Investigation on thermal degradation mechanism of poly(phenylene sulfide)

Response Surface Methodology Optimization of Resistance Welding Process for Unidirectional Carbon Fiber/PPS Composites

The use of thermoplastic composites (TPCs) as one of the lightweight solutions will inevitably encounter problems in connection. Resistance welding has the characteristics of high strength, simplicity, and high reliability, and is considered a very potential hot-melt connection technology. The resistance welding technology of unidirectional carbon fiber-reinforced polyphenylene sulfide composites (UCF/PPS) was systematically studied. The experimental results show that the 100-mesh brass mesh has the best resin wetting effect and heating efficiency, and the PPS/oxidized 100-mesh brass mesh composite resistance element (Ox-RE/PPS) has the highest welding strength. The welding failure mode changes from interface failure and RE failure to interlayer structure damage and fiber fracture. The single-factor experimental results show that the maximum welding strength is reached at 310 °C, 1.15 MPa, and 120 kW/m2. According to the conclusion of the single-factor experiment, the Box-Behnken method was further used to design a three-factor, three-level experiment, and a quadratic regression model was established according to the test results. The results of variance analysis, fitting curve analysis, and perturbation plot analysis proved that the model had high fitting and prediction abilities. From the 3D surface diagram analysis, the influence of power density is the largest, and the interaction between welding temperature and power density is the most significant. Combined with the analysis of Design Expert 13 software, the optimal range of process parameters was obtained as follows: welding temperature 313-314 °C, welding pressure 1.04-1.2 MPa, and power density 124-128 kW/m2. The average strength of resistance welding joints prepared in the optimal range of process parameters was 13.58 MPa.

The Influence of Thermal Parameters on the Self-Nucleation Behavior of Polyphenylene Sulfide (PPS) during Secondary Thermoforming

During the secondary thermoforming of carbon fiber-reinforced polyphenylene sulfide (CF/PPS) composites, a vital material for the aerospace field, varied thermal parameters profoundly influence the crystallization behavior of the PPS matrix. Notably, PPS exhibits a distinctive self-nucleation (SN) behavior during repeated thermal cycles. This behavior not only affects its crystallization but also impacts the processing and mechanical properties of PPS and CF/PPS composites. In this article, the effects of various parameters on the SN and non-isothermal crystallization behavior of PPS during two thermal cycles were systematically investigated by differential scanning calorimetry. It was found that the SN behavior was not affected by the cooling rate in the second thermal cycle. Furthermore, the lamellar annealing resulting from the heating process in both thermal cycles affected the temperature range for forming the special SN domain, because of the refined lamellar structure, and expelled various defects. Finally, this study indicated that to control the strong melt memory effect in the first thermal cycle, both the heating rate and processing melt temperature need to be controlled simultaneously. This work reveals that through collaborative control of these parameters, the crystalline morphology, crystallization temperature and crystallization rate in two thermal cycles are controlled. Furthermore, it presents a new perspective for controlling the crystallization behavior of the thermoplastic composite matrix during the secondary thermoforming process.

Additive Manufacturing of Poly(phenylene Sulfide) Aerogels via Simultaneous Material Extrusion and Thermally Induced Phase Separation

Additive manufacturing (AM) of aerogels increases the achievable geometric complexity, and affords fabrication of hierarchically porous structures. In this work, a custom heated material extrusion (MEX) device prints aerogels of poly(phenylene sulfide) (PPS), an engineering thermoplastic, via in situ thermally induced phase separation (TIPS). First, pre-prepared solid gel inks are dissolved at high temperatures in the heated extruder barrel to form a homogeneous polymer solution. Solutions are then extruded onto a room-temperature substrate, where printed roads maintain their bead shape and rapidly solidify via TIPS, thus enabling layer-wise MEX AM. Printed gels are converted to aerogels via postprocessing solvent exchange and freeze-drying. This work explores the effect of ink composition on printed aerogel morphology and thermomechanical properties. Scanning electron microscopy micrographs reveal complex hierarchical microstructures that are compositionally dependent. Printed aerogels demonstrate tailorable porosities (50.0-74.8%) and densities (0.345-0.684 g cm-3 ), which align well with cast aerogel analogs. Differential scanning calorimetry thermograms indicate printed aerogels are highly crystalline (≈43%), suggesting that printing does not inhibit the solidification process occurring during TIPS (polymer crystallization). Uniaxial compression testing reveals that compositionally dependent microstructure governs aerogel mechanical behavior, with compressive moduli ranging from 33.0 to 106.5 MPa.

A multifunctional integrated carbon nanotubes/polyphenylene sulfide composite: preparation, properties and applications

Although great progress has been achieved in polyphenylene sulfide (PPS) composites by the use of carbon nanotubes (CNTs), the development of cost-efficient, well dispersive and multifunctional integrated PPS composites has yet to be achieved because of the strong solvent resistance of PPS. In this work, a CNTs-PPS/PVA composite material has been prepared by mucus dispersion-annealing, which employed polyvinyl alcohol (PVA) to disperse PPS particles and CNTs at room temperature. Dispersion and scanning electron microscopy observations revealed that PVA mucus can uniformly suspend and disperse micron-sized PPS particles, promoting the interpenetration of the micro-nano scale between PPS and CNTs. During the annealing process, PPS particles deformed and then crosslinked with CNTs and PVA to form a CNTs-PPS/PVA composite. The as-prepared CNTs-PPS/PVA composite possesses outstanding versatility, including excellent heat stability with resistant temperatures up to 350 °C, corrosion resistance against strong acids and alkalis for up to 30 days, and distinguished electrical conductivity with 2941 S m^-1. Besides, a well-dispersed CNTs-PPS/PVA suspension could be used to 3D print microcircuits. Hence, such multifunctional integrated composites will be highly promising in the future of new materials. This research also develops a simple and meaningful method to construct composites for solvent resistant polymers.

Structural transformation and performance analysis of PPS-based bag filters in coal-fired power plants

Owing to the complicated environments, the service life of bag-filter or electrostatic-bag composite precipitators with polyphenylene sulfide (PPS) is greatly deviated from the ideal time. In this paper, the structural transformation of PPS-based bag filter materials collected from the coal-fired power plants with different loading units were investigated systematically. As the SO2 content increases, the surface evolution of PPS fibers from smoothness to crack occurs. An opposite trend is observed for melting point and cross breaking strength. The major reason for the failure of PPS-based bag filters is that working temperature (T) often passes through acid dew gas point (Ta), and the SO3 would be produced during the condensing of H2SO4 when T is lower than Ta. The SO3 with strong oxidation would attack the weak C-S bonds of PPS, resulting in the oxidation or even sulfonation of PPS-based bag filters. This work discloses the actual structural evolution of PPS and some corresponding rules under the complicated corrosive gases with high temperatures, which provides a guidance for prolonging the service life of PPS-based bag filters during the usage of coal-fired power plants.