Title of Invention

A PROCESS FOR PREPARATION OF HIGH PERFORMANCE CARBON FIBER REINFORCED NYLON-6 COMPOSITES

Abstract A process for preparation of carbon fiber reinforced Nylon - 6 composites, comprising feeding the Nylon - 6 and carbon fiber tows simultaneously into a twin screw extruder, the melt temperature in the extruder being maintained in the range 210 - 260° C and the screw r.p.m. of extruder being maintained in the range 20 - 60.
Full Text Form 2
THE PATENTS ACT, 1970
COMPLETE SPECIFICATION
(Section 10)







ORIGINAL
185/MUMNP/2001
20-2-2001

GRANTED
20-12-2004

The following specification particularly describes the nature of the invention and the , invention and the manner in which it is to be performed:


Field of the invention
The present invention relates to a process for the preparation of high performance carbon fiber reinforced Nylon - 6 composites using a co-rotating twin screw extruder. The composites of the invention exhibit very high mechanical properties at moderate concentrations of carbon fiber and enable injection molding, compression molding, thermoforming and other conventional techniques to be applied thereto for making even intricately shaped end products. Background of the invention
Nylon - 6 (polycaprolactam, - NH(CH2)sCO-) is a well known engineering thermoplastic that is tough and hard. It absorbs water (at 230 C and 50% relative humidity) in the range of 3 + 0.4%. Polyacrylonitrile based carbon fibers possess high mechanical strength and stiffness but are light in weight. Composites of Nylon-6 with carbon fiber offer high performance characteristics with a great versatility in design and fabrication.
Composites of Nylon - 66, another polymer in the family of Nylons, with materials such as glass fibers, carbon: fibers and talc are reported in the art. These composites are generally prepared by using melt extrusion. JP 0,352,953 (1991) describes the melt kneading of Nylon - 66 with glass fibers, talc and the like. JP 58,152,044 (1983) describes the rapid manufacture of heat and chemical resistant composites of Nylon-66 reinforced with carbon fibers having mechanical strength comparable to that of carbon fibers reinforced epoxy resins.
A method of making 7% glass fiber reinforced Nylon - 66 composite with a sizing
agent is described in JP 60,245,669 (1985). Preparation and properties of Nylon- 66
composite with chopped strands of carbon fibers is described in JP 60,53,544 (1985). Nylon -
46 composites with carbon fiber exhibiting high mechanical properties are claimed in JP
61,188,460 (1986). Improved Nylon - 6 compositions with glass fibers, talc and TiO2
exhibiting excellent injection moldability and good mechanical properties are described in JP
58,76,451(1983).
During processing of a carbon fiber reinforced thermoplastic polymer composite, such as Nylon - 6, severe reduction in fiber length and change in fiber orientation take place. The final fiber lengths in the composite are determined by the extent of fiber breakage during extrusion followed by molding of the composite for a given starting fiber length in the feed stock. Besides, during molding as the polymer melt is cooled in contact with the fiber surface


which may act as a nucleating agent, the polymer morphology in the fiber vicinity is altered giving rise to an interface which is known to exhibit significantly different properties in comparison to the neat matrix.
It is therefore necessary to devise a thermoplastic composite of Nylon - 6 and carbon fibers that has high performance characteristics with a great versatility in design and fabrication. Objects of the invention
It is an object of the invention to obtain high performance carbon fiber reinforced Nylon 6 composites that exhibit very high mechanical properties at moderate concentrations of carbon fiber and allow injection molding, compression molding, thermoforming and other conventional techniques to be applied for making even intricately shaped end products.
It is another object of the invention to provide a process for preparing high performance carbon fiber reinforced Nylon - 6 composites that exhibit very high mechanical properties at moderate concentrations of carbon fiber and allow injection molding, compression molding, thermoforming and other conventional techniques to be applied for making even intricately shaped end products.
It is another object of the invention to provide an improved process for the preparation of high performance carbon fiber reinforced Nylon - 6 composites that exhibit very high mechanical properties at moderate concentrations of carbon fiber using a twin screw extruder. Summary of the invention
Accordingly the present invention relates to high performance carbon fiber reinforced Nylon - 6 composites that are partially crystalline, with specific gravity in the range of 1.125 -1.135, melting point in the range of 215 - 220° C and water absorption in the range of 2.5 -3.0% according to ASTM D570, 23° C and 50% RH.
The present invention also provides a process for preparation of carbon fiber reinforced Nylon - 6 composites comprising feeding the Nylon - 6 and carbon fiber tows simultaneously into a twin screw extruder, the melt temperature in the extruder being maintained in the range 210 - 260° C and the screw r.p.m. of extruder, being_maintained in the range 20 - 60.
In one embodiment of the invention, the carbon fiber reinforced Nylon - 6 composite has a melt flow index in the range 1 -4 gms/10 min. when tested at 230° C under a load of 2.16
kg.
In another embodiment of the invention, the composites exhibit an average fiber length in extrudate and injection molded flexural bar in the ranges 1.0 to 5.0 mm and 0.5 to 4.0 mm, respectively.

In yet another embodiment of the invention, the composites exhibit higher glass transition temperature as compared to the neat Nylon - 6 and do not show significant differences in its melting point and the crystallization temperature on cooling the samples at a controlled rate of 10 C/min, when tested in.differential scanning calorimeter at a heating rate of l0°C/min.
In a further embodiment of the invention, the composites possess enhanced thermal stability as indicated by loss in weight in comparison to the neat Nylon - 6, when tested by thermogravimetric analysis at a heating rate of 1 0°C/min.
In another embodiment of the invention, the composites possess tensile strength and tensile modulus in the ranges 1,000 to 2,000 and 25,000 to 70,000 kg/cm2, respectively.
In a further embodiment of the invention, the composites exhibit flexural strength and flexural modulus in the ranges 190 to 2,500 and.40,000 to_ 1,20,000 kg/cm2.
In yet another embodiment of the invention, the composites exhibit heat deflection temperature in the range 190 - 210°C.
In a further embodiment of the invention, the composites exhibit an Izod impact strength (notched) in the range 5 - 10 kg. cm/cm and fracture toughness (KIC) in the range 5.00 -10.00 MPs. m½.
In a further embodiment of the invention, the composites contain about 20 wt% of carbon fiber and exhibit a flexural modulus around 1,20,000 kg/cm2, tensile strength around 1,900 kg/cm2, Izod impact strength (notched specimens) around 10 kg.sm/cm and heat deflection temperature 205° C.
The present invention also relates to a process for preparation of carbon fiber reinforced Nylon - 6 composites using an extruder, said composite being partially crystalline, with specific gravity in the range of 1.125 - 1.135,.melting point in the range of 215 - 220° C and water absorption in the range of 2.5 - 3.0% according to ASTM D570, 23° C and 50% RH.
In one embodiment of the invention, the carbon fibers are polyacrylonitrile based and are used in the form of continuous tows.
In another embodiment of the invention, the carbon fibers are surface treated with an adhesion promoter to provide good adhesion between the fibers and the Nylon - 6 matrix.
In another embodiment of the invention, the polymer feed rate is maintained in the range 15 gms/min. to 80 gms/min. or multiples thereof.
In yet another embodiment of the invention, the carbon fibers are fed in the form of tows in the range 10 - 50K, wherein K stands for 1000 filaments, or multiples thereof.

In a further embodiment of the invention the melt temperature in the extruder is maintained in the range 210 - 260° C and the screw r.p.m. of extruder in maintained in the range 20 - 60.
In yet another embodiment of the invention, the Nylon - 6 and carbon fiber tows are fed simultaneously into the twin screw extruder.
In a further embodiment of the invention, the starting fibers are continuous and the fibers in the extrudate are discontinuous.
In a further embodiment of the invention, the carbon fiber concentration in the feed is in the range 10-30 wt%. Detailed description of the invention
In the present invention, Nylon-6.granules.pre-dried at 110° C for 4 hours are fed into a heated twin screw extruder. The co-rotating screws of the extruder are designed in a particular manner by providing deeper screw flights which result in a greater free volume/unit length and lower average shear rate so as to allow minimum fiber attrition during processing. The high strength carbon fiber tows, also pre-dried at 110° C for at least one hour, are fed into the extruder in such a way that the fiber breakage is prevented to the maximum extent, but a the same time the fiber wetting with the molten matrix is achieved to the best possible extent.
Processing conditions of the extruder, such as, Nylon - 6 feed rate, carbon fiber feed rate, the temperature profile of the extruder and its screw speed significantly influence the residual fiber length (in the extrudate composite), the fiber concentration, its distribution and its wetting with Nylon - 6. Excess of fiber incorporation in Nylon - 6 enhances the melt viscosity of the composite which would adversely affect the retained fiber length of the composite. A judicious selection of the above mentioned processing conditions would help in getting the best results. The extrudate coming out of the extruder can be in one or two strands form. These continuous strands are to be cut carefully so that the fiber lengths are not severely damaged.
The carbon fiber reinforced Nylon - 6 composites are partially crystalline, with specific gravity in the range of 1.125 - 1.135, a melting point 215 - 220° C and water absorption 2.5 -3.0% (according to ASTM D570, 23° C and 50% RH).
The carbon fibers are polyacrylonitrile based and are used in the form of continuous tows. The tows are fed into a twin screw extruder directly. The fibers are preferentially surface treated with a chemical which would provide good adhesion between the fibers and the matrix (Nylon - 6).

The twin screw extruder is engaged for compounding with a preferred screw profile favoring minimum fiber breakage.
The carbon fibers reinforced Nylon - 6 composite are made by maintaining the polymer feed rate in the range 15 gms/min. to 80 gms/min. or its multiples. The carbon fibers are fed in the form of tows in the range 10 - 50K, (where K stands for 1000 filaments), or its multiples. The melt temperature in the extruder is maintained in the range 210 - 260° C and the screw r.p.m. of extruder in maintained in the range 20 - 60.
Preferably, the Nylon - 6 and carbon fiber tows are fed simultaneously into the twin screw extruder. The starting fibers are continuous and the fibers in the extrudate are discontinuous. The fiber concentration is in the range 10-30 wt%.
The melt flow index of the prepared Nylon - 6 composite with carbon fibers lies in the range 1 -4 gms/10 min. when tested at.230° C under a load.of 2.16 kg. The prepared composite exhibits an average fiber length in extrudate and injection molded flexural bar in the ranges 1.0 to 5.0 mm and 0.5 to 4.0 mm, respectively. It is noted that the prepared composite exhibits higher glass transition temperature as compared to the neat Nylon -6; and does not show significant differences in its melting point and the crystallization temperature (on cooling the samples at a controlled rate of 10° C/min) when tested in differential scanning calorimeter at a heating rate of 10°C/min.
The prepared Nylon - 6 composite with carbon fibers possesses enhanced thermal stability (as indicated by loss in weight) in comparison to the neat Nylon - 6, when tested in a thermogravimetric analysis at a heating rate of 10°C/min, and possesses tensile strength and tensile modulus in the ranges 1,000 to 2,000 and 25,000 to 70,000 kg/cm2, respectively.
The prepared composite exhibits flexural strength and flexural modulus in the ranges 1,200 to 2,500 and 40,000 to 1,20,000 kg/cm2. It is. observed that when the melt-extrusion method is used to make the Nylon - 6 composite with carbon fibers, the heat deflection temperature is in the range 190 - 210°C.
The resultant composite exhibits an Izod impact strength (notched) in the range 5-10 kg. cm/cm and fracture toughness (KIC) in the range 5.00 - 10.00 MPs.m The prepared composite with about 20 wt% of carbon fiber exhibits a flexural modulus around 1,20,000 kg/cm2, tensile strength around 1,900 kg/cm2, Izod impact strength (notched specimens) around 10 kg.Sm/cm and heat deflection temperature 205° C.
Injection molding is one process through which the prepared composite granules are shaped into desired object or standard specimens for evaluating various properties as well as the micro-structural details. In the present invention, composites prepared in the preferred

extruder are injection molded into standard ASIM specimens for testing tensile, fiexural, rockwell hardness, heat deflection temperature and fracture toughness properties. The micro-structural aspects of the composites, such as, retained fiber length distribution, skin - core thickness and the fiber matrix interphase are also investigated and optimised using the injection molded test specimen. EXAMPLE - 1
Pre-dried molding grade Nylon - 6 granules were taken in a feeder whose feeding rate was adjusted at 19 gms/min. The carbon fiber feed was maintained by feeding continuous strands, 18K, at the same time while the melt temperature in the extruder was kept at 240° C while the screw was rotating at 40 r.p.m. The extrudate composite strand (say composite A) coming out of the extruder was dipped in a trough of circulating water. Later, the strand was dried and granulated.
In another experiment, Nylon - 6 feed rate was kept at 75 gms/min. and all other conditions were maintained as indicated above in this example. The prepared composite (say Composite B) was dried and granulated as above. The composite granules in both these cases were molded using an injection molding machine equipped with a screw specially designed to process Nylon - 6 and its composites. All composites were processed under identical conditions as given in Table - 1.
Composites prepared under the above molding conditions, when analysed for their retained fiber lengths (after counting of 200 isolated fibers in each case) exhibited the following results given in Table - 2. The retained fiber lengths significantly influence mechanical properties of the composites.
Table - 1
Injection molding conditions for preparation of ASTM test specimens

Table-2
Retained fiber lengths in Composites A and 6

S. No. Composite No. average fiber lengths, in mm

In extrudate In molded specimen
1 A 1.23 0.36
2 B 1.38 0.59


Typical properties of the composites injection molded under the above conditions (Table - 1) are given in Table - 3 below. Table - 3
Properties of Composites A and B



EXAMPLE - 2
Dry granules of Nylon - 6 were taken in a feeder whose feeding rate was maintained at 27 gms/min. Dried carbon fiber tows, 18 K, were fed, as in Example - 1, while the melt temperature in the extruder was kept at 240° C and the twin screws were rotating at 30 r.p.m. The extrudate (say Composite C) was dipped in a trough of circulating water and then granulated as in Example - 1.
In a separate experiment, the speed of the twin screws was kept at 50 r.p.m. while all other parameters were maintained the same as in the case of composite C. Granules of this composite (say Composite D) were also prepared in the same fashion as was described in the case of Composite C The granules of both these composites were molded into standard ASTM specimen setting injection molding parameters as mentioned in Table - 1.
Retained fiber lengths of these composites are given in Table - 4. Table -4 Retained fiber lengths in Composites C and D

S.No. Composite No. of average fiber lengths, in mm


In extrudate In molded specimen
1. C 2.16 0.60
2. D 1.99 0.87


Typical properties of these composites, evaluated using injection molded specimens, are given below in Table-5.
Table - 5
Properties of Composites C and D

EXAMPLE - 3
As mentioned in the previous example feed rate of dry Nylon - 6 granules was kept gms/min; and carbon fiber tows, 18 K, were fed into the extruder, keeping the screw speed at 40 r.p.m. and maintaining the melt temperature in the extruder at 230° C. The extrudate (say Composite E) was cooled in water, dried and then granulated.
In another experiment, the melt.temperature was. maintained at 250° C while all other parameters were kept exactly the same as in the perpetration of Composite E. Granules of this Composite (say Composite F) were also obtained following the same procedure as described above for Composite E. Standard ASTM specimens for both these composites were prepared by injection molding the composites under identical conditions mentioned in Table - 1. Retained fiber lengths of the composites are given in Table - 6. Table - 6

Typical properties of these two composites are given in Table - 7.

Retained fiber length of Composites E and F


Table - 7
Properties of Composites E and F
EXAMPLE-4
In one experiment, feed rate of dried Nylon - 6 granules was kept at 27 gms/min and carbon fiber tows, 12L, were fed into the extruder while screw speed was maintained at 30 r.p.m. and melt temperature was at 240° C. The extrudate (say composite G) was cooled in water, dried and granulated.
A similar experiment was carried out, engaging carbon fiber tows, 24 K, and keeping all other extruder conditions constant, as in the case of Composite G. Granules of this composite (say Composite H) were also obtained following the same procedure adopted above. Injection molding of these two composites G and H was carried out under identical conditions as mentioned in Table - 1, to get ASTM standard specimens. Retained fiber lengths of these composites are given in Table - 8. Table-8

Typical properties of the composites are given in Table - 9.

Retained fiber lengths of Composites G and H


Table - 9
Properties of Composites G and H
EXAMPLE - 5
In another experiment dried granules of Nylon - 6, at a rate of 48 gms/min and carbon fiber tows, 30 K, were fed into the extruder while the screw speed was maintained at 30 r.p.m. with melt temperature controlled at 250° C. The extrudate (say Composite - I) was cooled in water, dried and then granulated. The granules were injection molded into ASTM standard specimens under the same conditions as mentioned in Table - 1. Typical mechanical properties of this composite are given below in Table - 10. Table - 10

Typical Properties of Composite -1


WE CLAIM:
1. A process for preparation of carbon fiber reinforced Nylon - 6 composites, comprising feeding the Nylon - 6 and carbon fiber tows simultaneously into a twin screw extruder, the melt temperature in the extruder being maintained in the range 210 - 260° C and the screw r.p.m. of extruder being maintained in the range 20 - 60.
2. A process as claimed in claim 1 wherein said composite is partially crystalline, with specific gravity in the range of 1.125 - 1.135, melting point in the range of 215 - 220° C and water absorption in the range of 2.5 - 3.0% according to ASTM D570, 23° C and 50% RH,
3. A process as claimed in claim 1 or 2 wherein the Nylon - 6 feed rate is maintained in the range 15 gms/min. to 80 gms/min. or multiples thereof.
4. A process as claimed in any one of claims 1 to 3 wherein the carbon fibers are fed in the form of tows in the range 10 - 50K, wherein K stands for 1000 filaments, or multiples thereof.
5. A process as claimed in any one of claims 1 to 4, wherein the carbon fibers are poly acry lonitrile based.
6. A process as claimed in any one of claims 1 to 5 wherein the carbon fibers are used in the form of continuous tows.
7. A process as claimed in any of claims 1 to 6 wherein the carbon fibers are surface treated with an adhesion promoter to provide good adhesion between the fibers and the Nylon - 6 matrix.
8. A process as claimed in any one of claims 1 to 7 wherein the starting fibers are continuous.
9. A process as claimed in any one of claims 1 to 8 wherein the carbon fiber concentration in the feed is in the range 10-30 wt%.
10. A process for preparation of carbon fiber reinforced Nylon - 6 composites substantially as herein described with reference to and as illustrated in the foregoing examples.

Dated this the 9th day of February, 2001.


Documents:


Patent Number 207866
Indian Patent Application Number 185/MUM/2001
PG Journal Number 43/2008
Publication Date 24-Oct-2008
Grant Date 29-Jun-2007
Date of Filing 20-Feb-2001
Name of Patentee INDIAN PETROCHEMICALS CORPORATION LIMITED
Applicant Address P.O. PETROCHEMICALS, DISTRICT VADODARA 391 346, GUJARAT
Inventors:
# Inventor's Name Inventor's Address
1 SODAGUDI, FRANCIS XAVIER INDIAN PETROCHEMICALS CORPORATION LIMITED P.O. PETROCHEMICALS, DISTRICT VADODARA 391 346, GUJARAT
PCT International Classification Number D01F 9/22
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA