PPS performance defects and four popular modification directions

Polyphenylene sulfide (PPS) has excellent mechanical strength, thermal stability, processing properties, the world's sixth largest engineering plastic. However, PPS is brittle, unable to self-lubricate, and easy to be oxidized at high temperatures, which limits its application in industry.

Main application field(cfrtp,cfrt)

Polyphenylene sulfide products come in different forms and grades, such as resins, fibers, filaments, films and coatings, and are widely used. The main application areas of polyphenylene sulfide include automotive industry, electrical and electronic, chemical industry, military defense, textile industry, environmental protection industry and so on.

PPS itself has good heat resistance, flame retardant, chemical resistance, should be a promising material, but there are some problems in pure PPS:

What are the application problems of PPS?

Unmodified PPS has some unavoidable defects:

Difficult processing: This is the biggest pain point of all high temperature resistant materials - high processing temperature, whether it is the molding process or processing energy consumption, will face great challenges. In addition, PPS is still prone to thermal oxidation crosslinking during the melting process, which leads to reduced fluidity and further increases the difficulty of processing.

Poor toughness: the molecular chain of PPS is rigid, the maximum crystallinity is as high as 70%, the elongation is low, and the welding strength is also ordinary. The final result is that the impact resistance of unmodified PPS is poor, which limits the application range.

High cost: PPS raw materials and general engineering plastics compared to the price is about 1-2 times higher, and some modified materials compared to the cost is not high;

Coating is difficult: resistance to chemical and medium is also a double-edged sword, and the surface coating and coloring performance of PPS is not ideal. Although this flaw is not a major problem at the moment, it is also a limiting factor for application.

The following is the study of PPS enhancement and toughening modification, friction modification, conductivity modification, rheological modification and oxidation resistance modification

1. Study on enhancement and toughening modification of PPS

PPS enhancement and toughening methods mainly include nanomaterials modification, fiber modification, alloy blending modification, chemical modification and so on.

Nanomaterial modification is generally divided into two types:

1) The fiber surface is treated with nanomaterials;

2) Direct reinforcement and toughening with nanomaterials as fillers.

The addition of fiber can reduce the amount of PPS, reduce the cost, and overcome the shortcomings of PPS, such as brittle fracture and low fracture strain, while maintaining the excellent performance of PPS. KhanSM et al. enhanced PPS by increasing the number of carbon fiber (CF) layers. The results show that when the number of CF layers increases from 4 to 20, the impact strength of the material increases from 2.60kJ/m2 to 7.20kJ/m2, and the hardness also increases significantly.

The modification of alloy blending can overcome the limitation of single polymer properties. Polyphenylene ether (PES) has excellent impact resistance and can effectively overcome the disadvantages of poor toughness of PPS. Thermoplastic polyurethane (TPU) has excellent toughness and can be used to toughen polypropylene, PPS, polyamide (PA), polyacetal and other thermoplastics.

Chemical modification is mainly through the introduction of active functional groups (amino, carboxyl, etc.) in PPS to strengthen and toughen the purpose.

2. Research on modification of PPS friction properties

Generally, the wear resistance of PPS composites is improved by alloy blending, adding filler to construct skeleton materials, etc., and its application range is expanded.

PA has excellent wear resistance, and its self-lubricating properties can improve the durability of PPS under sliding or rolling.

The nanomaterials can prevent the PPS molecular chain structure from creeping and sliding, or improve the bonding strength between the transfer film and the friction pair, and improve the friction performance of PPS.

The fiber can form a skeleton to protect the base material, effectively reducing the contact area of the material and thereby reducing its friction coefficient.

The addition of tungsten disulfide (WS2) or aluminum nitride (AlN) nanoparticles to PPS/SCF/Gr composites can further improve their frictional properties, because the nanoparticles produce a load-bearing friction film, which enhances the boundary lubrication ability of the sliding pair and alleviates the adhesive wear tendency of the friction surface.

3. Research on modification of PPS conductivity

The main method to modify the conductivity of PPS is to blend PPS with excellent conductive materials to improve the conductivity of PPS.

Cellulose fiber, metal fiber and long carbon fiber (LCF) can improve the conductivity of PPS.

This is due to the high porosity of the composite film and its better affinity for the liquid electrolyte, which reduces the interface resistance between it and the electrode.

4. Study on the modification of PPS rheology

JiangT et al. modified PPS using GF(RdGF,RcGF) with circular and rectangular cross sections respectively. The results show that the viscosity of PPS/RcGF composites is much lower than that of PPS/RdGF composites, because compared with RdGF,RcGF has higher flow sensitivity and lower symmetry, and its "network" structure is more likely to be destroyed at low shear rates.

Carbon nanotubes, Gr, cage polysesquioxane (POSS) and other nanomaterials can effectively reduce the melt viscosity of PPS and improve the melt processing performance.

5. Study on modification of PPS antioxidant properties

At present, the antioxidant properties of PPS are usually modified by surface coating, adding nanomaterials and adding antioxidants.

The surface coating method is a treatment method that covers the surface of PPS fibers or fiber products with a protective coating composed of antioxidants. BaiMQ et al. coated polybenzoxazine (PBA) on the surface of PPS fiber to improve its antioxidant properties. This is because the cross-linked macromolecular structure of PBA has a shielding effect, which effectively improves the antioxidant properties of PPS fiber. However, this method has some problems such as uneven surface coating and difficult removal, which limits its application range.

At present, the addition of nanomaterials is the most used method to modify the oxidation resistance of PPS. The addition of antioxidants during processing can also improve the antioxidant properties of PPS. The heat resistance of organic antioxidants is poor, and combining inorganic nanomaterials with organic antioxidants can improve the heat resistance of antioxidants.

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