Available online at www.sciencedirect.com Journal of the European Ceramic Society 30 (2010) 381–384 Fabrication and properties of composites from BST and polypropylene-graft-poly(styrene-stat-divinylbenzene) Kensaku Sonoda a,b,∗ , Tao Hu a , Jari Juuti a , Yasuo Moriya b , Heli Jantunen a a Microelectronics and Materials Physics Laboratories, EMPART Research Group of Infotech Oulu, University of Oulu, P.O Box 4500, FIN-90014 Oulu, Finland b Electronic Materials Department, NOF Corporation, Yebisu Garden Place Tower, 20-3, Ebisu 4-chome, Shibuya-ku, Tokyo 150-6019, Japan Available online 18 September 2009 Abstract In this work, ceramic–polymer composites were fabricated from barium strontium titanate powder (BST) and polypropylene-graft-poly(styrene- stat-divinylbenzene) (ER) using a twin-screw extruder. The compounding process was characterized by rheological measurements. The effects of volume loading of BST on dielectric and mechanical properties were investigated. The dielectric properties were measured as a function of frequency and BST loading. For example, the relative permittivity and loss tangent (tan δ) of the BST–ER composites at 1 GHz were gradually increased from 2.4 and 0.0001 to 28.5 and 0.0085, respectively, as the loading was increased from 0 to 50.5vol.%. Stearic acid (StA) was used as a surface-modifier of the BST. With an approximate surface coverage of 83%, an improvement in processability and a slight increase of the permittivity was observed, while tan δ remained low. The excellent dielectric characteristics of these composites, with high permittivity and low tan δ, make them attractive novel electronic materials for high frequency applications. © 2009 Elsevier Ltd. All rights reserved. Keywords: Extrusion; Ceramic–polymer composites; Dielectric properties; Mechanical properties; Functional applications 1. Introduction Materials employed in microwave devices and packages need to satisfy various requirements, such as low dielectric loss, appropriate relative permittivity, low moisture absorption, as well as suitable mechanical stiffness and a low coeffi- cient of thermal expansion. Recently, there has been huge interest in 0–3 ceramic–polymer composites because they are able to fulfill these demands. Composites using poly- mers such as PVDF (polyvinylidene fluoride), P(VDF-TrFE), silicone rubber, polyimides, polyvinylchloride, cyanoethy- lated cellulose, polystyrene, and polyurethane have been investigated. 1–8 One additional advantage available especially with thermoplastic–ceramic composites is a simple, 3D fab- rication process such as injection moulding of electronic components. The authors have reported the dielectric proper- ties of the barium strontium titanate (BST) and thermoplastic polyphenylene sulphide (PPS) and cycloolefine copolymer ∗ Corresponding author at: Microelectronics and Materials Physics Laborato- ries, EMPART Research Group of Infotech Oulu, University of Oulu, FIN-90014 Oulu, Finland. Tel.: +358 8 5532742; fax: +358 8 5532728. E-mail address: ksonoda@ee.oulu.fi (K. Sonoda). (COC) composites that possess low dielectric loss at high frequencies. 9,10 In this work, 0–3 ceramic–polymer composites were fabri- cated from barium strontium titanate (BST) and polypropylene- graft-poly(styrene-stat-divinylbenzene) (ER). ER is a novel polymer alloy with excellent dielectric properties (low rela- tive permittivity and low loss in the GHz region) based on polypropylene and polystyrene, which shows relatively high thermal stability and processability. 11 The effects of volume loading of BST powder on the dielectric and mechanical properties were investigated. Another task is to research the effect of coating the particle surface with stearic acid on the rheological, dielectric and mechanical properties of the composites. 2. Experimental procedures Barium strontium titanate (BST) with a composition of Ba 0.55 Sr 0.45 TiO 3 and polypropylene-graft-poly(styrene-stat- divinylbenzene) (Dammondex ® ER140, denoted as ER) were supplied from Praxair Inc. (USA) and NOF Co. (Japan), respectively. Stearic acid (StA) (Sigma–Aldrich Chemie GmbH, Germany) and ethanol (A Grade; Altia Oyj, Finland) were used for the coating of the particles. 0955-2219/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2009.08.019