The Effect of Silane Coupling Agents on a Composite Polyamide-6/Talc

THE EFFECT OF SILANE COUPLING AGENTS ON A COMPOSITE POLYAMIDE-6/TALC

H. WIEBECK1,^*, D.F. BORRELLY¹, C. XAVIER¹, P.S. SANTOS¹, S.A. ASCIUTTI² and M.P. CORRÊA²

¹DEQ - EPUSP - University of São Paulo, Av. Prof. Lineu Prestes, 580 - Conjunto das Químicas - Bloco 21 Cidade Universitária - CEP 05508-900 - São Paulo, SP - Brazil, e-mail: [e-mail]

²Petronyl Ind. e Com. de Poliamida Ltda., Estrada Itapecerica a Campo Limpo, 23 - CEP 06800 - Embu, SP - Brazil

(Received: February 17, 1998; Accepted: September 22, 1998)

Abstract - This paper evaluates the effect of the addition of silane agents on the mechanical properties (tensile strength, hardness and flexibility) of the composite polyamide-6/talc. For this purpose, 30% and 40% of a talc with and without the addition of silane agents were incorporated into polyamide-6. Three kinds of silane agents were used, resulting in nine formulations. Comparing the experimental results, it is concluded that the silane agents improve the mechanical properties of the composite material.

Keywords: Talc, organosilane, polyamide-6.

INTRODUCTION

Mineral fillers are usually defined as solid additives in a polymeric matrix (Katz and Milewski, 1987). Generally inert, they decrease the cost of the product, improve its dimensional stability, increase its weight and act as a noise reducer. They can stiffen the polymeric matrix (by increasing its elastic modulus and its resistance to creep and heat distortion) and increase its toughness, as well as modify its rheological, electric and permeability characteristics (Katz and Milewski, 1987; Trotignon, 1991; Rossi, 1991; Trotignon, 1993).

Inorganic matter can migrate to the surface of the composite due to incompatibilities on the polymer/mineral interface, creating rough appearance of the product and promoting damage, thus decreasing mechanical properties. (Katz and Milewski, 1987).

Organosilanes coupling agents can minimize the incompatibility by improving interaction at the polymer/mineral interface (Moreira et al., 1993).

The aim of this paper is to evaluate the use of one type of commercial Brazilian talc, with and without the addition of organosilanes, in modifying the mechanical properties of polyamide-6 (Katz and Milewski, 1987; Trotignon, 1991; Rossi, 1991).

PROCEDURE

Three different kinds of organosilanes were chosen due to their compatibility with the polymeric matrix. Initially, 0.5% by weight of each organosilane was incorporated into the talc by mechanical mixing, resulting in three different talc mixtures. Therefore, with the original talc, there were four different kinds of fillers. Each of these 4 fillers was mechanically mixed to polyamide-6, at 30 and 40% by weight. The composites were extruded and injected to obtain samples for mechanical tests, according to the following ASTM standards: Tensile Strength (ASTM D-638), Shore-D Hardness (ASTM D-570), Flexural Strength (ASTM D-790), Izod Impact (ASTM D-256), Water Absorption (ASTM D-570) and Melt Index (ASTM D-1238).

The tensile and flexural strength results were obtained at the crosshead speed of 5mm/min.

Raw Materials

Magnesita S.A., Talmag P-50 Talc

PETRONYL Ltda., Petromid 9200 B Polyamide-6

OSi Specialties Organosilanes:

- Silquest A-1100 (Aminopropyltriethoxysilane)

- Silquest A-1120 (Diaminosilane)

- Silquest A-1130 (Triaminosilane)

Treated Samples

Samples were made from nine different formulations:

- Pure Polyamide-6

- Polyamide-6/30% talc

- Polyamide-6/30% A-1100 silane-treated talc

- Polyamide-6/30% A-1120 silane-treated talc

- Polyamide-6/30% A-1130 silane-treated talc

- Polyamide-6/40% A-1100 silane-treated talc

- Polyamide-6/40% A-1120 silane-treated talc

- Polyamide-6/40% A-1130 silane-treated talc

Equipment

Hardness Meter Shore D

Microtest 7206-SB Hardness Meter Base

Versat 500 Universal Testing Machine (Panambra Ind. Tec. S.A.)

Emic Universal Testing Machine

RESULTS AND DISCUSSION

The results are shown in Table 1. In most cases, they represent the average of five values.

The addition of talc increases the polyamide-6 hardness, but the silane agents do not substantially affect its hardness.

The addition of talc decreases the polyamide-6 tensile strength, but the silane agents can increase its value. The best performing silane agent in the tensile strength tests was Silquest A-1120. The least improvement in performance was noted with Silquest A-1130. The composites with 30% talc showed better results than those with 40%. Stress-strain curves for the composites with 30% talc are shown in Figure 1.

Addition of talc and/or silane agents increases flexural strength. The best result was obtained for the composite with 30% talc treated with Silquest A-1120 while the worst result was obtained for the composite with 40% talc treated with Silquest A-1130. Flexural strength versus deformation curves for the composite with 30% talc are shown in Figure 2.

Table 1:
Results

Formulation	Tensile Strength (MPa)	Shore-D Hardness	Flexural Strength (MPa)	Izod Impact (J/m)	Water Absorption (%)	Melt Index (g/10 min)
Pure PA-6	65 ± 3	83 ± 1	32.1 ± 0.9	87 ± 12	1.65 ± 0.03	23 ± 2
30% Talc	60 ± 1	86.7 ± 0.5	51 ± 5	43 ± 3	0.85 ± 0.02	12.0 ± 0.3
30% Talc A-1100	65.1 ± 0.5	86.8 ± 0.4	59.78 ± 0.08	45 ± 4	0.86 ± 0.01	12.0 ± 0.3
30% Talc A-1120	67 ± 2	86.4 ± 0.7	68 ± 3	46 ± 5	0.83 ± 0.03	10.6 ± 0.1
30% Talc A-1130	64.9 ± 0.5	86.6 ± 0.5	64 ± 3	46 ± 3	0.84 ± 0.02	10.7 ± 0.3
40% Talc	54 ± 2	85.4 ± 0.5	53 ± 2	30 ± 4	0.61 ± 0.02	8.0 ± 0.3
40% Talc A-1100	63 ± 1	86.2 ± 0.4	61 ± 1	39 ± 3	0.80 ± 0.03	10.4 ± 0.1
40% Talc A-1120	64.9 ± 0.5	86.1 ± 0.3	56 ± 3	40 ± 4	0.699± 0.005	8.7 ± 0.2
40% Talc A-1130	62 ± 2	86.0 ± 0.7	54 ± 4	41 ± 4	0.72 ± 0.04	9.0 ± 0.3

Figure 1:
Stress-Strain Curves of the composite Polyamide-6 and 30% Talc and Different Silane Agents in Tension.

Figure 2:
Stress-Strain Curves of the composite Polyamide-6 and 30% Talc and Different Silane Agents in Flexure.

Addition of talc decreases the impact resistance. The worst results were obtained for the composite with 40% talc. The silane agents increase this resistance, the best being Silquest A-1130.

Addition of talc decreases water absorption, as the absorption value was observed to be the lowest for the composites with 40% talc. The change of water absorption due to addition of silane agents is more significant for the composite with 40% talc than for the composite with 30%.

Addition of talc decreases the flow rate, as the lowest results were obtained for the composites with 40% talc. For the composites with 30% talc the silane agents decreased the melt index, and for those with 40% talc, the silane agents increased the melt index.

Analyzing the interface talc/silane/PA-6, the talc lamellar surfaces and the PA-6 matrix form a very complicated structure. In fact, there are two kinds of interfaces: talc/silane (strong chemical bonding) and silane/PA-6 (conjugation of chemical bonding and interdiffusion).

Silquest A-1120 (diamine silane), which has small chemical groups, promotes better chemical bonding. This kind of silane was chosen due to the fact that PA-6 promotes hydrogen bonds.

The efficiency of the reaction of the diamine silane with the PA-6 matrix is demonstrated by the data presented in this paper. An excellent balance of properties was obtained with Silquest A-1120. Diamine silane promoted appropriate surface modification for the talc, maybe because of the chemical mobility of diamine silane attached to lamellar structures of the talc and the hydrogen bonds with the matrix. This complex bonding appears to be beneficial to the composite properties.

CONCLUSIONS

In general, the analyzed organosilane agents improved the mechanical properties of the polyamide-6/talc composite. The best mechanical properties were obtained with 30% talc. The best silane agent for the polyamide-6/talc composite was Silquest A-1120; it improved the mechanical properties, gave the lowest water absorption and lowered the melt index.

It was observed, as predicted by theory, that the composite with a particulate filler (like talc) may suffer a decrease in tensile strength and impact resistance, but other properties, such as flexural strength and dimensional stability, can be improved.

Another important factor is the decrease in water absorption which makes the shaping process easier.

Addition of talc decreases the flow rate, which enables changes in its shaping techniques, i.e., a high flow rate is ideal for injection and low flow rates are used for extrusion and blowing.

ACKNOWLEDGMENTS

The authors acknowledge the financial support received from FAPESP – Fundação de Amparo à Pesquisa do Estado de São Paulo – for this work (Projeto Temático n^o 1995/0544-0).

NOMENCLATURE

S Flexural strength, MPa

r Flexural deformation, %

Greek Symbols:

s Tensile strength, MPa

e Tensile deformation, %

• Katz, H.S. and Milewski, J.V., Handbook of Fillers for Plastics. Van Nostrand Reinhold, New York (1987).
• Moreira, J.C.G.; Girioli, J.C.; Agnelli, J.A.M. and Dulcini, S.L., Avaliaçăo do Tratamento Superficial de Cargas Inorgânicas e Análise de sua Influęncia no Desempenho de Compostos Poliméricos, Anais do II Congresso Brasileiro de Polímeros, Săo Paulo, October 5-8, pp. 9-15 (1993).
• Rossi, R.A., O Desempenho de Espécies Minerais em Promover Características de Reforços Termoplásticos. Anais do I Congresso Brasileiro de Polímeros, Săo Paulo, November 5-7, 1991, pp. 454-459 (1991).
• Trotignon, J.P., Mechanical Reinforcing Effect of Mineral Fillers in Polymer. Anais do I Congresso Brasileiro de Polímeros, Săo Paulo, November 5-7, pp. 391-398 (1991).
• Trotignon, J.P., Recent Advances on Mineral Reinforced Polymers. Anais do II Congresso Brasileiro de Polímeros, Săo Paulo, October 5-8, pp. 1-8 (1993).

*

To whom correspondence should be addressed.

Publication Dates

• Publication in this collection
  07 Dec 1998
• Date of issue
  Dec 1998

History

• Received
  17 Feb 1998
• Accepted
  22 Sept 1998