P1: vir 13-98-024 January 2, 1999 11:48
JOURNAL OF MATERIALS SCIENCE 34 (1999)535–544
Effect of elastomer interfacial agents on tensile
and impact properties of CaCO
F. SAHNOUNE, J. M. LOPEZ-CUESTA, A. CRESPY
Laboratoire Matrices, Mat ´eriaux Min ´eraux et Organiques – Ecole des Mines d’Al `es-6, avenue
de Clavi `eres, 30319 Al `es cedex, France
This work focuses on the modiﬁcation of the tensile yield strength of CaCO
brought about by the incorporation of SEBS elastomers. Two types of SEBS elastomers
were used, grafted and ungrafted with maleic anhydride functions. The grafted elastomer
encapsulates the ﬁller particles
and creates an adhesive interphase. The tensile yield
stress was increased with increasing content of grafted elastomer until a maximum value.
The inﬂuence of the interfacial area and the volume fraction of ﬁller were studied. It was
shown that the relative increase in tensile yield stress when increasing amount of
interfacial agent was added, both depends on the volume of ﬁller and the interfacial area.
Kluwer Academic Publishers
The addition of mineral ﬁllers to commercial thermo-
plastics reduces the overall cost of the composite and
offers an important means of achieving new combi-
nations of properties. The stiffness of polymers is ge-
nerally enhanced by the incorporation of high modulus
ﬁllers. The effect of mineral ﬁllers on the elastic modu-
lus of polymers has been widely studied and there are
many theoretical models available predicting the be-
havior of composites in the elastic zone.
The tensile behavior of ﬁlled polymer at higher strain
levelismorecomplexand depends onnon-elasticdefor-
mation mechanisms. The effect of ﬁllers on the tensile
strength of polymers has been studied by many authors.
Some theories and models have been proposed [1–8].
The elaboration of theoretical models is a very difﬁ-
cult task because of the great number of parameters
affecting the tensile strength of particulate composites.
The main parameters are: the ﬁller weight or volume
fraction, the particle shape, the particle size, the nature
of the matrix, and its adhesion to the ﬁller particles.
Among these factors, the interfacial adhesion is of car-
dinal importance and markedly inﬂuences the tensile
strength of ﬁlled polymers [2–4, 9].
In the case of poor interfacial adhesion, the tensile
strength generally decreases with increasing ﬁller load-
ing. During tensile deformation, the dewetting phe-
nomena i.e. loss of contact between the matrix and the
ﬁller particles [10–12] contributes together with shear
yielding to the non-elastic deformation. It produces a
situation in which the ﬁller cannot sustain much load
and the matrix may be considered as ﬁlled with voids.
Most of the models regard the matrix as the only stress-
bearing component in the composite when adhesion
is poor. They assume that the tensile strength of the
composite is proportional to the cross-sectional area of
the load-bearing polymer matrix. The incorporation of
ﬁller leads to an effectivedecrease in the cross-sectional
area of polymer and thus a decrease in tensile yield
strength. Moreover, when there is poor interfacial ad-
hesion, the ﬁller acts as stress concentrator in a more
effective manner. This effect also contributes to the re-
duction in tensile strength of the material .
Tensile strength is generally enhanced when inter-
facial adhesion is improved. This can be ascribed to
better stress transfer at the interface between the ma-
trix and the ﬁller [2, 3]. The improvement of interfacial
adhesion can prevent dewetting (i.e. loss of contact)
at the matrix-ﬁller interface during tensile deformation
. Therefore, well adhering ﬁller particles can bear
on part of the load applied to the matrix and contribute
to the tensile strength of the composite. The addition
of ﬁller combined with an efﬁcient coupling agent has
proved to be a way to enhance the tensile strength of
However, the increase in adhesion may produce local
changes in the micromorphology and the mechanical
propertiesof the polymer chains bonded to the ﬁller par-
ticles. That may result in the formation of a rigid poly-
mer layer surrounding the ﬁller particles. This rigid in-
terphase may have mechanical properties rather closer
to the ﬁller than to the matrix [13, 14]. It increases the
apparent volume fraction of ﬁller and leads to a stiffer
but more brittle composite.
Previous works  have shown that the encapsula-
tion of kaolin particles by latex improves impact prop-
erties of PP/kaolin. The embrittlement of the material
can be reduced if mineral ﬁllers are coated with a soft
interphase. Impact properties were also improved in
chalk ﬁlled PP  and HDPE  by coating chalk
particles with a liquid oligomer. However, the lack of
interfacial adhesion did not allow a good stress transfer
from the matrix to the ﬁller particles and no increase in
tensile strength was obtained.
1999 Kluwer Academic Publishers