Title of Invention	A PROCESS FOR PREPARATION OF CARBON FIBER REINFORCED COMPOSITES OF POLYBUTYLENE TEREPHTHALATE
Abstract	A process for preparation of high performance carbon fiber reinforced composites of polybutylene terephthalate by melt extrusion using an extruder, comprising feeding carbon fiber and PBT tows directly into an extruder, the polymer melt temperature in the extruder being maintained in the range 220-270°C and the screw speed of the said extruder being in the range 10-70 rpm.

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Form 2 THE PATENTS ACT, 1970 COMPLETE SPECIFICATION (Section 10) We, INDIAN PETROCHEMICALS CORPORATION LIMITED, a Government of India Company, incorporated under the Companies Act, 1956, of P. O. Petrochemicals, District Vadodara 391 346, Gujarat, India The following specification particularly describes ffid-aocortaimrf the nature of thWinvention and the manner in wfrieli it is to be performed: / CARBON FIBER REINFORCED COMPOSITES OF POLYBUTYLENE TEREPHTHALATE AND A^ MELT-EXTRUSLON PROCESS FOR THE PREPARATION THEREOF Field of the invention The present invention relates to high performance carbon fiber reinforced composites of polybutylene terephthalate (PBT). The composites exhibit very high mechanical properties with excellent dimensional stability at moderate carbon fiber loading and enable injection molding, compression molding and thermo-forming etc. to be applied thereto for making any end product. The present invention also relates to a process for the preparation of high performance carbon fiber reinforced composites of polybutylene terephthalate by compounding in a twin screw extruder. Background of the invention Polybutylene terephthalate, (also called polytetramethylene terephthalate) is a semi-crystalline polymer with a very sharp melting^ point at 225°C. It is used predominantly as an injection molding resin. Unreinforced PBT products are opaque in thick sections, somewhat translucent in thin walled parts, and transparent in quenched films. Unreinforced PBT resins exhibit good tensile strength, toughness, and low moisture absorption, resulting in excellent dimensional stability. The smooth but hard resin surface results in low static and dynamic coefficient of friction. Composite materials owe their unique balance of advanced performance properties to the combination of matrix resins and reinforcement fibers. It is the fibers that are primarily responsible for strength, stiffness and toughness. Carbon fibers used in this invention are produced from polyacrylonitrile precursor. These fibers have a density 1.78 g/cc and possess tensile strength above 3.0 Gpa and modulus 220 Gpa. The composite of PBT with carbon fiber offers high performance characteristics with a great versatility in design and fabrication. In the case of fiber reinforced composites, it is well known that the highest possible properties can be achieved from the highest loading of the longest fibers. Long fibers 2 reinforced thermoplastic composites extended the performance boundaries/limitations of the long fiber reinforced thermoset composites, in terms of materials handling, fabrication strategies and performance under service conditions. Fiber reinforced composites contain four elements: the fibers, the matrix resin, organization of the fibers in the matrix and the interface between them. It is the reinforcing fibers, which carry the load and so determine the stiffness and strength of the composite. The resin supports the fibers, particularly under compression loading, and is responsible for transferring load from one fiber to another. The resin also plays an essential role during fabrication since it is the medium by which elements of the structure are joined together to form a whole, and, in addition, it protects the relative fragile fibers from abrasion. It is important that every fiber should be wetted by the resin and the resin should be uniformly distributed throughout the composite structure. It is reported that PBT when compounded with carbon fibers and metal-coated mica would give rise to electrically conductive composition. A method of making such composition is described in JP 01,282,245. The compositions when injection molded into standard specimens and tested showed tensile strength 1,840 Kg/cm2 and flexural modulus 1,70,000 Kg/cm2. Another method of preparing electrically conducting PBT compositions with carbon fibers and some other ingredients is described in US 4,559,164. A method of preparing electronic shields using PBT, conductive fibers and conductive powders is disclosed in JP 61,16,957. Objects of the invention It is an object of the invention to obtain high performance carbon fiber reinforced PBT 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 thereto 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 PBT composites that exhibit very high mechanical properties at 3 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 PBT composites that exhibit very high mechanical properties at moderate concentrations of carbon fiber using a twin screw extruder. Summary of the invention The present invention relates to a process for preparation of high performance carbon fiber reinforced composites of polybutylene terephthalate using an extruder, said composite being partially crystalline, has specific gravity in the range of 1.30-1.45 (ISO DR 823) and water absorption 0.09-0.5% (according to ASTM D570, at 23° & 50% RH). The starting polymer has a melting point 220-225°C and has a fast rate of crystallization. In one embodiment of the invention, the carbon fibers are preferably polyacrylonitrile base. In a further embodiment of the invention, the carbon fibers are used in the form of continuous tows. In still another embodiment of the invention, the tows are fed directly into an extruder, preferably twin screw extruder. The fibers are preferentially surface treated with a chemical (finish) which would provide good adhesion between the fibers and the said matrix (PBT). In yet another embodiment of the invention, the twin screw extruder is engaged for compounding with a preferred screw profile favoring minimum fiber breakage. In a further embodiment of the invention, the polymer feed rate is maintained in the range 10-70 gm/min. or its multiples. In yet another embodiment of the invention, the carbon fibers are feed into the extruder in the form of tows in the range 15-70 K or its multiples, wherein K stands for 1000 filaments. 4 In another embodiment of the invention, the polymer melt temperature in the extruder is maintained in the range 220-270°C. In yet another embodiment of the invention^ the screw speed of the said extruder is controlled in the range 10-70 rpm. In still another embodiment of the invention, the said polymer and the said fibers are fed simultaneously into the twin screw extruder and the resultant composite obtained by the melt extrusion method. In a further embodiment of the invention, the starting fibers are continuos and the fibers in the composite are discontinuous. In another embodiment of the invention, the carbon fiber concentration is in the range 10-40 wt%. In a further embodiment of the invention, the melt flow indices of the final composite are in the range 3-7 gms/10 min. when tested at 240°C under a load 1.16 kg. In another embodiment of the invention, the said composites exhibit a number average fiber length in extrudate and injection molded flexural bar in the ranges 1.8 to 6.0 mm and 0.6 to 4.5 mm respectively. In a further embodiment of the invention, the resultant composite does not exhibit significant difference in its melting point as compared to the neat PBT, but the crystallization temperature is shifted to higher temperature (on cooling the samples at a controlled rate of 10°C/min) when tested in a differential scanning calorimeter at a heating rate of 10°C/min. In a further embodiment of the invention, the the resultant composite of PBT and carbon fibers exhibits enhanced crystallinity as indicate by the A/m value where A is the area under the crystallinity peak obtained while cooling the molten composite and m is the mass of the matrix component, when measured by a differential scanning calorimeter, during crystallization kinetics. 5 In a further embodiment of the invention, injection molded standard (ASTM) test specimens of the PBT-carbon fiber composites exhibit tensile strength and tensile modulus in the ranges 900-1,800 Kg/cm2, respectively. In a further embodiment of the invention, the resultant composites exhibit flexural strength and flexural modulus in the ranges 1,000-3,500 Kg/cm2 and 70,000-2,00,000 Kg/cm2, respectively. In yet another embodiment of the invention, resultant composites of PBT and carbon fibers exhibit heat deflection temperature in the range 190-220°C. In yet another embodiment of the invention, the prepared composites exhibit an Izod impact strength for un-notched specimens in the range 36.0-50.0 Kg.cm/cm, for notched specimens in the range 4.0-10.0 Kg.cm/cm and fracture toughness (KIC) in the range 3.80-8.00 Mpa mA. In another embodiment of the invention, the resultant composite contains about 30 wt% of carbon fiber and exhibits a flexural modulus of around 1,90,000 Kg/cm2 tensile strength around 1,600 Kg/cm2, Izod impact strength (for notched specimens) around 9.0 kg.cm/cm and heat deflection temperature 220°C. Detailed description of the invention During processing of a carbon fiber reinforced thermoplastic composite, such as PBT, severe reduction in fiber length and changes 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. It can be said that the factors leading to the reduction in fiber length especially in those composites with long-fiber reinforcements, are numerous and complex. For given material and design parameters, the degree of fiber length reduction as a function of operating parameters varies between the extreme values. These are defined by the initial length of the fibers (or that of the fibers fed into the molten polymer, here, it is continuous fiber of infinite length) and by a 6 minimum fiber length below which values should not fall. The requirement for a minimum fiber length results from the fact that for effective transmission of stress from the matrix to the fibers a certain fiber length designated as the "critical fiber length" (in conjunction with a specific fiber diameter) is necessary. In addition to these considerations, during molding 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 the present invention, PBT granules, even though non-hygroscopic, were pre-dried at 130°C for three hours, before they are fed into a heated twin screw extruder. The co-rotating screws of the extruder are designed so as to provide deeper screw flights which result in a greater free volume/unit length and lower average shear rate in order to retain maximum fiber length during extrusion. Carbon fiber tows, also pre-dried at 110°C for a least one hour, are fed into the extruder in such a way that the fiber breakage is prevented to the maximum extent, but at the same time the fiber wetting^ with the molten matrix is achieved to the best possible extent. The extrudate coming out of the extruder can be in one or several strands for. These continuous strands are cut carefully so that the fiber lengths are not severely damaged. Quality of compounding depends upon various parameters set during processing. Some significant parameters that would affect the performance of the composite are PBT feed rate, carbon fiber feed rate, temperature profile of the extruder and its screw speed. Certain other factors such as pre-drying conditions. Cooling through temperature, screw design parameters, die design parameters, injection molding conditions, fiber surface treatment and atmospheric conditions also influence the quality of compounding and hence the properties of the composite. It is well known that the processing parameters influence the residual fiber length (in composite), the fiber concentration, its distribution and its wetting with PBT. In order to get best results, a judicious selection of the above mentioned processing conditions is required. 7 The composite granules are shaped into standard test specimen, for evaluating various properties as well as micro structural details, using an injection-molding machine. Injection molding is a process through which the prepared composite granules can shaped even into a desired end product. In the present invention, composites granules are injection molded into standard ASTM test specimens for testing tensile, flexural, lzod impact, heat deflection temperature and fracture toughness properties. The micro structural aspect of the composites, such as retained fiber lengths distribution and fiber-matrix are also examined and optimized using the injection molded test specimens. The present invention will be explained further in detail, by way of examples, which are merely illustrative in nature. The invention is not intended to be limited in its scope by these examples. Example: 1 The co-rotating twin screw extruder with preferred screw design mentioned above was maintained at a screw speed 20 rpm. Molding grade, pre-dried, PBT granules were fed, through the feed port of the extruder, at the rate 20 gms/min. After the polymer is completely melted, (melt temperature 230°C) pre-dried carbon fiber continuous strands, 18 K, were allowed to enter the extruder. The fibers bread down in between the two co-rotating screws and get mixed with molten PBT. The extrudate composite containing^ PBT and carbon fiber was pulled through the die in the form of ^stand. The composite/strand flsay composite-1) emerging from the die was then allowed to pass through a cooling^ trough. Later, the strand was dried and granulated. The composite granules thus obtained were molded into ASTM standard test specimens using an injection-molding machine. All composites pertaining to this invention are molded under identical injection molding conditions given below in Table 1. Composites prepared under the above molding conditions were analyzed for their fiber concentrations as well as their length distribution. The mechanical properties of a composite are influenced by the retained fiber lengths; and hence for every composite the fiber lengths distribution was studied by counting at least 200 isolated fibers in an injection molded flexural bar. 9 Typical properties of the composite-1 injection molded under the above conditions (Table-1) are given below in Table -2. EXAMPLE: 2 Dried granules of PBT were taken in feeder whose feeding rate was maintained at 50 g/min. Dried carbon fiber tows, 42 K, were fed into the molten polymer as described in Example-1^ while the melt temperature in the extruder was kept at 250°C and the twin screws were rotating at 20 rpm. The composite extrude (say composite-2) was dipped in a trough of circulating water and then granulated as in Example-1. The composite granules were molded into standard ASTM test specimens setting injection molding parameters as mentioned in Table 1. 10 Typical properties of this composite evaluated using^ injection-molded specimens are given below in Table 3. EXAMPLE : 3 In this experiment dried granules of PBT at a rate of 20 gm/min. were fed into the extruder while the screw speed was maintained at 35 rpm with melt temperature controlled at 240°C. The composite extrudate (say composite -3) 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 4. 11 Table 4 : Properties of Composite - 3 Izod impact strength 1. Un-notched Kg.cm/cm D256 44.0 2 Notched Kg.cm/cm D 256 8.2 Head deflection temperature °C D648 211 Fracture toughness MPajn.*4 E399 4.63 EXAMPLE : 4 As described in the previous examples feed rate of dried PBT granules was kept at 35 g/min. while carbon fiber tows, 42 K, were fed into the twin screw extruder, keeping the screw speed 50 rpm and controlling, melt temperature in the extruder at 250°C. The composite extrudate (say composite-4) was cooled in trough of water, dried and then granulated. Standard ASTM test specimens of this composite were prepared by injection molding the composite granules under identical conditions as mentioned in Table 1. The carbon fiber concentration and retained fiber lengths were estimated as in the previous examples. 12 Typical properties of the composite-4 are given below in Table 5. Table 5: properties of Composite-4. EXAMPLE: 5 In this experiment, feed rate of dried PBT granules were kept at 20 g/min. and carbon fiber tows, 30 K, were fed into the extruder while screw speed was maintained at 50 rpm. And melt temperature in the extruder barrel was at 2.5 0°C. The composite extrudate (say composite-5) was cooled in water, dried and granulated. 13 Injection molding of composite -5 was also carried out under identical conditions as mentioned in Table 1, to get ASTM standard test specimens. The fiber content and the retained fiber lengths of composite -5 were also estimated. Typical properties of this composite are given in Table 6. We claim: 1. A process for preparation of high performance carbon fiber reinforced composites of polybutylene terephthalate by melt extrusion using an extruder, comprising feeding carbon fiber and PBT tows directly into an extruder, the polymer melt temperature in the extruder being maintained in the range 220-270°C and the screw speed of the said extruder being in the range 10-70 rpm. 2. A process as claimed in claim 1 wherein the starting polymer has a melting point 220-225°C and has a fflst rate of crystallization. 3. A process as claimed in claim 1 or 2 wherein the carbon fibers are polyacrylonitrile based. 4. A process as claimed in any preceding claim wherein the carbon fibers.are used in the form of continuous tows. 5. A process as claimed in any preceding claim wherein the carbon fibers are surface treated with a conventional adhesive to provide good adhesion between the fibers and the PBT matrix. 6. A process as claimed in any preceding claim wherein the said polymer and the said fibers are fed simultaneously into the twin screw extruder and the resultant composite obtained by the melt extrusion method. 7. A process as claimed in any preceding claim wherein the starting fibers are continuous and the fibers in the composite are discontinuous. 8. A process as claimed in any preceding claim wherein the carbon fiber concentration is in the range 10-40 wt%. 9. A process as claimed in any preceding claim wherein the polymer feed rate is maintained in the range 10-70 gm/min. or multiples thereof. 10. A process as claimed in any preceding claim wherein the carbon fiber feed rate is maintained in the range of 15-70 K or multiples thereof wherein K is 1000 filaments.

Documents:

186-mum-2001-abstract(20-2-2001).pdf

186-mum-2001-abstract(granted)-(4-5-2007).pdf

186-mum-2001-cancelled pages(21-12-2004).pdf

186-MUM-2001-CANCELLED PAGES(21-5-2001).pdf

186-MUM-2001-CLAIMS(20-2-2001).pdf

186-mum-2001-claims(21-12-2004).pdf

186-MUM-2001-CLAIMS(AMENDED)-(21-2-2004).pdf

186-mum-2001-claims(granted)-(21-12-2004).doc

186-mum-2001-claims(granted)-(4-5-2007).pdf

186-mum-2001-correspondence(24-12-2004).pdf

186-MUM-2001-CORRESPONDENCE(IPO)-(12-7-2007).pdf

186-mum-2001-correspondence(ipo)-(4-5-2007).pdf

186-MUM-2001-DESCRIPTION(COMPLETE)-(20-2-2001).pdf

186-mum-2001-description(granted)-(4-5-2007).pdf

186-MUM-2001-FORM 1(20-2-2001).pdf

186-mum-2001-form 1(21-5-2001).pdf

186-mum-2001-form 19(19-7-2004).pdf

186-MUM-2001-FORM 2(COMPLETE)-(20-2-2001).pdf

186-mum-2001-form 2(granted)-(21-12-2004).doc

186-mum-2001-form 2(granted)-(21-12-2004).pdf

186-mum-2001-form 2(granted)-(4-5-2007).pdf

186-MUM-2001-FORM 2(TITLE PAGE)-(COMPLETE)-(20-2-2001).pdf

186-mum-2001-form 2(title page)-(granted)-(4-5-2007).pdf

186-mum-2001-form 3(20-2-2001).pdf

186-MUM-2001-POWER OF AUTHORITY(20-2-2001).pdf