conditions can be compared to determine the extent of process-induced degradation and analyze the by-products in the form of oligomeric species formed under each processing condition. Thus, the MALDI-TOF technique can facilitate a rapid quantitative study of degradation of bioabsorbable polymers at various stages of processing. A better understanding of process-induced degradation will help to design absorbable biomaterials, such as scaffolds, with better control of their in vivo performance.

Soy Dietary Supplements - Quantitation of Isoflavonoids, Quality Control, and Content Uniformity using NMR Spectroscopy

Herbal-based dietary supplements are a rapidly expanding market with increasing regulatory controls in many countries. NMR spectroscopy is a powerful tool for measuring, testing, and controlling the composition of these products. Soy-based supplements can contain both specific chemical ingredients such as genistin and a mixture of herbs or other biological ingredients. Using rapid and fully-automated NMR techniques, products like these can be tested for potency of labeled ingredients as well as the overall character of the product. In this study, three different over the counter formulations were investigated for potency, the presence of process-induced degradation, and content uniformity using a single, 3 minute per sample analysis. Verification and quantitation of the labeled isoflavonoid ingredients was straightforward, showing reasonable agreement with the expected results. The presence of genistein, a degradant created during the extraction of genistin from soybeans, was quantitated in each sample. The ratio of genistein to genistin indicates the harshness of the extraction process used to manufacture the raw soy material. Finally, PCA analysis was used to investigate the variability of the products with respect to each other and within tablets of the same product.

Soy Dietary Supplements - Quantitation of Isoflavonoids, Quality Control, and Content Uniformity using NMR Spectroscopy

Herbal-based dietary supplements are a rapidly expanding market with increasing regulatory controls in many countries. NMR spectroscopy is a powerful tool for measuring, testing, and controlling the composition of these products. Soy-based supplements can contain both specific chemical ingredients such as genistin and a mixture of herbs or other biological ingredients. Using rapid and fully-automated NMR techniques, products like these can be tested for potency of labeled ingredients as well as the overall character of the product. In this study, three different over the counter formulations were investigated for potency, the presence of process-induced degradation, and content uniformity using a single, 3 minute per sample analysis. Verification and quantitation of the labeled isoflavonoid ingredients was straightforward, showing reasonable agreement with the expected results. The presence of genistein, a degradant created during the extraction of genistin from soybeans, was quantitated in each sample. The ratio of genistein to genistin indicates the harshness of the extraction process used to manufacture the raw soy material. Finally, PCA analysis was used to investigate the variability of the products with respect to each other and within tablets of the same product.

Effects of the sputtering deposition process of metal gate electrode on the gate dielectric characteristics

Effects of the N2-introduced reactive sputtering deposition of metal gate electrodes on the gate leakage current and the dielectric reliability of the W/WNx and W/TiN metal gate MOS capacitors are investigated. The gate dielectric characteristics of W gate MOS capacitor are degraded during the sputtering deposition of the gate electrode. However, the sputtering process-induced degradation of the dielectric characteristics is improved by increasing N2 flow ratio during the deposition of WNx gate electrode. This improvement is considered to be due to the termination of the dangling bonds in the surface-damaged layer in the gate dielectric by the surface nitridation. The nitridation of ∼1.5 at.% is found to effectively improve both gate leakage characteristics and dielectric reliability of the W/WNx gate MOS capacitor to a level comparable to those of the poly-Si gate. The characteristics of W/WNx gate MOS transistors are also improved by the surface nitridation through the decrease of the gate leakage current. However, the surface nitridation enhances the electron trapping probability under substrate injection, which results in the lower activation energy of CVS–Qbd of metal gate MOS capacitors.

Optimization of YBa2Cu3O7−δ submicrometer structure fabrication

We present a study of the sputter etching step in the fabrication sequence of YBa2Cu3O7−δ submicrometer structures down to 200 nm linewidth. We identify oxygen effusion as the main reason for process-induced degradation of superconductivity. Oxygen reloading by plasma oxidation after pattern transfer efficiently recovers both the transition temperature Tc and the critical current density jc of the YBa2Cu3O7−δ submicrometer structures. Liquid-nitrogen cooling of the substrate is shown to efficiently suppress oxygen effusion during sputter etching. Critical current densities above 106 A/cm2 at 77 K are obtained for 0.75 μm wide and 10 μm long bridges.

Post-growth process-induced degradation in thin gate oxides

The mechanism of degradation in thin gate oxides due to postoxidation processing steps has been investigated using charge to breakdown QBD as a diagnostic tool. The QBD degradation is also correlated with trap generation rate in thin gate oxide. Controlled annealing experiments show that the gate oxide degradation is not related to the diffusion of phosphorous or other mobile ion impurities from the polysilicon film into the gate oxide. The degradation is caused by stress build up in silicon dioxide film with high-temperature annealing, due to viscous shear flow of the gate oxide at polysilicon/silicon dioxide and silicon dioxide/silicon interfaces. In another experiment, where the thickness of polysilicon was taken as a parameter, it is shown that degradation has a direct correlation with the polysilicon thickness which may be related to the mechanical stress.