polyamide 6/chopped glass fiber composite

polyamide 6/chopped glass fiber composite

 

Investigation and optimization of mechanical and impact properties of recycled polyamide 6/chopped glass fiber composite

 

Mohammad Javad Shirkavand 1 *, Dariush Bahramian 2, Alireza Taji 3

1. Research and Development department, Nirumand Polymer Pars Co., r-d@npolymer.com

2. Research and Development department, Nirumand Polymer Pars Co., dbahram@aut.ac.ir

3. Research and Development department, Nirumand Polymer Pars Co., a.taji@gmail.com

Abstract

Polyamide 6 as an engineering plastic is used in diverse industrial applications due to possessing high mechanical properties and outstanding thermal stability. Polyamide 6 reinforced glass fiber has the highest consumption among other PA6 composites. However, when it comes to industrial applications the main problem of these composites is their weakness in impact strength. For this reason, a different approach of increasing impact strength and optimizing other properties has been investigated in this paper. Besides, a surface modifier additive was introduced and utilized to reinforce composite interface. Finally, by adding a distinct amount of thermoplastic elastomer and by optimizing its composition to homogenize and prevent phase separation, composite’s impact strength was enhanced.

 

Keywords: Polyamide 6- composite- surface modifier- mechanical properties- impact strength

Introduction

Polyamide 6 is one of the engineering polymers with good mechanical and thermal properties that can be used in special circumstances. In applications that a solid polymer with good dimensional stability and high temperature is required at the same time, polyamide 6 is one of the main choices (Meincke, 2004: 739).

However polyamide 6 has very good mechanical properties such as high modulus and strength, low toughness and impact resistance of this polymer is major disadvantage. In order to increase toughness of the compounds based on polyamide 6, we need another polymer with high toughness such as polypropylene copolymers (Gonzalez-Montiel, 1995: 4587). Although the blend of polyamide 6 with polypropylene increases the impact resistance of the finished product, it may have negative effects on other mechanical properties such as tensile modulus and flexural strength. For this reason, one of the fundamental challenges in compound designing is always making an appropriate balance between toughness and strength in the final compound, with regard to desired application (Bai, 2004: 3063).

On the other hand, in the case of obtaining higher modulus and preserving other mechanical properties, it is inevitable to utilize mineral fillers and reinforcements such as glass fiber (GF) in composite. However, optimizing the mechanical properties of ternary system based on PA6 / PP / GF composites with high stiffness and suitable toughness is a hard work (Laura, 2003: 3347).

Another challenge in the preparation of polyamide 6 – polypropylene compound is the difference of these materials in compatibility in the mixing approach. Polyamide 6 is a polymer with polar functional groups and polypropylene is a non-polar polymer, thus these two polymers are thermodynamically immiscible. In order to overcome this problem, coupling agents additives must be used in the formulation of the desired compound. Coupling agents commonly known as oligomers or polymers with dual nature in Adherence. Most of these materials are series of polyolefin or thermoplastic elastomer, functionalized with maleic anhydride as the polar coupling agent (Chow, WS, 2003: 7427).

In this study, by utilizing a surface modifier additive, the effect of interface bonding agent on mechanical properties of composite samples has been discussed. Therefore, the effect of adding a thermoplastic elastomer on the mechanical and impact properties of composites has been studied.

 

 

Experimental

 

Material

In this study, 6AB-24R is a commercial grade of polyamide 6 produced by Niroumand Polymer Co. This type of polyamide 6 is recycled and should be degassed preferably 4-6 hours at 90 ̊C temperature. The surface modifier which is used to strengthen the interface between the polymer composite parts was prepared by Niroumand Polymer Co. This additive is

a combination of several surface modifiers and chemical compatibilizers with the name of NB-NX100. LG polyolefin elastomer product with hardness of 60A used to improve impact resistance of composites. Chopped surface modified glass fiber suitable for polyamide with fiber length of 4 mm was used as reinforcement.

 

Sample Preparation

Manufacturing process of polyamide6-glass fiber composite was performed by a co-rotating twin screw extruder with L/D ratio equal to 36 and equipped with side feeder technology. Samples with different composition were produced by applying the same process conditions. Specimen of mechanical experiments were made by injection molding machine and tested.

 

 

Results and discussion

Due to lack of toughness and fragility of polyamide 6, processing approach has usually some problems. Accordingly, with the addition of 30% glass fiber to matrix, the resulting composite becomes more fragile. What is important to improve the processing of polyamide glass fiber composite more efficiently, is to intensify the interface of matrix and fiber, and also to add a soft material to reduce the fragility of the material after cooling. One of the industrial ways to modify the interface and also improve the impact of polyamide6 glass fiber composites is the use of an ethylene-based copolymer or terpolymer with functional groups on its chain. Furthermore, another additive are added to the polymerization reaction for thermal stability of the resulted polymer. This producing method restricts the final properties of composite and causes to cost-increase. In this study, taking into account the economic aspect of the final product, a certain amount of additive NB-NX100 added to composite and after optimizing the process of composites, different percent of a thermoplastic elastomer used to obtain mechanical properties and impact strength at the same time.

It was observed that by adding 5% of the surface modifiers, producing process became better. However, similar imported additive caused to improve process by adding more quantity than Niroumand Polymer’s additive. It is important that polyamide molecules are polar, thus the polar compatibilizer additive causes melt uniformity and ability of withstanding stress after leaving the die by bonding polyamide’s molecules and glass fiber. The surface modifier quantity has a direct effect on adhesion between parts of glass fiber reinforced polyamide composites. Consequently, by adding more quantity of surface modifier in the composite, it was observed that the homogeneity of the melt output became further.

In the next step of producing, various amounts of a thermoplastic elastomer were added to the composition. By adding this soft material to the formulation, in addition to improving process conditions, the impact properties of the final composite considerably increased. Moreover, if the amount of thermoplastic elastomer in the composite matrix exceeds a certain level, the mechanical properties of composite substantially decrease because of its non-polar nature.

However the processing temperature of polyamide is high and about 260°C, and this temperature degrade thermoplastic elastomer, regulating a convenient profile temperature is a critical issue. Table 1 shows processability of composite production using different percentages of surface modifier. As it is shown in Table 1, by adding 5% of the surface modifier masterbatch, processing became efficiently possible which reveals that a proper bonding between polymer and glass fiber has been made.

In the next step, by adding thermoplastic elastomer the impact resistance of composite was improved, as it is shown in Table 2.

 

As the results show, by adding the optimum amount of surface modifier masterbatch into composite formulation, in addition to improving processability, tensile strength and flexural modulus also show a significant increase. The reason for this increase in properties is creation of a strong interface bonding between the glass fiber and polyamide matrix. This interface is not well-formed in less percentage of additives.
Also addition of thermoplastic elastomer to the composition of the composite (Toughened PA5 G), it was observed that impact resistance and crack growth resistance significantly increased.

Conclusion

In this study, glass fiber-reinforced recycled polyamide6 composite was made by using compatibilizer additive masterbatches, and then after finding the appropriate percentage of this additive which caused to improve the conditions of the process and the final properties, a thermoplastic elastomer was used to increase impact resistance. The results showed that addition of this rubber phase to the formulation, leads to increase impact resistance, while the mechanical properties showed little changes. Thus, by using described method in this study, the ability of making recycled polyamide6 and glass fiber composite possessing physical and

mechanical properties similar to pure material based composites is provided.

 

 

References

  1. Bai, S. L., Wang, G. T., Hiver, J. M., and G'Sell, C., Polymer, 45, 3063-3071, 2004.

 

  1. Chow, W. S., Ishak, Z. M., Karger-Kocsis, J., Apostolov, A. A., and Ishiaku, U. S., Polymer, 44, 7427-7440, 2003.

 

  1. Gonzalez-Montiel, A., Keskkula, H., and Paul, D. R., Polymer, 36, 4587-4603, 1995.

 

  1. Laura, D. M., Keskkula, H., Barlow, J. W., and Paul, D. R., Polymer, 44, 3347-3361, 2003.

 

  1. Meincke, O., Kaempfer, D., Weickmann, H., Friedrich, C., Vathauer, M., and Warth, H., Polymer, 45, 739-748, 2004.

 

 

Table 1. Influence of different amounts of surface modifier on processability

Sample

GF content (%)

Additive content (%)

Processability

6AB-24R

--

--

improper

PA2G

30

2

improper

PA4G

30

4

improper

PA5G

30

5

proper

PA6G

30

6

proper

 

 

 

 

Table 2. Mechanical and impact properties of composites and effect of different amount of surface modifier

 

 

Sample

Tensile strength (MPa)

Strain (%)

Izod impact strength (Kj/m2)

Flexural modulus

6AB-24R

50

10

3.5

2200

PA4G

90

7

4

6000

PA5G

130

8

6

8000

Toughened-PA5G

125

13

10

7500

 

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