Mechanical and thermal properties of syndiotactic polypropene filled with glass beads and talcumby F. Stricker, M. Bruch, R. Mülhaupt

Polymer

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Year
1997
DOI
10.1016/s0032-3861(97)00065-7
Subject
Organic Chemistry / Polymers and Plastics

Text

ELSEVIER PII: S0032-3861(97)00065-7

Polymer VoL 38 No. 21, pp. 5347-5353, 1997 © 1997 Elsevier Science Ltd

Printed in Great Britain. All rights reserved 0032 -3861/97/$17.00 + .00

Mechanical and thermal properties of syndiotactic polypropene filled with glass beads and talcum

F. Stricker, M. Bruch and R. MLilhaupt*

Freiburger Materialsforschungszentrum und Institut for Makromolekulare Chemie der

Albert-Ludwigs-Universitat, S efan-Meier-Strage 21, D-79104 Freiburg L Br., Germany (Received 24 May 1996; revised 25 October 1996)

Glass bead- and talcum-reinforced polypropene composites based on syndiotactic polypropene (s-PP) and isotactic polypropene (i-PP) were prepared to study mechanical nd thermal properties and to identify influence of PP type and stereoregularity. Composites based on s-PP gave higher notched Izod impact strength than those based on i-PP, accompanied by lower Young's modulus and yield stress. The experimental Young's moduli and yield stresses of composites based on highly stereoregular s-PP and i-PP were in good agreement with theoretical predictions according to Kerner and Nicolais-Narkis, respectively.

The higher elative Young's modulus and yield stress of composites based on s-PP of low stereoregularity were attributed to strong interfacial adhesion and can be described by the theory of Jancar. Lap shear tests confirmed strong glass polymer interactions. Investigations ofcrystallization show the nucleating effect of glass beads and talcum in the case ofi-PP as well as s-PP. With increasing filler volume fraction, PP degree of crystallinity decreases. Dynamic mechanical nalysis of glass bead-reinforced s-PP composites show an unexpected relaxation occurring at 55°C. © 1997 Elsevier Science Ltd. (Keywords: syndiotactic polypropene; composites; mechanical properties)

INTRODUCTION

Highly syndiotactic polypropene (s-PP) was synthesized by Ewen in 1988 by means of homogeneous metallocenebased catalysts I. From the point of view of industrial application, s-PP and its compounds are of less interest than isotactic polypropene (i-PP), because of its lower stiffness, although it exhibits good toughness 2. In contrast, i-PP is used in a wide range of applications because of its attractive combination of low price, heat distortion temperature above 100°C and high stiffness.

It is common practice to lower costs and improve mechanical properties of thermoplastics by incorporating fillers. Talcum, mica and calcium carbonate are widely applied as reinforcing components 3-5. Advantages in stiffness and dimensional stability are usually accompanied by decreased yield and ultimate strength. Poor adhesion between filler and matrix is a primary cause of low strength and poor thermomechanical properties, especially at high filler volume fractions. Because of the regular shape, glass beads are interesting for theoretical investigations, e.g. calculation of Young's modulus and tensile yield stress under consideration of interfacial adhesion 6,7.

The present paper describes the influence of glass beads and talcum on the mechanical, thermal and dynamic mechanical properties of reinforced s-PP. Composites based on s-PP of different degree of stereoregularity and i-PP are compared. Interfacial interactions were investigated by means of a lap shear test, bonding together filler * To whom correspondence should be addressed and polymer. The results were compared with morphological studies of fracture surfaces, imaged by environmental scanning electron microscopy (ESEM).

Aminopropyl-functionalized glass beads of 5 #m average diameter and talcum of 30 #m average diameter were blended together with PP in a twin-screw blender with counter-rotating screws at 60 rpm and 200°C for s-PP and 240°C for i-PP, respectively. Mechanical and thermal properties were studied as a function of both type and volume fraction of the filler.

EXPERIMENTAL

Materials

Table 1 summarizes data concerning polypropene types used in this work. All polymers were commercial grades, supplied by Shell and Mitsui. Aminopropylfunctional glass beads (Potters-Ballotini 5000 CP-03, average diameter of 5 lzm), containing 0.02 wt% coating of aminopropyltrimethoxysilane d talcum (Luzenac

OOS, average diameter of 10#m) were used as filler component. 0.2wt% Irganox 1010/Irgafos 168 (4/1 wt%) were added as stabilizer during the melt processing.

Composite preparation

All composites were prepared under identical mixing and moulding conditions. Filler volume fractions were varied between 0 and 30vo1%. Melt blending was performed in a Haake Rheomix 90 twin-screw kneader equipped with a 60 ml mixing chamber that was preheated at 200°C for preparation of s-PP compounds and 240°C

POLYMER Volume 38 Number 21 1997 5347

Glass bead and talcum-reinforced polypropylene composites. F. Stricker et al.

Table 1 Syndiotactic and isotactic polypropene used in this study rr a mm a Mn b

Polypropene Material (%) (%) (g mol- ] ) M . /Mn (°C) (°C) Source

Syndiotactic SPH-4 82.2 3.9 106.000 1,7

Syndiotactic SPH-40 91.1 - 80.000 1.7

Isotactic KM 6100 - 96.0 50.000 7.6 6.0 130 Mitsui 6.1 132 Mitsui 0.9 172 Shell a Triads determined by 13C n.m.r. b Molecular weight from g.p.c, vs polystyrene standards c Tg from dynamic mechanical nalysis in a Rheometrics solid analyser d Tm determined with heating rate of 10°Cmin -I in a Perkin-Elmer DSC-7 for i-PP, respectively. Typically PP was kept together with the stabilizers, for 1.5rain at 200°C and 240°C, respectively. Then the filler was added. After 4 rain total mixing time the sample was quickly recovered and quenched between metal plates. Sheets of 2ram thickness were prepared by compression moulding in an evacuated press (Schwabenthan Polystat 100), annealing at 2 I0 and 250°C, respectively, for 10 min and quenching to room temperature between water-cooled metal plates. Rectangular bars of a dimension of 60 mm x 10 mm x 2 mm were cut out of these plates for evaluation of mechanical properties.

Mechanical properties