MACROMOLECULAR
DIVISION
COMMISSION ON POLYMER CHARACTERIZATION AND PROPERTIES
WORKING PARTY ON STRUCTURE AND PROPERTIES OF
COMMERCIAL POLYMERS
Blends containing core-shell impact modifiers Part 1. Structure
and tensile deformation mechanisms (IUPAC Technical Report)
C. B. Bucknall
Advanced Materials Department, Cranfield University,
Bedford MK43 0AL, UK
Abstract: Two impact modifiers, based respectively on polybutadiene
(PB) and poly(butyl acrylate-co-styrene) (PBA), are compared in blends
with four glassy polymers: polycarbonate (PC), poly(methyl methacrylate)
(PMMA), poly(styrene-co-acrylonitrile) (PSAN), and poly(vinyl chloride)
(PVC). Dynamic mechanical tests show glass transitions at about -80
°C in PB and -15 °C in PBA. Both modifiers have grafted PMMA
shells, which are seen in the transmission electron microscope (TEM)
to be about 10 nm thick. The two-stage PB particles have 200-nm-diameter
polybutadiene cores, whereas the three-stage PBA particles have 260-nm-diameter
PMMA cores, with 20-nm thick PBA rubber inner shells. Under tension,
the PB particles cavitate to form single voids on reaching a critical
volume strain, and subsequently offer little resistance to dilatation.
By contrast, tensile tests performed in situ in the TEM show that the
PBA shells form fibrils that are anchored to the rigid core, and act
as constraints on further dilatation: the stresses developed in the
PBA fibrils can be sufficient to draw fibrils from both the PMMA core
and the PSAN matrix. There is evidence that the PMMA shells can debond
from the matrix both in cryogenic fracture and in fatigue at 23 °C.
Tensile dilatometry shows that the PB particles cavitate at higher strains
than the PBA particles, but that the PB particles then cause a rapid
volume increase, leading to a low strain at break. By contrast, the
PBA particles produce a more controlled dilatation, and higher strains
to break. Later papers in this series treat the mechanical and rheological
behavior of these blends in more detail.
> Download full text of the report - [pdf
file - 549 KB]
> Link to Part 2: Melt rheology of
rubber-toughened plastics
> View corresponding
project
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