Preparation of kaolinite-nylon6 composites by blending nylon6 and a kaolinite-nylon6 intercalation compound

Abstract

Polymer/clay nanocomposites, in which exfoliated smectite clay nanosheets are highly dispersed in polymer matrices, exhibit excellent tensile property, gasbarrier property, thermostability, flame retardance, etc. [1–3]. Polymers utilized for this purpose are various, including nylon [4, 5], epoxy resin [6, 7], polyurethanes [8], polyimides [9], nitrile rubber [10], polyesters [11], poly(propylene) [12, 13], poly(styrene) [14, 15], and polysiloxanes [16]. However, the kind of clays used for the formation of this type of nanocomposites is limited to swelling smectite clays, such as montmorillonite. It has been pointed out that the property of polymer/clay nanocomposites also depends on the kind of smectite clays [5]. This prompted us to survey the possibility of the formation of this type of nanocomposites by the use of different kinds of clays. Kaolinite, a 1:1 type clay mineral, is different from 2:1 type smectite clay minerals and has a larger aspect ratio. The surface of the aluminosilicate is composed of SiO4 tetrahedral sheets and AlO2(OH)4 octahedral sheets which can be utilized for the formation of hydrogen bondings with some polymers. Due to its unique structural feature, polymer/kaolinite nanocomposites would exhibit different behaviors from those of polymer/smectite nanocomposites. However, the intercalation capablity of kaolinite for polymers is very low and only a few intercalation compounds with a limited range of polymers have been reported [17–22]. We have recently clarified that methoxy-modified kaolinite [23] is an excellent intermediate for intercalating various organic species [24] and reported the formation of a kaolinitenylon6 intercalation compound [25]. In the present study, blended composites were prepared by employing nylon6 as a polymer matrix and a kaolinite-nylon6 intercalation compound or kaolinite as an inorganic filler, and their mechanical properties were measured. Because there are no reports on the mechanical properties of kaolinite–organic intercalation compounds blended with polymers, the present results contribute to the prediction of the properties of polymer/kaolinite nanocomposites to be developed in future where the nanosheets of kaolinite would be well dispersed in polymer matrices. A kaolinite–nylon6 intercalation compound (kaolinite-nylon6) was prepared according to a method reported previously by using a kaolinite–6-aminohexanoic acid(AHA) intercalation compound as a precursor [25]. Nylon6/kaolinite–nylon6 was obtained by melt mixing between nylon6 (commercial grade, 1015B, Ube Industries Co.) and kaolinite–nylon6 by a twin-screw extruder (S-1KRC, Kurimoto Ltd.). The temperature of nylon6 was 240 ◦C and a rotational speed was 300 rpm with the amount of feed by 1300 g h−1. Nylon6 blended without clay (nylon6 (blended)) and with unmodified kaolinite (nylon6/ kaolinite) were prepared for comparison. Nylon6 Clay Hybrid (NCH [4, 5], commercial grade, 1015C2, Ube Industries Co.), composed of organically modified smectite and nylon6, was used as a reference. Tensile and Izod impact tests were carried out according to the methods of ASTM D-638 and ASTM-D256, respectively. After the blending for the formation of nylon6/ kaolinite–nylon6, the basal spacing of kaolinite–nylon6 was slightly reduced to 1.15 nm from that of original kaolinite–nylon6 (not shown). This result indicates that the layered structure of kaolinite was not exfoliated but retained. The mechanical properties of the samples are listed in Table I. Tensile strength and tensile modulus of