Polymer blends is a subject of great importance for academic
as well as industrial interest. The objective of this research programme
is to study the miscibility of polymer blends. Polymer blends
in general are of three types: amorphous-amorphous; amorphouscrystalline;
and crystalline-crystalline systems. This work is concerned
with crystalline-crystalline type polymer blends and is restricted
to polyolefin crystalline polymers only.
Firstly an outline of crystalline-crystalline polymer blends
mainly concentrating on polyolefin blends has been given in an introductory
chapter. This chapter presents relevant fundamentals rather
than being an extensive critical review of the literatures.
In the first phase of the work three polyolefins (low-density
polyethylene, high-density polyethylene and linear low-density polyethylene)
have been melt mixed to prepare three sets of binary blends
covering the entire range of compositions. A variety of experimental
techniques were used to assess the miscibility of the blends prepared.
The whole experimental programme can be subdivided into three major
areas: the first is concerned with structural characterisation;
the second area with the melt properties; and the third with the
mechanical properties of the polymers in the solid state. Polymers
(including their blends) and experimental techniques are detailed in
Experimental results are discussed and concluded individually
in four subsequent chapters. Chapter 3 gives mainly the information
of molecular structure of the three polyolefins. Characterisation of
crystalline structure of polyolefins and their mixtures has been covered
in Chapter 4. Chapter 5 is concerned with melt properties of
polyolefins and their blends; whereas Chapter 6 deals with solid
state mechanical properties. In these last two chapters an attempt
has been made to correlate, where possible, the structures with their
properties. From the experimental investigations it has been found that
the system of linear low-density and high-density polyethylene blends
is miscible whereas the system of low-density and high-density polyethylene
is not. Structural characterisation has shown that the
low-density and linear low-density polyethylene blends system is
immiscible at all compositions, although some mechanical,compatibility
has been found from melt property and mechanical property measurements.
The second phase of the work was mainly concerned with the application
of polyolefin blends. Film has been manufactured from polyolefin
blends (including their components) and evaluated. Linear low density/
high-density and low-density/linear low-density polyethylene
systems have been selected for this part of the work (Chapter 7).
Essential to the understanding of the blends involving linear
low-density polyethylene, is appreciation of the molecular structure
of the homopolymer. A preliminary characterisation of linear lowdensity
polyethylene has revealed that its structure is more complex
than might have been foreseen.
Finally in Chapter 8 overall concluding remarks have been made
based on the conclusions drawn from all investigations carried out
in this research programme and reported in the individual chapters.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.