Increasing Polypropylene High Temperature Stability by Blending Polypropylene-Bonded Hindered Phenol Antioxidant

Monitoring Polypropylene Chain-Scission for Dissolution-Based Recycling by In Situ Near Infrared and Raman Spectroscopy

Within the context of polypropylene recycling by dissolution, the potential degradation of polypropylene in solution has been investigated using in situ NIR and Raman spectroscopy. Pure polypropylene, completely free of additives, and commercial polypropylene, low in additives, are degraded on purpose under different conditions. Genetic algorithm combined with partial least squares (GA-PLS) models have been built based on near-infrared (NIR) spectra, and partial least squares (PLS) models based on Raman spectra, to predict the mass average molar mass and the chain-scission rate, respectively, during the degradation process. The variables used in the GA-PLS model from NIR spectra suggest that the main variability is related to physical changes via the baseline. In Raman, a baseline drift due to coloration during the degradation has been used to correlate the spectra with the degradation phenomenon. Both techniques show good predictive performances and can potentially be implemented for real-time supervision of degradation during recycling processes.

Functional Polyolefins and Composites

Polyolefins are simple hydrocarbons that require additional chemical modifications or functional additives to give them custom functions. Recent research in the development of functional polyolefins has surpassed the traditional approach of simply improving surface properties by incorporating polar moieties. Creating custom functionalized polyolefins by using specific functional units has attracted increasing attention. This review summarizes advances in preparing custom functionalized polyolefin materials using functional units such as comonomers, chain-transfer agents, post-polymerization modification reagents, and functional fillers. Exploring new functional units and innovative synthetic strategies will further enhance the performance and expand the applications of functional polyolefins.

Nickel-catalyzed in situ synthesis of UHMWPE/TiO2 composites with enhanced mechanical properties and adjustable photocatalytic degradabilities

Expanding the application field of polyolefin materials through functionalization has been a research hotspot in the past three decades. Here, a TiO2-supported anilinenaphthoquinone nickel catalyst was assembled and applied for in situ ethylene polymerization with high activity (>2000 kg mol-1h-1) to produce ultra-high molecular weight polyethylene (UHMWPE)/TiO2 composites with unique physicochemical performance. The UHMWPE/TiO2 composite films and fibers prepared by in-situ ethylene polymerization are superior to the samples from the blend system in issues such as TiO2 dispersibility, mechanical property, and photocatalytic degradability. The mechanical properties (strength up to 26.8 cN/dtex, modulus up to 1248.8 cN/dtex) of the obtained UHMWPE/TiO2 composite fibers are significantly improved with a very low dosage of TiO2 (as low as 1.4 wt‰). Moreover, UHMWPE/TiO2 composites obtained by coating Al2O3 and SiO2 on the surface of TiO2 not only retain the strong absorption of ultraviolet rays, but also effectively weaken the photocatalytic degradation effect.

Continuous preparation and antibacterial mechanisms of biodegradable polylactic acid/nano-zinc oxide/additives antibacterial non-wovens

Biodegradable polylactic acid (PLA)/nano‑zinc oxide (ZnO)/additives non-woven slices were prepared by melt blending method. The effects of antibacterial agent nano-ZnO, antioxidant pentaerythrityl tetrakis-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate (1010), and chain extender multi-functional epoxy (ADR), on the melt flow rate, mechanical properties, thermal stabilities and micromorphology of the slices were investigated. The melt flow rate decreased from 26.94 g/10 min to 17.76 g/10 min, and the tensile strength increased from 10.518 MPa to 30.427 MPa with the increase of nano-ZnO and additives content. The slices were further spunbonded. The wettability and antibacterial properties of PLA/nano-ZnO/additives antibacterial non-wovens were studied, and the antibacterial action mechanism was clarified. The results showed that the biodegradable PLA/nano-ZnO/additives antibacterial non-wovens were prepared continuously successfully. The prepared non-woven fabrics exhibited good hydrophobicity and antibacterial properties. The mechanism study shows that zinc ion produced by nano-ZnO and photocatalytic reaction make the fabrics have good antibacterial activity at low nano-ZnO content. When nano-ZnO concentration reaches 1.5 wt%, the antibacterial rate against Escherichia coli and Staphylococcus aureus reaches 98.52 % and 98.13 %, respectively.

Elucidating the effects of naturally weathered aged-polypropylene microplastics and newly procured polypropylene microplastics on raw 264.7 macrophages

In this work, we investigated weathered aged-PPMPs and naturally obtained polypropylene microplastics (NP-PPMPs) with raw 264.7 macrophages, which causes cytotoxicity and an imbalance in the intracellular system.

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.

Enzyme-catalyzed synthesis of 4-methylcatechol oligomer and preliminary evaluations as stabilizing agent in polypropylene

In the present work, 4-methylcatechol oligomer has been prepared by using enzyme-catalyzed polymerization in water and preliminary evaluations as stabilizing agent in polypropylene (PP) was performed. In comparison with intrinsic PP, the oxidation onset temperature of the 4-methylcatechol oligomer/PP composite increased by 66°C, and the oxidation induction time increased by 40 min. In addition, the mixing of a 4-methylcatechol oligomer with PP (i.e., in the formation of a 4-methylcatechol oligomer/PP composite) did significantly enhance the long-term stability of PP in a thermal oxidative environment. Moreover, the tensile strength of this composite did not significantly decrease after aging for 800 h in an air atmosphere at 120°C. These results show that the addition of a 4-methylcatechol oligomer will markedly delay the aging and degradation of PP materials, even under extreme conditions. Thus, an enzyme-catalyzed polymerization of phenol compounds may provide a new avenue toward the preparation of novel antioxidants.

Superhydrophobic polypropylene sorbent derived from discarded face masks: A highly efficient adsorbent for oil spill sorbent

Globally, an estimated 130 billion face masks are used and disposed of every month. Thus, recycling or upcycling discarded face masks has attracted significant attention due to economic benefits and environmental concerns. To reduce the amount of used face masks going to waste, this study features a superhydrophobic face mask prepared by simple chemical modification with environmentally preferable alkane solvents (n-hexane, n-heptane, and n-decane), that is effective as a sorbent for oil spill cleanup. All alkanes examined increased the surface roughness of the face masks and improved face mask hydrophobicity. The heptane treated face mask (at 90 °C for 1 h), can adsorbed Arabian light crude oil up to 21 times of their weight on the water surface. In addition, chloroform, toluene, gasoline, and diesel were adsorbed 18, 13, 8 and 16 times, respectively. More importantly, heptane has a high recycling efficiency as a treatment solvent and is reusable for at least 10 cycles of mask surface treatment. Consequently, this inexpensive and easily fabricated material is a promising development in waste face mask (WFM) upcycling.

The synthesis and properties research of functionalized polyolefins

This work demonstrated a tandem ROMP/hydrogenation approach for the preparation of functionalized polyolefins and their properties were investigated.

A Multi-functional Chromone-modified Polyethylene via Metal-free C−H Activation

Post-modification of polyolefins via cutting-edge C−H activation has recently emerged as an attractive methodology for the incorporation of precise functionalities, thus expanding their applicability and creating value-added materials. In this...

Highly efficient and recyclable polyolefin-based magnetic sorbent for oils and organic solvents spill cleanup

The oil dispersants have been applied in a broad oil pollution area, but the dispersed oil caused environmental problems during sedimentation. Unlike oil dispersants, flake type polyolefin-based oil absorbent (PA) is not emulsified and shows excellent swelling characteristic for oil removal. However, the sprayed PA flakes cannot be fully collected due to its tiny architectures, the uncollected flakes can cause unintentional secondary pollution. In this study, we develop a kind of flake type polyolefin-based magnetic absorbent (PMA) hybridized with magnetic nanoparticle, to facilitate the collection process. The magnetic nanoparticle is uniformly dispersed in PMA due to the hydrophobic functionalization of iron oxide nanoparticle. This enables the convenient collection of isolated sorbent flakes even when they were placed in the marine system and show a desirable oil recovery performance up to about 37 times for organic solvent. Moreover, oil-soaked PMA flakes can be fully converted into refined oil via a pyrolysis process. After pyrolysis, the thermally undecomposed compounds, which comprise of carbon residue and magnetic nanoparticle, can be also separated by a magnet. The as-prepared flake type PMA possesses good oil recovery performance, fast magnetic response, and efficient oil recycling, thus representing an environmentally promising method for oil spill cleanup.

The Martini Model in Materials Science

The Martini model, a coarse-grained force field initially developed with biomolecular simulations in mind, has found an increasing number of applications in the field of soft materials science. The model's underlying building block principle does not pose restrictions on its application beyond biomolecular systems. Here, the main applications to date of the Martini model in materials science are highlighted, and a perspective for the future developments in this field is given, particularly in light of recent developments such as the new version of the model, Martini 3.

Enabling Superior Thermo-Oxidative Resistance Elastomers Based on a Structure Recovery Strategy

Thermo-oxidative process leads to the structure damage of elastomers, such as the scission of main chains and destruction of crosslinks. The problem that damaged structure brings about the deterioration of mechanical properties has not been solved by the conventional anti-aging methods. Inspired by self-healing process, a structure recovery strategy for recovering the damaged structure induced by thermo-oxidative process is proposed, which endows elastomers with superior thermo-oxidative resistance. The high reactivity between 1,3-diisopropenylbenzene and free radicals realizes high recovery efficiency (from 83% to 118%); the changes in topology structure during recovery process make much more rubber chains bear external stress and improve mechanical properties significantly (from 18.5 to 29.6 MPa). This work paves the way for the development of elastomers with superior thermo-oxidative resistance, meanwhile this work is helpful to push the theoretical research of self-healing to practical application.

Improved Breakdown Strength of Polypropylene Film by Polycyclic Compounds Addition for Power Capacitors

In this paper, an improved method for the electric performance of polypropylene (PP) film was proposed to promote the safety and stability of power capacitors. Modified PP films containing three different polycyclic compounds were prepared, which showed good thermal properties and decreased DC conductivity. The DC breakdown strength of the modified PP films under both positive and negative voltage is increased compared with that of the original film. The deep traps introduced by polycyclic compounds and the decreased carrier mobility give an explanation of the decreased DC conductivity. A quantum chemistry calculation was further performed to clarify the mechanism for improving electrical performance, presenting that polycyclic compounds with a high electron affinity and low ionization energy can capture high-energy electrons, protecting the PP molecular chain from attack, and then increase the breakdown strength. It is concluded that the modified PP films by polycyclic compounds have great potential in improving the insulating properties of power capacitors.

Improving electric thermal stability of polypropylene by chemically linking small amount of hindered phenol groups

Thermal stability of polypropylene (PP) over a broad temperature is critical for many applications. Hindered phenol (HP) groups have been utilized in PP for thermal-oxidative protection. This paper studies thermal stability of the electret property of PP linked with 0.2 mol% HP. It is observed that small amount of chemically linked HP groups improves electret thermal stability as reflected by the higher peak temperature of the thermally stimulated discharge curve and about 65% increase in the trap level. In addition, the HP groups in PP generate “rigid backbones” which maintain the PP film shapes to temperatures near the melting (~ 150 °C), compared with pristine PP at 70 °C.

Preparation and crystalline transformation of functionalized poly(1-butene) containing PFPU and mPEG side chain

A series of 1-butene/pentafluorophenylundec-1-ene ester random copolymers were synthesized under the Ziegler–Natta catalyst system. The content of the pentafluorophenyl (PFP) group in the copolymer can reach up to 0.59 mol%. The DSC test found that the PFP groups attached to the PB main chain retard the crystalline transformation of Form II to Form I. Nucleophilic aromatic substitutions of pentafluorophenyl ester occurred with biocompatible poly(ethylene glycol) methyl ether (mPEG) introduced into the side chain of PB under very mild conditions. The results show that not only is the crystallization rate of mPEG functionalized PB increased, but also T_m, T_c, χ_c and the crystalline phase transition rate of Form II to Form I are also enhanced. Among them, mPEG with a M_n of 500 has the best promoting effect. On the other hand, the hydrophilicity of mPEG-functionalized PB is improved, and it is proportional to the chain length of mPEG. However, the experimental results show that the regularity of the PB structure is the determinant of the rate of crystallization and phase transition.

A series of 1-butene/pentafluorophenylundec-1-ene ester random copolymers were synthesized under the Ziegler–Natta catalyst system.

Synthetic Phenolic Antioxidants: A Review of Environmental Occurrence, Fate, Human Exposure, and Toxicity

Synthetic phenolic antioxidants (SPAs) are widely used in various industrial and commercial products to retard oxidative reactions and lengthen product shelf life. In recent years, numerous studies have been conducted on the environmental occurrence, human exposure, and toxicity of SPAs. Here, we summarize the current understanding of these issues and provide recommendations for future research directions. SPAs have been detected in various environmental matrices including indoor dust, outdoor air particulates, sea sediment, and river water. Recent studies have also observed the occurrence of SPAs, such as 2,6-di-tert-butyl-4-methylphenol (BHT) and 2,4-di-tert-butyl-phenol (DBP), in humans (fat tissues, serum, urine, breast milk, and fingernails). In addition to these parent compounds, some transformation products have also been detected both in the environment and in humans. Human exposure pathways include food intake, dust ingestion, and use of personal care products. For breastfeeding infants, breast milk may be an important exposure pathway. Toxicity studies suggest some SPAs may cause hepatic toxicity, have endocrine disrupting effects, or even be carcinogenic. The toxicity effects of some transformation products are likely worse than those of the parent compound. For example, 2,6-di-tert-butyl-p-benzoquinone (BHT-Q) can cause DNA damage at low concentrations. Future studies should investigate the contamination and environmental behaviors of novel high molecular weight SPAs, toxicity effects of coexposure to several SPAs, and toxicity effects on infants. Future studies should also develop novel SPAs with low toxicity and low migration ability, decreasing the potential for environmental pollution.

Thermally Stable Low-Loss Polymer Dielectrics Enabled by Attaching Cross-Linkable Antioxidant to Polypropylene

Polymer dielectrics with low-loss and high-temperature tolerance are extremely desirable as electrical energy storage materials for advanced electronics and electrical power applications. They can allow fast switching rates during power conversion and therefore achieve high power densities without thermal issues. Here, we explore polypropylene (PP), the state of the art dielectric polymer, and present an innovative approach to substantially improve the thermal stability and concurrently reduce the dielectric loss of PP. In particular, cross-linkable antioxidant groups, hindered phenol (HP), are incorporated into PP via well-controlled chemical synthesis. The grafted HP can simultaneously serve as radical scavenger and cross-linker, thereby constraining thermally decomposed radicals and charge transport in the synthesized PP-HP copolymer. As a result, the upper-temperature limit of PP-HP is greatly extended to 190 °C and the electrical loss is even gradually reduced upon thermal annealing. The copolymer after heating under 190 °C exhibits better dielectric properties than the PP without any thermal treatment. The experimental results indicate that the PP-HP copolymers are promising materials for high-temperature, low-loss, and high-voltage dielectric applications.

Light-mediated olefin coordination polymerization and photoswitches

This review outlines photoswitchable, transition metal-based olefin coordination polymerization catalysts ranging from homogeneous to heterogeneous, and monometallic to bimetallic regimes.

Design, fabrication and anti-aging behavior of a multifunctional inorganic–organic hybrid stabilizer derived from co-intercalated layered double hydroxides for polypropylene

The concomitant presence of HALS/DBHP co-intercalated within the LDH structure strongly improved the anti-aging performance of PP, which opens the pathway for potential future research of high-performance PP associated with hybrid fillers.