Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2000-11-08
2003-10-21
Wilson, James O. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S018700, C536S030000, C536S045000, C536S047000, C536S055100
Reexamination Certificate
active
06635755
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to oxidized polymeric carbohydrates and products made thereof. The invention particularly relates to oxidized cellulosic fibrous materials and polysaccharides such as starch.
The cellulosic fibrous material, which is usually known as pulp and which can be used as a starting material in accordance with an embodiment of the invention, is normally used to make paper or nonwoven products. It is mainly composed of cellulose that is obtained from plant cells and that may more or less contain a number of accompanying substances.
The accompanying substances may relate e.g. to lignin, which—in addition to cellulose—represents a main component in lignified plant cells.
In the case of chemical pulping processes, however, the lignin may be dissolved in an approximately quantitative manner, whereby cellulose and, depending on the pulping process, also hemicelluloses are left behind. As an industrial product that is obtained from lignified plant parts by means of chemical pulping, cellulose is generally referred to as pulp. Cellulose also occurs in a purer form, e.g. in cotton or linters. Usually just purification or removal of fats and waxes is needed to recover the cellulose, because these plant fibers contain next to no lignin.
A paper of an untreated cellulose-containing fibrous material usually loses 95% to 97% of its dry strength when saturated with water, so that it normally cannot be used in the moistened or wet states. This is due to the fact that paper products to an extent develop a dry strength as a result of inter-fiber hydrogen bonds. If the paper product is moistened, the water breaks up the hydrogen bonds and therefore reduces the strength of the paper product.
There are two important techniques for increasing the wet strength of paper products that have already been in use for some time. One technique prevents the water from reaching and breaking up the hydrogen bonds, e.g. by coating the paper product with a water-repellent material. The second approach is to provide the paper product with additives or reagents that promote the formation of inter-fiber bonds.
To increase the wet strength according to the first technique, poly(ethylene imines), polyamide epichlorohydrin resins and urea or melamine formaldehyde condensates are for example used as wet-strength agents. The use of such synthetic resins results in permanent wet strength. On the other hand, however, enhanced wet strength can also be achieved by addition of water-soluble starches or starch derivatives. This effect is nevertheless only temporary and decreases as soon as the starch derivative dissolves. Apart from the aforementioned additives, modified soluble cellulose derivatives are used as wet-strength agents. In this way, for example, the addition of carboxymethyl cellulose is usual as an additive besides the aforementioned polyamide epichlorohydrin resins.
DESCRIPTION OF THE RELATED ART
To bond cellulose fibers together according to the second technique, thereby increasing the strength, U.S. Pat. No. 5,873,979 teaches the reaction of the cellulose's hydroxy functions with a C2-C9 dicarboxylic acid.
Modified techniques for increasing the strength of paper in the wet state are taught in the following applications filed by the Procter & Gamble Company: WO 97/36051, WO 97/36053, WO 97/36037, WO 97/36054 and WO 97/36052.
WO 97/36051 describes paper that exhibits a temporary wet strength and which is obtained by linking a polyhydroxy polymer (e.g. cellulose) to 1,2-disubstituted alkene carboxylic acid, oxidative cleavage of the double bond of the alkene carboxylic acid into aldehyde functions and crosslinking the hydroxy groups of the polyhydroxy polymer with the aldehyde functions.
WO 97/36053 describes a paper product exhibiting temporary wet strength and comprising (a) cellulosic fibers and (b) a binder which has (b-i) a polyaldehyde polymer and (b-ii) a water-soluble polysaccharide with cis-OH groups.
WO 97/36037 describes the aldehyde-modified cellulosic fibers upon which the paper product according to WO 97/36051 is based.
WO 97/36054 discloses a compound that bestows temporary wet strength on paper products and which comprises the ozone oxidation product (containing aldehyde groups) of a polysaccharide in which the OH groups in at least one recurrent unit of the polysaccharide are OH groups in cis position. This document also describes a paper product that comprises cellulosic fibers in combination with the above compound and a method of producing the compounds of the paper product.
WO 97/36052 describes a paper product exhibiting initial wet strength and comprising
(a) cellulosic fibers having free aldehyde groups originating from cellulosic fibers that include a polysaccharide (preferably galactose and/or mannose) in which the OH groups of least a part of the recurrent units are OH groups in cis position, in combination with
(b) a water-soluble polymer having functional groups that can react with the aldehyde groups.
Since cellulose exhibits OH groups in trans position, it is not meant with the polysaccharide defined under item (a) and the hemicellulose portion of pulps that have a high proportion of hemicellulose is to be oxidized and the oxidation product used as a “binder”. Hemicelluloses are derived from (poly)saccharides with OH groups in cis position (e.g. galactose, mannose) that can be rapidly oxidized into aldehyde groups and which can then form (hemi)acetal bonds in accordance with the teaching of this document, such bonds holding the paper product together.
Oxidized starch is known in addition to oxidized cellulose products. For instance, DE-A-197 46 805 discloses a starch that is oxidized at the C6 carbon atom of the glucose units, and discloses its use as a super-absorber, as a seed and fertilizer carrier, as a soil ameliorant, as a material in galenics or as an adhesive and binder. According to U.S. Pat. No. 3,137,588, a starch that contains COOH groups can be obtained by hypochlorite oxidation. After crosslinkage with a metal (Zr, Ti), this produces a water-insoluble coating of cellulosic tissue.
DE-A-1,241,433 and DE-A-1,211,142 both disclose dialdehyde polysaccharides such as dialdehyde starch or cellulose containing aldehyde functions at C2 and C3.
BRIEF SUMMARY OF THE INVENTION
The invention's object is to improve the strength of carbohydrate networks.
This object is solved by a polymeric carbohydrate with functional groups, these groups relating to aldehyde groups formed at positions C2 and/or C3 as well as at position C6 (corresponding to FIG. 1) of the anhydroglucose units of the polysaccharide chain, as well as by paper and nonwoven (products) obtained thereform such as tissue (products).
DETAILED DESCRIPTION OF THE INVENTION
Oxidized Polysaccharide or Polysaccharide-Based Material
The oxidized polysaccharide or polysaccharide-based material of the invention comprises aldehyde groups formed at positions C2 and/or C3 as well as at position C6 of the anhydroglucose units of the polysaccharide chain.
With the term “polysaccharide” it is meant a pure carbohydrate, such as starch or cellulose, whereas “polysaccharide-based material” refers to materials containing a polysaccharide as major component, such as pulp, the major component of which is &agr;-cellulose. Hereinafter both alternatives will be meant, if not stated otherwise, when using the wording “polysaccharide”.
The wording “polysaccharide” further is intended to distinguish the claimed carbohydrates from oligosaccharides which are typically obtained by condensation of 2 to about 7 monosaccharide units.
According to a preferred embodiment the polysaccharide comprises aldehyde groups at positions C2, C3 and C6 of at least some anhydroglucose units of the polysaccharide chain.
These aldehyde groups are obtained by complete or partial oxidation of the primary and/or secondary hydroxyl groups of the anhydroglucose units so as to produce a polymeric carbohydrate that may also exhibit trialdehyde anhydroglucose units.
In a preferred embodiment, a partial oxidation has taken place ra
Besemer Arie Cornelis
Bragd Petter
Gunnars Susanna
Jaschinski Thomas
Lewis Patrick
SCA Hygiene Products GmbH
Young & Thompson
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