Degradation Of Polypropylene Research Articles

Experimental analysis on products distribution, characterization and mechanism of waste polypropylene (PP) and polyethylene terephthalate (PET) degradation in sub-/supercritical water

Supercritical water (SCW) treatment of plastics is a clean technology in the ‘waste-to-energy’ path. In this work, PP and PET plastics were processed by sub-/supercritical water. The results showed that temperature was the most important factor of the PP and PET degradation. The influence of factors on the degradation of plastics follows the following order: temperature > residence time > plastic/water ratio. These factors influenced the yield of gas products by promoting or inhibiting various reactions (such as reverse water gas shift reaction, methylation reaction, and Fischer-Tropsch synthesis reaction). Besides, the composition of liquid oil was also analyzed. The main composition of the liquid oil produced by PET was benzoic acid and acetaldehyde, which were generated from the decarboxylation of terephthalic acid (TPA) and dehydration reaction of ethylene glycol (EG). The liquid oil from PP was mainly long-chain olefins, long-chain alkanes, cycloalkanes, etc., which were formed by the interaction of various methyl, alkyl, hydroxyl, and other free radicals. This study could build fundamental theories of plastic mixture treatment.

The programmed sequence-based oxygenase screening for polypropylene degradation

Enzymatic degradation of plastic is an effective means of plastic recycling and pollution control. However, the strong chemical inertness of polypropylene plastic (PP) severely impedes its oxidative cleavage, making it resistant to degradation. In this study, based on sequence screening of Hidden Markov Model (HMM), a dioxygenase (HIS1) was identified and characterized to be effective in PP oxidation. Various kinds of PP products, including plastic films, microplastics, and disposable water cups or bags, were HIS1-degraded with cracks and holes on the surface. The hydrophobic binding was the primary force driving oxidative degradation in the specific cavity of HIS1. The discovery of HIS1 achieved a zero breakthrough in PP biodegradation, providing a promising candidate for the selection and evolution of degrading enzymes.

A Study of the Friction Stir Lap Welding of AA5052 and Polypropylene.

Friction stir lap welding (FSLW) remains a pioneering technique for creating hybrid joints between AA5052 aluminium alloy and polypropylene (PP), particularly with the metal-on-top configuration. Building upon previous research, this study introduces a tapered fluted pin tool design and investigates its effectiveness in the welding process. Our results, supported by ANOVA, chemical, and microstructural analyses, reiterate that the optimal welding parameters stand at a rotational speed of 1400 RPM and a traverse speed of 20 mm/min. This combination produces a joint tensile strength of 3.8 MPa, signifying 16.54% of the weaker material's inherent strength. Microstructural evaluations revealed a unique composite of aluminium chips intermeshed with PP, strengthened further by aluminium hooks. Crucially, mechanical interlocking plays a predominant role over chemical bonding in achieving this joint strength. The study underscores the absence of significant C-O-Al bonds, hinting at the PP degradation without the thermo-oxidation process. Additionally, joint strength was found to inversely correlate with the interaction layer's thickness. The findings fortify the promise of FSLW with the novel fluted pin design for enhancing joints between AA5052 and PP, emphasising the potential of mechanical interlocking as a principal factor in achieving high-quality welds.

Exposure to irregular microplastic shed from baby bottles activates the ROS/NLRP3/Caspase-1 signaling pathway, causing intestinal inflammation

Irregularly shaped microplastics (MPs) released from infant feeding bottles (PP-IFBs) may exhibit increased cytotoxicity, in contrast to the commonly studied spherical MPs. This study presents an initial analysis of the thermal-oxidative aging process of plastic shedding from feeding bottles, and investigates the inflammatory response induced by these atypical MPs in human intestinal cells (Caco-2). The PP-IFBs' surface displayed non-uniform white patches and increased roughness, revealing substantial structural alteration and shedding, especially during actions such as shaking, boiling water disinfection, and microwave heating. FT-IR and 2D-COS analyses revealed that oxygen targeted the C–H and C–C bonds of polypropylene molecular chain, producing RO· and ·OH, thereby hastening polypropylene degradation. When human intestinal cells were exposed to MPs from PP-IFBs, oxidative stress was triggered, resulting in lowered glutathione levels, augmented reactive oxygen species (ROS), and heightened lipid peroxidation. Elevated levels of pro-inflammatory cytokines (IL-6 and TNFα) signified an active inflammatory process. The inflammatory response was notably more intense when exposed to MPs released through boiling water disinfection and microwave heating treatments, primarily due to the larger quantity of MPs released and their higher proportion of smaller particles. Furthermore, the NLRP3 inflammasome was identified as critical in initiating this inflammatory chain reaction due to the mitochondrial ROS surge caused by MPs exposure. This was further validated by inhibitor studies, emphasizing the role of the ROS/NLRP3/Caspase-1/IL-1β signaling pathway in in promoting intestinal inflammation. Therefore, swift actions are recommended to protect infants against the potential health effects of MPs exposure.

Improvement of the Mathematical Model for Quality Assurance in the Determination of Kinetic Parameters of Thermal Degradation of Polypropylene Through Thermogravimetric Analysis

AbstractRobust mathematical treatment of the Ozawa/Flynn/Wall isoconversion method is conducted to determine the value and uncertainty of the activation energy and pre‐exponential factor for the degradation of polypropylene in thermogravimetric analysis experiments at constant heating rates. The present work employs mathematical models and uncertainty propagation techniques based on the Guide to the Expression of Uncertainty in Measurement to estimate the Arrhenius activation energy and pre‐exponential factor due to the uncertainty of the integration constant b, both in a linear and a third‐degree reciprocal polynomial model with respect to x. The error arising from Doyle's linear approximation in the improper integral of temperature in the Arrhenius equation is examined, and an alternative method is proposed to correct this error, reducing it to 0.032% in the working interval of −200 ≤ x ≤ −15, where x = −E/RT. Given the increased sensitivity of modern thermogravimetric analysis equipment, these improvements are considered essential for obtaining reliable results that align with experimental precision limits compared to previous works. Thus, this allows for the development of an enhanced quality assurance framework by providing more robust uncertainty estimation and a better understanding of the method. Moreover, this approach can be applied to other similar polymer system.

Influence of gossipol azomethines on thermal-oxidative degradation of polypropylene

The article discusses the influence of gossypol azomethines on the antioxidant activity of polypropylene (PP) and the induction period of polymer oxidation. Thermostabilizing activity of the studied compounds during the thermal oxidation of PP was determined and the inhibiting groups that are involved in the inhibition of the thermal-oxidative degradation of the polymer at high temperatures were identified.

Degradation of polypropylene by fungi Coniochaeta hoffmannii and Pleurostoma richardsiae

The urgent need for better disposal and recycling of plastics has motivated a search for microbes with the ability to degrade synthetic polymers. While microbes capable of metabolizing polyurethane and polyethylene terephthalate have been discovered and even leveraged in enzymatic recycling approaches, microbial degradation of additive-free polypropylene (PP) remains elusive. Here we report the isolation and characterization of two fungal strains with the potential to degrade pure PP. Twenty-seven fungal strains, many isolated from hydrocarbon contaminated sites, were screened for degradation of commercially used textile plastic. Of the candidate strains, two identified as Coniochaeta hoffmannii and Pleurostoma richardsiae were found to colonize the plastic fibers using scanning electron microscopy (SEM). Further experiments probing degradation of pure PP films were performed using C. hoffmannii and P. richardsiae and analyzed using SEM, Raman spectroscopy and Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR). The results showed that the selected fungi were active against pure PP, with distinct differences in the bonds targeted and the degree to which each was altered. Whole genome and transcriptome sequencing was conducted for both strains and the abundance of carbohydrate active enzymes, GC content, and codon usage bias were analyzed in predicted proteomes for each. Enzymatic assays were conducted to assess each strain’s ability to degrade naturally occurring compounds as well as synthetic polymers. These investigations revealed potential adaptations to hydrocarbon-rich environments and provide a foundation for further investigation of PP degrading activity in C. hoffmannii and P. richardsiae.

Accelerated in vitro oxidative degradation testing of polypropylene surgical mesh.

Polypropylene (PP) surgical mesh had reasonable success in repair of hernia and treatment of stress urinary incontinence (SUI); however, their use for the repair of pelvic organ prolapse (POP) resulted in highly variable results with lifelong complications in some patients. One of several factors that could be associated with mesh-related POP complications is changes in the properties of the implanted surgical mesh due to oxidative degradation of PP in vivo. Currently, there are no standardized in vitro bench testing methods available for assessing the susceptibility to oxidative degradation and estimating long-term in vivo stability of surgical mesh. In this work, we adapted a previously reported automated reactive accelerated aging (aRAA) system, which uses elevated temperatures and high concentrations of hydrogen peroxide (H2 O2 ), for accelerated bench-top oxidative degradation testing of PP surgical mesh. Since H2 O2 is highly unstable at elevated temperatures and for prolonged periods, the aRAA system involves a feedback loop based on electrochemical detection methods to maintain consistent H2 O2 concentration in test solutions. Four PP mesh samples with varying mesh knit designs, filament diameter, weight, and % porosity, were selected for testing using aRAA up to 4 weeks and characterized using thermal analysis, Fourier-transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) and scanning electron microscopy (SEM). Additionally, the oxidation index (OI) values were calculated based on the FTIR-ATR spectra to estimate the oxidative degradation and oxidation reaction kinetics of PP surgical mesh. The OI values and surface damage in the form of surface flaking, peeling, and formation of transverse cracks increased with aRAA aging time. The aRAA test method introduced here could be used to standardize the assessment of long-term stability of surgical mesh and may also be adopted for accelerated oxidative degradation testing of other polymer-based medical devices.

The interactions between mixed waste from discarded surgical masks and face shields during the degradation in supercritical water

The widespread use of surgical masks made of polyolefin and face shields made of polyester during pandemics contributes significantly to plastic pollution. An eco-friendly approach to process plastic waste is using supercritical water, but the reaction of mixed polyolefin and polyester in this solvent is not well understood, which hinders practical applications. This study aimed to investigate the reaction of waste surgical masks (SM) and face shields (FS) mixed in supercritical water. Results showed that the optimal treatment conditions were 400 °C and 60 min, achieving a liquid oil yield of 823.03 mg·g−1 with 25 wt% FS. The interaction between polypropylene (PP), polyethylene terephthalate (PET), and iron (Fe) in SM and FS mainly determined the production of liquid oil products such as olefins and benzoic acid. The methyl-branched structure of PP enhanced PET hydrolysis, resulting in higher production of terephthalic acid (TPA). The degradation of PP was facilitated by the acidic environment created by TPA and benzoic acid in the reaction. Moreover, the hydrolysis of PET produced carboxylic acid, which coordinated with Fe3+ to form Fe-H that catalyzed the polymerization of small olefins, contributing to higher selectivity for C9 olefins. Therefore, this study provides valuable insights into the degradation mechanism of mixed PPE waste in supercritical water and guidance for industrial treatment.

A novel marine bacterium Exiguobacterium marinum a-1 isolated from in situ plastisphere for degradation of additive-free polypropylene

As the ecological niche most closely associated with polymers, microorganisms in the ‘plastisphere’ have great potential for plastics degradation. Microorganisms isolated from the ‘plastisphere’ could colonize and degrade commercial plastics containing different additives, but the observed weight loss and surface changes were most likely caused by releasing the additives rather than actual degradation of the plastics itself. Unlike commercial plastics that contain additives, whether marine microorganisms in the ‘plastisphere’ have adapted to additive-free plastics as a surface to colonize and potentially degrade is not yet known. Herein, a novel marine bacterium, Exiguobacterium marinum a-1, was successfully isolated from mature ‘plastisphere’ that had been deployed in situ for up to 20 months. Strain a-1 could use additive-free polypropylene (PP) films as its primary energy and carbon source. After strain a-1 was incubated with additive-free PP films for 80 days, the weight of films decreased by 9.2%. The ability of strain a-1 to rapidly form biofilms and effectively colonize the surface of additive-free PP films was confirmed by Scanning Electron Microscopy (SEM), as reflected by the increase in roughness and visible craters on the surface of additive-free PP films. Additionally, the functional groups of –CO, -C-H, and –OH were identified on the treated additive-free PP films according to Fourier Transform Infrared (FTIR). Genomic data from strain a-1 revealed a suite of key genes involved in biosurfactant synthesis, flagellar assembly, and cellular chemotaxis, contributing to its rapid biofilm formation on hydrophobic polymer surfaces. In particular, key enzymes that may be responsible for the degradation of additive-free PP films, such as glutathione peroxidase, cytochrome p450 and esterase were also recognized. This study highlights the potential of microorganisms present in the ‘plastisphere’ to metabolize plastic polymers and points to the intrinsic importance of the new strain a-1 in the mitigation of plastic pollution.

Functionalizing MXene with PEPA‐containing polyphosphazene towards highly fire‐safe polypropylene

AbstractPhosphorus‐nitrogen intumescent flame retardant (IFR) is one of the most promising halogen‐free flame retardants in enhancing the fire safety of polypropylene (PP), but its efficiency needs to be further improved. Herein, a novel single‐component polyphosphazene IFR containing pentaerythritol caged phosphate (PEPA) functionalized titanium carbide nanosheet (MXene), named PZS‐MXene, was prepared. When the amount of PZS‐MXene was 25 wt%, PP/PZS‐MXene classed a UL‐94 V‐0 rating with the limiting oxygen index of 32.7%. Compared with PP, its peak of heat release rate, total heat release rate and total smoke production rate were reduced by 74.5%, 33.0%, and 19.8%, respectively. The flame‐retardant mechanism revealed that PZS‐MXene quenched high‐active free radicals to inhibit the degradation of PP during the combustion. MXene rapidly catalyzed the carbonization of PZS to form high‐quality intumescent char layer on its surface. Besides, MXene acted as the supporting skeletons and exerted the layered barrier effect to improve the compactness of the intumescent char layer, thus effectively inhibited the degradation and combustion of PP. This work provided new insights for the efficient halogen‐free flame‐retardant PP.

Polypropylene Degradation Catalyzed by Tantalum Hydrides Supported on Sulfated Alumina

Polypropylene Degradation Catalyzed by Tantalum Hydrides Supported on Sulfated Alumina

Deciphering the role of fungus in degradation of polypropylene from hospital waste.

Health and environmental consequences are unavoidable when it comes to management of hospital waste (HW) disposables. In order to eradicate the HW, this study isolated a novel fungus SPF21 from a hospital dumping yard to degrade Polypropylene (PP). We measured the attributes of PP inoculated with fungus using mass loss, Fourier trans-form infrared (FTIR), contact angle (CA), and scanning electron microscopy (SEM). The weight of PP exposed to SPF21 was reduced by 25% in 90 days. The SEM images reveal that there are pores all over the sample surface; they alsocaused voids during the biodegradation of PP. FTIR analysis indicates that the spectra of treated mask pieces show the absence of peak at 1746cm-1 and the appearance of a new peak at 1643cm-1 . A period of 90-day exposure to the fungal isolate SPF21 reduced the CA of PP by 44.8% when compared to the nonexposed PP samples, suggesting that the surface of PP turned more hydrophilic after exposure. Moreover, our study on PP degradation by the fungus Ascotricha sinuosa SPF21 appears to be promising from the perspective of environmental, health, and economic hazards. Our results indicate that biodegradation greatly facilitates fungus deposition and changes PP film morphology and hydrophilicity.

An atomic insight into reaction pathways and temperature effects in the degradation of polyethylene, polypropylene and polystyrene

Increasingly severe environmental pollution has spurred widespread concern regarding thermoplastics degradation. However, a lack of better understanding at the atomic level hinders the regulation of the related degradation processes. Through theoretical studies of three different typical plastics, first-principles calculations showed two basic reaction pathways for degradation: depolymerization and hydrogen-transfer-induced chain scission. The analyses of the reaction rates were consistent with those of the degradation energy barriers. Even at high temperatures, the differences in depolymerization and hydrogen transfer reactions in reaction rates and thermal perturbation probabilities are still greater than three orders of magnitude. Moreover, dynamic simulations confirm the existence of two reaction pathways and demonstrate that the two pathways occur sequentially. Our findings enrich the understanding of the basic processes of plastic degradation and may provide a reference for pyrolytic processing in waste management.

The role of physicochemical marble processing wastewater treatment sludge in the production of new generation pyrolysis char from waste polypropylene

ABSTRACT The effects of marble processing wastewater physicochemical treatment sludge (K1) on polypropylene (PP) waste pyrolysis were investigated by lab-scale batch pyrolysis system. PP-K1 proportions and pyrolysis temperature were studied as variables and both were found to have influences onto pyrolysis char, oil/tar, gas fractions distribution, as well as pyrolysis char characteristics (determined via SEM, EDX, FTIR, TGA and XRD analyses). The influence of K1 could be related to its high mineral composition (CaCO3, CaMg(CO3)2 and (Mg0.03Ca0.97)(CO3)) which also detected in the char products. K1 acts as catalyst and remained unchanged in thermochemical reactions below 700°C. The main thermal degradation of PP occurs around 400–470°C, although it starts at about 300–350°C, whereas, K1 resulted in more thermal degradation at 300°C pyrolysis. As K1 dose increased, pyrolysis chars became more thermally stable with the pyrolysis temperature. Diverse types of chars in terms of porosity, thermal strength and chemical structure were produced with PP + K1 as compared to the PP chars. For example, with 10%–20% K1 doses, the chars are in aromatic structure while chars become aliphatic when K1 dosage increased to 30% or above. The structural diversity made these chars new products that can be used as raw material for subsequent purposes. This study provided a basis for the chars’ physical and chemical properties which are needed for further research to develop new generation evaluation areas for them. Therefore, a new symbiotic upcycling approach has been presented for PP wastes and marble processing wastewater treatment sludge.

Quantification of Polymer Surface Degradation Using Fluorescence Spectroscopy.

One solution to minimizing plastic pollution is to improve reuse and recycling strategies. Recycling, however, is limited by the overall degradation of plastics being used, and current techniques for monitoring this plastic degradation fail to observe this in its early stages, which is key for optimizing reusability. This research seeks to develop an inexpensive, reproducible, and nondestructive technique for monitoring degradation of polyethylene (PE) and polypropylene (PP) materials using Nile red as a fluorescent probe. Changes in Nile red's fluorescence spectra were observed upon exposure to stained, aged PE and PP samples. As the surface hydrophobicity of the plastic decreases, Nile red's fluorescence signal undergoes a corresponding signal shift to longer wavelengths (lower energy). The trends seen in the fluorescent profile were related to more commonly used measurements of plastic degradation, namely, the carbonyl index from infrared spectroscopy and bulk crystallinity from calorimetry. Results demonstrate clear trends in fluorescence spectra shifts as related to the chemical and physical changes to the plastics, with trends dependent on the polymer type but independent of polymer film thickness. The strength of this technique is divided into two defined fits of the fluorescence signal; one fit characterizes the degradation throughout the whole range of degradative oxidation and the other is tailored to provide insight into the early stages of degradation. Overall, this work establishes a characterization tool that assesses the extent of plastics' degradation, which may ultimately impact our ability to recover plastics and minimize plastic waste.

A DFT mechanistic study on the N‐acyloxyamine‐initiated controlled degradation of polypropylene

AbstractN‐acyloxyamine is an excellent radical initiator for the controlled degradation of polypropylene (PP). Irgatec CR 76 (CR‐76) is one of the most important N‐acyloxyamines for the controlled degradation processes. The experiments show that 2 wt% CR‐76 caused a degradation and lowering of Mw to over 50% and of Mn in 10%–15%. The density functional theory (DFT) calculated results indicate that the NO bond cleavage of enol‐CR‐76 is the easiest to generate nitrogen (N˙) and ˙CH2COO radicals. In the controlled degradation process of PP, compared with the generated nitrogen (N˙), nitroxyl (NO˙), and nitrogen peroxide (NOO˙) radicals, the produced small molecule radicals such as CH3COO˙, (CH3)2CH˙, and (CH3)2CHCH2˙ radicals show better activity in the hydrogen abstraction process of PP. In addition, the NO˙, NOO˙, and ROO˙ (R = (CH3)2CH) radicals were proposed to be of importance in the radical coupling and β‐scission of PP˙ radical after the hydrogen abstraction in the controlled degradation of PP. This provide new insights into the controlled degradation of PP. Furthermore, thereby some theoretical guidance could be provided into the design of new N‐acyloxyamine radical initiator for the controlled degradation of polymers.

Elucidating pathways of polypropylene chain cleavage and stabilization for multiple loop mechanical recycling

AbstractMechanical recycling is a decisive contribution for a sustainable circular economy of polypropylene (PP) but faces the challenge of processing‐induced and use‐phase accumulated molecular damage, exacerbated by multiple loop recycling. In this contribution, the molecular origin of degradation of PP under up to 30 repetitive reprocessing loops is analyzed together with the influence of stabilization, and processability data linked to changes of the entire molecular weight distribution. By comparison of experiments with simple Monte Carlo simulations, a coupled mechanism of random scission and shear‐induced cleavage can be inferred, while stabilizing additives effectively protect the material from progressing along this combined degradation pathway.

Polypropylene Degradation on Co-Rotating Twin-Screw Extruders.

Nowadays, usable plastic materials with defined properties are created by blending additives into the base polymer. This is the main task of compounding on co-rotating twin-screw extruders. The thermal and mechanical stress occurring in the process leads to a mostly irreversible damage to the material. Consequently, the properties of the polymer melt and the subsequent product are affected. The material degradation of polypropylene (PP) on a 28 mm twin-screw extruder has already been studied and modeled at Kunststofftechnik Paderborn. In this work, the transferability of the previous results to other machine sizes and polypropylene compounds were investigated experimentally. Therefore, pure polypropylene was processed with screw diameters of 25 mm and 45 mm. Furthermore, polypropylene compounds with titanium dioxide as well as carbon fibers were considered on a 28 mm extruder. In the course of the evaluation of the pure polypropylene, the melt flow rates of the samples were measured and the molar masses were calculated on this basis. The compounds were analyzed by gel permeation chromatography. As in the previous investigations, high rotational speeds, low throughputs and high melt temperatures lead to a higher material degradation. In addition, it is illustrated that the previously developed model for the calculation of material degradation is generally able to predict the degradation even for different machine sizes by adjusting the process coefficients. In summary, this article shows that compounders can use the recommendations for action and the calculation model for the material degradation of polypropylene, irrespective of the machine size, to design processes that are gentle on the material.

Thermochemical Degradation of Polypropylene – Energy and Exergy Analysis in a Tubular Reactor

Thermochemical Degradation of Polypropylene – Energy and Exergy Analysis in a Tubular Reactor