Skip to main content

Full text of "USPTO Patents Application 10687092"

See other formats


10 



15 



20 



BACKGROUND OF THE INVENTION 

The present invention relates to a 

fiber used to make composite materials. The invention 

• .articular to a method for making such 
relates m particular 

polymer-grafted natural fibers. 

It is well known that composite materials are used 
in many applications on account of their excellent 
m echanical properties. The mechanical properties of 
composites are a function of the properties of the 

individual components. 

Composites consist basically of two distinct 
phases: a first continuous phase (matrix) and a second 
disP ersed phase. In many cases, the continuous phase 

, mt > r A second component is dispersed 
(matrix) is a polymer. A secon 

4-^ make the second 
in the first continuous phase to make 

dispersed phase. 

, he disP ersed phase in composites is usually 
de signed to improve the mechanical properties of the 
matrix . The dispersed phase may have very different 

,-. s form and dimensions, depending on the 
properties, form an 

^ has to perform within the 

specific function it has to p 

composite . 



1 



V 



0 



Many known composites are reinforced with fibers 
such as, for example, glass, carbon or synthetic 
polymer fibers. 

Composites consisting of a polymer matrix with 
5 natural fibers as the reinforcing agent have only 

recently been introduced. The natural fibers most used 
for this purpose are of plant origin, and in 
particular, cellulose fibers. 

The interest in materials reinforced with natural 
10 fibers can be ascribed to the following reasons: 

natural fibers are obtained from renewable, low- 
cost sources; 

natural fibers have very good mechanical 
properties ; 

15 natural fibers have a low specific weight compared 

to the synthetic or glass fibers usually used; 

natural fibers are environmentally friendly since 
they are biodegradable and burn easily and can 
therefore be conveniently disposed of after use. 

2 0 To ' obtaiii composites with good mechanical 

properties, the adhesion between the continuous phase 
(matrix) and the dispersed phase (fiber) must be 
optimized, since the mechanical load applied to the 
matrix must be effectively transferred to the fiber. In 

2 5 a composite, it is the fiber component that confers the 

good mechanical properties. The effectiveness of the 



2 



<>1 



adhesion at the interface between fiber and matrix 
depends largely on the surface properties of both 
components. Usually, the surface properties are 
, correlated to parameters such as surface tension and 
5 polarity. The surface properties of the polymer 

matrices currently available on the market, used in the 
preparation of composites, are very different from the 
surface properties of natural fibers. However, to 
obtain good adhesion at the interface between fiber and 
10 matrix, the surface tension and polarity of the two 

components must be very similar. 

The continuous phase (matrix) or the dispersed 
phase (fiber) can be chemically modified in numerous 
ways to suitably change the surface properties. 
15 One way of chemically modifying the surface of a 

fiber is by grafting polymer chains onto it. 

A fiber can be grafted with polymer chains which 
polymerize in situ or with ready-made polymer chains. 

In the first type of grafting process, it is 
20 difficult to control the degree of polymerization and 

hence the length of the grafted chains. 

The second process allows polymer chains of 
different types and preset length to be grafted. 

US patent 3,492,082 discloses a process for the 
25 preparation of polymer-grafted cellulose fibers. 

In US patent 3,492,082 the grafted cellulose fibers 



3 



are prepared by converting the hydroxyl groups of the 
cellulose into hydroperoxide groups through the 
formation of an intermediate sulphonate ester group. 
The cellulose containing the hydrogen peroxide groups 
5 is subsequently reacted with a reactive monomer to 

yield the grafted cellulose material. The following 
monomers are used; styrene; butadiene; acrylonitrile ; 
N-vinylpyrrolidone ; acrylamide; and others. These 
monomers are capable of polymerizing with the 

10 hydroperoxide groups on the cellulose fiber in the 

presence of a free-radical initiator. 

Hence, US patent 3,492,082 describes a free-radical 
type, in situ polymerizing process. The free-radical 
polymerization produces on the fiber grafted chains 

15 with a very wide length distribution. The chain length 

of the polymer grafts thus varies considerably and 
cannot be predetermined. The kinetics of the free 
radical grafting reaction are difficult to control. 

US patent 4,857,588 discloses a process for the 

2 0 preparation of cellulose fibers with ready-made polymer 

grafts . 

US patent 4,857,588 describes a process in which 
the cellulose material is first treated with an aqueous 
sodium hydroxide solution. The cellulose material is 
2 5 then treated with sodium methoxide in methanol in order 

to convert the hydroxyl groups of cellulose into 



4 



salified oxy groups with sodium in a quantity ranging 
from 0.25 to 33.3%. 

Next, the resulting cellulose material is contacted 
with a ready-made organic compound having a chain with 
an electrophilic functional group at one end. 

The main disadvantage of the fibers treated using 
the method described in US patent 4,857,588 is that the 
fibers are subjected to a very drastic pre- treatment in 
an alkaline solution which alters their original 
structural, chemical and mechanical properties. 

The treatment described by US patent 4,857,588 
(NaOH in 5N aqueous solution) , modifies the crystal 
structure of the native cellulose fibers, as clearly 
shown by the X-ray diffraction spectrum. Indeed, 
following treatment as . taught by US patent 4,857,588 
the spectrum shows the reflections typical of the 
crystal structure of regenerated cellulose known as 
cellulose II, as shown in Figure IB. 

Therefore, one of the aims of the present invention 

is to ptovide ;natural fibers whose surface properties 

# ' * 

are modified in such a way as to obtain composite 
materials having ' improved mechanical properties. 

Another aim of the present invention is to provide 
a process for the preparation of polymer-grafted 
natural fibers which leaves the mechanical properties 
of the fiber unchanged. 



SUMMARY OF THE INVENTION 

According to one aspect of it, as described in 
claim 1 hereof, the present invention provides a 
5 process for the preparation of polyether-graf ted 

natural fibers. 

This process keeps the mechanical properties of the 
natural fiber unchanged. Indeed, the chemical 
modifications do not affect the body of the fiber and 
10 do not alter its structure. Only the outer surface of 

the grafted natural fibers obtained using this process 
is modified. 

Another advantage of the process according to the 
present invention is in that it reduces the 

15 hydrophilicity of the fiber so that the surface 

properties of the fibers become similar to those of the 
polymers used as matrices, thus improving the adhesion 
between the fiber and the polymer matrix. The dependent 
claims describe preferred embodiments of the process 

2 0 according to the present invention. 

The invention also relates to a polyether-graf ted 
natural fiber, as described in the corresponding 
independent claim, made preferably but not necessarily 
using the process according to the present invention. 

25 The polyether-graf ted natural fiber according to 

the present invention is highly compatible with the 



6 



polymer matrices of numerous composite materials. Its 
surface properties are modified to improve the adhesion 
between it and the matrix of the composite material. 
Further, since only the surface structure of the 
5 natural fiber is modified, the body of the grafted 

fiber remains unchanged and maintains its mechanical 
resistance. The resulting composite material therefore 
has better mechanical properties than composite 
materials known up to now. 

10 In a preferred embodiment, the grafted natural 

fiber is a cellulose fiber and the polyether has a 
general formula (I) , as described below. 

The invention also relates to a composite material 
comprising polyether-graf ted natural fibers, as 

15 described in the corresponding independent claim, made 

preferably but not necessarily using the process 
according to the present invention. 

In a preferred embodiment, the composite material 
comprises cellulose fibers grafted with a polyether 

2 0 having a general formula (I) , as described below. 

The present invention further relates to the use of 
polyether-graf ted natural fibers made preferably but 
not necessarily using the process according to the 
present invention for the preparation of composite 

2 5 materials, as described in the corresponding 

independent claim . 



7 



In a preferred embodiment, the natural fibers used 
in the preparation of the composite materials are 
cellulose fibers prepared according to the process 
taught by the present invention. 

5 

BRIEF DESCRIPTION OF THE DRAWINGS 

Further technical characteristics and advantages of 

the invention are apparent from the detailed 

description which follows, with reference to the 

10 accompanying drawings, in which: 

Figure 1A shows a wide-angle X-ray diffraction 

spectrum of a grafted fiber made according to the 

present invention; 

Figure IB shows a wide-angle X-ray diffraction 

15 spectrum of a fiber that was pre-treated in NaOH 5 N 

according to the teachings of prior art; 

Figures 2A and 2B show, respectively, the changes 

in the polarity and surface tension of the cellulose 

with changing in both degree of substitution (DS) and 
t 

20 molecular weight (MW) of the polyether graft (in this 

case/ ' polyethylene oxide) . 

DESCRIPTION OF THE PREFERRED EMBODIMENTS 

In the present description, the term "natural 
25 fibers" denotes any natural fibers having on their 

surfaces hydroxyl groups on which a ready-made polymer 



8 



chain can be grafted. 

The fibers used are preferably the cellulose fibers 
of certain plants. Of these, cotton, flax and hemp 
fibers are preferred. 

According to the present process, the natural 
fibers first undergo a pre- treatment . During this pre- 
treatment step, the natural fibers are dried. 

The pre-treatment step is preferably performed 
under vacuum at a temperature in the range of from 5 0 °C 
to 100 °C for a time of between 2 and 4 8 hours. 

Subsequently, the pre-treated fibers are contacted 
with a first solution comprising an alkaline reagent. 
In a first preferred embodiment, the first solution 
comprises an anhydrous solvent such as, for example, 
tetrahydrof uran (THF) and an alkali such as, for 
example, potassium- tert-butylate and a crown ether such 
as 18-crown-6. 

The potassium- tert-butylate and the crown ether are 
present preferably in equimolar quantities. 

Advantageously, the quantity of potassium- tert- 
butylate exceeds the total quantity of hydroxyl groups 
of the natural fiber. The reaction occurs in an 
anhydrous environment in an inert atmosphere. 

The natural fibers are preferably allowed to react 
with the solution for a time ranging from 1 to 6 hours 
and at a temperature in the range of from 30°C to 80°C. 



9 



During this step, the hydroxyl groups in the 
natural fibers are converted into alcoholates via the 
alkaline reagent. In the present description, the 
alcoholate groups are also referred to as oxy groups. 
5 The alcoholates are in the salified form with the 

cation of the alkali used: in this case, the cation is 
the potassium cation. 

The use of potassium- tert -butylate with 18 -crown- 6 
is advantageous because the crown ether acts as a phase 
10 transfer agent since it protects the potassium cation 

and at the same time makes it available for the 
alcoholate . 

This step is designed to activate the natural 
fibers before grafting the polyether chains on the 
15 salified oxy groups. 

In a second preferred embodiment, the first 
solution comprises an anhydrous solvent, such as, for 
example, methyl alcohol and an alkali such as, for 
example, sodium methylate. The reaction occurs in an 
2 0 anhydrous environment in an inert atmosphere. 

The natural fibers are preferably allowed to react 
with the solution for a time ranging from 1 to 48 hours 
and at a temperature in the range of from 20°C to 80°C. 
During this step, the hydroxyl groups in the 
25 natural fibers are converted into alcoholates via the 

alkaline reagent. 



10 



The alcoholates are in the salified form with the 
cation of the alkali used: in this case, the cation is 
the sodium cation. 

This step is another way of activating the natural 
5 fibers before grafting the polyether chains on the 

salified oxy groups. 

If the fibers are activated according to the second 
preferred embodiment (sodium methylate) , the process 
comprises a further, filtering step. In practice, the 
10 solution containing the natural fibers and the sodium 

methylate is filtered in order to remove the solvent 
and reagent dissolved in it. The solvent and the 
reagent consist, for example, of methyl alcohol and 
sodium methylate. 
15 After filtering, washings in anhydrous 

tetrahydrof uran (THF) are performed to remove all 
traces of alkaline reagent. 

According to the present invention, the polyether 

chains are ready-made before being grafted on the 

I 

2 0 activated fiber^ 

i 

Subsequently, the natural fibers with the salified 
oxy groups are reacted with a polyether in an inert 
atmosphere . 

Preferably the polyether is one having an aliphatic 
25 or aliphatic/aromatic group at one end and a leaving 

group at the other end. 



11 



10 



15 



Advantageously, the polyether, having the general 
formula (I) , is a polyether f unct ionalized by a group 
that favors nucleophilic substitution (a good leaving 
group) : 

R[-0-X-] m Y 

where : 

m is between 1 and 2 00; 

R is an aliphatic or aliphatic/aromatic group; 
Y is a functional leaving group; 

and where X has the general formula (II) 



Ri 

I 

-c- 
I 

R 2 



(id 



where : 

n is between 1 and 20; 

R2 is either hydrogen or a linear or branched Cl- 
C4 alkyl group; and 

Rl is the same as or different from R2 and is 
either hydrogen or a linear or branched C1-C4 
alkyl group; 



20 



or where X has the general formula (III) 



12 




having at the positions of the ring a) , b) , c) and d) 
one or more substituting groups which may be the same 
or different from each other and which may be a group 
5 comprising a halogen or a linear or branched C1-C4 

alkyl . 

As . stated above, m may be between 1 and 200, but 
ideally, m is between 4 and 60. 

Preferably, the aliphatic R group is either 
10 hydrogen or a linear or branched C1-C4 alkyl group. 

Preferably, the aliphatic/aromatic R group is a 
benzyl group . 

As stated above, n may be between 1 and 20, but 
ideally, n is between 2 and 5. 
15 Ri may be the same as or different from R2 and may 

be either hydrogen or a linear or branched aliphatic 
group. Preferably, Rl and/or R2 are either hydrogen or 
a linear or branched C1-C4 alkyl group. 

At the ring positions labeled a) , b) , c) and d) , 
2 0 there may be one or more substituting halogens chosen 

from chlorine, bromine and iodine. 

■Preferably, the ring presents two substituting 
groups between positions a) , b) , c) and d) . 



13 



In the present description, linear or branched Cl- 
C4 alkyl group (or alkyl) means a methyl, ethyl, n- 
propyl, isopropyl, n-butyl, sec-butyl, isobutyl or 
tert -butyl group. 
5 The polyether of general formula (I) has at its two 

ends an R and a Y group. The Y group is a functional 
leaving group which favors nucleophilic substitution. 

Preferably, the Y group is a group of those 
commonly used to favor nucleophilic substitution. 
10 Halides of chlorine, bromine or iodine can be used to 

good advantage as the Y group. Alternatively, the Y 
group is a mesylate group. 

Preferably, the polyethers of general formula (I) 
are polyoxy ethylene R - ( - O - CH 2 - CH 2 - ) m -Y, polyoxy- 
15 propylene R- ( -0-CH 2 -CH 2 - CH 2 -) m -Y, polyethylene 

terephthalate R- ( -CO-Ph-CO-0-CH 2 - CH 2 -0-) m -Y . 

The pre-treated and activated natural fibers can be 

reacted with the polyether in the presence of an 

anhydrous solvent at a temperature within a range of 

t 

20 from 3p°fc to 8C| 0 C for a time of between 1 and 24 hours. 

I'deally, however, the reaction is made at a 
temperature in a range of from 60°C to 80°C. 

It is during this step that the polyether 
derivative is grafted onto the activated natural 
25 fibers. In practice, the polyether of general formula 



14 



(I) reacts with the salified alcoholate to yield Cell- 
CD- [X-0] m -R. 

On being grafted onto the fiber, the polyether 
loses the leaving Y group. 
5 Advantageously, after the grafting step, the 

grafted natural fibers undergo one or more steps of 
filtering and one or more steps of washing with a 
solution containing water and/or acetone and/or ether. 
Lastly, a step of drying the grafted natural fibers can 
10 be carried out. The reactions described above are made 

in heterogeneous phase and in an anhydrous environment . 

The process will be further illustrated by the 
following Examples without restricting the scope of the 
inventive concept . 
15 EXAMPLE 1: cellulose fiber grafted with CH 3 - (0-CH 2 - 

CH 2 )n-CH 2 -CH2-I (n=43, MW=2000) 
Pre- treatment step 

The fibers are dried under vacuum for 16 hours at 
80°C. 

20 Activation step 

The following are added to a 2 00 ml anhydrous THF 
solution: 

8 mM (8 ml IN solution in anhydrous THF) of 
potassium-tert-butylate and 8 mM (2.1 g) of 18-crown-6 
25 ether. 

The solution is heated to a temperature of 70°C in 



15 



an inert atmosphere . 

1 g of fiber is added and the solution containing 
the fibers (sol. 1) is allowed to react for 3 hours at 
70°C. 

5 Grafting step 

A solution of 6 mM (12 g) of PEO-I (MW=2000) in 30 
ml of anhydrous THF is prepared (sol. 2) . 

This solution (sol. 2) is added to the reactor 
(sol. 1) and allowed to react for 5 hours at 70°C. 
10 The reaction is extinguished with water. The fibers 

are filtered and washed in abundant water, acetone and 
ethyl ether and then dried under vacuum at 80 °C for 16 
hours . 

EXAMPLE 2: cellulose fiber grafted with CH 3 - (0-CH 2 - 
15 CH 2 )n-CH2-CH2-S02-CH 3 (n=5, MW=350) 

Pre - trea tmen t st ep 

The fibers are dried under vacuum for 16 hours at 
80°C. 

Activation step 

2 0 The following are added to a 20 0 ml anhydrous THF 

solution: 

8 mM (8 ml IN solution in anhydrous THF) of 
potassium tert-butylate and 8 mM (2.1 g) of 18-crown-6 
ether . 

25 The solution is heated to a temperature of 70°C in 

an inert atmosphere . 



16 



1.5 g of fiber are added and the solution 
containing the fibers (sol. 1) is allowed to react for 
5 hours at 7 0 °C. 
Grafting step 

5 A solution of 27 mM (13 g) of PEO-S0 2 -CH 3 (MW=350) 

in 15 ml of anhydrous THF is prepared (sol. 2) . 

This solution (sol. 2) is added to the reactor 
(sol. 1) and left to react for 3 hours at 70°C. 

The reaction is extinguished with water. The fibers 
10 are filtered and washed in abundant water, acetone and 

ether and then dried under vacuum at 100°C for 16 
hours . 

EXAMPLE 3: cellulose fiber grafted with CH 3 - (0-CH 2 - 
CH 2 ) n -CH 2 -CH 2 -I (11=13, MW=750) 

15 Pre- treatment step 

The fibers are dried under vacuum for 16 hours at 
80°C. 

Activation step 

43 mM (1 g) of metallic sodium is added to a 50 ml 
2 0 solution? of CH3OH and allowed to react for 3 0 minutes 

at 2b 6 C. 

1 g of fiber is added to this solution (containing 
sodium methylate in methanol) in an inert atmosphere 
and the solution, containing the fibers (sol. 1) is 
25 allowed to react for 20 hours at 25°C. 

After filtering and washing several times with 



17 



anhydrous THF, 3 0 ml of anhydrous THF are added, still 
in an inert atmosphere (sol. 1). 
Grafting step 

A solution containing 10 mM (7.5 g) of PEO-I 
(MW=750) in 20 ml of anhydrous THF is prepared (sol. 
2) . 

This solution (sol. 2) is added to the reactor 
(sol. 1) and allowed to react for 3 hours at 70°C. 

The fibers are filtered and washed in abundant 
water, acetone and ether and then dried under vacuum at 
80°C for 16 hours. 

The natural fibers treated using the process 
according to the present invention were analyzed by 
TOF-SIMS (Time of Flight Secondary Ion Mass 
Spectrometry) in order to check the fiber surface for 
polyether chains. This technique measures the mass of 
the ion fragments that peel off the surface as a result 
of ion bombarding. The fibers treated according to the 
present invention show TOF-SIMS signals typical of the 
fragmentation products of the polyether grafts. 

The micro and macro structural characteristics of 
the natural fibers treated according to the process of 
the present invention were analyzed using a scanning 
electron microscope and wide-angle X-ray diffraction. 
The result is shown in Figure 1A. 

As shown by the X-ray diffraction spectra, all the 



18 



chemical treatments performed on the cellulose fibers 
leave the native crystal structure unchanged. The 
spectrum before and after chemical modification reveals 
no differences and exactly matches the crystal 
structure of the natural cellulose, referred to as 
cellulose I. 

A few preparations of f unctionalized polyethers of 
formula (I) are shown in the examples below. 
EXAMPLE 4: Preparation of a polyether of the formula 
(I) having a mesylate group at one end and an alkyl 
group at the other end 

A solution (a) containing 60 mM of a 
poly (oxyethylene) of the formula CH 3 - ( -0-CH 2 -CH 2 - ) n -0H, 
with n=16 and molecular weight 750 in 100 ml of CH 2 C1 2 
and 75 mM of triethylamine is prepared. 

Another solution (b) containing 65 mM of CH 3 -S0 2 -C1 
in 3 0 ml of CH 2 C1 2 is prepared. 

At the temperature of 0°C, the solution (b) is 
added to the solution (a) dropwise. The reaction is 
maintained at 0°C for 3 hours. During the reaction, the 
triethylamine chlorohydrate precipitates. Water is 
added and the triethylamine chlorohydrate solubilizes. 
The organic phase is separated. Subsequently, the 
organic phase is concentrated in volume. The liquid 
organic phase contains CH 3 - ( -OCH 2 -CH 2 - ) 16 -0-S0 2 -CH 3 which 
will be used to graft the natural fibers according to 



the process of the present invention. 

EXAMPLE 5: Preparation of a polyether of the formula 
(I) having a halogen group at one end and an alkyl 
group at the other end 

5 A solution containing 54 mM of mesylate, as pre- 

pared in example 4, in 100 ml of acetone is prepared. 

Another solution containing 100 mM of Nal (10 g) in 
100 ml of acetone is prepared. 

At the temperature of 25°C the sodium iodide 
10 solution is added to the mesylate solution dropwise and 

the reaction maintained for 48 hours. This yields a 
pale yellow solution containing sodium 

methanesulphonate salt (CH 3 -S0 3 -Na) . 

Subsequently, the solution is filtered and concen- 
15 trated, diluted in methylene chloride and washed with 

an aqueous solution of Na 2 S 2 0 3 . The solution, con- 
centrated again, contains the poly (oxyethylene) mono- 
methyl -ether iodide which will be used to graft the 
natural fibers according to the process of the present 
2 0 invention. * 

tf;he process according to the present invention has 
several advantages. The first advantage is in that the 
process chemically modifies mainly the outer surface of 
the natural fibers to improve the adhesion between 
25 fiber and polymer matrix in composite materials. 

Improved adhesion between fiber and polymer matrix 



20 



> 

1 s 



yields a composite material with improved mechanical 
properties . 

The fibers grafted using the process taught by the 
present invention have numerous applications in the 
5 field of polymer matrix composites where the 

reinforcing phase consists of natural fibers from 
renewable sources and not glass fibers and/or synthetic 
fibers . 

The polyether-graf ted natural fibers can be used to 
10 good advantage in the preparation of composite 
materials. The advantage of these materials is that 
they have a lower density than composite materials that 
use carbon or glass fibers. The table shows the 
specific weight (p) of certain synthetic/natural fibers 
15 used as reinforcing agents in polymer matrix 
comp osites : 



Reinforcing agents 


p (g/cm 3 ) 


Glass fibers 


2 .5-2 .6 


Carbon fibers 


1 . 7-1 . 8 


Aramid fibers 


1 . 5 


Natural fibers 


1.2-1.6 



The fibers treated according to the process taught 
by the present invention differ considerably from the 
same fibers treated using the processes taught by prior 
20 art. Indeed, unlike fibers treated according to prior 

art, fibers treated with the process of the present 



21 




invention maintain their original fiber structure. 
Furthermore, the surface properties differ from those 
of fibers yielded by known processes since the polymer 
grafts themselves are different and the surface 
5 properties depend directly on the type of polymer 

grafts. 

The table below shows, by way of example, the 
surface tension and polarity of some select classes of 
polymers that can be used as matrices for the 
10 preparation of composite materials with natural fibers: 



Table 1 



POLYMERS 


SURFACE TENSION 


POLARITY 




Dyn/ cm 




Polyolef ins 


30-40 


0 


Polyethers 


30-45 


0 .003-0 .28 


Polyesters 


40-50 


0.15-0.29 


Polyamides 


31-49 


0 . 15-0 .43 


Acrylics 


30-42 


0 . 03-0 .25 


Metacrylics 


29-41 


0.16-0.28 


Epoxy resins 


24-51 


0 . 017-0 . 43 


Cellulose acetate 


46 


0.3 


Cellulose* 


55 


0 .82 



* Value calculated using the group contribution method (D.W. Van 
Krevelen "Properties of Polymers", 3rd Ed. 1990, Elsevier, 
Amsterdam) 



22 



All the values shown in Table I are experimental 
values (J. Bandrup, E.H. Immergut, E.A. Grulke, 
"Polymer Handbook", 4th Ed., 1999, Wiley, New York), 
except for the value for cellulose, which is 
5 calculated. 

As shown in Table I, the surface tension and 
polarity values for the polymer families which can be 
used as matrices in composite materials are lower than 
the value for cellulose. 

10 It is precisely to reduce the surface tension and 

polarity of cellulose that polymer chains of different 
length, that is, of different molecular weight (MW) , 
are grafted according to the process taught by the 
present invention. 

15 Figures 2A and 2B show the changes in the polarity 

and surface tension of the cellulose with the changes 
in both the degree of substitution (DS) and molecular 
weight (MW) of the polyether graft (as an example, the 
two figures show the changes of y and % for chains of 

2 0 polyethylene o^ide with molecular weight 3 50, 75 0 and 

2000|. The valJes shown were calculated using the group 
contribution method. They are not experimental data. 

On the right of the graphs, the values for the 
various categories of potential matrix polymers are 

2 5 shown. 

Polyethylene oxide (PEO) was chosen because it 



23 



presents a good level of compatibility with numerous 
polymers . 

The polyether chains which are grafted on the 
activated natural fibers are ready-made chains. The use 
5 of ready-made polyether chains makes it possible to use 

chain grafts whose molecular weight is predetermined 
according to the extent of the variation that is 
desired in the surface properties (especially 
hydrophilicity) of the fiber. 



24