Process for preparing a spinnable, isotropic cellulose solution

Details Process for preparing a spinnable, isotropic cellulose solution Process for preparing a spinnable, isotropic cellulose solution

1998-08-06

2000-10-31

Lee, Howard C.

Organic compounds -- part of the class 532-570 series

Organic compounds

Carbohydrates or derivatives

536124, C08B 500

Patent

active

061404977

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention pertains to a process for preparing an isotropic, spinnable solution 94-100 wt. % of which is composed of the following constituents:
2. Descriscption of Related Art
Such a process is known from GB patent publication 263 810, which describes the dissolution of linters cellulose in 85-90% H.sub.3 PO.sub.4. The dissolution of cellulose can be facilitated by adding other reagents, such as glacial acetic acid and ethanol or homologues thereof. The overall time needed to obtain a homogeneous solution amounts to several hours. The solution can be used, e.g., for spinning artificial silk.
The process is also known from SU 1348396 and SU 1397456. In these publications various examples are provided of the dissolution of cellulose in 80-85% H.sub.3 PO.sub.4. These publications show that the dissolving process takes up to several hours (or a multiple thereof) and that during the process there may be a substantial decrease of the degree of polymerization (DP) of the cellulose. The solutions can be used to make fibres or films.


SUMMARY OF THE INVENTION

Surprisingly, a simple process has now been found by means of which a homogeneous, spinnable, isotropic cellulose solution can be obtained. The invention consists in that a solution of cellulose is obtained by adding water before, during or after the dissolving of the cellulose in a 72-85 wt. % of P.sub.2 O.sub.5 containing solvent, calculated on the overall quantity by weight of water, phosphoric acid, and the anhydrides thereof at the time before any extra water had been added.
A solution is considered to be isotropic when in a state of rest at room temperature it is not birefringent.
A spinnable solution is a solution which is suitable for being converted into fibres or filaments through extrusion, coagulation, and winding.
The term phosphoric acid in this patent application refers to all inorganic acids of phosphorus and their mixtures. Orthophosphoric acid is the acid of pentavalent phosphorus, i.e. H.sub.3 PO.sub.4. Its anhydrous equivalent, i.e. the anhydride, is phosphorus pentoxide (P.sub.2 O.sub.5). In addition to orthophosphoric acid and phosphorus pentoxide there is, depending on the quantity of water in the system, a series of acids of pentavalent phosphorus with a water-binding capacity in between those of phosphorus pentoxide and orthophosphoric acid, such as polyphosphoric acid (H.sub.6 P.sub.4 O.sub.13, PPA).
The phosphorus content of the solvent is determined by converting the quantity by weight of phosphoric acid in the solvent into the equivalent quantity by weight of the accompanying anhydride and residual water. Thus converted, orthophosphoric acid is composed of 72.4 wt. % of phosphorus pentoxide and residual water, and H.sub.6 P.sub.4 O.sub.13 is composed of 84 wt. % of phosphorus pentoxide and residual water.
The weight percentage of phosphorus pentoxide in the solvent is calculated by starting from the overall quantity by weight of phosphoric acid including its anhydrides and the total quantity of water in the solvent, converting the acids into phosphorus pentoxide and water, and calculating the percentage of said overall quantity by weight made up by phosphorus pentoxide.
In this description water derived from cellulose or from substances which are part of the other constituents and water which is added to obtain the solution are not included in the calculation of the concentration of phosphorus pentoxide in the solvent.
In order to effect more rapid dissolution of the cellulose, the solvent preferably contains 72-80 wt. % of phosphorus pentoxide.
The weight percentage of phosphorus pentoxide in the solution is calculated by starting from the overall quantity by weight of phosphoric acid including its anhydrides and the total quantity of water in the solution, converting the acids into phosphorus pentoxide and water, and calculating which percentage of said overall quantity by weight is made up by phosphorus pentoxide. For that reason in this description water derived from

REFERENCES:
patent: 4196282 (1980-04-01), Franks et al.

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