Properties And Application Of Polyphenylene Sulfide (PPS)

Polyphenylene Sulfide (PPS) is a linear polymer compound composed of benzene ring and sulfur atoms arranged alternately, it is the sixth largest engineering plastics after polyamide, polyformaldehyde, polycarbonate, thermoplastic polyester, polyphenylene ether, it has better heat resistance, drug resistance, mechanical properties and electrical properties and flame retardant. In the special engineering plastics, PPS than polyarylate, polyether ether ketone, polyethersulfone, Polyimide, fluoroplastics and other development speed.

PPS can be processed through extrusion, injection molding methods, but also through biaxial stretching made of film, made of fibers and fabrics through fibrillation, through the use of fibers and other inorganic fillers to fill the enhancement of modification, so that many of its excellent properties to obtain further play, is a very promising engineering plastics.

PPS is a benzene ring in the right position connected to the sulfur atom and the formation of rigid polymer backbone, polymer crystallinity is high.PPS resin is usually white or almost white powder or bead products, density of 1.34 ~ 1.36g / cm3, the melting point of 280 ° C. As a crystalline thermoplastic polymer, PPS resin has a high crystallinity and a high density. As a crystalline thermoplastic polymer, linear PPS crystallinity up to 70%, glass transition temperature of 92 ℃, decomposition temperature greater than 400 ℃.

PPS is divided into straight chain type and crosslinked two kinds. Straight chain type has excellent toughness and elongation; and crosslinked type has its own unique properties: crosslinking and curing in the presence of oxygen, more than 200 ℃ heat treatment, the melt flow rate drops sharply. Cross-linked PPS heat resistance and creep resistance is good. In order to improve the cross-linked PPS, and developed a semi-cross-linked PPS.

Due to the poor impact resistance of PPS, need to use reinforcing fibers (such as glass fibers, carbon fibers, aramid fibers, etc.) filler modification, after enhancement can greatly improve the mechanical properties and heat resistance.

1. Mechanical properties

PPS has excellent heat resistance, can be used in a wide range of temperatures, its tensile strength, flexural strength and flexural modulus of elasticity are listed in the forefront of engineering plastics, PPS strength retention rate at high temperatures is much higher than PBT, PET, PC and other engineering plastics. Reinforced PPS in the impact resistance, strength, hardness and most of the mechanical and physical properties have been improved, therefore, PPS molding compounds are almost all glass fiber or mineral reinforced.

Straight chain PPS resin and crosslinked PPS resin in the structure of certain differences, and therefore there are differences in their mechanical properties, Table 1-1 is crosslinked PPS and straight chain PPS performance table.

2. Thermal properties

PPS is a crystalline polymer, the highest degree of crystallinity up to 65%, its crystallization temperature is 127 ℃, the melting point of up to 280 ~ 290 ℃, in the air 430 ~ 460 ℃ above the beginning of decomposition, thermal stability is far beyond the PA, PBT, POM and PTFE and other engineering plastics, reinforced by the composite with glass fibers, the heat distortion temperature of the PPS can reach 260 ℃, the long-term use of the temperature is the highest in the thermoplastics, up to 220 ~ 240 ℃. Long-term service temperature is the highest among thermoplastics, which can reach 220~240℃. In addition, its resistance to solder heat performance is much higher than other engineering plastics, making it suitable for the production of electrical and electronic components.PPS also has good thermal insulation, but add appropriate fillers, can also produce good thermal conductivity of the PPS composite materials.PPS's excellent thermal stability is also manifested in the high-temperature environment of the strength retention rate and high-temperature thermal aging after the strength retention rate.

PPS resin has excellent flame retardant properties, the oxygen index of the resin powder is 46~53, it can burn on the flame, but not dripping, self-extinguishing after leaving the fire, the smoke rate is lower than that of halogenated polymers, and it can reach the standard of UL94U-D without the addition of flame retardant.

3. Dimensional stability

PPS has excellent dimensional stability, molding shrinkage of 0.15% to 0.3%, the lowest up to 0.01%, water absorption of only 0.05%, therefore, it has a high thermal stability. 300 ℃ PPS is not melting below the state of high elasticity, heated to 400 ~ 500 ℃ stable and does not decompose. Cross-linked PPS can withstand temperatures above 600°C. PPS is not deformed under high humidity. Despite the high melting temperature, the viscosity of the melt is low and the flowability is good, PPS is suitable for the production of precision parts or thin-walled products.

4. Chemical resistance

The corrosion resistance of PPS is similar to that of PTFE, which is known as "King of Plastics" and has excellent corrosion resistance. It can resist acid, alkali, hydrochloric acid and other chemicals erosion, at 200 ℃ below insoluble in any organic solvents. In addition to strong oxidizing acid and fuming nitric acid, chlorosulfonic acid, fluorine acid, almost not subject to all inorganic media erosion. Above 250℃, it is only soluble in biphenyl, biphenyl ether and their halogenated substitutes. At high temperature even the best solvent chlorinated biphenyl can only dissolve 10%. In boiling concentrated hydrochloric acid, PPS does not undergo any change. PPS has good processability is far better than PTFE, making PPS in the petroleum, chemical and automotive industries and sectors need oil resistance, corrosion resistance has a wider range of uses.

PPS also has good weathering and radiation resistance, after 2000h wind erosion, the rigidity is basically unchanged, the tensile strength is only a slight decrease.PPS by a large dose of radiation (106 Gy), its performance is basically unchanged, will not occur viscous and decomposition phenomenon.

5. Electrical properties

PPS has excellent electrical properties, dielectric constant of 3.9, electrical susceptibility is small, dielectric strength (breakdown voltage strength) as high as 19kV / mm, resistivity as high as 1016Ω - cm. Compared with other engineering plastics, its dielectric constant is small, dielectric loss angle tangent value is low, arc resistance can be as high as 185s, equivalent to or even more than thermosetting plastics, thermosetting plastics can be replaced for arc-resistant high-voltage insulation parts. It can replace thermosetting plastics and be used for arc-resistant high-voltage insulating parts. Especially valuable is, in high temperature, high humidity, frequency and other conditions, PPS can still maintain excellent electrical insulation, PPS and conductive filler composite, can also be made of conductive PPS composite materials, used as anti-static and electromagnetic shielding materials.

6. Adhesion

PPS has excellent adhesive properties, metal and non-metal, as long as the material is stable above 350 ℃ can be bonded. Impact resistance is very good, the bonding strength is above 25MPa. The bonding strength of PPS is greater than the cohesive force of glass.

Modification and application of polyphenylene sulfide

1. Reinforcement and blending of PPS

The structural modification of PPS is mainly the introduction of modified groups in the main chain of PPS or benzene ring, the modified products are polyphenylene sulfide ketone (PPSK), polyphenylene sulfide sulfone (PPSS), polyphenylene sulfide phthalamide (PPSA), etc., these modified products make the mechanical properties of PPS, electrical properties, corrosion resistance and other properties to be improved.

PPS blending is mainly glass fibers, carbon fibers and inorganic filler filler enhancement modification to improve the impact strength and tensile strength, etc., so that the cost of the product can be greatly reduced. PPSBR-111 new grade, containing 68% of glass fibers and mineral fillers (such as ultrafine calcium carbonate, etc.), with excellent dimensional stability and high temperature strength retention, its tensile strength of 164MPa, flexural modulus of 18.5Ga, tensile strength, and flexural modulus of 18.5Ga, flexural modulus of 18.5Ga. Its tensile strength is 164MPa and flexural modulus is 18.5GPa.

PPS / PTFE alloy with fluorine resin excellent sliding, heat resistance and chemical resistance and polyphenylene sulfide mechanical properties and heat resistance, so that the amount of fluorine resin is greatly reduced, can reduce costs by 15%. At present, more high-performance alloys, such as PPS / PES (polyethersulfone), PPS / PSF (polysulfone), PPS / PAR (polyaromatic ester), PPS / LCP (liquid crystal polymers), PPS / silicone and so on, has also been developed.

2. Application areas

PPS has excellent comprehensive performance and low price, widely used in nuclear energy, rockets, satellites, weapons, space, aviation, automotive, electronics, electrical, automotive, machinery, chemical, sports equipment, office facilities and medical equipment and other fields. In the machinery industry, PPS is used as structural, insulating, wear-resistant and sealing materials for the manufacture of bearings, bearing cages, pump bodies, pump wheels, valves, pipe fittings, flow meters, sealing rings, compressor parts, gears, insulation panels, aerosol dispensers, indicator gauges, pulleys and so on. In electronic and electrical appliances, PPS mechanical properties, electrical insulation properties, heat resistance, chemical corrosion resistance, moisture absorption is small, dimensional stability, especially at 200 ℃ still has good rigidity and dimensional stability, with high temperature, high-frequency conditions, excellent electrical properties, especially suitable for the production of high-temperature, high-frequency conditions of the electrical components. PPS is used to manufacture brushes, brush holders, starters, coils, shields, blades and rotor insulating parts in electric motors. In electrical appliances, PPS is used to make connectors, transformers, resistors, skeletons in relays, H-class winding frames, coil tubes, switches, sockets, TV channel knobs, solid state relays, motor rotors, capacitor shrouds, brush handles, magnetic sensor sensors, trimmer capacitors, electrolytic capacitors, fuse support parts, contact circuit breakers, etc. PPS is also used in the manufacture of automotive parts that require heat-resistant and high-frequency components. PPS is widely used in automobiles as hoods, exhaust treatment parts, brush handles, ignition parts, gasoline pumps, seat valves, plugs, carburetors, oil distributor parts, radiator parts, rotating parts, composite fittings, regulating valves, body panels, etc. PPS can be used in heat-resistant corrosion-resistant equipment and parts, such as PPS can be used for heat-resistant and corrosion-resistant equipment and parts, such as all kinds of corrosion-resistant pumps, pipes, valves, containers, reaction kettles, wastewater and exhaust gas filters, as well as heat-resistant, pressure-resistant, acid-resistant petroleum drilling parts.