COMPOSITES SCIENCE AND TECHNOLOGY Composites Science and Technology 67 (2007) 390–398 www.elsevier.com/locate/compscitech

Mechanical properties of woven glass fabric reinforced in situ polymerized poly(butylene terephthalate) composites Z.A. Mohd Ishak

a,*

, Y.W. Leong b, M. Steeg c, J. Karger-Kocsis

c

a

c

School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia b Advanced Fibro Science, Kyoto Institute of Technology, Sakyo-ku Matsugasaki, 606-8585 Kyoto, Japan Institut fu¨r Verbundwerkstoffe GmbH, Technische Universita¨t Kaiserslautern, Erwin-Schroedinger Str, Geb 58, D-67663 Kaiserslautern, Germany Received 19 December 2005; received in revised form 17 July 2006; accepted 12 September 2006 Available online 1 November 2006

Abstract Cyclic butylene terephthalate (CBT) has been polymerized in situ at T = 190 C in the presence and absence of woven glass fabric (WGF). The thermal properties of the in situ polymerized poly(butylene terephthalate) (ISP-PBT) were compared with those of a commercial injection molded PBT (IM-PBT). It was found that the crystallinity of IM-PBT is markedly lower than that of ISP-PBT rendering the latter more brittle. WGF-reinforced (ca. 50 vol.%) ISP-PBT composites were fabricated by compression molding at T = 190 C using displacement and pressure-controls. Effects of the molding condition were investigated in tensile, three-point bending, short beam shear and dynamic mechanical thermal analysis tests. Both tensile and flexural properties (stiffness and strength), as well as inter-laminar shear strength, were enhanced when the molding occurred under pressure-controlled instead of displacement-controlled conditions. Scanning electron microscopic (SEM) inspection revealed excellent wet-out of the fibers and good interfacial bonding between the fibers and ISP-PBT.  2006 Published by Elsevier Ltd. Keywords: Cyclic oligomers; Cyclic butylene terephthalate; Continuous fiber polymer composites; Thermoplastic composites; Poly(butylene terephthalate)

1. Introduction Considerable efforts have been devoted on combining thermoplastic resins such as polypropylene (PP), polyamide (PA), polyetherimide (PEI), polyphenylene sulphide (PPS), polyethersulphone (PES) and polyetheretherketone (PEEK) with various forms of continuous fiber reinforcements (e.g., unidirectional, woven fabrics) to produce thermoplastic composite materials [1,2]. One of the obvious targets was to replace thermoset based composites which have monopolized various applications viz. aerospace, automotive and sports industries. Thermoplastics offer a number of important advantages over thermosetting resins. *

Corresponding author. Fax: +6 4 594 1011. E-mail addresses: zarifi[email protected] (Z.A. Mohd Ishak), [email protected] (Y.W. Leong), [email protected] (M. Steeg), [email protected] (J. Karger-Kocsis). 0266-3538/$ - see front matter  2006 Published by Elsevier Ltd. doi:10.1016/j.compscitech.2006.09.012

Low scrap/good recyclability, better toughness/damage tolerance, unlimited shelf-life, and rapid fabrication cycle are some of their attractive features. On the contrary, thermoset composites suffer several drawbacks such as brittleness, lack of post forming and welding, poor recyclability, and often even moderate process efficiency. However, one of the main issues that are frequently raised in using thermoplastics as polymer matrices is their melt viscosities which are in the range of 100–10,000 Pa s. This creates serious problems in wetting and impregnation of reinforcing fibers, resin flow during fabrication and removal of entrapped air. One approach, which seems to be a promising route, is to develop thermoplastic resins which have the ability to be polymerized reactively like thermosetting resins but possesses the properties of thermoplastics. This has been achieved recently via the introduction of cyclic oligomers. Cyclic oligomers, such as cyclic butylene terephthalate

Z.A. Mohd Ishak et al. / Composites Science and Technology 67 (2007) 390–398

(CBT), have a low processing viscosity which can be as low as 0.02 Pa s (water-like). Since cyclic oligomers may be transformed into linear high molecular weight thermoplastics via entropically-driven ring-opening polymerization in a short time scale (