ANTEC 2003
May 5 & 6, Nashville, Tennessee
Technical Program
Another comprehensive and stimulating program ably put together
on this occasion by Elizabeth Takacs of McMaster University. Rotational Molding
Division Chairman Marshall Lampson presented her with an award for outstanding
effort in organizing this great event.
David D'Agostino of McMaster University won the student paper
award (triggering a special congressional investigation into judging practices)
and will have his paper reprinted in the next issue of the RMD newsletter.
The Best Paper Award was given to Louise Pick of Queen's
University for her excellent presentation of her paper entitled "The Effect
of Thermal Relaxation on The Crack Initiation Resistance of Rotomolded Linear
Low Density Polyethylene", co-authored with Eileen Harkin-Jones. Well done
Louise!
There were three sessions in total covering Composites and Foams
(M15), Process Technology (M33) and Material Formulation and Properties (T13).
I've listed the papers below and a brief review of their content.
Session M15 — Composites and
Foams in Rotational Molding
Mechanical Properties of Rotationally Moulded Nanocomposites
P.R. Hanna, T. McNally, E.M. Harkin-Jones, P. McMillian, Queen’s
University Belfast
Nanocomposites have shown great promise in nylon applications
- the race is on to try and make them work in polyethylene and, of course, in
rotational molding. Paul's work showed that there are challenges to successfully
separating the platelets in the clays that are used as nanocomposite reinforcement. Further efforts on mixing technology and modification to the
polymers and/or clay to make them more compatible are necessary (I favor the
second route).
Polyethylene Nanocomposites - Investigating the Tensile
Properties of Polyethylene Nanocomposites for Rotational Moulding
M.J. Murphy, R. Truss, P. Halley, D. Martin, C. Ang, University
of Queensland
Elizabeth stepped into the breach to present this paper at
the last moment as the speaker was unable to attend. Tests were performed on
compression molded samples of rotomolded material (?) and showed up to a 25%
increase in tensile performance. One of the major conclusions was that the
compatibilizer between the polymer and the reinforcing agent was more important
than the mixing process.
Novel Foam Composite Having Thick Skin and Core-Stiffening
Dividers
H. Sekiguchi, N. Shiina, A. Kitaichi, E. Oda, Shiina Kasei Co.,
T. Kemmotsu, The Furukawa Electric Co.Ltd., H. Miyairi, Tokyo Medical and Dental University
Hideo Sekiguhci presented a new technology for creating
foamed cross-sections using a novel foam pellet produced as a co-extrusion with
a foam core and solid skin. The solid material around the foamed core produces
stiffening features between surfaces in a closely spaced rotomolded part.
Interesting stuff. Hideo is looking for licensing partners in the US.
Investigation of the Processing Characteristics and Mechanical
Properties of Metallocene Catalysed Polyethylene Foams for Rotational Moulding
E.V. Archer, E.M. Harkin-Jones, The Queen’s University
Belfast, A-M. Fatnes, Borealis AS
Eddie compared the performance of metallocene based materials
with Ziegler Natta based materials when producing foams. Both materials can be
used effectively for foams although the higher moduli of the metallocene base
resins appeared to translate into stiffer foams (direct correlation between
density and stiffness). Higher melt indices appeared to interfere with the
ability of materials to form stable foam structures (collapsing cells as
viscosity levels fell).
The Effect of Coupling Agents on Foaming with Polymer
Microspheres in Rotational Molding
D. D'Agostino, E. Takács, J. Vlachopoulos, McMaster
University
David has examined molding polymer microspheres composed of
an acrylic shell containing an expanding gas core. Commonly used in other
processes such as ink printing for raised letters, the acrylic shells can
expand from 30 microns to 120 microns. This study examined the effect of
coupling agents on the bond between the polymer matrix and the microspheres.
The coupling agents increased low shear viscosity values for the materials
used and suppressed the foaming reaction. This produced a corresponding drop
in mechanical properties.
Manufacturability of Fine-Celled Cellular Structures in
Rotational Foam Molding
R. Pop-Iliev, D. Xu, C.B. Park, University of Toronto
Chul examined the underlying theory of foam formation and the
rotational molding process in relation to producing very fine celled foams.
Experimental and simulation studies concluded that due to the short lived nature
of small bubbles, it is not possible to produce fine-celled foam structures in
rotational molding.
Session M33 — Process Technology
in Rotational Molding
Oil Heating and Cooling Machines for the Rotational Moulding of
Plastics
R.J. Crawford, Queen’s University Belfast,
M.J. Wright, Dundalk Institute of Technology
Michael presented details of an oil heating system for
rotational molding and then compared energy efficiencies with electrical and
direct heating systems. Oil heating offers higher energy efficiency numbers.
Open flame gas heating reportedly also produced lower energy costs than direct
heating ovens. The use of oil for heating allowed the control of heat flow to
specific mold areas and a reduction in molding cycle time.
The Effect of Direct Electrical Heating on the Cycle Time and
Mechanical Properties of Rotationally Molded Polyethylene Parts
M.P. Kearns, C. Daly, R.J. Crawford, Queen’s University
Belfast
Mark discussed the use of electrical heating elements
attached to the surface of standard rotational molds (MECHTM).
Electrical heating was found to be more efficient by a factor of at least ten
over gas heating. However, molding cycles are longer than for standard molding
machines - primarily due to upper limits currently imposed by the heating
elements and adhesive system required.
The Effect of Cooling Rate on Rotationally Molded Parts
G. McDowell, E.M. Harkin-Jones, R.J. Crawford, W. McMinn, Queen’s
University Belfast, M.C. Cramez, University of Minho
Gareth carried out a study of a range of cooling conditions
on part properties as characterized by bubble content (cross-sectional and
through surface), impact strength and warpage. Higher density parts warped
more, longer cooling cycles produced lower impact and, curiously, water
cooling immediately from the oven actually helped to reduce bubbles in the
cross-section. Answers to this mystery on a postcard please.
Gareth also talked briefly about the KKontrolTM
system which uses hard-wired high temperature slip rings mounted in the head
of the rotational molding arm for data collection. We look forward to hearing
more about this development.
The Effect of Thermal Relaxations on the Crack Initiation
Resistance of Rotomolded Linear Low Density Polyethylenes
L.T. Pick, E.M. Harkin-Jones, Queen’s University Belfast
Louise presented her work on evaluating materials using
Dynamic Mechanical Thermal Analysis and impact testing to improve
understanding of the relationship between crack initiation energy and test
conditions. A relationship was found that allows the behavior of a polymer to
be predicted across a wide range of conditions by carrying out a small number
of tests. Complicated stuff and well presented.
Rotational Molding of Micropelletized Polypropylene-Based
Copolymers
S.K. Baczek, Pennsylvania College of Technology,
M.E. Starsinic, Rotational Molding Center of Excellence
Stanley (last to submit his presentation) presented a study
that looked at eliminating the grinding step for polypropylene by using
micropelletization. The results showed that good room temperature impact
performance could be achieved (low temperature was still non-existent) and
tensile and flexural strengths comparable to commercial polyethylene
materials. The target market is automotive but there is still that issue of
low temperature impact....
Rotational Molding Process Control
A. Spence, R. Scott, Centro Inc.
Alvin analyzed Rotolog temperature profiles during molding
for an alternative way of describing the cure level of a molded part.
Measuring the area under the temperature curve above the melting point of the
material he was able to develop a 'Degree of Cure' value for a given cycle.
This DoC measure may give an indication of bubble content and final material
properties. The data suggested that a relationship between thickness and cycle
time could be measured.
Optimization of a Rotationally Molded Pressure Vessel
M. McElhaney, N. Carroll, Penn State Erie, the Behrend
College
Double-act Neil and Mike (just in the process of completing
their degrees at Penn State) showed how an optimizing design package could be
used to create alternative designs for rotationally molded tanks. The software
produced some cool designs that in theory could reduce deflections over more
traditional ribbing designs.
Session T13 — Material
Formulation and Properties
Performance of a Rotationally Molded Thermotropic Liquid
Crystalline Polymer
E. Scribben, D.G. Baird, Virginia Tech
The search for new materials for rotational molding is
perhaps the most important research area that exists for the process. Eric
described the next stage in his evaluation of Liquid Crystal Polymers (LCPs)
for rotational molding. They offer extremely high stiffness and tensile
strength. Earlier work had looked at material rheology and concluded that the
properties were equivalent to polyethylene (?). The molded samples contained
significant surface and cross-sectional voids that affected appearance and
part strength. It was thought that the low permeability of the material
prevented the bubbles from dissolving. (Material elastic properties and mold
heating rates are likely candidates for evaluation)
Rotomoldability of Cyclic Polybutyleneterephthalate
R.S. Al-Zubi, P. Larson, Poly Processing Company,
Y-F. Wang, Cyclics Corporation
Raed's work described the evaluation of cyclic PBT (CPBT) in
a production environment. The material starts as a solid and turns into a
water-like liquid during heating before reacting to form a solid part. Parts
could be produced successfully but the tensile and impact results were less than
expected and not yet acceptable for freestanding parts. They have good barrier
properties and tests showed that they may be useful as lining materials for XLPE
tanks used in fuel applications.
Metallocene Based Polyolefins for Rotational Molding
Applications
E. Maziers, ATOFINA Research
Metallocene materials have been of considerable interest
for rotational molding over. Eric introduced new materials being developed by
Atofina in Europe. These include both mPP and mPE materials. They offer
narrower molecular weight distributions than materials based on Ziegler Natta
catalysts. Shrinkage levels for mPP were similar to Z-N PP but observed
warpage was lower. One interesting factor was that the mPP material had much
better transparency than Z-N PP.
Effects of Particle Morphology on the Processability of Ethylene
Copolymers for Rotational Molding Applications
C.T. Bellehumeur, W. Lin, University of Calgary, M.
Weber, NOVA Chemicals Corporation
Continuing their work on evaluating material properties vs.
molding / sintering behavior, Celine presented a study on the effect of
changes in material formulation and processing history on material
processability. The effect of the thermal history of the material was found to
be limited on material sintering. However, it was shown that the addition of
nucleating agents could have a negative effect on sintering (this was not so
great with mPE).
Particle Size Distributions in Rotomolded Parts
B.A. Graham, ExxonMobil Chemical Canada
Blair's paper described a study on how powder particle size
variation occurred both through the wall section and across the surface of
molded parts. Smaller particles showed slightly more tendency to stick to the
center areas of the mold wall first (heat distribution) while larger particles
tended to stick later in the process. The separation process is not absolute
in terms of building strata as factors such as small particles tacking to
larger particles and dust in the inside mold atmosphere settling later
affected this. Cross-eyed students at Akron University forced to count
individual particles are very grateful that this project is over.
Plasma Modified Polyolefin Powders for Rotational Molding
D.E. Boersch, Rota Consult GmbH,
D. Knoth, D. Pfitzmann, ARPLAS Gesellschaft für
Plasmatechnologie GmbH
Erich presented information on a plasma modification
process developed by ARPLAS in Germany for the treatment of polyethylene
powders prior to molding. The treated powder retains the attributes of surface
reactivity after molding enabling parts to be painted, foamed or coated.
Surface energies for PE can be raised from 28-34 mN/m to 40-56 mN/m enabling
paint to adhere sufficiently well to pass cross-hatch testing.
