Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
  • C08B15/02—Oxycellulose; Hydrocellulose; Cellulosehydrate, e.g. microcrystalline cellulose
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B31/00—Preparation of derivatives of starch
  • C08B31/18—Oxidised starch

Definitions

• the present invention relates to a process for reducing the viscosity of polysaccharides, especially starch, by oxidativc degradation without metal catalysts.
• Starch is economically relevant both as a foodstuff and for non-food applications. Worldwide the annual starch production is about 26 million tons.
• One of the largest non-food users of starch derivatives is the paper industry. In this field starch solutions with high starch content (25 wt.%) and low viscosities are much desired.
• Important features of starch derivatives arc an improved initial wet strength of the paper sheet, a better printability, a better retention of cationic additives and applicability as glue. The demand for these starch derivatives is several million tons a year.
• Starch has to be subjected to a viscosity-reducing treatment, before it can be used on an industrial scale.
• the starch is generally treated oxidatively in an alkaline medium at increased temperature (40-60°C). This treatment takes 4-15 hours at about 60°C, for example in case hypochlorite is used as an oxidising agent together with sulphuric acid or phosphoric acid.
• Disadvantages of this method are the amount of salt produced in addition to chlorine-containing derivatives, and a high proportion of short chain starch molecules.
• the peroxysulphuric acid has to be prepared in situ from hydrogen peroxide and sulphuric acid, or else a salt of the acid has to be used, which has the disadvantage of generating salts as byproducts.
• the reactivity of pcracetic acid is lower and results in longer reaction times.
• An ob)ect of the im cntion is to ⁇ dc a piocess for reducing the v iscosity of starch and other polysaccharides with simple means, without the use of heav ⁇ metals and salt-producing agents, and without oiganic -product It is also an object to prov ide a v iscosity-ieducmg pioccss which allows the starch granule to remain intact, for easier working, di ving and handling of the product
• This object is achiev ed b ⁇ means of a pioccss whcicin the polysacchande is oxidised using hydrogen peroxide in the picscncc of an acv latcd poly sacchande as an activator
• any wholh of partially watci -soluble poh saccha ⁇ dc can be used These comprise firstly starch (c.g potato, corn. wa ⁇ v maize, tapioca, wheat, ⁇ cc and other starches) and fractions and deriv ativ es thcicof. such as aim lose, floe gels, ethox latcd starch and carboxymeth l starch Furthci moic.
• the solubilitv of cellulose deriv ativ es and inulm and deriv ati es thereof and pentosans such as w lans can be impro ed or their viscosity can be reduced with the process of the inv ention
• Carbohydrate deriv atives such as N-acylated, carbox latcd, carbow methylated, alkv latcd, hv droxyalkylatcd, hydrogenated and dehydrogenated dci n ativ es can also be treated according to the ention
• the acylated carbohydiatc used as a catah st can be any oligo- or poly ⁇ sacchande which is wholh or pai tiallv acv latcd It was found that only a small amount of acylated carbohy drate is ncccssai v to cnsuic an efficient reaction It is often sufficient if for each 700 anl diogkicosc (oi othci monosaccharide) units, one acylated monosaccharide unit is picscnt Picfciahh at least one and especially at least four monoacv latcd monosacchandc units ai c picscnt for each 100 units In particular an av erage of 0 06-0 2 acv latcd monosacchandc units is present m the total of non-acylated and acylated polysaccharidc.
• acylated comprises alkanoylatcd (formylated, acetylatcd, propionylatcd, etc.), bcnzoylated, sulphatated, phosphory latcd etc..
• the acylated carbohydrate can simply be obtained by treatment of a carbo- hydrate with an acylating agent such as acetic anhydride using standard methods.
• acylated carbohydrates are commcrciallv available, such as acetyl starch having a DS of about 2.5% or 8%.
• An advantage of the use of an acylated carbohydrate is that the oxidation reaction proceeds smoothly and no undesired by-products arc formed; the acylated polysaccharidc or its oxidation product can be part of the treated polysaccharidc product without any inconvenience.
• the acylated carbohydrate can advantageously be a derivative of the same carbohydrate to be treated.
• the treatment of starch can suitable be performed using acetylated starch as the activator.
• the acv latcd carbohydrate can be prepared in situ, e.g. by acylation with the corresponding carboxylic anhydride at pH 8-9.5 in a concentrated solution or suspension of the carbohydrate. The acylation may then be followed by the oxidation, but oxidation may also be started during acylation.
• the amount of hydrogen peroxide to be used is entirely dependent on the desired degree of oxidation.
• An amount of 1 wt.% is sufficient in general for achieving an effective viscosity degree.
• the hydrogen peroxide can be added at once, but it has been found that better products arc obtained when the hydrogen peroxide is added gradually or in portions, for example over a period from 5 minutes to 3 hours.
• the reaction can be performed at room temperature, but preferably at increased temperature, generally from 20 to 90°C. in particular from 40°C to 5°C below the pasting temperature, which pasting temperature is at about 65°C for most starch types. This results in a viscosity-reduced product still having a granular structure.
• the reaction time is from several minutes to several hours at that temperature, depending on the particular polysaccharidc and the desired degree of viscosity reduction.
• the polysaccharidc is preferably treated at a relatively high concentration. such as 10-55 wt.%, in particular 33-50 % by weight.
• the treatment is carried out under neutral to alkaline conditions, i.e. at a pH between 5 and 12, especially between 8 and 11, in particular between 9 and 1 1 .
• the treatment can advantageously be carried out in two or more stages, i.e. addition of peroxide at neutral pH (5-8.5) and subsequent reaction at alkaline pH (8.5-1 1 ).
• the acylation can be performed under slightly alkaline conditions (pH 7.5-9.5), during or after acylation peroxide is added with some pH decrease (e.g. pH 6-8.5) and oxidation is completed at higher pH (8.5-11 ).
• the product obtained by the process of the invention is essentially free of chlorine (as salt or covalcntly bound), i.e. not abov e natural abundance ( ⁇ 20 ppm) and of transition metals.
• the carboxyl content is preferably between 0.2 and 5, especially between 0.5 and 3 wt.%.
• the viscosity is preferably below 4000 Brabender units (at 25 w.t% dry substance and at 40°C) and in particular below 1000 Brabender units.
• Viskograph E The results arc given below in Brabender units at 40°C; V" means viscosity at 5 wt.%.
• Table 1 summarises the results of the product after 3 hours and after 6 hours. The result of the treatment using only hydrogen peroxide after 3 hours is also given for comparison.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Biochemistry (AREA)
• Materials Engineering (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Polysaccharides And Polysaccharide Derivatives (AREA)
• Cosmetics (AREA)
• Paper (AREA)
• Medicinal Preparation (AREA)

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• 1996
  • 1996-02-29 NL NL1002494A patent/NL1002494C2/nl not_active IP Right Cessation
• 1997
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  • 1997-02-28 CA CA002247109A patent/CA2247109A1/en not_active Abandoned
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• 1998
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