Bright peat moss product and method for making same

Peat moss having increased wettability and increased brightness while maintaining its absorbency and structural integrity is provided. The peat moss is treated so as to chemically graft onto its structure, unhydrolized polymeric chains of the general formula: ##STR1## wherein R.sup.1 and R.sup.2 are selected from the group consisting of hydrogen and --CH.sub.3, X and Y are selected from the group consisting of --CN, --COONH.sub.2 and --OCH.sub.3 and wherein m and n are integers which when summed together equal at least 500.

TECHNICAL FIELD 
The present invention relates to a process for producing a bright peat moss 
product that is still capable of being used as an absorbent. 
BACKGROUND OF THE ART 
Peat moss belongs to the genus sphagnum and is a plant that grows from the 
top while the bottom part dies and changes into peat. Chemically, peat 
moss consists of about 50%, by weight, lignin and humic acid with the 
remainder consisting of hemicellulose, cellulose, waxes and nitrogen 
compounds. Physically, peat moss leaf is one cell layer thick, the cells 
having thin, lignified walls. The cells or pores of the leaflike structure 
are generally evenly distributed about the surface of the leaf and range 
in size from about 15 to 40 microns in diameter. It is on the surface and 
on the walls of the pores that the lignin is primarily distributed and as 
a result, the peat exhibits a dark brown to yellow color. 
Primarily because of the pore structure, peat moss has the ability to 
absorb and hold relatively large amounts of water within the capillaries 
formed by the pores, and so has found considerable use in the 
horticultural industry. Additionally, peat moss has been used in water 
treatment techniques. 
It has also been suggested by various prior investigators that peat moss be 
used as an absorbent dressing for body fluids in such products as sanitary 
napkins, tampons, or diapers. Such use, however, has not found wide 
acceptance and it is believed that this lack of acceptance is related to 
the problem of color, i.e., the consumer or user does not like the unduly 
dark color of peat moss. 
While many processes exist for bleaching lignin, particularly lignin found 
in wood pulp, it is believed that no such prior process could produce a 
peat moss product which has the satisfactorily high brightness to suit 
consumer preferences. One achievement in this direction is described in a 
commonly assigned patent application filed in the U.S. Pat. and Trademark 
Office in Feb. 21, 1978 as Ser. No. 879,833, now U.S. Pat. No. 4,170,515 
by Drs. Jean-Marc Lalancette and Bernard Coupal. In accordance with that 
application, peat moss may be bleached, using a bleaching process which 
takes place under acid conditions, to obtain structurally integral product 
having a color level on the Hunter Scale of up to about 75. Unfortunately, 
when attempts are made to increase the severity of the bleaching process 
or prolong the process in an effort to obtain still whiter peat moss, the 
structural integrity of the product is destroyed, the leaf collapses and 
the structure creating the capillaries responsible for the absorptive 
properties of the peat moss disappears. The reason for this is believed to 
be that the same lignin and humic acid, disposed on the surface of the 
leaf, which gives peat moss its dark color also prevents the peat moss 
from collapsing and is responsible for the property of maintaining 
capillary structure when wet. To bleach peat moss brighter in color than 
about 75 on the Hunter Scale requires removal of the lignin which, in 
turn, causes the undesirable collapse of the peat moss structure. 
Accordingly, bright absorbent peat moss and a method for making the same 
has heretofore eluded the art. 
SUMMARY OF THE INVENTION 
It has now been discovered that peat moss may be provided by a process 
wherein the peat moss is substantially brightened without destroying its 
structural integrity. More specifically, a process has been devised for 
modifying the surface of the peat moss so that the undesirable color 
effect of the lignin is mitigated without removal of the lignim, thereby 
preserving the native structure of the peat moss. Not only is the native 
structure of the product preserved but it has also been discovered that 
the resulting product has increased wettability and at least comparable 
absorbency as compared to the untreated product. 
In accordance with this invention, peat moss is treated so as to chemically 
graft onto its structure unhydrolyzed polymeric chains of the general 
formula: 
##STR2## 
wherein R.sup.1 and R.sup.2 are selected from the group consisting of 
hydrogen and --CH.sub.3, X and Y are selected from the group consisting of 
--CN, --COONH.sub.2 and --OCH.sub.3 and wherein m and n are integers which 
when summed together equal at least 500. Preferably, the polymer chains 
are formed from monomers selected from the group consisting of 
acrylonitrile, acrylic acid, acrylamide and derivatives and mixtures 
thereof. 
It has been discovered that by undergoing this grafting treatment, the 
grafted peat moss can exhibit increases in brightness to values of more 
than 80 and preferably more than 85 units when measured on the Hunter C 
Scale (ASTM Test D2244) and that this is true even when starting with peat 
moss which has already undergone a brightening process such as, for 
example, the aforementioned bleaching process described in the above 
identified patent application Ser. No. 879,833 now U.S. Pat. No. 
4,170,515. Additionally, it has been discovered that this occurs without 
detrimental effects on absorbency or wettability. In fact, it has been 
found that wettability, as measured by the Drop Test described herein, 
will be substantially increased. Surprisingly, for reasons not yet 
understood, it has been discovered that if the grafting process used for 
peat moss includes a hydrolysis step such as has been employed in prior 
processes such as that described in U.S. Pat. No. 3,889,678, issued on 
June 17, 1975 to P. K. Chatterjee and R. F. Schwenker, Jr., then the 
advantageous brightening effect is totally lost and the resulting product 
has a permanent yellowish cast. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The starting peat moss is preferably that portion of a peat bog obtained 
from the top 30 cm depth and is of the Sphagnum type. While it is of 
course preferable to start with the most absorbent peat moss if the 
ultimate use is for absorbent products, this is not essential to the 
working of this invention. However, preferably the peat moss should be 
selected to have the capacity of holdingg at least 15 times its weight of 
water. 
The raw peat moss is screened to remove roots and branches. It has been 
found that the portion of the untreated peat moss which passes through a 
ten mesh screen and remains on a 100 mesh screen is the most absorbent. 
Accordingly, the preferred starting peat moss is screened to be from about 
0.15 mm (100 mesh) to about 1.8 mm. (10 mesh) in size. 
The starting native peat moss has a whiteness of about 50 to about 55 as 
measured on the Hunter Scale. It is therefore preferable to treat this 
starting material by bleaching the same prior to applying the teachings of 
this invention so that the highest degree of whiteness can be obtained. A 
suitable bleaching system now known in the art is described in the 
above-identified U.S. Pat. application Ser. No. 879,833 now U.S. Pat. No. 
4,170,515. In accordance with this process, screened peat moss is formed 
into a slurry of a pumpable consistancy and then treated with active 
chlorine in combination with an alkali metal or alkaline earth metal 
carbonate or hydroxide. The treatment is carried out at a pH of 7 or less. 
Preferably the treatment consists of treating the peat moss with calcium 
or sodium.carbonate or hydroxide while maintaining the pH at 7 followed by 
adding gaseous chlorine to the slurry along with sodium or calcium 
hypochlorite, again while maintaining the slurry at pH 7 or less. This 
treatment is followed by dewatering the slurry and then washing with acid 
to produce a bleached peat moss which has a whiteness value of up to about 
75 on the Hunter Scale. 
A preferable method of bleaching is to employ multiple steps in a bleaching 
sequence that includes first, chlorination using gaseous chlorine, then 
caustic extraction and finally, hypochlorite bleaching. By this method, 
peat moss having a whiteness of as high as 80 on the Hunter Scale may be 
obtained. 
Irrespective of how the starting peat moss is bleached, in accordance with 
this instant invention, the bleached peat moss is slurried in water and 
then washed in acid to remove undesirable cations such as calcium or 
sodium. The washed peat moss is then again slurried in water and monomer. 
In each case, the peat moss should be slurried in the minimum quantity of 
monomer required to insure a uniform dispersion and reaction. Generally, a 
slurry of preferably about 2%, by weight of solids ensures a good 
dispersion of the peat moss and an economical and efficient use of 
chemicals. 
The monomers added to the slurry from which the polymer chains are formed 
and grafted to the peat are all vinyl compounds having the general 
structure 
##STR3## 
wherein R is selected from the group consisting of --H, or --CH.sub.3 and 
Z is selected from the group consisting of --CN, --COOH, --COONH.sub.2, or 
--OCH.sub.3. Mixtures of these monomers may also be employed. Preferred 
monomers are those selected from the group consisting of acrylonitrile, 
acrylic acid, acrylamide or such derivatives of acrylonitrile such as 
ethyl acrylate, methyl methacrylate or mixtures of these such as 
acrylonitrile-ethyl acrylate or acrylonitrile-methyl methacrylate. 
While the detailed mechanism of polymerizing and grafting these monomers 
onto the peat moss is not fully known, it is believed that one possibility 
is that grafting and polymerization takes place through a free radical 
mechanism whereby the free radical is situated on the lignin covered peat 
moss surface which surface serves as a reducing agent and the polymeric 
chain attaches to this reducing agent through a carbon linkage to produce 
a grafted product. 
The grafting reaction may be initiated with an ionic initiator (e.g., 
alkali hydroxides), a cationic initiator (e.g., a Lewis acid such as boron 
trifluoride), or even radiation (e.g., ultraviolet, gamma, or 
X-radiation). It is preferred, however, that the polymerization and 
grafting be carried out by the free-radical copolymerization mechanism 
using a free radical initiator such as, for example, ceric ion, ferrous 
ion, cobaltic ion, cuprous ion, and the like. The ceric ion initiator is 
preferred. 
Because most free radical reactions are inhibited by the presence of 
oxygen, it is desirable to flush out essentially all the oxygen from the 
reaction mixture and reaction vessels by bubbling a non-oxidizing gas such 
as nitrogen, helium, argon, etc. through the system prior to the addition 
of the free radical initiator. It is also been found advantageous to add 
the free radical initiator after the monomers have been dispersed in the 
peat moss-water slurry. 
The pH range used for the reaction depends on the particular initiator 
used. One could employ anywhere from a highly acidic pH to a highly basic 
pH, depending on the particular initiator. For the preferred ceric ion 
initiator, the pH should be acid, i.e., less than seven, and preferably 
should be about 1 to about 3. 
The temperature of the reaction may be anywhere from room temperature 
(about 20-30.degree. C.) to the normal boiling point of the lowest boiling 
component of the reactive mixture. At elevated pressures, higher 
temperatures may be employed. The reaction mixture may also be cooled 
below room temperature if desired. 
The resulting product is a peat moss having the above-defined unhydrolyzed 
polymer chains grafted thereto, said grafted chains being present in a 
quantity of about 5 to about 100% of the weight of the original peat moss 
(on a bone dry peat moss basis). Brightness of the resulting product is 
increased to a value of more than 80 and preferably more than 85 units on 
the Hunter Scale. 
The wettability of the resulting product is substantially increased as 
measured by the Drop Test. The Drop Test represents the required time in 
seconds for a single drop of a 1%, by weight, sodium chloride water 
solution to be completely absorbed and disappear when dropped onto the 
flat and dry surface of a peat moss web. In the case of the peat moss of 
this invention, the wettability increased such that a drop disappears in 
less than one second. In fact the disappearance time is essentially 
instantaneous. 
Absorbency also increases slightly as measured by the following test: 
About 1 gram of the peat moss of this invention is dried at 105.degree. C. 
for one hour and is than immersed in a 1% by weight sodium chloride water 
solution for 5 minutes to assure complete saturation of the peat moss. Wet 
peat moss is then collected by filtering from the excess sodium chloride 
solution and is than weighted. The absorbency is expressed as the ratio of 
the wet weight of the peat moss to its dry weight. The product of this 
invention will exhibit an absorbency (weight ratio) of at least 10 and 
preferably at least 15 grams wet per gram dry. 
In commonly assigned U.S. Pat. Nos. 3,889,678 and 4,105,033, the grafting 
of hydrolyzed polymer chains onto wood pulp and starch are described as 
increasing the absorbency of these materials. It has been discovered that 
if these teachings are followed in the case of grafting to peat moss, the 
main object of this invention, namely, the increase in brightness is 
frustrated. While a highly absorbent product results, the effect of 
hydrolysis of grafted peat is disadvantageously to produce a yellow-like 
product having permanently reduced whiteness.

Having described embodiments of the process and product of the present 
invention, the following examples describe specific preferred embodiments. 
The illustrated experimental conditions are not intended to limit the 
scope of the present invention. As used in these examples, all percentages 
are by weight of aqueous slurry. 
EXAMPLE I 
One gram samples of peat moss, having been screened to pass through a 10 
mesh screen and remain on a 100 mesh screen are bleached to the brightness 
level of 80 on the Hunter Scale by the multistage bleaching process of 
chlorination, caustic extraction and hypochlorite treatment. The samples 
are each dispersed in a mixture of 25 ml of water and 15 ml of N 
hydrochloric acid for five minutes. The peat moss is then collected by 
filtration and transferred to 125 ml stoppered flasks. Various quantities 
of acrylonitrile monomer is added to each flask with an appropriate amount 
of nitric acid and water. The peat moss slurry is stirred for a few 
minutes to ensure good dispersion, and then various quantities of ceric 
ammonium nitrate in a nitric acid solution is added with continuous 
stirring for a few minutes. 
It is observed that the peat moss volume increases significantly in the 
first ten minutes of the reactions. The grafting is terminted after an 
hour, and the grafted peat is filtered, washed with water and dried. The 
percent add-on, based on bone dry peat moss, is calculated. 
It is found that the grafting only occurs in highly acidic conditions, and 
there is no grafting in neutral or basic slurries. It is also found that 
the percent of add-on increases with ceric ion concentration and with 
concentration of acrylonitrile. The following Table I summarizes the data 
obtained: 
TABLE I 
______________________________________ 
Effect of Ceric Concentration and Acrylonitrile 
Concentration on the Grafting of Acrylonitrile 
onto Peat Moss 
______________________________________ 
Ceric Ion (mmole/l) 
Sample (at 1.72% peat moss, 6.4% acrylonitrile) 
% Add-On 
______________________________________ 
1 4 10.7 
2 6 34.7 
3 8 52.6 
4 12 146.3 
5 16 263.9 
______________________________________ 
Acrylonitrile (%) 
Sample (at 1.72% peat, 10 mmole/l) 
% Add-On 
______________________________________ 
6 1.6 7.6 
7 3.2 16.8 
8 6.4 75.1 
9 12.8 96.7 
10 16.0 80.0 
______________________________________ 
The grafted polyacrylonitrile peat exhibits an exceptional bulkiness, an 
enhanced wettability (to the point of instantaneous absorption, i.e., 0 
second by drop test) and a surprising brightness and color stability and 
can absorb more than 18 times its own weight of 1% sodium chloride 
solution. 
EXAMPLE II 
Samples of one gram of peat moss, previously bleached by the chlorination, 
caustic extraction and hypochlorite sequence to a brightness level of 80 
on the Hunter Scale, are dispersed in a mixture of 25 ml of water and 15 
ml of hydrochloric acid normal for five minutes before being grafted with 
acrylic acid. The grafting is carried out in 125 ml stoppered flasks. 
Various amounts of water are first added to each flask and then various 
quantities of acrylic acid are introduced. The flasks are stoppered and 
shaken for a few minutes before the addition of ceric ammonium nitrate. 
After half an hour, the peat moss is collected and washed with water. 
It is found that grafted polyacrylic acid peat moss exhibits an 
instantaneous wettability even at very low percent add-ons. The peat moss 
bulkiness increases with the degree of grafting, and the percent add-on 
can be higher than 90% under nitrogen conditions. Grafted peat moss also 
shows a substantial gain in brightness and an absorption capacity as high 
as 21 times its own weight of aqueous solution. 
The following Table II summarizes some of the experimental conditions of 
the grafting of acrylic acid onto peat: 
TABLE II 
______________________________________ 
Grafting of Acrylic Acid onto Peat 
(Peat 1.8%, Acrylic Acid 8%) 
Sample Ceric (mmole/l) % Add-On 
______________________________________ 
1 4 1.62 
2 6 7.08 
3 8 8.50 
4 10 14.95 
5 12 31.75 
6 10(Nitrogen Condition) 
90.00 
______________________________________ 
EXAMPLE III 
A four gram sample of peat moss, bleached by the chlorination, caustic 
extraction and hypochlorite sequence, is first washed with 150 ml of 0.3 N 
hydrochloric acid and grafted with acrylamide. This is accomplished by 
placing the peat moss in a 500 ml flask with 100 ml of water and 10 g of 
the acrylamide and stirring the slurry for 5 minutes. 125 ml of ceric 
ammonium nitrate solution of 20 mmole per liter in nitric acid normal is 
added, and the reaction is carried out for two hours under nitrogen 
conditions. At the end of the reaction, the resulting grafted peat moss is 
filtered and washed with water. The grafted acrylamide peat moss is 
exceptionally bright and hydrophylic. The peat moss is highly bulky 
possesses an absorbency of above 25 times its own weight of 1% sodium 
chloride solution, and can be wetted instantaneously.