Hyperbranched Vitrimer for Ultrahigh Energy Dissipation.

Polymers are ideally utilized as damping materials due to the high internal friction of molecular chains, enabling effective suppression of vibrations and noises in various fields. Current strategies rely on broadening the glass transition region or introducing additional relaxation components to enhance the energy dissipation capacity of polymeric damping materials. However, it remains a significant challenge to achieve high damping efficiency through structural control while maintaining dynamic characteristics.  In this work, we propose a new strategy to develop hyperbranched vitrimers (HBVs) containing dense pendant chains and loose dynamic crosslinked networks. A novel yet weak dynamic transesterification between the carboxyl and boronic acid ester was confirmed and used to prepare HBVs based on poly (hexyl methacrylate-2-(4-ethenylphenyl)-5,5-dimethyl-1,3,2-dioxaborinane) P(HMA-co-ViCL) copolymers. The ABn-type of macromonomers, the crosslinking points formed by the dynamic covalent connection via the associative exchange, and the weak yet dynamic exchange reaction are the three keys to developing high-performance HBV damping materials. We found that P(HMA-co-ViCL) 20k-40-60 HBV exhibited ultrahigh energy-dissipation performance over a broad frequency and temperature range, attributed to the synergistic effect of dense pendant chains and weak dynamic covalent crosslinks. This unique design concept will provide a general approach to developing advanced damping materials.

Tailoring Thermal Transport Properties of Graphene Paper by Structural Engineering.

As a two-dimensional material, graphene has attracted increasing attention as heat dissipation material owing to its excellent thermal transport property. In this work, we fabricated sisal nanocrystalline cellulose/functionalized graphene papers (NPGs) with high thermal conductivity by vacuum-assisted self-assembly method. The papers exhibit in-plane thermal conductivity as high as 21.05 W m-1 K-1 with a thermal conductivity enhancement of 403% from the pure cellulose paper. The good thermal transport properties of NPGs are attributed to the strong hydrogen-bonding interaction between nanocrystalline cellulose and functionalized graphene and the well alignment structure of NPGs.

A Combined Self-Consistent Method to Estimate the Effective Properties of Polypropylene/Calcium Carbonate Composites.

In this work, trying to avoid difficulty of application due to the irregular filler shapes in experiments, self-consistent and differential self-consistent methods were combined to obtain a decoupled equation. The combined method suggests a tenor γ independent of filler-contents being an important connection between high and low filler-contents. On one hand, the constant parameter can be calculated by Eshelby's inclusion theory or the Mori⁻Tanaka method to predict effective properties of composites coinciding with its hypothesis. On the other hand, the parameter can be calculated with several experimental results to estimate the effective properties of prepared composites of other different contents. In addition, an evaluation index σ f ' of the interactional strength between matrix and fillers is proposed based on experiments. In experiments, a hyper-dispersant was synthesized to prepare polypropylene/calcium carbonate (PP/CaCO3) composites up to 70 wt % of filler-content with dispersion, whose dosage was only 5 wt % of the CaCO3 contents. Based on several verifications, it is hoped that the combined self-consistent method is valid for other two-phase composites in experiments with the same application progress as in this work.

Water-Induced shape memory effect of nanocellulose papers from sisal cellulose nanofibers with graphene oxide.

A novel water-induced shape memory nanocomposites were prepared by introducing graphene oxide (GO), which was based on microcrystalline cellulose nanofibers (MSF-g-COOH) extracting from sisal fibers. The results showed that the water-induced shape memory properties of MSF-g-COOH were significantly improved by the strong hydrogen bonding interaction between MSF-g-COOH and GO, It leads to some additional physically cross-linked points in MSF-g-COOH. On the other hand, at 0.5wt% GO loading, tensile strength and Young modulus of the nanocomposite increased from 139 to 184MPa, and from 5.77 to 8.54GPa, respectively, compared to those of pure MSF-g-COOH. Furthermore, a water-induced model was proposed to discuss the water-induced shape memory behaviors of the MSF-g-COOH/GO nanocomposites. This study provides a framework for developing a cellulose based shape memory polymers (CSMPs) and better understanding the shape recovery mechanism in water-induced CSMPs.

[Determination of antioxidant residues in polymer food package using gas chromatography].

A new method for the determination of antioxidants, butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA) and tertiary butylhydroquinone (TBHQ) in plastic food package by gas chromatography-electron capture detection (ECD) was developed. The antioxidants were extracted by cyclohexane with ultrasonic extraction, separated by an HP-50 + chromatographic column (30 m x 0.53 mm x 1 microm) and quantified by external standard method with an ECD detector. The average recoveries of antioxidants were 88% -93%, 92% - 101% and 83% -97% for BHT, BHA and TBHQ, respectively, at the spiking levels of 3.00 - 10.0 mg/kg. The corresponding relative standard deviations (RSDs, n = 5) were 2.01% - 2.89%, 2.11% - 3.19% and 2.99% - 4.02%, respectively. The limits of detection (S/N = 3) were 0.5, 0.5 and 0.8 mg/kg for BHT, BHA and TBHQ, respectively. The proposed method has been applied to the analysis of 5 kinds of polymer food package. The results indicated that all the above antioxidants were found in the practical polymer food package samples. Plastic food package contained BHT and BHA with the concentrations varying from 6.3 to 7.8 mg/kg and rubber food package contained all the three antioxidants with the concentrations varying from 9.3 to 28.4 mg/kg. This method is accurate, sensitive, highly reproducible and suitable for the analysis of residual antioxidants in polymer food package.

[Determination of 2,6-di-tertbutyl-4-methylphenol in an aviation jet fuel by high performance liquid chromatography].

The content of antioxidant of 2,6-di-tertbutyl-4-methylphenol(BHT) in a new aviation jet fuel (HDF-1) was determined by high performance liquid chromatography. The influences of the volume ratio of methanol and acetate buffer and the flow rate for BHT separation from HDF-1 were studied and the best analysis conditions were obtained. The optimum volume ratio is 85:15 and the optimum flow rate is 1 mL/min. The relation of BHT mass fraction and its peak area has been analyzed and simulated. It was found that they had a good linear relationship.