Thermal-oxidative effect of a co-condensed nanosilica-based antioxidant in polypropylene

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.

In Situ Grafting of Silica Nanoparticle Precursors with Covalently Attached Bioactive Agents to Form PVA-Based Materials for Sustainable Active Packaging

Sustainable antibacterial–antioxidant films were prepared using in situ graftings of silica nanoparticle (SNP) precursors with covalently attached bioactive agents benzoic acid (ba) or curcumin (cur) on polyvinyl alcohol (PVA). The modified PVA-SNP, PVA-SNP-ba and PVA-SNP-cur films were characterized using spectroscopic, physicochemical and microscopic methods. The prepared films showed excellent antibacterial and antioxidant activity, and increased hydrophobicity providing protection from undesired moisture. The PVA-SNP-ba films completely prevented the growth of the foodborne human pathogen Listeria innocua, whereas PVA-SNP-cur resulted in a 2.5 log reduction of this bacteria. The PVA-SNP-cur and PVA-SNP-ba films showed high antioxidant activity of 15.9 and 14.7 Mm/g TEAC, respectively. The described approach can serve as a generic platform for the formation of PVA-based packaging materials with tailor-made activity tuned by active substituents on silica precursors. Application of such biodegradable films bearing safe bioactive agents can be particularly valuable for advanced sustainable packaging materials in food and medicine.

Nondestructive Strategy to Effectively Enhance the Interfacial Adhesion of PBO/Epoxy Composites

Low interfacial adhesion seriously limits the wide application of PBO fiber in composites. To solve this problem, a novel hierarchical reinforcement strategy was developed by introducing epoxy sizing, nanoreinforcement of amino-functionalized silicon dioxide (SiO₂-NH₂), and an interfacial compatibilizer of 2,6-bis(2-hydroxy-4-aminophenyl) benzobisoxazole (HABO) onto poly(p-phenylene benzobisoxazole) (PBO) fibers via a facile dip-coating approach. SiO₂-NH₂ and HABO were uniformly dispersed in epoxy sizing, forming an active interface layer. On this basis, wettability, surface roughness of the PBO fiber, and compatibility with the resin matrix were significantly improved, which gave 88.4 and 40.4% enhancement in the interfacial shear strength and interlaminar shear strength of the corresponding composites, respectively. Moreover, it should be noted that the outstanding mechanical and thermal properties of the PBO fiber were not impaired during the sizing treatment. In summary, our work provides an effective and damage-free approach to improve the interfacial adhesion of PBO/epoxy composites.

Polypropylene-Based Nanocomposite with Enhanced Aging Stability by Surface Grafting of Silica Nanofillers with a Silane Coupling Agent Containing an Antioxidant

Simultaneous improvement in the mechanical properties and lifetime of polymer nanocomposites is crucially significant to further extend the versatility of polymer materials and reduce environmental impact. In this study, we fabricated reinforced polypropylene (PP)-based nanocomposites with improved aging stability by the addition of surface-modified well-ordered silica nanospheres with a silane coupling agent (SCA) containing hindered phenol antioxidant as a filler. Uniform grafting of the SCA on the filler surface contributed to homogeneous dispersion of the filler into the matrix, leading to improved properties (e.g., stiffness and ductility) and uniform distribution of the antioxidant component into the entire nanocomposite by filler dispersion. The grafting of SCA also likely provides an inhibitory effect on antioxidant migration, which leads to loss of polymer stability during the aging process. This novel idea for the material design of PP-based nanocomposites, which simultaneously enhances their mechanical properties and lifetime, is promising for application in the fabrication of various types of polymer nanocomposites.

Immobilization of rubber additive on graphene for high-performance rubber composites

It is still a challenge to achieve simultaneous improvements in aging resistance, mechanical strength, thermal conductivity and dielectric constant of rubber composites via incorporation of graphene obtained by conventional methods. Herein, an effective and green method was proposed to simultaneously reduce and functionalize graphene oxide (GO) with 2-mercaptobenzimidazole (antioxidant MB) via a one-pot method. GO was successfully reduced by MB which was also chemically grafted on the reduced GO (G-MB). G-MB sheets were uniformly dispersed in rubber with strong interfacial interaction, and graphene-graphene conductive paths were formed through intermolecular H-bonding between the grafted antioxidant molecules. Consequently, rubber composites with G-MB showed higher thermal conductivity, mechanical strength and dielectric constant than rubber composites with hydrazine hydrate reduced GO (rGO). Moreover, the thermo-oxidative aging resistance of rubber composites with G-MB was also superior to that of rubber composites with rGO because of the elimination of blooming effect of the grafted MB molecules. Thus, this work may open a new way for the eco-friendly functionalization and reduction of GO and may boost the development of high-performance, functional graphene-elastomer composites.

DBHP-Functionalized ZnO Nanoparticles with Improved Antioxidant Properties as Lubricant Additives

In this article, 3-(3,5-di- tert-butyl-4-hydroxyphenyl) propionic acid (DBHP)-functionalized ZnO (DBHP-ZnO) nanoparticles were synthesized by decomposing the organometallic precursor Zn(DBHP)₂ under alkaline conditions. This in situ surface modification method can induce small-sized ZnO nanoparticles (5 nm) and form strong linkage between DBHP and ZnO nanoparticles. DBHP as an organic compound hindered phenol antioxidant that not only improved the dispersion stability of the prepared DBHP-ZnO nanoparticles in the lubrication oil but also scavenged free radicals produced during the oxidation process of oil. Compared with DBHP, the thermal stability of the prepared composite antioxidant was greatly enhanced by introducing inorganic ZnO nanoparticles, which was proved by the results of the thermogravimetric analysis test. A rotary oxygen bomb test, pressurized differential scanning calorimetry, and free-radical-scavenging method all showed that DBHP-ZnO nanoparticles had better antioxidant properties than DBHP under high temperature in the base oil of di- iso-octylsebacate (DIOS). The activation energy of the oxidation process was used to analyze this result by the model-free methods, including the Flynn-Wall-Ozawa method and the Kissinger equation. The calculated results showed that DIOS containing DBHP-ZnO nanoparticles have the lowest reaction constant and the longest half-life period compared to those of individual DBHP and ZnO nanoparticles, which is attributed to the combined action of the organic-inorganic composites. Besides, DBHP-ZnO nanoparticles as the additive are able to improve the antiwear ability of DIOS to some extent. Therefore, the as-prepared DBHP-ZnO nanoparticles with desired dispersibility as well as better thermal stability and antioxidant ability than DBHP in the DIOS base oil could be a potential high-performance nanocomposite additive for a synthetic lubricant base oil like DIOS.

Antioxidant Nanomaterial Based on Core⁻Shell Silica Nanospheres with Surface-Bound Caffeic Acid: A Promising Vehicle for Oxidation-Sensitive Drugs

The design of efficient, biocompatible, and easily prepared vehicles for drug delivery is a subject of great interest for medicine and pharmaceutical sciences. To achieve the above goals, surface functionalization is critical. Here, we report a hybrid nanocarrier consisting of core⁻shell silica nanospheres and the antioxidant caffeic acid linked to the surface, to evaluate their in vitro antioxidant capacity, their capability to protect oxidation-sensitive compounds incorporated in nanoparticles, and to study the interaction with bovine serum albumin protein. The results show that the radical-scavenging activity of immobilized caffeic acid is attenuated in the silica nanospheres; however, other antioxidant properties such as Fe2+-chelating activity and singlet oxygen quenching are enhanced. In addition, caffeic acid is protected from binding to proteins by the nanoparticle, suggesting that this nanosystem is more likely to maintain the antioxidant activity of caffeic acid in biological media. Finally, the natural antioxidant barrier on the nanocarrier is able to delay the degradation of a compound incorporated into this nanovehicle. Considering all findings, this work proposes a suitable tool for pharmaceutical and cosmetic industries as an antioxidant nanocarrier for oxidation-sensitive drugs.