Comparison of properties of long/short glass fiber reinforced PPS composites

The resin matrix of thermoplastic composites involves general and special engineering plastics, and PPS is a typical representative of special engineering plastics, commonly known as "plastic gold". Performance advantages include the following aspects: excellent heat resistance, good mechanical properties, corrosion resistance, self-flame retardant up to UL94 V-0. Due to the advantages of the above properties, and compared with other high performance thermoplastic engineering plastics and has the characteristics of easy processing and low cost, PPS has become an excellent resin matrix for the manufacture of composite materials.

PPS plus short glass fiber (SGF) composite has the advantages of high strength, high heat resistance, flame retardant, easy processing, low cost, and has been applied in automotive, electronics, electrical, machinery, instruments, aviation, aerospace, military and other fields.

PPS lengthened glass fiber (LGF) composite material has the advantages of high toughness, low warpage, fatigue resistance, good product appearance, etc. It can be used in water heater impeller, pump shell, joint, valve, chemical pump impeller and shell, cooling water impeller and shell, home appliance parts and so on.

So what are the specific differences between short glass fiber (SGF) and long glass fiber (LGF) reinforced PPS composites?

In this paper, the comprehensive properties of PPS/SGF (short glass fiber) composite and PPS/LGF (long glass fiber) composite were compared. The PPS/LGF composite was prepared by melt impregnation process and the PPS/SGF composite was prepared by melt blending twin-screw granulation process. The reason for using the melt impregnation process is that the fiber bundles can be impregnated in the impregnation mold without causing damage to the fiber. Finally, through the comparison of the mechanical properties of the two data, the technical support for the application side of the technical personnel in the selection of materials.

Mechanical property analysis

The reinforced fiber added in the resin matrix can form a supporting skeleton, and the reinforced fiber can effectively bear the external load when the composite is subjected to external force. At the same time, energy can be absorbed through fracture, deformation and other ways to improve the mechanical properties of the resin. The following figures show the tensile and bending properties of PPS/SGF and PPS/LGF composites with different glass fiber contents respectively.

It can be seen that the tensile strength and bending strength of the composite gradually increase with the increase of the amount of glass fiber. The main reason is that when the content of glass fiber increases, more glass fiber in the composite material will bear the action of external force. At the same time, due to the increase in the number of glass fiber, the resin matrix between the glass fiber becomes thinner, which is more conducive to the construction of glass fiber reinforced frame. Therefore, with the increase of glass fiber content, more stress is transferred from the resin to the glass fiber under external load, which effectively improves the tensile and bending properties of the composite.

The tensile and bending properties of PPS/LGF composites are higher than those of PPS/SGF composites. When the glass fiber mass fraction is 30%, the tensile strength of PPS/SGF and PPS/LGF composites is 110MPa and 122MPa, respectively. The bending strength was 175MPa and 208MPa, respectively. The flexural elastic moduli were 8GPa and 9GPa, respectively.

The tensile strength, bending strength and bending elastic modulus of PPS/LGF composites are increased by 11.0%, 18.9% and 11.3% compared with those of PPS/SGF composites. The length retention rate of PPS/LGF composites is higher. Under the condition of the same glass fiber content, the composites have stronger load resistance and better mechanical properties.

See, when the content of glass fiber is low, the impact strength of the composite decreases. The main reason is that the low content of glass fiber cannot form a good stress transfer network in the composite material, so that the glass fiber exists in the form of defects under the impact load of the composite material, resulting in the overall impact strength of the composite material is reduced.

The above defects refer to the glass fiber tip or crack tip; The induction point of failure of thermoplastic composites is the glass fiber tip or crack tip, from which it spreads until the composite is completely destroyed. When the glass fiber content is small, the glass fiber tip is added to the composite material. At this time, the effect of the glass fiber tip on the fracture of the composite material is greater than the effect of the glass fiber reinforcement, so the impact performance will be decreased to a certain extent.

With the increase of the glass fiber content, the glass fiber in the composite can form an effective spatial network, and the reinforcement effect is greater than that of the glass fiber tip. Under the action of external load, the external load can be transferred to the reinforced fiber better, thus improving the overall performance of the composite. In the PPS/LGF system, the glass fiber is longer and the spatial network is more dense. Reinforced glass fiber bearing capacity is stronger, its impact strength is also better. When the mass fraction of glass fiber is 30%, the impact strength of PPS/LGF is increased by 19.4%, from 31kJ/m2 to 37kJ/m2, and the notch impact strength is increased by 54.5%(from 7.7kJ/m2 to 11.9kJ/m2).

When the mass fraction of glass fiber is 30%, the thermal deformation temperature of PPS/SGF and PPS/LGF composites reaches 250℃ and 275℃ respectively. The thermal deformation temperature of PPS/LGF composites is 10% higher than that of PPS/SGF composites. The main reason is that the introduction of glass fiber makes the network skeleton of reinforced fiber formed inside the composite material, which greatly improves the heat resistance of the composite material. The size of the glass fiber in PPS/LGF is longer, and the heat resistance improvement advantage is more obvious.

It can be seen that the glass fiber is well dispersed in the resin. With the increase of the glass fiber content, the construction of the reinforced fiber network inside the composite becomes more perfect. This is also the main reason that the overall mechanical properties of composites increase with the increase of glass fiber content. Compared with PPS/SGF and PPS/LGF composites, the glass fiber retention rate of PPS/LGF composites is higher, which is also the main reason for the better mechanical properties of PPS/LGF composites.

In conclusion, the tensile strength, flexural strength, flexural elastic modulus, notched impact strength and non-notched impact strength of PPS/LGF composites are improved compared with those of PPS/SGF composites. The thermal deformation temperature of 30% glass fiber reinforced PPS/SGF composite can reach 250℃, and the thermal deformation temperature of PPS/LGF composite can reach 275℃.

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