The influence of reactive modification on the compatibility of polyolefins with non-olefinic thermoplastics
Henry C.A. Lim
2134/8372
https://repository.lboro.ac.uk/articles/thesis/The_influence_of_reactive_modification_on_the_compatibility_of_polyolefins_with_non-olefinic_thermoplastics/9230648
Polyethylene (PE) resins being non-polar in nature and having a high degree
of crystallinity have limited miscibility and compatibility when blended with
polar polymers. The miscibility and compatibility of these blends are generally
worsened when they are prepared by direct injection moulding without a precompounding
process. Such situations are commonly encountered in
particular by polymer converters when blending colour and/or additive
concentrates, commonly known as masterbatches. Typically, masterbatches
are mixtures containing high loading of pigments and/or additives
predispersed in a suitable solid vehicle (commonly known as carrier) such as
a polyethylene resin. These masterbatches are usually used for the
colouration of a wide range of polymers and the carrier used must therefore
be compatible with these matrix (host) polymers.
The preliminary stage of this study involved the investigation of the properties
of blends based on high density polyethylene (HDPE) and a range of
engineering thermoplastics (ABS, PC, PBT, PA6), prepared by injection
moulding. Five different types of compatibilisers namely, ethylene-vinyl
acetate (EVA) copolymer, ethylene-methyl acrylate (EMA) copolymer,
ethylene-glycidyl methacrylate (E-GMA) copolymer, ethylene-methyl acrylateglycidyl
methacrylate (E-MA-GMA) terpolymer and maleic anhydride grafted
HDPE (HDPE-g-MAH) copolymer were evaluated with respect to their
efficiencies in compatibilising HDPE with the four engineering polymers. The
pre-compounded HDPE/compatibiliser binary blends at 2 different blend ratios
(1:1 and 3:1) were added at 15 wt% concentration to each engineering
thermoplastics and test samples were produced directly by injection moulding.
Results of mechanical testing and characterisation of the blends showed that
glycidyl methacrylate compatibilisers, E-MA-GMA, in particular have the most
universal compatibilising effectiveness for a range of engineering
thermoplastics including ABS, PC, PBT, and PA6. Blends compatibilised with
E-MA-GMA compatibiliser had the best notched impact performance
irrespective of matrix polymer type. The presence of an acrylic ester (methyl
acrylate) comonomer in E-MA-GMA resulted in increased polarity of the
ii
compatibiliser leading to improved miscibility with the polar matrix polymers
demonstrated by fine blend morphologies, melting point depression and
reduction in crystallinity of the HDPE dispersed phase.
The second stage of this study involved the reactive modification of HDPE
using a low molecular weight di-functional solid diglycidyl ether of bisphenol A
(DGEBA) type epoxy resin compatibilised with HDPE-g-MAH in an attempt to
improve its compatibility with ABS, PBT and PA6. The maleic anhydride
moieties in HDPE-g-MAH served as reactive sites for anchoring the epoxy
moieties while the HDPE backbone was miscible with the HDPE resin. An
excessive amount of reactive groups resulted in the formation of crosslinked
gels while the addition of EVA co-compatibiliser helped in the reduction of gel
content and further improved the dispersion of the epoxy. The effectiveness of
epoxy grafted HDPE (with and without EVA co-compatibiliser) in
compatibilising ABS/HDPE, PBT/HDPE, and PA6/HDPE was investigated by
injection moulding of 5 wt% functionalised HDPE with these matrix polymers
into test bars for mechanical testing, and characterisation by differential
scanning calorimtery (DSC) and optical microscopy. The reactively
functionalised HDPE blends, improved the mechanical properties of ABS and
PA6 blends especially with EVA as co-compatibiliser. However, the
mechanical properties of PBT blends were unmodified by the functionalised
HDPE which was believed to be due to end-capping of the PBT chain-ends by
ungrafted epoxy resins.
2011-05-16 10:02:52
Reactive compatibilisation
Miscibility
Compatibiliser
Compatibility
Solubility
Mechanical properties
High density polyethylene
Epoxy
Acrylonitrile-butadiene-styrene
Polycarbonate
Poly(butylene terephthalate
Polyamide 6
Ethylene-vinyl acetate
Ethylene-methyl acrylate
Ethylene-glycidyl methacrylate
Ethylene-methyl acrylate-glycidyl
Maleic anhydride
Universal masterbatches
Materials Engineering not elsewhere classified