Polyphenylene Sulfide (PPS): A Comprehensive Guide on High Heat Plastic

What is polyphenylene sulfide (PPS)?

• Exceptional mechanical strength
• Dimensional stability
• Electrical insulation properties
• Resistance to flame, chemical, and high temperature

How is PPS manufactured?

• Increase in molecular weight
• Increased toughness
• Loss of solubility
• Decrease in melt flow
• Decrease in crystallinity
• A darkening in color (a brownish color in contrast to this linear PPS grades are off-white)

The reaction of sodium sulfide and dichlorobenzene in a polar solvent to produce Polyphenylene sulfide (PPS)

What are the main types of PPS?

What are the properties of polyphenylene sulfide (PPS)?

1. Crystal Structure and Physical Properties: PPS is a semi-crystalline polymer.


• The unit cell is orthorombic (a=0.867 nm, b=0.561 nm, c=1.026 nm)
• The heat of fusion for an ideal PPS crystal was calculated as 112 J/g
• Depending on the thermal history, molecular weight, and cross-linked status (linear or not) the degree of crystallinity ranges from 0.30 to 0.45%
• Amorphous and crosslinked PPS can be prepared by:
  • Heating the material above the melting temperature
  • Cooling it to around 30°C below the melting temperature, and
  • Holding it for several hours in the presence of air


2. Dimensional Stability: PPS is an ideal material of choice to produce complex parts with very tight tolerances. The polymer exhibits excellent dimensional stability even when used under high temperature and high humidity conditions.


3. Electrical Properties: PPS has excellent electrical insulation properties. High volume resistivity and insulation resistance are retained after exposure to high-humidity environments. It has a less pronounced O₂ sensitivity. It can be conveniently doped to get high conductivity.


4. Thermal Properties and Fire Resistance: PPS is a high-temperature specialty polymer. Most of the PPS compounds pass UL94V-0 standard without adding flame retardant. PPS can be resistant at 260°C for a short time and used below 200°C for a long time.


5. Mechanical Properties: PPS has high strength, high rigidity, and low degradation characteristics even in high-temperature conditions. It also shows excellent fatigue endurance and creep resistance. PPS has a lower elongation to break, a higher cost, and is rather brittle. Today, PPS is available in different forms and grades such as compounds, fibers, filaments, films and coatings.


6. Chemical Properties: PPS has good chemical resistance. If cured, it is unaffected by alcohols, ketones, chlorinated aliphatic compounds, esters, liquid ammonia, etc. It also tends to be affected by dilute HCl, nitric acids, and concentrated sulfuric acid. It is insensitive to moisture and has good weatherability.

How additives optimize PPS properties?

• Unfilled Natural
• 30% and 40% glass filled
• Glass mineral filled
• Conductive and Anti-Static Grades
• Internally lubricated bearing grades

• carbon nanofillers (expanded graphite (EG) or ultrasonicated EG (S-EG), CNTs) or 
• inorganic nanoparticles.

• In order to lower the melt flow i.e., achieve high viscosity, additives such as alkali metal silicate, alkali metal sulfite, amino acids, and oligomers of a silyl ether may be added.
• During polymerization, if calcium chloride is added, the molecular weight will increase.
• The impact resistance can improve with the inclusion of block copolymers in the initial reaction.
• Sulfonic acid esters along with a nucleating agent would improve the crystallization rate.
• The addition of an alkali metal or alkali earth metal dithionate in the mixture would increase the heat stability and lower the crystallization temperature.

What are the processing conditions for PPS?

• injection molding,
• extrusion blow molding, and
• extrusion applications.

1. Pre-drying: It occurs at 150-160°C for 2-3 hrs or 120°C for 5 hours. It enhances molded the appearance of products and prevents drooling. For carbon fiber-filled grades, pre-drying is particularly important. This is because the moisture absorption is high due to the carbon fibers.


2. Injection Molding: To have higher productivity, a mold temperature of 50°C followed by post-crystallization at 200°C is possible. But it is not recommended for applications requiring high dimensional stability.
   
   
   • Because of its low viscosity, mold tightness has to be checked
   • Cylinder temperature: 300-320°C
   • Mold temperature: 120-160°C, to obtain good crystallization and minimize warping
   • Injection pressure: 40-70MPa
   • Screw Speed: 40-100 rpm


3. Extrusion: Commonly available for fiber and monofilament production as well as tubing, rod, and slab.
   
   
   • Drying conditions: 121°C for 3 hrs
   • Mold Temperature: 300-310°C
   • Melt Temperature: 290-325°C

Is PPS recyclable?

• Mechanical recycling methods, such as grinding or shredding
• Chemical recycling methods, such as depolymerization

Is PPS toxic?