Shujuan Wang

Thermal stability of phenolic resin: new insights based on bond dissociation energy and reactivity of functional groups

Density functional theory (DFT) was applied to model molecules of phenolic resin (PR) to interpret the relationship between the atomistic structure and thermal properties of the cured PR. The bond dissociation energy (BDE) of C–C (in methylene bridges) and C–O bonds (in hydroxyls), as well as the Fukui function of hydroxyl, benzene and methylene groups, were calculated. The isomers of bisphenol-F and the methyl substituents have a slight effect on the BDEs of C–C and C–O bonds, while the oxidized structures, such as p-benzoquinone and aldehyde groups, lead to a drastic decrease in the C–C bond BDEs. The high reactivity of the carbon atoms in the benzene groups and the oxidized structures results in an increased possibility of being attacked by free radicals and protects the methylenes from being attacked, but it will also lead to ring-opening reactions and weight loss. These results provide a great opportunity to understand the relationship between the atomistic structure and the thermal stability of the cured PR, which plays a pivotal role in the design and optimization of thermal stable polymers.

Room-temperature fully recyclable carbon fibre reinforced phenolic composites through dynamic covalent boronic ester bonds

The cross-linked structures of traditional thermosetting resins not only endow carbon fibre-reinforced polymer (CFRP) composites with excellent performance, but also make their efficient recovery a real challenge. The goal of this paper is to create reversible thermosets using dynamic boronic ester bonds as cross-links in replacement of traditional irreversible covalent bonds. Specifically, we used phenylboronic acid (PBA) to crosslink traditional novolac resin (NR), namely PBNR. By combining the reprocessability of thermoplastics with the desirable chemical and thermal stability of conventional thermosets, controlled degradation and full recycling of cross-linked resins and CFRP composites under ambient conditions were realized through a gentle alcoholysis process. The PBNR/CFRP composites fabricated by hot-pressing showed excellent mechanical properties. The multiple recycling experiments revealed near-total recovery of the clean fibre cloth and binder materials, which could be reprocessed into composites with similar mechanical properties to fresh materials. Dynamic boronate bonds have been demonstrated to open up a new pathway for full recycling of thermosetting resins and CFRP composites, which has a great impact in aeronautical, astronautics, adhesive, coating, or electronic packaging fields.

Pendulum hardness of polyurethane coatings during curing

Purpose – This paper aims to disclose the evolution of pendulum hardness of two-component acrylic polyurethane coatings during the cure process and attempts to describe the quantitative relationship between pendulum hardness and curing time. These findings are helpful for the study of fast curing acrylic polyurethane coatings. Design/methodology/approach – The pendulum hardness method was used to monitor the hardness of two-component acrylic polyurethane coatings during curing. The quantitative relationship between pendulum hardness and curing time can be obtained with Avrami equation. Findings – The evolution of coating pendulum hardness can be divided into three stages. By using the Avrami equation that explained the influence of both the acid value and the curing temperature on the drying speed of hydroxyl acrylic resin, the evolution of coating pendulum hardness during curing can also be accurately described. Research limitations/implications – It should be noted that the physical meaning of the Avram...

Blends of pre‐irradiated polypropylene powder and syndiotactic 1,2‐polybutadiene: isothermal and nonisothermal crystallisation kinetics

Purpose – The purpose of this paper is to study the isothermal and nonisothermal crystallisation kinetics of pure polypropylene (PP), 1 kGy pre‐irradiated PP and 1 kGy pre‐irradiated PP/syndiotactic 1,2‐polybutadiene (s‐1,2 PB) (90/10) blends by differential scanning calorimetry.Design/methodology/approach – The Avrami equation, modified Avrami equation, Ozawa equation and the treatment by combining the Avrami and Ozawa equation were used to analyse the isothermal and nonisothermal crystallisation of various samples.Findings – The s‐1,2 PB acted as a heterogeneous nucleation agent during the crystallisation of the PP/s‐1,2 PB blends and accelerated the crystallisation rate. The Avrami exponent n of the blends implied that the isothermal crystallisation kinetics of the blends followed a three‐dimensional growth via heterogeneous nucleation. The modified Avrami equation was limited to describe the nonisothermal crystallisation process of pure PP and 1 kGy pre‐irradiated PP, but it was successful for the ble...