Mechanical, thermal and morphological properties of glass fiber and carbon fiber reinforced polyamide-6 and polyamide-6/clay nanocomposites
Introduction
In recent years, polyamide-6/clay nanocomposites have been commonly used in engineering plastics. There are five methods to prepare polyamide-6/clay: (1) intercalation methods, (2) in-situ methods, (3) solution mixing methods, (4) direct dispersion methods, and (5) other methods [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. Polyamide-6/clay nanocomposites prepared by mechanical blending polyamide-6 and montmorillonite may cause a phase separation in a twin-screw extruder.
For the past decades, polyamides have been successfully reinforced by glass fiber, carbon fiber and other inorganic reinforcements [1]. In these composites, reinforcements may not dispersed homogeneously in microscopic level. However, polyamide-6/clay nanocomposites is a molecular composite in which the silicate monolayers of montmorillonite is 1 nm in thickness and 100 nm in width which are uniformly dispersed in the polyamide-6 matrix [2], [3], [4], [5].
Polyamide-6 molecules and the silicate layers are bonded through ionic bonds. Polyamide-6 is in molten state by injection molding or extrusion process. Injection-molded polyamide-6/clay shows excellent strength, elastic modulus, heat distortion temperature [4], [5], [6], and water barrier properties, compared with neat polyamide-6 resin [7]. Polyamide-6/clay films prepared from the molten pellets using an extruder show excellent gas barrier properties [8]. A high extensional flow caused typically by the fiber drawing operation, the molecular chain axis of the polymer is oriented along the drawing direction [9]. In the thin polyamide-6 film prepared from the molten pellets using an extruder with a T-die, the silicate layers have planar orientation and the chain axis of polyamide-6 crystallites (γ form) were parallel to the film surface while within this film plane, they were randomly oriented [10].
In contrast, the crystallites in the pure polyamide-6 film were three-dimensionally randomly oriented. The orientation of polyamide-6 crystallites in polyamide-6 was also assumed to be promoted by the presence of anisotropy silicate monolayers dispersed separately. Although the high aspect ratio of silicate nanolayers is ideal for reinforcement, the nanolayers are not easily dispersed in most polymers due to their preferred face-to face stacking in agglomerated tactics [11]. Dispersion of the clay into discrete monolayers is further hindered by the intrinsic incompatibility of hydrophilic layered silicates and hydrophobic engineering plastics [11].
As was first demonstrated by the Toyota group more than 10 years ago, the replacement of inorganic exchange cations in the galleries of the native clay by alkylammonium surfactants can compatibilize the surface chemistry of the clay. The complete dispersion of clay nanolayers in a polymer optimizes the number of available reinforcing elements for carrying an applied load and deflecting cracks. The coupling between the tremendous surface area of the clay and the polymer matrix facilitates stress transfer to reinforcement phase, allowing for such tensile, flexural strength, elongation and toughness [11].
In this study, mechanical, thermal and morphological properties of polyamide-6 and polyamide-6/clay (3 wt.% clay) reinforced with different weight percents of glass fiber and carbon fiber were investigated. The effects of glass fiber and carbon fiber on the properties of polyamide-6 composites and polyamide-6/clay nanocomposite were also discussed.
Section snippets
Materials and sample preparation
The polyamide-6 pellets (M7536A) were received from BASF, USA. The polyamide-6/clay pellets contain 3.0 wt.% (1.6 vol.%) montmorillonite (M1030D) were obtained from Unitka, Japan. Sample were prepared by the following procedures: polyamide-6 and polyamide-6/clay were mixed mechanically with E-glass fiber (#473, 6-mm long, Taiwan Glass Industry, Taiwan) and carbon fiber (PA6-2, 6-mm long, GRAFIL, USA), separately. Samples were extruded by a twin-screw extruder at a rotational speed 20 rpm. The
Mechanical properties
In this study, polaymide-6 and polyamide-6/clay were prepared by mixing with different weight percents (10, 20 and 30 wt.%) of glass fiber and carbon fiber. All results are listed in Table 1. Table 1 shows that the tensile and flexural strength of neat polysmide-6/clay is higher than those of neat polyamide-6, but the notched Izod impact strength of neat polyamide-6 is higher than that of neat polyamide-6/clay. Tensile and flexural strength and modulus of the both composite systems increased
Conclusions
(1) Tensile strength of polyamide-6/clay containing 30 wt.% glass fiber is 11% higher than that of polyamide-6 containing 30 wt.% glass fiber, while the tensile modulus of nanocomposite increases by 42%. Flexural strength and flexural modulus of neat polyamide-6/clay are similar to polyamide-6 reinforced with 20 wt.% glass fiber.
(2) Heat distortion temperatures of polyamide-6/clay and polyamide-6 are 112°C and 62°C, respectively. Consequently, the heat distortion temperature of fiber reinforced
Acknowledgements
This research was supported by the National Science Council, Taiwan, Republic of China, under the Contract No. NSC-89-2216-E-007-016.
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