Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Patent
1996-01-02
1997-10-28
Edwards, Newton
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
428395, 528272, 528308, 5283082, 524109, 525437, 525444, D02G 300, C08G 6302, C08J 515, C08F 2000
Patent
active
056816553
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns polyester fibres with a high elastic modulus.
Polymers with high elastic modulus and high stress at break have been the subject of many research activities for a long time.
Nevertheless, there are few polymers commercially manufactured which combine high mechanical properties with the low cost of the used monomers.
The Kevlar fibre produced by Du Pont is an example of a material which can be included in this definition.
Alternatively, fibres with high mechanical properties can be obtained by the reconstruction of superstructures of polymers already existing, which are able to give the desired performances.
In the fibres area, spinning in the solid state, the high speed melt spinning, zone orientation, high pressure crystallization, superorientation, and zone annealing are procedures adopted to obtain completely extended crystalline chains.
In the case of fibres, the ideal situation of a super-structure is when molecules belonging to amorphous regions with even length and even strength at break (tie molecules) cross the crystalline regions without lamelles.
It is known that the deflection and the stress breakage of the fibres propagate through the amorphous regions: this phenomenon causes an extremely low tensile modulus in comparison to the theoretical value (about 1/10-1/100 of the theoretical value).
U.S. Pat. No. 4,917,848 discloses a process for producing high tenacity and high modulus fibres by melt-spinning a polyester resin, wherein the unoriented filaments are subjected to post-polymerization in a heating liquid medium and then to multi-stage drawing. The elastic modulus of the obtained drawn filament is at most 30.6 GPa.
SUMMARY OF THE INVENTION AND DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENTS
It has been now unexpectedly found a method to obtain polyester fibres with very high elastic modulus.
The fibres of the present invention show an elastic modulus equal or higher than 37 GPa and can reach 110 or more GPa.
The stress at break of these fibres is usually between 300 and 600 MPa.
The fibres are obtained, according to known processes by spinning polyester resin mixed in the melt state with polyfunctional compounds capable of increasing the intrinsic viscosity of the polymer by addition reactions in the solid state with the end groups of the polyester resin. The fibres obtained in this way are submitted to an upgrading treatment in the solid state carried out under stretching. The upgrading treatment in the solid state leads to an increase of the intrinsic viscosity of the resin.
The treatment is carried out at temperatures generally comprised between 150.degree. C. and 240.degree. C. from a few minutes to one or more hours.
The fibres are maintained under stress during the heating treatment using stretching ratios from 1:2 to 1:8 referred to the fibre before heating. As started supra the fibres are obtained with conventional spinning processes.
The stretching ratios usually used in this stage are between 1:2 and 1:4.
The preferred polyfunctional compounds are dianhydrides of aromatic tetracarboxylic acids. The dianhydride of the pyromellitic acid is the most preferred compound. The compounds are used in quantities usually between 0.05 and 2% by weight on the resin.
The mixing of the resin with the polyfunctional compound, is carried out by the extrusion of the mixture in single or twin screw extruders. Controrotating non-intermeshing twin screw extruders are the preferred ones. The residence time is usually less than 200 sec. A short residence time avoids excessive resin reactions in the melt state. The temperature in the extruder is generally between 200.degree. and 350.degree. C. The resin added with the polyfunctional compound is pelletized and, the granules are then ready for the spinning.
The polyester resins used in the process of the present invention are the product of the polycondensation reaction of a bicarboxylic aromatic acid, such as terephthalic acid or its derivatives as the dimethyl ester or naphthalene bicarboxyl
REFERENCES:
patent: 2615784 (1952-10-01), McClellan et al.
patent: 3520770 (1970-07-01), Shima et al.
patent: 4176101 (1979-11-01), Leslie et al.
patent: 4917848 (1990-04-01), Kurita et al.
patent: 5382628 (1995-01-01), Stewart et al.
patent: 5391330 (1995-02-01), Jones et al.
patent: 5416148 (1995-05-01), Farah et al.
patent: 5461092 (1995-10-01), Laugher
Al Ghatta Hussain Ali Kashif
Cobror Sandro
Severini Tonino
Edwards Newton
Manzo Edward D.
Murphy Mark J.
Ringsred Ted K.
Sinco Engineering S.p.A.
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