Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B11/00—Preparation of cellulose ethers
  • C08B11/02—Alkyl or cycloalkyl ethers
  • C08B11/04—Alkyl or cycloalkyl ethers with substituted hydrocarbon radicals
  • C08B11/08—Alkyl or cycloalkyl ethers with substituted hydrocarbon radicals with hydroxylated hydrocarbon radicals; Esters, ethers, or acetals thereof

Definitions

• the present invention relates to a process for preparing cellulose ethers having an enhanced resistance to breakdown by biological agents such as enzymes and the like.
• the invention relates to a two step process for making bioresistant cellulose ethers which have a relatively low molar substitution (MS) level relative to those bioresistant cellulose ethers of the prior art.
• MS molar substitution
• Cellulose ethers are widely used as thickeners in a range of industrial applications, for example latex paints and the like.
• the cellulose ether is susceptible over a long period of time to breakdown by biological agents. Breakdown of the cellulose ether results, in the case of paints, in an overall decrease in viscosity and hence a deterioration in the coating properties of the paint.
• the paint loses its ability to cover any surface to which it is applied, has a greater tendency to drip or run and can undergo irreversible pigment sedimentation during storage.
• Cellulose ethers are usually prepared from a cellulose source, e.g. wood cellulose or cotton cellulose, by a process which consists of (1) reacting the cellulose with aqueous alkali, e.g. sodium hydroxide, in a solvent to prepare an alkali cellulose intermediate and then (2) treating the alkali cellulose with an etherifying agent such as an alkylene oxide to produce a water soluble hydroxy functionalised cellulose ether.
• a cellulose source e.g. wood cellulose or cotton cellulose
• MS value defines the number of molecules of alkylene oxide which have reacted with each anhydro-glucose unit in the cellulose. In general terms the higher the MS value the better the solution properties of the cellulose ether although this had to be balanced against the cost of using larger amounts of the alkylene oxide.
• the cellulose ether is a hydroxy ethyl cellulose (HEC)
• HEC hydroxy ethyl cellulose
• a two stage process has now been devised which produces a cellulose ether having good bioresistance and good solution properties at MS values of less than 3.6 and will produce a product having such properties at an MS value in the range 1.6 to 3.0.
• the process involves adding a boron containing compound in the first stage of the process.
• the present invention provides a process for the production of a cellulose ether which process comprises (1) in a first stage reacting cellulose with an alkali metal hydroxide and an etherifying agent to produce an intermediate product comprising a cellulose ether having an MS value in the range 0.6 to about 1.3 and (2) in a second stage reacting the intermediate product with further or residual alkali metal hydroxide and etherifying agent, to produce a cellulose ether having an MS value in the range 1.6 to 3.0 characterised in that in the first stage a boron containing compound is added.
• the alkali metal hydroxide used in the process is preferably sodium hydroxide, lithium hydroxide, potassium hydroxide or a mixture thereof.
• the etherifying agent is preferably a compound which is able to produce a hydroxyalkyl cellulose ether on reaction with the alkali cellulose.
• the etherifying agent is an alkylene oxide, preferably a lower alkylene oxide such as ethylene oxide, propylene oxide or one of the butylene oxides. Most preferably the lower alkylene oxide used is ethylene oxide.
• this can be any convenient natural source of cellulose such as purified wood, cotton linters, jute, hemp, sisal and the like.
• any boron containing compound which is soluble in the first stage reaction medium can be used, it is preferable to use boric acid, a borate salt, for example borax, or an oxide of boron or a lower alkyl ester of boric acid e.g. trimethyl borate. It will be appreciated by those skilled in the art that in most cases the boron containing compound will be converted in the first stage reaction medium into the corresponding borate salt. Hence usually the cheapest source of boron will be used by those operating such a process.
• the boron containing compound may be added either directly to the first stage reaction medium, or it may be introduced with one or more of the other reactants. For example In some cases it is convenient to dissolve the boron containing compound in the aqueous solution of alkali metal hydroxide and introduce it in this way.
• the boron containing compound is suitably added so that the weight ratio of the boron containing compound to cellulose In the first stage is In the range 0.002 to 0.3. The preferred range is 0.02 to 0.2.
• the first stage of the process can be carried out for example as described in GB 688,486 with the exception that the boron containing compound is added.
• the reaction mixture can take the form of a paste or a slurry depending on the solvent to cellulose ratio. If a solvent is used it is preferably a lower aliphatic alcohol such as isopropanol or tertiary butanol.
• the first stage is preferably operated at a temperature in the range 15 to 100°C.
• the cellulose is converted into an intermediate cellulose ether having an MS value in the range 0.6 to 1.3 via an alkali cellulose.
• the reaction mixture can either be neutralised (partially or completely) with acetic acid and then fed to the second stage or it can be purified.
• This purification can be achieved by, for example, neutralising the first stage product with acetic acid and subsequently washing it with a polar solvent to extract the boron.
• the first stage product is contacted with further or residual alkali metal hydroxide, further alkylene oxide and solvent, to produce a cellulose ther having an MS value in the range 1.6 to 3.0 preferably 1.8 to 2.6.
• the conditions used are similar to those used for the first stage but preferably with a lower alkali: cellulose ratio (0.05-0.15).
• the final cellulose ether product is separated from the reaction mixture and purified. The invention is illustrated by the following examples.
• a bioresistant hydroxyethyl cellulose was prepared using a two step process under slurry conditions, (a) Stage 1

Landscapes

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

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• 1987
  • 1987-03-14 GB GB878706120A patent/GB8706120D0/en active Pending
• 1988
  • 1988-03-03 EP EP19880902132 patent/EP0304454A1/en not_active Withdrawn
  • 1988-03-03 JP JP63502202A patent/JPH0643442B2/ja not_active Expired - Lifetime
  • 1988-03-03 BR BR888806039A patent/BR8806039A/pt unknown
  • 1988-03-03 WO PCT/EP1988/000160 patent/WO1988007059A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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