Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
This invention relates to processing natural fibre together with polyolefin
plastic for
manufacture of reinforced composites and particularly, to process for
improving adhesion
between plastic and fibre and reinforcing composite by improving its strength,
creep and
heat deformation properties.
Incorporation of discontinuous fibres into a polymer matrix to make reinforced
composites is well known. For example, Goettler U.S. Pat. No. 4,376,144
describes vinyl
chloride polymer composite of this type in which an isocyanate bonding agent
was used
to disperse fibre and to improve adhesion thereto. However, the environmental
regulation
restricts the use of isocyanate in many of such industrial applications.
1t is also known that the dispersion of short oellulosic fibres into a polymer
matrix can be
improved by pretreating the fibre with a lubricant and a plastic polymer. U.S.
Pat. No.
3,943,079 to Hawed describes such a fibre treatment. Boustany and Coran U.S.
Patent
No. 3,697,364 described a predispersion process with rubber latex or other
substances
which reduce fiber-to-fiber interaction and improved composite properties when
they are
incorporated in a plastic matrix. In general, a "predispersed" fibre is not
easy to feed
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because of its low bulk density. Moreover, pretreating the fibre and then
mixing the
treated fibre into polymer matrix demands both time and equipment. The present
invention simplifies the fibre dispersion and composite manufacturing process
by first
incorporating an imide additive and then activating the additive at a suitable
process
temperature range which promotes in-situ fibre dispersion and fibre-to-
polyolefin
adhesion.
SUMMARY OF THE INVENTION
It has now been discovered that reinforced natural fiber-polyolefin composite
is simply
prepared by melt processing polyolefinic plastic with particulate as well as
short ellulosic
fibre in a processing temperature range 200 to 240 °C in the presence
of an imide dditive.
It has also been found that when the imide is activated with a co-additive
during melt
processing of lignocellulosic fibre particularly, wood fibre with polyolefin
improved
fiber-to-plastic adhesion at a processing temperature range of 180-
230°C low enough to
prevent undesired fibre degradation.
According to the present invention, reinforced composites are made of
cellulose and
lignocellulosic fibres dispersed in a polyethylene, polypropylene or ethylene-
propylene
copolymer matrix which includes a reinforcement additive which is chosen from
a group
of substituted maleimide with or without an activator, selected from thiazole,
thiuram and
dithiocarbamate derivatives. Composite containing 40 to 80 % of polyolefin by
weight
and 20 to 60% of natural fibre by weight, based on the total weight of
composite is a
subject of our study. The imide reinforcement additive used in this discovery
has the
general chemical structure:
2
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z - R3
RI
Formula 1
where R,, can be a selection from hydrogen, alkyl, aryl, cyclohexyl and N-
substituted
imide , imide ester; R2 and R3 can be H, alkyl or aryl group.
Subjecting lignocellulosic or cellulose flour or fibre to the shear forces,
resulting from a
first stage intensive mixing any proportion of polyolefin plastic ranging
between 15 to
85% by dry basis weight of composite and a fiber proportion ranging from 20 to
50 parts
with the afore mentioned reinforcement additive ranging from 0.05 - 5%,
effects
dislogging of fibre bundles, their dispersion in the molten plastic matrix and
improve
fibre-to-plastic adhesion. By reinforcement additive is meant an auxiliary
material which
is first decomposed at the processing temperature and is then facilitated
dispersion of
fibre and adhesion between fibre and plastic. The additive is believed to
produce the
aforesaid effect only above the decomposition temperature of the said additive
during
melt mixing and processing by reducing the surface energy difference between
polymer
plastic and fibre or by improving acid-base interaction. Regardless of the
correct
explanation, it is observed that decomposition of the imide additive in the
melt mixture of
polyolefin polymer and natural fibre under thermo-kinetic action resulted in
mechanical
strength enhancement of composite. It is in the aforesaid sense of
decomposition of
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additive and abetting the thermo-kinetic forces in dispersing and adhering the
fibre to
molten polymer.
The invention also includes reinforced composite, which is a melt-processed
mixture of
natural fibre, polyolefm, imide additive and a minor amount of an activator,
dibenzthiazyl
disulfide or other thiazole derivative. By activator it is meant a secondary
additive which
is believed to reduce melt processing temperature of the aforesaid mixture by
decomposing imide additive at a temperature below the processing temperature
of the
said composite. The ratio of the activator proportion to the aforementioned
imide additive
of the invention falls within a range of 0.01 to 0.3.
Processing of the above mentioned polyolefins and lignocellulosic fibres with
the imide
additive and activator lead to pre-mixed composites which upon further
processing results
into composite product having a heat distortion temperature above 90°
centigrade at 1.8
MPa load and a relative creep of less than 200% at 30% load of the respective
flexural
strength of composites at 40° centigrade.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Natural cellulosic fibres are cellulosic and lignocellulosic fibres containing
lignin,
cellulose and hemicellulose. Examples of natural cellulosic fibres include
wood-based
fibres, seed-based fibres such as cotton, and bast fibres such as flax and
kenaf. Among
wood-based fibres hardwood and softwood fibres and woodflours are preferred.
Wood
flour in particle size range 20 mesh to 200 mesh can be used and a preferred
range is
between 40 and 100 mesh. The wood fibres have aspect ratio in the range 10 to
200 and
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more preferred range is between 50 and 100. Lignocellulosic fibers of the
present
invention are the wood fibres and recycled newsprint with an aspect ratio of
10 to 250.
Bast fibre either flax or kenaf is preferred. Preferred aspect ratio is 10 to
250, with a
more preferred range of 20 to 100. In some instances, it is desirable to use
mixtures of
fibres having two widely different aspect ratios. A preferred aspect ratio of
fibre ranges
from 10 to 50. An increased mixing time is good for fibre-to-plastic adhesion
and
reduced mixing time prevents undesired fibre breakage and increase process
economy.
The plastic polymer of the invention is selected from the group of
thermoplastic
polyolefins. The term "thermoplastic" refers to plastics materials which,
soften on heating
and harden on cooling and the materials retain this property when reprocessed
The plastic
matrix contained in the composite is described as being "polyolefin plastic"
and includes
polyethylene, polypropylene and copolymers of ethylene and propylene.
Copolymer
comprises of a major portion of propylene and a minor portion of ethylene.
The flours described as "particulate" to distinguish from cellulosic or
lignocellulosic
short fibres having high aspect ratio (length divided by average diameter) and
from
inorganic fillers of any shape and size as taught in U.S. Pat. No.
5,494,948.(Mica-
reinforced polypropylene resin composition; Ikezawa, Yuji , Nagoya, Japan
(Sumitomo
Chemical Company, Limited, Osaka, Japan; February 27, 1996).The "short fibres"
are
described as chopped organic fibres having aspect ratio less than 500 to
distinguish them
from inorganic fibres of any length and diameter. A "plastic matrix" is a
polymer which
forms the dominant phase surrounding the flour and/or fibre. A "composite" is
a
combination of plastic and cellulose or lignocellulosic fibre or flour or both
in which
flour and fibre are dispersed in plastic matrix.
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The additive of the invention is an unsaturated imide of heterocyclic
structure. The
preferred form of the additive is meta substitutions of benzene ring with
maleimide,
represented by the structural formula:
R2
z- R3
R~
where R ~ , R2 = H and
R,= ~o~=~
Formula 2
The additive is used in the composites of the invention in sufficient amount
to achieve
good dispersion of fibres and/or flours in polyolefin as well as reinforcement
effect on the
resulting composites. The "reinforcement" which refers to improvement of
properties, is
used to distinguish from the properties of finished composites without any
imide additive.
The amount of imide additive can be as low as 0.05 parts by weight by 100
parts by
weight of the composite, up to 3 parts by weight or more, on the same basis.
The amount
of imide additive required can also expected to vary with the amount of
cellulose and
lignocellulosic flour or fibre, the type and nature of fibre or flour as well
as the type of
polyolefin plastic used.
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The mechanism of the reinforcement is not known, however, it is thought that
the two
active functional groups of maleimide moiety in the additive react with
polyolefin and
hydroxyl group of cellulose and lignocellulose fibres or flours, forming a
chemical bond
herewith.
The reinforcement additive can be premixed with fibre or flour, or it can be
preblended
with a small amount of powder form of polyolefin, in order to facilitate
dispersion of the
additive in the composite. This premixing process is optional depending on the
type of
mixing equipment used in order to melt the polyolefin plastic and to disperse
the fibres in
molten polymer. The reinforcement additive can be incorporated into the
composites of
the invention by mixing the reinforcement additive therewith, at the same time
the flour
or fibres are combined with the polyolefin plastics. A high speed thermo-
kinetic mixer
such as K-mixer can be used to melt-mix polyolefin, fibre and reinforcement
additive
without predispersing the said additive.
The reinforcement additive can also contain other imide compounds, such as
4,4'-
diantipyrylmethane, 2- methyl, N-phenylmaleimide, N-cyclohexylmaleimide, N-
ethyl-
maleimide. Mixtures of one or more of the other imide compounds can be present
along
with the N, N - 1,3 phenylenedimaleimide as in Structure formula 2, but their
effect is
inferior thereto in the present invention.
An unexpected beneficial result is noted in that the cellulosic flour or fibre
and polyolefin
plastic compositions, which contain the reinforcement additive of the present
invention
show a significant improvement of the final properties.
The effectiveness of the reinforcement additive of the present invention is
surprising,
since it would not be expected that an imide additive which is designed to use
as a
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crosslinking agent for elastomers, could be so effective even without any
activator, in
improving dispersity of natural fibres or woodflour and thereby reinforcing a
plastic
matrix containing polyethylene, polypropylene or their copolymer.
The effect of obtaining a reinforcing effect on the composite of the present
invention is of
course, to provide a natural fibre- or wood flour-filled polyolefin composite,
which has
maximum strength, stiffness, heat deflection temperature (HDT) and resistance
to creep.
Creep and mechanical properties of the modified wood fibre reinforced
thermoplastic
composites were reported by Sain, Law and Balatinecz (J. Appl. Polym. Sci.,77,
2000,
260) and Sain and Kokta (J.Appl.Polym.Sci.,54, 1994, 1545). With optimum
reinforcement effect which thought to increase not only the adhesion between
fibre or
woodflour and polyolefin matrix but chemically attach some part of the
additive of the
present invention to the composite to impart resistance to deformations under
stress and
heat.
The fibre or flour, polyolefin and additive can be melt-mixed by following the
teaching of
Goettler U.S. Pat. No. 4,376,144 and of Hamed..U.S. Pat. No. 3,943,079 to
produce
composite premix of the present invention. A high intensity thermo-kinetic
mixer such as
K-mixer is advantageously used, and the materials, polyethylene or
polypropylene or
propylene-ethylene copolymer, cellulosic and lignocellulosic flour or fibre,
reinforcement
additive and other ingredients, can all be charged initially. The order of
addition of
material is not critical. However, other charging sequence can be used if
desired.
The temperature of melt-mixing of the present invention should be sufficiently
high to
decompose the reinforcement additive and to melt polyolefin plastic. The dump
temperature of the premixed composite should be above 190° centigrade.
The preferred
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dump temperature range is 200 to 230° centigrade. Higher temperature is
preferred for
better reinforcement properties of resulting composite. However, other dump
temperature
can be selected depending on the mixing equipment. Higher temperature can be
used, but
excessive heat can be harmful over a period of time. The residence time of the
compound
in the mixer should not exceed more than few minutes for a high intensity
mixer and
longer time can be used for extruder or other low speed mixer. Effective
mixing time for
a high speed mixer is between 30 seconds to 3 minutes. Usually, it will be
economical to
mix as rapidly as possible. Precaution should be taken to avoid excessively
high
temperature and/or long residence time that might burn fibre or woodflour.
A mixing temperature of the present invention lower than 200 centigrade may be
used
only if an activator is added along with the reinforcement additive. For a
discussion of
activator used for elastomer crosslinking, see Handbook of Elastomers, Ch. 8
p.249 et
seq (A.Y: Coran, author), Ed. A.K. Bhowmik and H.L. Stephens, Mercel Dekker
Inc.,
New York, 1988. Activators of this invention usually can be an organic
compound
containing an active sulfur (S.) or active hydrogen (H.). The examples of
effective
activators are various thiazole, thiuram , dithiocarbamate compounds.
Preferred
compounds are thiazole and its derivative. Typical thiazole and its derivative
are
mercaptobenzthiazole and dibenzothiazyl disulfide. A compatible blend of two
or more
activators can be used. Example of a preferred blend is dibenzthiazyl
disulfide and
tetramehtylene thiuram disulfide. Other activators, which also can be used,
are
mercaptobenzthiazol, tetraethyl thiuram disulfide, zinc diethyl
dithiocarbamate and some
other sulfur donor such as tetraethyl thiuram tetrasulfide, tetramethyl
thiuram tetrasulfide.
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In use activators has the effect not only to lower processing temperature well
below the
decomposition temperature of imide reinforcement additives, but also of
improving
efficiency of decomposed reinforcement additive.
The effective temperature range for melt-mixing plastics, fibre, wood flour,
reinforcement
additive along with activator is between 175 to 230° centigrade.
Preferred temperature
range for composites prepared with an activator is between 185 to 225°
centigrade. The
effectiveness of the activator of the invention is surprising, since it allows
melt-mixing
and subsequent processing to be carried out at a significantly low temperature
thereby
preventing any undesired decomposition or burning of lignocellulosic
materials.
Again, the time of mixing will usually be minimized, and will of course,
depend on a
number of factors, type of mixer, degree of shear obtained, type of activator,
the
proportion of the ingredients, the batch size and batch temperature. The
premixed
composite of this invention is then subjected to optional pelletization or
granulation
process to make the composite of this invention easily processible in extruder
or other
molding equipment.
The proportions of the ingredients will be usually be dictated by the
properties described
in the final product. The amount of polyolefin used will be at least
sufficient to process
the compounded premix in a conventional processing equipment such as extruder,
injection molder etc. without the requirement of additional plastic addition.
Usually at
least 15 parts of polyolefin plastic by weight per 100 parts by weight of
composite.
Generally no more than 85 parts of polyolefin plastic by weight per 100 parts
of
composite by weight will be used, although higher plastic levels can be used
if desired.
50- 80 parts by weight of the composite by weight of the polyolefin selected
from
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polyethylene, polypropylene and a mixture of polypropylene and ethylene
propylene
copolymer has been used in the composite of this invention.
To make the composite 20-50 parts by weight of the cellulose and cellulosic
fibres
selected from wood flour, bleached kraft, thermomechanical pulp, recycled
newsprint and
flax having particle size of 20 - 100 mesh have been used effectively. Given
the wide
variety of formulations which can be used effectively within the scope of the
invention,
the optimum ratios of polyolefin to fibre or flour can be readily determined
by statistical
experimentation.
As stated before, the effective level of reinforcement additive selected from
maleimidopropionate, hydroxysuccinimide ester derivative, dimaleimides and
hydroxyl
succinimide derivative in the composite of the invention is from 0.05 to 5
parts per 100
parts of composite by weight. All part of the other ingredients must be added
in the melt-
mixing stage. The premixed composite of this invention obtained from melt-
mixing
process is then pelletized or granulated as desired for further processing or
it can be used
as is for making compression molded products.
When activator is added to reduce the melt-mixing and subsequent processing
temperatures, the amount of activator is normally small. For example,
activator /imide
additive ratio is approximately between 0.01 and 0.3. The preferred level of
the activator
selected from thiazole, thiuram and dithiocarbomate compounds such as
dibenzthiazyldisulphide, 2-mercaptobenzthiazole, tetramethylthiuramdisulphide
and
cyclohexylbenzthiazyl sulphonamide, in the composites of the invention is from
10 to
20% by weight of the reinforcement additive. The activator is generally added
together
with other ingredients during the melt-mixing stage. A preferred way to
introduce
CA 02350112 2004-02-26
activator is premixing fibre or flour with imide additive and activator before
adding to the
mixer.
Processing of premixed composite to give the formation of a product is further
performed
in an extruder, compression molder or injection molder. The processing
temperature for
making products from the premixed composite of this invention is very critical
because
further reinforcement of the properties of finished product depends on the
processing
temperature. Premixed composites prepared without activator according to this
invention
can be processed in any temperature range between 180 to 240°
centigrade. Effective
processing temperature for extrusion, injection molding or compression molding
according to this invention is between 200 to 240° centigrade for
composites without any
added activator. More preferred temperature for activator-free composites is
between 220
to 235° centigrade. Temperature above 230° centigrade can be
used provided precaution
has been taken to prevent thermal degradation of cellulosic fibre during the
process.
Preferred processing temperature for premixed composites containing an
activator of the
present invention is between 180 to 240°C. More preferred temperature
range is 200 to
230°C.
According to this invention, the premixed composites contain the
aforementioned
ingredients when processed in extruder, injection or compression molding
equipment
produce composite finished products having superior stiffness, strength, heat
deformation
resistance and creep resistance properties compared to composites products
without imide
additive. The preferred temperature for injection molding is between 220 to
240°
centigrade and for compression molding is between 210 to 230°C.
Injection, compression
and extrusion processes are used to produce test samples to evaluate
performance of the
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composites. Also good surface finish of the composite products has been
achieved by
employing a higher processing temperature range between 220 to 230°
centigrade.
A better understanding of the invention can be obtained by reference of the
following
specific examples, in which all parts are by weight unless otherwise
indicated.
EXAMPLE I
In order to compare the effect of various imide additives of this invention in
a composite
formulation, a series of compounds were prepared containing the imide
additives, as well
as controls. Imide compounds having at least one unsaturation were used as
property
modifiers. The imide compounds which were used in the composites are: N-
cyclohexyl
maleimide (Imide A); N-succinimidyl 3-maleimidopropionate (Imide B); 3-
maleimidobenzoic acid N-hydroxysuccinimide ester (Imide C); N, N' 1,3-
phenylenedimaleimide (imide D). These imide compounds differ in their chemical
structure and melting points. Table 1 gives the composition. Samples H and I
contained
no fibers. Samples A to D contained polyethylene and approximately 40% wood
flour and
about 0.75% of Imide A, Imide B , Imide C and Imide D respectively. Samples E
and F
contained polypropylene and approximately 40% wood flour and about 0.75% Imide
A
and Imide D respectively. Sample H contained a mixture of about 45%
polypropylene,
15% ethylene-propylene copolymer, 40% wood flour and about 0.75% of Imide D.
Table 1. Composite formulations
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Composition A B C D E F G H I J K
PE 60 60 60 60 100 60
PP 60 60 45 100 60
EP Copolymer 15
Wood flour 40 40 40 40 40 40 40 40 40
(60/80 mesh)
Imide A 0.75 0.75
Imide B 0.75
Imide C 0.75
Imide D 0.75 0.75 0.75
Imide A: N-cyclohexyl maleimide; Imide B:N-succinimidyl 3-maleimidopropionate;
Imide C: 3-maleimidobenzoic acid N-hydroxysuccinimide ester; Imide D: N, N'
1,3
phenylenedimaleimide.
Mixing was done in a laboratory K mixer fitted with high speed mixing screw.
The
polyolefin plastics and fibers were compounded in this high speed
thermokinetic mixer
and the dump temperature was about 200-205° centigrade. The residence
time of samples
in compounding machine varied between 1.5 to 2.5 min.
After the mixes were discharged they were allowed to cool and then granulated
with a
laboratory scale BrabenderTM granulator. The granulated products were then
extruded and
injection molded to prepare test specimens according to ASTM standard methods.
The
extrusion temperature was between 190 to 230° centigrade depending on
the extrusion
zones, head and die. For injection molding a temperature of about 230°
centigrade was
used.
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Samples were then tested using Instron machine for tensile and flexural
properties.
ASTM standards D 638M-89 and D 790M-90 were used for tensile and flexural
tests.
Tensile and flexural data are presented in Table 2. The addition of various
imides causes
Table 2. Mechanical properties
Sample Tensile Tensile FlexuralFlexural Breaking
mod., strength,Modulus Strength,elongation,
GPa MPa GPa MPa
A 2.3 30.8 2.5 58.3 3.8
B 2.4 31.2 2.6 62.1 3 .1
C 2.4 32.5 2.6 63.9 2.9
D 2.6 33.8 2.9 68.7 3.4
E 2.7 34.8 3.2 72.5 2.6
F 2.9 38.6 3.2 75.1 2.8
G 2.6 36.7 2.8 68.8 3.6
H 0.7 20.8 1.0 33.6 7.9
I 1.1 30.9 1.4 48.9 9.8
J 2.3 22.8 2.3 51.3 3.8
K 2.3 28.7 2.9 64.7 2.5
sharp increase in the mechanical properties of the composites. Typically it
results in an
increase of modulus and strength of composites, but a decrease in the
elongation.
Depending on the type of imide additives the improvement of modulus and
strength were
IS
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different. For example, imide A resulted in the minimum improvement and imide
D
induced maximum improvement in strength and modulus. The observation is true
for
polyethylene as well as for polypropylene matrices. Elongation was somewhat
improved
by addition of about 15 parts ethylene-propylene copolymer. The standard
deviation for
mechanical properties varied within ~ 5% indicating good reproducibility of
data. The
addition of ethylene-propylene copolymer marginally reduces the strength
properties over
polypropylene-based composites containing an imide additive. However, the
properties
were significantly higher than unmodified PP-wood flour composites. Composites
made
with polypropylene showed more improved tensile and flexural properties over
composites prepared from polyethylene both with and without Imide modifiers.
Therefore, the drop in mechanical strength of virgin polymers, namely,
polyethylene and
polypropylene due to addition of 40 parts of wood flour were more than
compensated by
the addition of only 0.75 parts of any of the four imide additives and the
best imide
additive for the composite property reinforcement was Imide D followed by
Imide C,
Imide B and Imide A.
EXAMPLE II
An illustrative of composite compositions comprising of both polyolefin
plastic and
imide additive is separately treated with three different kinds of fiber in a
high speed
mixer and then separately extruded and injection molded. To evaluate the
effect of imide
additives on composites made by using various fiber sources, a comparison was
run in
which fibers were selected from agro-sources, from recycled fiber source as
well as from
processed pulp such as, bleached kraft. The composites were made by the same
process
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Table 3. Composite formulations
Composition L M N O P Q R S
PE 70 70
PP 70 70 70 70 70 70
EP Copolymer
Bleached kraft 20 20 30 30
ONP 30 30
Flax 40 40
Imide C 0.75
Imide D 0.75 0.75 0.75
as described in Example I. The composites were prepared as shown in Table 3,
following,
in which all parts are by weight. .The dump temperature for bleached kraft and
ONP (old
newsprint) did not exceed 205°C and for flax it below 200°C.
Samples L, N, P and R were controls, containing no imide additive. Sample M,
O, Q and
S were prepared with Imide D additive. Samples L and M contained ONP as fiber
source,
samples N, O, P and Q contained bleached kraft as fiber source and samples R
and S
contained flax as fiber source. Samples L, M, P and Q contained 30 parts
fiber, samples N
and O contained 20 parts fiber and samples R and S contained 40 parts fiber.
The samples
after compounding in high speed mixer were injection molded at 220°C to
230°C using a
laboratory injection molder. Test results are set forth in Table 4, following.
Table 4. Mechanical properties
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Sample Tensile Tensile FlexuralFlexural Breaking
mod., strength,Modulus Strength,elongation,
GPa MPa GPa MPa
L 1.9 24.5 2.3 52.8 5.3
M 1.85 30.7 2.4 61.6 5.5
N 1.7 34.5 2.0 56.6 5.4
O 1.6 39.1 2.1 64.3 5.4
P 2.15 32.4 2.7 60.9 3.1
Q 2.3 43.3 2.9 70.3 3.8
R 2.3 22.2 3.8 50.0 2.0
S 2.5 27.9 3.9 59.4 1.9
The tensile test results in Table 4 indicate that composites containing imide
D additive
(samples M, O, Q and S) give very good mechanical strength and the tensile
modulus and
tensile strengths are much higher than their controls. The flexural test data
also indicate
that the addition of imide additive significantly improved the flexural
strength of
composites filled with three different fibers. This indicates that imide D is
a very good
property enhancer for polyethylene and polypropylene composites filled with
ONP,
bleached kraft or flax fiber. Highest mechanical property was achieved for
composite
made with bleached kraft followed by ONP and flax. Increase in bleached kraft
concentration in composite from 20 parts to 30 parts resulted in further
property
improvement in presence of Imide D.
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EXAMPLE III
An illustrative of another embodiment, there are charged to a high speed mixer
variable
quantities of polypropylene and wood flour and a constant amount of 0.75 part
Imide D
additive. In one composition 25 parts of polypropylene was replaced by an
equal amount
of ethylene-propylene copolymer. Five compositions as given in Table 5 were
melt mixed
a high speed in a thermo-kinetic mixer and dumped at 200°C. The
compounds were then
injection molded in the temperature range 220° centigrade to
230° centigrade.
Table 5. Composite formulations
Composition T U V W X
PP 80 70 60 50 25
EP Copolymer 25
Wood flour 20 30 40 50 50
(20/40mesh)
Imide D 0.75 0.750.75 0.750.75
The tensile and flexural properties of composites with variable amount of wood
flour are
illustrated in Table 6. Increasing wood flour content from 20 to 50 wt% showed
further
improvement of mechanical properties over pure polyolefin as in composition H
and I of
Table 2 as well as improvement of mechanical strength over unmodified controls
as set
forth in Examples I and II. Strength improvement was maximum for composition
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Table 6
Sample Tensile Tensile FlexuralFlexural Breaking
mod., strength,Modulus Strength,elongation,
GPa MPa GPa MPa
T 1.73 30.8 1.81 52.8 5.4
U 2.1 33.7 2.32 61.3 4.1
V 2.4 34.6 2.85 63.8 3.2
W 3.2 36.8 4.1 68.3 2.7
X 2.7 33.5 2.8 60.8 3.6
containing 40 part of wood flour and with 50 part of wood flour the strength
properties
decreased marginally over composite containing. 4'0 part wood flour. However,
all
composites in samples T to X showed improved tensile and flexural properties
over pure
polyethylene and polypropylene.
EXAMPLE IV
In still another embodiment using thermo mechanical pulp (TMP), polypropylene
and an
imide additive, Imide D, there are charged to an high speed thermo-kinetic
mixer 70 parts
of polypropylene, 30 parts of TMP and four different concentrations of Imide D
additive
ranging from 0.1 part to 5 parts as given in Table 7. The dump temperature was
205°
centigrade and then the composite samples Y, Z, AA and AB were injection
molded in
CA 02350112 2004-02-26
Table 7. Composite formulations
Composition Y Z AA AB AC
PP 70 70 70 70 70
TMP 30 30 30 30 30
Imide D 0.1 1 2 5 0
the temperature range 220° centigrade to 230°centigrade. Test
results of the composites
are given in Table 8, following.
Table 8. Mechanical properties
Sample Tensile Tensile FlexuralFlexural Breaking
mod., strength,Modulus Strength,elongation,
GPa MPa GPa MPa
Y 2.5 34.9 3.3 68.2 2.8
Z 2.5 44.7 3.45 76.3 3.1
AA 2.6 41.9 3.3 75.2 2.8
AB 3 .2 3 7.8 3 .7 72.5 2.0
AC 2.6 34.4 3.2 61.3 2.6
The tensile strength in Table 8 indicates that concentration of Imide D
additive has a
strong improvement effect on mechanical properties. One part of Imide D
improved
tensile and flexural strengths by about 30% over control sample AC. and
further increase
of Imide D additive to 2 parts and 5 parts resulted in a marginal decrease in
strengths of
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composites. However, the tensile and flexural properties of composites Y, Z,
AA and AB
are significantly higher than controls without imide additives as well as pure
polyolefins.
Use of only 0.1 part of imide also resulted in improved flexural strength
compared to the
control. Test results indicate that use of Imide D additive in any
concentration range
between 0.1 to 5 parts improves tensile and flexural properties of polyolefin-
natural fiber
composites.
EXAMPLE V
As illustrative to yet another embodiment, there are charged to a high speed
thermo-
kinetic mixer 70 parts polypropylene, 30 parts TMP and 0.75 part Imide D. The
dump
temperature was 205° centigrade. These compounded samples as given in
Table 9 were
then injection molded at three different temperatures 190°, 210°
and 230° centigrade
respectively for samples AD, AE and AF respectively. The composite samples
after
injection molding were tested for tensile and flexural properties.
Table 9.
Composition AD AE AF
Injection molding temperature,190 210 230
C
PP 70 70 70
TMP 30 30 30
Imide D 0.75 0.75 0.75
Table 10 gives the tensile and flexural strength and modulus values for these
composites.
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Table 10. Mechanical properties
Sample Tensile Tensile FlexuralFlexural Breaking
mod., strength,Modulus Strength,elongation,
GPa MPa GPa MPa
AD 2.1 27.8 2.4 61.5 2.9
AE 2.5 36.7 3.1 72.5 3.1
AF 2.6 41.9 3.3 75.2 2.8
Use of high injection temperature improved tensile and flexural strengths of
composite. A
temperature of 230° centigrade produced highest improvement in strength
and modulus.
Injection temperature above 230° centigrade was not successful because
it initiated
burning of TMP. High processing temperature provided somewhat darker samples
with
excellent surface finish. Injection temperature lower than 210°
centigrade developed
strength and modulus properties inferior to virgin polyolefins and no
reinforcement effect
was observed. It is because Imide D does not decompose below 195°
centigrade. It is then
essential to process polyolefin-natural fiber compositions with imide additive
above the
decomposition temperature of the imide.
EXAMPLE VI
The following illustrate embodiments of the invention in which composites are
prepared
using activators which decrease the melt-mixing and processing temperatures of
composite. Several activators are used either alone or in combination. The
activators used
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are dibenzthiazyl disulfide (MBTS); 2-mercaptobenzthiazole (MBT), Tetramethyl
thiuram disulfide (TMT); and cyclohexyl benzthiazyl sulphenamide (CBS). Three
different imide additives are used and they are N, N' 1,3 phenylenedimaleimide
(Imide
D); methyl, 1,3 phenylenedimaleimide (Imide E); 4-(Maleimidomethyl)-1-
cyclohexanecarboxylic acid N-hydroxysuccinimide (Imide F)
Table 11. Composite formulations
Composition AG AH AI AJ AK
PP 70 70 70 - 70
PE 70
TMP 30 30 30 30 30
MBTS 0.3 0.1 0.3
TMT 0.1 0.1
CBS 0.2
MBT 0.1 0.1
Imide D 1.0 1.0 1.0
Imide E 0.75
Imide F 0.75
MBTS: dibenzthiazyl disulfide; MBT:2-mercaptobenzthiazole,
TMT: Tetramethyl thiuram disulfide; CBS: cyclohexyl benzthiazyl
sulphenamide. E:4 methyl, 1,3 phenylenedimaleimide; F:4-(Maleimidomethyl)-1-
cyclohexanecarboxylic acid N-hydroxysuccinimide
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To a high shear thermo-kinetic mixer, the ingredients shown in compositions AG
to AK
are charged separately and mixed at high speed until the dump temperature
reached 195°
centigrade. The compositions were then separately injection molded in the
temperature
range 200 to 210° centigrade to produce test samples. The test results
are shown in Table
12 , following.
Table 12. Mechanical properties
Sample Tensile Tensile FlexuralFlexural Breaking
mod., strength,Modulus Strength,elongation,
GPa MPa GPa MPa
AG 2.4 43.8 3.6 72.2 3.9
AH 2.1 38.7 2.97 68.5 3.1
AI 2.1 37.9 2.9 66.9 3.2
AJ 1.97 32.7 2.5 63.8 4.8
AK 2.3 42.7 3.5 71.8 4.1
The tensile test results in Table 12 indicate that addition of activators
helped to reduce
process temperature without significant sacrifice in strength and modulus. The
processing
temperature used in this case is 210° centigrade but the properties are
significantly better
than composition AE for PP composite of Table 10, Example V and sample M for
PE
composite of Table 4, Example II which can be used as controls. It is further
found that
MBTS is most effective and a combination of MBTS and TMT is least effective in
reducing the processing temperature. The suitable concentration range for
activator is
CA 02350112 2004-02-26
found to be in the range of 10 to 40% by weight of Imide additive. It is also
evident from
results in Table 12 that Imide E and Imide F additives are less effective than
Imide D
additive in reinforcing tensile and flexural properties of the said composites
because the
tensile and flexural strength and modulus for samples AH and AI are inferior
to sample
AG.
EXAMPLE VII
The following illustrates another embodiment in which the samples H, I, L, M,
P, Q, R, S,
Y, Z, AA, AB, AD and AG are melt mixed in a high speed thermo-kinetic mixer at
200°
centigrade dump temperature followed by injection molding at 230°
centigrade except for
sample AD which was processed at 190° centigrade, to prepare test
samples for
measuring heat distortion temperature and creep properties. The heat
deflection
temperature was measured according to ASTM standard D 648 at 1.8 MPa load. The
creep test was conducted at 40° centigrade for 1 day according to ASTM
standard D
2990. The stress level for creep measurement was 30% of the room temperature
ultimate
flexural strength of respective molded materials. The test results are given
in Table 13
and Table 14 as follows:
Table 13. Thermal properties
Sample H L M AG
HDT, C 51 92 105 107
Initial strain 28 6.3 4.8 4.2
(x 10'3 mm/mm)
Relative creep 380 250 189 181
(%)
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Table 14. Thermal properties
Sample I P Q R S Y Z AA AB AD
HDT,C 54 98 108 96 105 101 111 113 116 110
Initial 20 3.7 2.8 - - - - 2.4 - 2.7
strain
(x
10-3 mm/mm)
Relative 425 195 140 - - - - 121 - 135
creep
(%)
It is evident from Table 13 results that heat distortion temperature and creep
resistance of
composites are significantly higher than virgin PE (sample H). Again the
addition of
Imide D (sample M and AG) further increased heat distortion temperature and
creep
resistance of unmodified composite (sample L). Again, increase of
concentration of Imide
D has a positive effect on heat distortion temperature and creep resistance
(sample M and
sample AG).
Results from Table 14 revealed that both creep resistance and heat distortion
temperature
of virgin PP can be significantly improved by adding natural fiber and Imide
additive.
There is almost 100% increase in the heat distortion temperature of PP when a
composite
is prepared from this virgin PP in combination with 30 parts of bleached kraft
and 0.75
part of Imide D. The same composite sample (sample Q) has improved creep
resistance of
virgin PP (sample I) and unmodified composite (sample P) significantly by
yielding a
relative creep of 140% against 195% for composite without Imide D additive.
Again
increase of Imide D concentration from 0.75 parts to 2 parts in composite
(sample AA)
further improved heat distortion temperature and relative creep. On the other
hand, a
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CA 02350112 2004-02-26
lower processing temperature during molding process such as for Sample AD, the
heat
distortion temperature and the relative creep resistance are inferior to the
composites
which is processed at higher temperature with same chemical ingredients
(sample Q). in
other word, higher process temper~u~e improved creep resistance and heat
distortion
temperature as well. Again, both wood fiber (bleached kraft) and nonwood fiber
(Samples
R and S) showed improvement in croep resistance and heat distortion
temperature when
Imide additive is added. Results in Table 12 further indicate that increasing
imide
additive concentration fi~om 0.1 part to 5 part improved heat distortion
temperature of
composites by about 15° centigrade (samples Q, Y, Z, AA, A13). All
these composites
have a very smooth surface finish with no unpleasant odour and they are also
extruded to
obtain strips of very high surface finish.
Although the invention has been illustrated by typical examples, it is not
limited thereto.
Changes and modifications of the examples of the invention herein chosen for
purposes
of disclosure can be made which do not constitute depaitume from the spirit
and scope of
the invention.
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