Shengling Jiang

Development of eco-friendly brake friction composites containing flax fibers

Eco-friendly brake friction composites with good friction performance were developed. The raw materials utilized were selected according to eco-friendly criterion that natural products should be preferably chosen. The formulations are composed of plant flax fiber, mineral basalt fiber, and wollastonite as reinforcements, natural graphite as solid lubricant, zircon as abrasive, vermiculite and baryte as functional and space fillers, and cardanol-based benzoxazine-toughened phenolic resin as binder. To isolate the flax fibers, chemical and physical methods including drying, room temperature alkaline solution, and acid steam treatment were performed and fibers with micro-fibrillated structure on the surface were formed. A new cardanol-based benzoxazine synthesized by the reactions among cardanol, aniline, and formaldehyde was used as toughening for phenolic resin. The effects of both the content of treated flax fibers and friction temperature on friction performance, friction coefficient and specific wear rate, of the friction composites were evaluated by the extension evaluation method.

Effects of walnut shells on friction and wear performance of eco-friendly brake friction composites

The paper addresses utilization of 0–14.6 vol.% alkaline-treated walnut shell powders (WSPs) as a functional filler in the proposed eco-friendly brake friction materials. Five non-asbestos friction material samples containing WSP and jute fibers from biomass as biodegradable components were prepared, also including several from natural resources, such as wollastonite, basalt fibers, zircon, barite, and vermiculite. The friction-wear properties of the prepared composites were tested by using Chase friction performance testing device. Furthermore, an extension evaluation method was introduced to rank the composites based on their overall friction-wear characteristics. The coefficient of friction (COF) and wear rate of the samples could be effectively improved, especially for the sample with a WSP content ≤5.6 vol.%. With confirmation of the analysis and characterization results, chars were very possibly formed by the degradation of organic ingredients, such as WSP and jute fibers, which played a key role in affecting the friction performance of the friction composites.

Hydrosoluble hybrid and multifunctional polysiloxane-based photoinitiators for initiating gradient photopolymerization of acrylamide aqueous solution

A novel hydrosoluble hybrid polysiloxane photoinitiator (W–Si–HBP2–HHMP2) and a hydrosoluble four-functional polysiloxane benzophenone photoinitiator (W–Si–HBP4) were synthesized based on 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl propan-1-one (HHMP), 4-hydroxybenzophenone (HBP) and aminopolysiloxane, and their structures were confirmed by 1H NMR, 13C NMR, 29Si NMR and FTIR. The solubility in water, the photochemical properties, and the self-floating ability of the photoinitiators were evaluated. Both the photoinitiators exhibited great water solubility, high hydrogen abstraction rate constant (more than 7.0 × 109 M−1 s−1), excellent photoinitiating efficiency and relatively good self-floating ability. The initiating efficiency of the polysiloxane photoinitiators was improved by appropriate increase of photosensitive groups in the molecules, but without compromise to the self-floating ability. Remarkably, the hybrid photoinitiator W–Si–HBP2–HHMP2 efficiently initiated photopolymerization without an amine coinitiator due to the interaction between the HBP and HHMP groups. This led to the reduction of the dosage of the amine coinitiator, and even no amine coinitiator, thereby mitigating the harm to materials and the environment derived from the amine coinitiator. Therefore, W–Si–HBP2–HHMP2 has great potential for application in green chemical industry. Moreover, gradient properties, involving molecular weight, glass transition temperature (Tg), and thermostability, of the polyacrylamide (PAM) rods prepared by using W–Si–HBP2–HHMP2 and W–Si–HBP4 were explored by GPC, differential scanning calorimetry (DSC) and thermogravimetry (TG).

Structure and properties of kaolinite intercalated with potassium acetate and their nanocomposites with polyamide 1010

The intercalation complex marked as KAA was a modified kaolinite (KA) with potassium acetate as an intercalating agent, which was used as a reinforcement to prepare polyamide 1010 (PA1010) matrix nanocomposites (PKAA) by melt compounding. X-Ray diffraction results indicated that the interlayer basal spacing increased from 0.720 nm (KA) to 1.411 nm (KAA), after an intercalation process with an intercalation ratio of 99.7%. The nanocomposite with 2 wt% KAA exhibited the best comprehensive mechanical properties, including tensile strength, elongation at break, and notched impact strength. Furthermore, the thermal performance of these nanocomposites could be effectively improved, which manifested as the elevated glass transition temperature and thermal decomposition temperature in the test results of the dynamic mechanical thermal analysis and thermogravimetric analysis (TGA). The melting point and crystallization behavior of PKAA were also increased due to results from the differential scanning calorimetry. Besides, the bilayer inserting model was simulated by Materials Studios software to further understand the structure-function relationship of PKAA.

Intramolecular-initiating photopolymerization behavior of nanogels with the capability of reducing shrinkage

A series of nanogels possessing both benzophenone and hydrogen-donating groups in the skeleton were synthesized and characterized. The photochemical properties and photoinitiation mechanism of the nanogels were investigated by ultraviolet absorption spectroscopy, real-time infrared spectroscopy, laser flash photolysis and electron spin resonance. The nanogels have a strong absorption characteristic centered at 275 nm. Compared to the bare benzophenone, the nanogels have longer triplet state lifetime that reached up to 1.9 μs. Furthermore, the nanogels can generate both alkyl radicals and amino radicals that can effectively initiate the polymerization of acrylate monomers. More importantly, the nanogels can significantly reduce the volume shrinkage of UV-cured materials and the migration of photolysis fragments. The nanogels should have potential applications for preparing more environmentally friendly materials.

Reducing volumetric shrinkage of photopolymerizable materials using reversible disulfide-bond reactions

We introduce a new strategy for reduction in volumetric shrinkage of free radical photopolymerization. Our strategy is based on the reversible reaction of disulfide bonds under UV irradiation. Here, we synthesized 2,2′-dithiodiethanol diacrylate (DSDA), an acrylate monomer with disulfide bonds. The homolytic photocleavage of DSDA under UV irradiation generates thiyl radicals that can initiate polymerization. Volumetric shrinkage can decrease to 0.1% through a repeated “contraction–expansion–contraction” volume-adjustable process. We identified the mechanism that underlies volumetric shrinkage reduction. The photocleavage rate of DSDA under UV irradiation is slower than that of the added photoinitiator. Moreover, in the presence of the photoinitiator, most of the generated thiyl radicals undergo restoration and exchange reactions instead of polymerization initiation or chain termination. The free volume and structure of the polymer network are effectively tuned by the dynamic and reversible processes of gradual disulfide-bond homolysis and recombination during fast photopolymerization.

Self-healing Supramolecular Polymer Composites by Hydrogen Bonding Interactions between Hyperbranched Polymer and Graphene Oxide

A self-healing supramolecular polymer composite (HSP-GO) was designed and prepared via incorporation of modified graphene oxide to hyperbranched polymer by hydrogen-bonding interactions. The polymer matrix based on amino-terminated hyperbranched polymer (HSP-NH2) was synthesized by carboxylation, Curtius rearrangement, and amination of hydroxyl-terminated hyperbranched polyester (HP-OH), while the modified graphene oxide was prepared by transformation of hydroxyl to isocyanate and further to carbamate ester. Spectroscopic methods were utilized to characterize the obtained polymer composites. Stress-strain test was selected to carefully study the self-healing property of HSP-GO. It is found that a small amount of modified graphene oxide (up to 2 wt%) improves the glass transition temperature (Tg), tensile strength, Young’s modulus, and self-healing efficiency of the polymer composites. After healed at room temperature for 10 min, the addition of modified graphene oxide improves the self-healing efficiency to 37% of its original tensile strength. The experiment result shows that the self-healing efficiency is related to the density of hydrogen bonding site and the molecular movement.

Synthesis and Thermal Stability of Novel Poly(M-Carborane-Siloxanes) with Various Pendant Groups

Poly(m-carborane-siloxanes) with various pendant groups (P15-P46) were synthesized via polycondensation of m-carborane-containing disilanols (1-4) and highly active bisureidosilanes (5 and 6). The obtained polymers exhibit controlled molecular weight by carefully adjusting the monomer ratio. Standard spectroscopic techniques including FTIR and NMR were utilized to characterize these polymers and satisfactory results were obtained. TGA analysis indicated that the thermal cyclization of polysiloxanes under nitrogen was greatly postponed by the incorporated m-carborane cage, since the siloxane bonds within the main chain were strengthened by the inductive effect of the latter. DSC and FTIR results confirmed that both siloxane unit and carborane cage were oxidized at elevated temperature under air, which contributed to the transformation of the polymers into the mixture of SiO2 and B2O3. Therefore, high char yield was obtained. Besides, the electronic effect of pendant groups greatly influenced the degradation behavior of m-carborane-containing polysiloxanes, having nothing to do with their position. The initial degradation temperature (T d5) increases with varying substituent in the order: CH2CH2CF3 < CH3 ≈ Ph < CH=CH2.

Synthesis, Amphiphilic Property and Thermal Stability of Novel Main-chain Poly(o-carborane-benzoxazines)

Five poly(o-carborane-benzoxazines) were synthesized via Mannich reaction of o-carborane bisphenol, paraformaldehyde, and diamine, and their structures were well characterized. Light transmission and 1H NMR in D2O confirmed that poly(o-carborane-benzoxazines) with PEG segments showed excellent water solubility and amphiphilic property. TGA analyses were conducted under nitrogen and air, and the results showed that the polymers own high initial decomposition temperatures owing to the shielding effect of carborane moiety on its adjacent aromatic structures. Besides, poly(o-carborane-benzoxazines) own high char yield at elevated temperatures, for the boron atom could combine with oxygen from the polymer structure or/and the air and be oxidized to form boron oxide, and thus the polymer weight is retained to a large extent. PEG segments had an adverse effect on the initial decomposition and char yield, and thus their concentration should be adjusted to control the polymers thermal stability.

Synthesis and characterization of carborane-containing poly(hydroxy ethers) with excellent thermal stability

Abstracto-Carborane-containing poly(hydroxy ethers) (P1, P2 and P3) were synthesized via “advancement reaction” of o-carborane-containing bisphenol (4) and diglycidyl ether of bisphenols (DGEBA and 1). FTIR and 1H-, 13C-, and 11B-NMR were utilized to characterize the obtained polymers. TGA test was conducted under nitrogen and air. It is found that the shielding effect of carborane moiety on its adjacent aromatic structures contributes to high initial decomposition temperatures, while oxygen in air has an adverse effect on the initial decomposition temperature. The oxygen can combine with polymer chain to form peroxide and hydroperoxide groups, which are more reactive during the degradation process. Besides, o-carborane-containing poly(hydroxy ethers) have high char yield at elevated temperatures. The boron atom combines with oxygen from the polymer structure or/and from air, thus to form a three-dimensional network linked with B—O—B and B—C bonds, and retain the polymer weight to a large extent.