Method for the dry cationization of galactomannans (II)

A method is disclosed for the dry cationization of galactomannans by means of reaction with alkylene epoxides in an alkaline medium in the presence of water at 5.degree. to 60.degree. and in the presence of a finely divided, hydrophilic silica.

INTRODUCTION AND BACKGROUND 
The present invention relates to a dry method for the preparation of 
cationic galactomannans by means of reaction with alkylene epoxides in the 
presence of water in an alkaline medium. 
Galactomannans are an important group of vegetable hydrocolloids which 
occur as reserve carbohydrates, analogous to starch, especially in the 
seed endosperm of many Leguminosae (legumes). However, only guaran (guar 
gum) and carubin (fine carob [Saint John's bread] flour) are of practical 
industrial significance. Guaran occurs in the endosperm of guar beans 
(Cyamopsis tetragonoloba L.), which belong to the order of Leguminosae, 
family Papilionaceae. Guar is an old cultivated plant which is cultivated 
today especially in India, Pakistan and Texas on a large scale. 
Guaran contains 64% mannose and 36% galactose. The mannose structural 
elements linked in a beta-(1,4)-glycosidic bond form long, unbranched 
chains to which individual galactose molecules are attached in 
alpha-(1,6)-bonds. Both mannose as well as galactose are present in 
pyranose form. The average molecular weight of guaran is around 220000. 
Guaran is soluble in cold water. 
Native and modified galactomannans based on fine guar flours and fine carob 
flours are used industrially today in many different areas, e.g. in the 
petroleum, textile, paper, food, pharmaceutical, cosmetic and explosives 
industries as well as in mining and in water treatment. The native 
galactomannans have been known for years in the manufacture of paper as a 
"wet end additive" for increasing paper strengths. As a result of 
modification, the properties of the products can be reinforced or products 
with completely new properties can be created. 
In order to improve the natural affinity of galactomannans for cellulose 
and thus be able to achieve a better retention of the fine fibers, there 
is the possibility of cationizing galactomannans. 
European Pat. No. A0 146 911 discloses a method in which 
2,3-epoxypropyltrimethyl ammonium chloride is reacted in an alkaline, 
aqueous medium at 52.degree. C. 
According to European Pat. No. A0 130 946, this reaction is likewise 
performed in an alkaline medium which, however, contains sodium 
tetraborate in addition and is partially neutralized by acetic acid before 
the addition of the cationizing reagent. 
Great Britian Pat. No. 1,136,842 contains more precise data about products 
like those obtained in the reaction of 2,3-epoxypropyltrimethyl ammonium 
chloride with galactomannans in an alkaline, aqueous medium. 
According to these publications, the cationized product must be dried, then 
ground and sieved before further usage. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method for the 
preparation of cationized galactomannans in which agitating energy is 
expended only briefly and the cationized galactomannans can be utilized 
without additional aftertreatment (sieving, drying, etc.). 
In attaining this and other objects of the invention, a feature of the 
invention resides in a method for the dry cationization by means of 
reaction of galactomannans with alkylene epoxides in an alkaline medium in 
the presence of water the reaction is carried out at 5.degree. to 
60.degree. C. in the presence of a fine, hydrophilic silica and an 
alkaline material selected from the group consisting of alkali metal 
silicates and/or alkali metal aluminates or of a mixture of alkali metal 
hydroxides or oxides or alkaline earth metal hydroxides or oxides and 
alkali metal carbonates or of a mixture of one or more of these 
hydroxides, oxides or carbonates with an alkali metal silicate and/or 
alkali metal aluminate. 
The pH of a galactomannan modified in this manner is equal to, or greater 
than, 9 (1% by weight solution). 
DETAILED DESCRIPTION OF THE INVENTION 
Native or modified galactomannans or substances of any origin containing 
galactomannans can be used for the preparation of cationic galactomannans 
according to the method of the invention. Native fine guar flour is used 
with particular advantage. 
The etherification of the of the galactomannans is performed according to 
the invention with alkylene epoxides known in the art of the general 
formula 
##STR1## 
in which n is a number from 1 to 3 and R.sub.1, R.sub.2 and R.sub.3 
signify the same or different alkyl groups with 1 to 4 carbon atoms or 
R.sub.1 is benzyl and X.sup..crclbar. signifies chloride, bromide, 
sulfate or acetate. 2,3-epoxypropyltrimethyl ammonium chloride is 
preferred. 
A variant of the method of the invention can be carried out by allowing the 
reaction with the above-mentioned epoxides to occur in the presence of 0.5 
to 5% by wt. of a compound which corresponds to one of the following 
formulas: 
##STR2## 
These compounds are preferably used in a mixture with the epoxides 
according to formulas (I) or (II) and can also be present therein in the 
form of the associated chlorohydrins. 
The conversion to the epoxides corresponding to formulas (III) to (v), 
which react with the galactomannans, then occurs at the latest in the 
reaction medium. Mixtures of this type are prepared with advantage by 
using the amounts of the corresponding tertiary amines necessary for 
forming the portions of the epoxides specified in accordance with the 
invention with formulas (III) to (Y) in the preparation of the epoxides 
with formulas (I) and (II), as is described e.g. in U.S. Pat. No. 
3,135,782. 
These epoxides or chlorohydrins can also be separately prepared and mixed 
with the epoxides according to formulas (I) or (II) in the specified 
proportion. 
It is generally advantageous to use approximately 0.005 to 0.5 mole 
epoxide, preferably 0.05 to 0.30 mole epoxide, per mole galactomannan, 
calculated as anhydroglucose unit (molar mass 162.15) in the dry 
substance. 
The specific surfaces of the finely divided silicas used are between 60 and 
700 m.sup.2 /g preferably 100 and 450 m.sup.2 /g (BET measurement 
according to DIN 66131, N2 adsorption at the temperature of liquid 
nitrogen, preceding heating of the specimen at 110.degree. C.). These 
products are known in the art. 
These silicas are used in an amount of 0.1 to 3.0, preferably 1.0 to 2.0% 
by wt. in relation to the galactomannan (bone-dry). 
It is preferable to use hydrophilic, precipitated silicas with a specific 
surface of 190 to 450 m.sup.2 /g especially a spray-dried, precipitated 
silicic acid with a specific surface of 190 m.sup.2 /g. 
According to the invention, the reaction mixture contains the alkaline 
acting substance(s) mentioned above especially an alkali metal 
metasilicate and/or alkali metal aluminate, in an amount of amount of 0.5 
to 8.0% by wt., especially 1.5 to 4.5% by wt., and 10 to 60% by wt., 
preferably 20 to 30% by wt. water, all values in relation to the amount of 
galactomannan (bone-dry) added. 
Mixtures of alkali metal hydroxides or oxides or alkaline earth metal 
hydroxides or oxides and alkali metal carbonates can also be used. 
Mixtures of one or more of these oxides, hydroxides or carbonates with an 
alkali metal silicate and/or alkali metal aluminate are also suitable 
The term "alkali" as used herein signifies in particular sodium or 
potassium, and the term "alkaline earth metal" in particular signifies 
calcium. 
Sodium metasilicate is used in particular as the silicate. 
In an especially suitable embodiment the alkaline acting substance is used 
in the combined form of a powdery mixture with finely divided, hydrophilic 
silica. This combination is called "activator" in the following text. 
The activator consists of 10 to 50% silica and 90 to 50% by wt. of these 
alkaline substances. 
The following procedure is used in accordance with the invention: The 
mixture of galactomannan, alkaline acting substance(s), silica and 
alkylene epoxide, which is generally added as aqueous solution, is 
homogenized in an intensive, high-efficiency, mixer. 
The epoxide solution is finely distributed with advantage and added to, 
preferably sprayed onto the galactomannan present in commercial form with 
a water content of approximately 7 to 15% by wt. 
The alkaline acting substance(s) and the silica can be added to the 
galactomannan either before or after. 
The powdery activator is preferably mixed with the galactomannan before the 
addition of the epoxide solution. The epoxide solution and the alkaline 
component can also be added simultaneously into the mixing unit. 
The mixture which accumulates during the preparation of the epoxide by 
means of reacting the corresponding halohydrin with alkaline acting 
substances such as e.g. alkali metal hydroxide can be used immediately if 
the alkali halogenide produced thereby in the final product is not 
susceptible of creating a risk of corrosion. The latter product so 
obtained is neither washed nor neutralized and can be used directly. 
The cationization reaction can be performed either in a mixing unit or also 
after homogenization outside of the mixing unit, in a storage silo or in 
the appropriate packages provided for shipment. 
If the reaction is to take place in a mixing unit, yields of 40-60% are 
achieved after 6 to 24 hours at 30.degree. to 60.degree. C. 
However, the preferred embodiment proceeds as follows: The reaction mixture 
is homogenized at 5.degree. to 40.degree. C. in an intensive mixer within 
10 seconds to 25 minutes, then removed and the cationization reaction is 
allowed to proceed to the end in the provided storage container such as 
e.g. a silo at the same temperatures. 
It has proven to be advantageous in this instance to preferably carry out 
the reaction under ambient temperature conditions in the manufacturing 
plant which may fluctuate as a function of seasonal variations; that is, 
from 18.degree. to 30.degree. C. especially 20.degree. to 25.degree. C. 
The cationic galactomannans prepared in accordance with the method of the 
invention are generally present as a finely divided, dry powder and can be 
directly used after the reaction. 
Especially suitable intensive mixers are e.g. plowshare mixers with one or 
more knife heads for discontinuous and continuous operation or humidifying 
flow mixers especially for continuous operation. This equipment is known 
in the art. 
Thus, additional reaction containers are superfluous according to the 
invention since, after the intensive mixing, the reaction mixture can be 
filled into the packages provided for shipment or into a storage silo and 
there react to completion. 
The brief dwell time in the mixing unit makes possible at the same time for 
the dry cationization to be performed in a continuous manner. This is 
contrasted with the state of the art where only a batchwise cationization 
was considered feasible due to the long mixing times. 
The cationic galactomannans prepared in accordance with the invention are 
suitable for use in the petroleum, textile, pharmacological, cosmetics and 
explosives industries as well as in mining and in water treatment. 
The use of cationic galactomannans (primarily guar) in the paper industry 
has proven to be especially advantageous. Bursting pressure, tearing 
strength, layer resistance, retention, page formation and the distribution 
of fibers in the manufacture of paper are positively influenced. 
In contrast to native guar, cationic guar disperses better and has less of 
a tendency to cause dewatering problems on a sieve. Also, the material is 
easier to grind during the manufacture of paper if cationic guar is added. 
Cationic guar is also suitable as auxiliary dewatering agent and drying 
accelerator. 
The following activator types were used for the cationization of guar 
(guaran). 
TABLE 1 
______________________________________ 
Activator mixtures 
Composition 
Type (% by weight) 
______________________________________ 
PC-#01 69.45% sodium metasilicate 
30.55% silica 
(spray-dried silica; 190 m.sup.2 /g) 
PC-#02 40.30% sodium metasilicate 
24.25% calcium hydroxide 
35.45% silica 
PC-#03 72.12% sodium aluminate 
27.88% silica 
PC-#04 33.14% sodium metasilicate 
37.70% sodium aluminate 
29.16% silica 
PC-#05 43.44% sodium aluminate 
22.97% calcium hydroxide 
33.59% silica 
______________________________________ 
A spray-dried, hydrophilic silica with 190 m.sup.2 /g spec. surface (BET) 
was used as silica in all examples.

EXAMPLES 
1000 g (5.551 moles) native guar flour (moisture content 10.0%, insoluble 
nitrogen content 0.477%) was intensively mixed (plowshare mixer) in each 
instance for 5 min. with the indicated activator and the reagent solution, 
which contained 210.42 g (corresponding to a theoretical DS of 0.250) 
2,3-epoxypropyltrimethyl ammonium chloride in each instance, was sprayed 
on within 3 min. with the mixer running. 
After a further 15 min. mixing time, the reaction material was packed into 
polyethylene bags and analyzed after 4 days storage time. Mixing and 
storage were performed at room temperature (20.degree. C.). The yield and 
the degree of substitution (DS) were determined by nitrogen determination 
according to Kjeldahl on the washed-out product. 
Wash solution: iso-propanol/water (60:40% by wt.). 
TABLE 2 
______________________________________ 
Activator Reagent solution 
No. Type Amount Amount pract. DS Yield 
______________________________________ 
1 PC-#01 46.89 g 472.66 g 
0.1188 47.5% 
2 PC-#02 40.77 g 472.85 g 
0.0710 28.4% 
3 PC-#04 51.12 g 471.91 g 
0.1064 42.6% 
4 PC-#05 48.96 g 473.25 g 
0.1110 44.4% 
5 PC-#06 42.93 g 47l.52 g 
0.0785 31.4% 
______________________________________ 
The composition of the metasilicate used is: 48.+-.1% SiO.sub.2, 51.0.+-.1% 
Na.sub.2 O, and that of the aluminate: 52-55% Al.sub.2 O.sub.3, 37-39% 
Na.sub.2 O. 
Further variations and modifications of the foregoing will be apparent from 
the foregoing and are intended to be encompassed by the claims appended 
hereto. 
German priority application No. P 37 26 984.4 is relied on and incorporated 
herein.