Yukun Chen

Dynamically Vulcanized Biobased Polylactide/Natural Rubber Blend Material with Continuous Cross-Linked Rubber Phase

We prepared a biobased material, dynamically vulcanized polylactide (PLA)/natural rubber (NR) blend in which the cross-linked NR phase owned a continuous network-like dispersion. This finding breaks the traditional concept of a sea-island morphology formed after dynamic vulcanization of the blends. The scan electron microscopy and dissolution/swell experiments provided the direct proof of the continuous cross-linked NR phase. This new biobased PLA/NR blend material with the novel structure is reported for the first time in the field of dynamic vulcanization and shows promise for development for various functional applications.

Design of Self-Healing Supramolecular Rubbers by Introducing Ionic Cross-Links into Natural Rubber via a Controlled Vulcanization

Introducing ionic associations is one of the most effective approaches to realize a self-healing behavior for rubbers. However, most of commercial rubbers are nonpolar rubbers without now available functional groups to be converted into ionic groups. In this paper, our strategy was based on a controlled peroxide-induced vulcanization to generate massive ionic cross-links via polymerization of zinc dimethacrylate (ZDMA) in natural rubber (NR) and exploited it as a potential self-healable material. We controlled vulcanization process to retard the formation of covalent cross-link network, and successfully generated a reversible supramolecular network mainly constructed by ionic cross-links. Without the restriction of covalent cross-linkings, the NR chains in ionic supramolecular network had good flexibility and mobility. The nature that the ionic cross-links was easily reconstructed and rearranged facilitating the self-healing behavior, thereby enabling a fully cut sample to rejoin and retain to its original properties after a suitable self-healing process at ambient temperature. This study thus demonstrates a feasible approach to impart an ionic association induced self-healing function to commercial rubbers without ionic functional groups.

Preparation and properties of carboxylated styrene-butadiene rubber/cellulose nanocrystals composites.

A series of carboxylated styrene-butadiene rubber (XSBR)/cellulose nanocrystals (CNs) latex composites were successfully prepared. The vulcanization process, morphology, dynamic viscoelastic behavior, dynamic mechanical property, thermal and mechanical performance of the XSBR/CNs composites were investigated in detail. The results revealed that CNs were dispersed uniformly in the XSBR matrix and formed a strong filler-filler network. The dynamic mechanical analysis (DMA) showed that the glass transition temperature (T(g)) of XSBR matrix was shifted from 48.45 to 50.64 °C with 3 phr CNs, but decreased from 50.64 to 46.28 °C when further increasing CNs content up to 15 phr. The composites exhibited a significant enhancement in tensile strength (from 16.9 to 24.1 MPa) and tear strength (from 43.5 to 65.2 MPa) with loading CNs from 0 to 15 phr. In addition, the thermo-gravimetric analysis (TGA) showed that the temperature at 5% weight loss of the XSBR/CNs composites decreased slightly with an increase of the CNs content.

Crosslinked bicontinuous biobased PLA/NR blends via dynamic vulcanization using different curing systems

In this study, blends of entirely biosourced polymers, namely polylactide (PLA) and natural rubber (NR), were prepared through dynamic vulcanization using dicumyl peroxide (DCP), sulphur (S) and phenolic resin (2402) as curing agents, respectively. The crosslinked NR phase was found to be a continuous structure in all the prepared blends. The molecular weight changes of PLA were studied by gel permeation chromatography. Interfacial compatibilization between PLA and NR was investigated using Fourier transform infrared spectroscopy and scanning electron microscopy. The thermal properties of blends were evaluated by differential scanning calorimetry and thermogravimetric analysis instrument. It was found that the molecular weight of PLA and interfacial compatibilizaion between PLA and NR showed a significant influence on the mechanical and thermal properties of blends. The PLA/NR blend (60/40 w/w) by DCP-induced dynamic vulcanization owned the finest mechanical properties and thermal stability.

Flame-Retardant Properties of PP/Al(OH)3/Mg(OH)2/POE/ZB Nanocomposites

The flame-retardant composites of polypropylene (PP) were prepared using a twin-screw extruder by compounding PP with either aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), zinc borate (ZB), polyolefin elastomer(POE) and nanometer calcium carbonate (nano-CaCO3). The flame retardant properties of these composites, including oxygen index (OI), horizontal burning speed (V), and smoke density rank (SDR) were measured. The results showed that the OI increased linearly, while the V and the SDR decreased nonlinearly with an increase of the filler weight fraction, and the effect of the specimen thickness on the V was significant. The reduction of the V of the flame-retardant PP composites decreased with increasing the specimen thickness. The addition of the nano-CaCO3 and POE could improve the flame-retardant properties of the composites.

Cellulose nanocrystals reinforced foamed nitrile rubber nanocomposites

Research on foamed nitrile rubber (NBR)/cellulose nanocrystals (CNs) nanocomposites is rarely found in the literatures. In this paper, CNs suspension and NBR latex was mixed to prepared the foamed NBR/CNs nanocomposites. We found that the CNs mainly located in the cell walls, effectively reinforcing the foamed NBR. The strong interaction between the CNs and NBR matrix restricted the mobility of NBR chains surrounding the CNs, hence increasing the crosslink density of the NBR matrix. CNs exhibited excellent reinforcement on the foamed NBR: a remarkable increase nearly 76% in the tensile strength of the foamed nanocomposites was achieved with a load of only 15 phr CNs. Enhanced mechanical properties make the foamed NBR/CNs nanocomposites a promising damping material for industrial applications with a potential to reduce the petroleum consumption.

Self-Healing Natural Rubber with Tailorable Mechanical Properties Based on Ionic Supramolecular Hybrid Network

In most cases, the strength of self-healing supramolecular rubber based on noncovalent bonds is in the order of KPa, which is a challenge for their further applications. Incorporation of conventional fillers can effectively enhance the strength of rubbers, but usually accompanied by a sacrifice of self-healing capability due to that the filler system is independent of the reversible supramolecular network. In the present work, in situ reaction of methacrylic acid (MAA) and excess zinc oxide (ZnO) was realized in natural rubber (NR). Ionic cross-links in NR matrix were obtained by limiting the covalent cross-linking of NR molecules and allowing the in situ polymerization of MAA/ZnO. Because of the natural affinity between Zn2+ ion-rich domains and ZnO, the residual nano ZnO participated in formation of a reversible ionic supramolecular hybrid network, thus having little obstructions on the reconstruction of ionic cross-links. Meanwhile, the well dispersed residual ZnO could tailor the mechanical properties of NR by changing the MAA/ZnO molar ratios. The present study thus provides a simple method to fabricate a new self-healing NR with tailorable mechanical properties that may have more potential applications.

Synthesis and Characterization of Low Viscosity Aromatic Hyperbranched Poly(trimellitic anhydride diethylene glycol) Ester Epoxy Resin

Low viscosity aromatic hyperbranched poly(trimellitic anhydride diethylene glycol) ester epoxy resin (HTDE) was synthesized from the reaction between epichlorohydrin (ECH) and carboxyl-ended hyperbranched poly(trimellitic anhydride diethylene glycol) ester (HTD). HTD was prepared from inexpensive materials A2 (diethylene glycol, DEG) and B3 (trimellitic anhydride, TMA) monomers by a pseudo-one step method. Molecular weight of the HTD was calculated by its acid value with a “Recursive Probability Approach”, and its degree of branching (0.62∼ 0.71) was characterized by model compounds and 1H-NMR-minus spectrum technology. HTDE has an epoxy equivalent weight of < 530 g/mol and its viscosity of < 700 cp, respectively. The structure of the AB2 monomer, HTD and HTDE were also characterized by MS, 1H-NMR and FT-IR spectra technology. HTDE is an ellipsoid-like molecular with a size of < 10.34 nm. This low viscosity novel epoxy resin has important applications in the fields of “no-solvent” coatings.

Stress-Strain Behaviors and Crosslinked Networks Studies of Natural Rubber-Zinc Dimethacrylate Composites

The stress-strain behaviors of natural rubber (NR)-zinc methacrylate (ZDMA) composite have been studied by uniaxial tension. The results indicated that there was a large reinforcement by ZDMA and the NR/ZDMA composites exhibited a high stress-softening effect. Meanwhile, the recovery stretch curve was close to the second stretch curve; thus a weak stress recovery of the composites was shown. The analysis of crosslink density indicated that the damage to the crosslink network was mainly due to the breakage of ionic crosslinks at low strain (100%). A more developed ionic crosslink network was formed at a higher content of ZDMA. When the vulcanizate is subjected to loading in tension, the ionic crosslink network will suffer the force first. Next, the slippage of ionic bonds will take place under the stress. A new ionic crosslink network might be formed rapidly after the ionic bonds were broken during the stretching. Therefore, it could not return to the initial state. The analysis of crosslink density and stress recovery indicated that the rubber chains could be adsorbed to the ZDMA aggregates due to the formation of poly-zinc methacrylate (PZDMA). A molecular analysis of NR/ZDMA composites is proposed in the last part of this article.

Structure and Properties of Dynamically Cured Thermoplastic Vulcanizate Based on Poly(vinylidene fluoride), Silicone Rubber, and Fluororubber

Thermoplastic vulcanizates (TPVs) based on poly (vinylidene fluoride) (PVDF), silicone rubber (SR) and fluororubber (FKM) were prepared via dynamic vulcanization. Morphology characterization showed that spherical rubber particles were dispersed separately and “connected” by “bridge” in the TPV with 10 wt.% FKM, but agglomerated together with higher FKM content. The mechanical properties of TPVs were improved, especially tear strength and elongation increased from 24 kN.m−1 and 23% to 103 kN.m−1 and 306%, respectively, with FKM increased from 10 wt.% to 50 wt.%. Rheology studies and dynamic mechanical properties results showed that the compatibility between PVDF and rubber phase was improved by FKM. GRAPHICAL ABSTRACT