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|Title: ||Toughness enhancement of poly(ethylene terephthalate) with chemically modified high molecular weight polyethylene|
|Authors: ||Ophir, Amos|
|Issue Date: ||1997|
|Publisher: ||© A. Ophir|
|Abstract: ||The present work was concentrated on exploring and developing a toughening
material system to be used in engineering products made of high crystalline
PET [poly(ethylene terephthalate)]. The work addressed some fundamental
objectives in the technology. of crystallised PET (CPET) related to toughness
PET is widely used in fibres and oriented films but is also an attractive material
for moulded products, owing to its high melting point and solvent resistance.
Crystalline PET, however, is brittle and susceptible to hydrolytic degradation
through water absorption.
The polymeric toughening system was based on suitably modified UHMWPE
(ultra high molecular weight polyethylene) a crystalline polymer with very high
fracture toughness under plane strain conditions, low water absorption, but with
a relatively low melting point. Being a thermoplastic it has a modulus about
1,000 times higher than the equivalent hydrocarbon elastomer usually used to
toughen PET and polyamides. Hence, deterioration of strength and stiffness is
Blending PET with UHMWPE produces coarse microstructures and poor
mechanical properties due to lack of compatibility of the two polymers.
Compatibility is expected to be improved by reducing the interfacial tension
and increasing the adhesion between the two phases; the first will reduce the
size of the dispersed phase, while the latter would improve the mechanical
properties. Compatibilisation of a pair of immiscible polymers, like in blend
of PET with UHMWPE, can be achieved by incorporation of reactive units
along the main chains of the UHMWPE, which are capable of strong
interactions with the matrix component (PET).
The methods used in this investigation involved smface grafting and irradiation
treatment to produce chemically active groups on the UHMWPE polymer chain
to achieve the required level of interfacial adhesion assisting the agglomerate
particle breakdown into small size and to develop strong bonding to the PET
when the two polymers are blended in a high shear mixing.
The results obtained with several modified UHMWPE powders incorporated
into PET by melt mixing showed a clear formation of small primary particles of
UHMWPE strongly bonded to the matrix, thereby achieving a vast
improvement in toughness while preserving other important fundamental
properties related to both the end product and the material processing.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Materials)|
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