This invention relates to the field of aviation, space and ballistic technology and corresponding industrial applications. Still further the present invention relates to development of a thermoplastic matrix composite with relatively far lesser weight for aerospace and ballistic applications . Still further the present invention addresses the problem of providing a recyclable polymer composition for aerospace and ballistic industry requirements.. Furthermore, this invention is aimed at providing a polymer composite with enhanced fire resistant and increased mechanical properties.

BACKGROUND OF INVENTION: -

With ever increasing pressure to improve operational efficiency and reduce fuel consumption in the aerospace sector, airframe manufacturers and airlines are continuously looking for the most efficient ways to reduce aircraft weight, One obvious way of reducing the weight of an aircraft is to look for viable substitute materials that possess the same or superior performance of traditional materials but with less weight. Polymer composites augmented their reputation in aerospace industry for their outstanding mechanical properties and low weight. A wide range of composite material forms are discovering usage in today’s aerospace and aviation industry segments. These materials are finally gratifying the promise of providing manufacturers with a cost-competitive alternative to aluminum alloys. The new Airbus 380 and Boeing 787 are using about 50 to 60% thermosetting polymeric composites vs. 20% aluminium.

Thermoplastic matrix composites are advantageous over thermosetting matrix composites because of improved damage tolerance, shorter production times and inherent recyclability (via melt reprocessing). However, the need to establish new fabrication techniques has been a barrier to the introduction of thermoplastics as matrices for continuous fiber composites. PEK is a high performance engineering polymer whose properties can be enhanced through fiber reinforcement. PBO fiber reinforced PEK composites are desirable materials for high performance components due to their excellent mechanical and chemical resistance properties. PEK’s desirable properties arise due to its aromatic structure and its ability to crystallize. PEK shows a glass transition (Tg) at around 1600 C and a melting peak in the region of 3700

Moreover, thermosetting polymeric composites have severe disadvantages because once cured, the thermoset can no longer be re-melted or re-processed. Therefore, in course of time there will be huge debris from thermosetting composites not only from aerospace sectors but also from automotive and transportation sectors and consequently, alternative of thermosetting composite is mandatory.

Thermoplastics do not have crosslinks and therefore, can be reprocessed which is a great advantage when compared to thermosetting polymers. While heating a thermoplastics material, there is no change in molecular weight resulting in compromise mechanical properties. In thermoplastics the increased molecular weight makes processing increasingly difficult due to increased melting temperatures. However, thermoplastics with increased fracture toughness making them a desirable candidate for aerospace applications.

OBJECT OF THE INVENTION: -

It is a primary object of the present invention is to provide a thermoplastic polymeric composite i.e., Polyether Ketone (PEK) resin based long carbon fiber (with fabric configuration) composite and which can be recyclable and consequently there will be no debris formation in course of time which is inevitable for thermosetting composite.

It is another aspect and object of the invention to provide a PEK, which can offer the highest heat and fire resistance and mechanical properties (Tensile strength > 150 MPa) retention over +3700 C of any unfilled polymer and therefore, inclusion of long PBO fabric will result significant increase in tensile strength and modulus of the composite material used for space, aviation and ballistic applications.

It is further object of the invention to provide, . PBO fabric in PEK resin, the surface of PBO fabric was modified by atmospheric pressure plasma treatment and this process could essentially increase the wetting leading to very strong adhesion with the PEK matrix interface in the polymer composite system, resulting in tensile strength of the PEK-PBO fiber composite close to 1500 MPa. SUMMARY OF THE INVENTION :-

State-of-the-art review reveals that, in respect of application of polymeric composite for aviation and defence, still it is depending on thermosetting polymeric composite and not much research has been envisaged on development of high temperature resistant thermoplastic composite. It is possible that processing of high temperature resistant polymer appears to be difficult.

Firstly, thickness 0.1 mm PEK film was manufactured from PEK resin by high temperature (425 0 C) and high pressure (10 Bar) compression molding. Thereafter, surface of PEK film and PBO Fabric were modified by atmospheric pressure plasma treatment. It is observed that there is considerable decrease in contact angle of de-ionized water on PEK film and PBO Fabric resulting in increase in surface energy of PEK and PBO fabric leading to increase in adhesion between PEK films to PBO fabric.

DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE DRAWINGS :-

Polyether Ketone (PEK) a high temretaure resistant thermoplastic polymer is processed with poly(p-phenylene-2,6-benzobisoxazole) fiber which is termed as PBO fiber under high temperature press (Temperature: 4250 C and Pressure: 10 bar) with appropriate process parameters; results successful impregnation of PEK with PBO fabrics.

The PEK resin used for this investigation is essentially manufactured indigenously and tThe PEK (PBO fabric is processed under high temperature press results thermally stable high performance thermoplastic polymeric composite up to 5700 C for short duration and 2800 C for long duration. Thermal stability of this compiste is highly promising in terms of application to future generation aviation such as hypersonic aircraft and defence. Tensile testing of the composite is carried out according to ASTM D 3039-2008 standard. It is observed that tensile strength of the composite is 1500 MPa. During stacking there were three layers of PEK film, each with 0.1 mm thickness and one layer of PBO fabric each with 0.5 mm thickness and again three layers of PEK film shown with schematic diagram in Figure 1. Therefore, resultant % of PBO fabric is maximum 60 %. However, with an optimum thickness of PEK film, PBO fabric up to 70 to 80 % volume fraction can be achieved. This composite was exposed to gamma radiation.of 2700 kGy, elevated temperature of 2800 C, agresive acidic environment of pH 1 and aggressive alkaline environment of pH 12, and the results reveal that there is almost 100 % retenation of strength after exposoed to aggressive environments. Further this 10 mm thick composite, consisting of 63 layers of PEK film with 20 layers of PBO fabric can completely stop bullet of 9 mm pistol with a speed of 440 m/sec with back facing signature of 26 to 29 mm and qualified NIJ level 3 A standard shown in figure. Hybrid composite with front facing using silicon foam (2 mm thickness), boron carbide (6 mm thickness), silicon foam (2 mm thickness) and back facing using PEK-PBO fabric composite with 12 to 15 mm thickness can complete stop hard steel bullet of AK 47 with a speed of 720 m/sec and back facing signature of 20 to 31 mm. Therefore, hybrid composite with these combination is qualified for NIJ level 3+ standard. By optimizing the thickness of hybrid composite with same composition, it can be upgrded to NIJ level 4 standard. Schematic diagram of hybrid composite is shown in Figure 2

PEK- PBO fabric composite after high temperature compression molding.

The figure 6 reveals that when PEK- PBO fabric is processed under high temperature compression molding results successful impregnation of PEK with PBO fabrics.

When PEK-PBO fabric is processed under high temperature press; results thermally stable high performance thermoplastic polymeric composite up to 5700 C. This could be for short duration, however, results looks highly promising in terms of application to hypersonic aircraft. Tensile testing of the composite is carried out according to ASTM D 3039-2008 standard. It is observed that tensile strength of the composite is 1500 MPa. This is because during stacking there were three layers of PEK films, each with 0.1 mm thickness and one layer of PBO fabric each with 0.5 mm thickness. Therefore, resultant % of PBO fabric is maximum up to 60 %. It is to be noted that tensile strength of PBO fiber is 5900 MPa, resulting in high tensile strength of the composite.

Figure 7: Tensile strength of PEK-PBO fabric composite at ambient condition, elevated temperature, acidic environment, alkaline environment and gamma radiation

When the PEK-PBO fabric composite is exposed to elevated temperature of 2800 C, high acidic environment, high alkaline environment and gamma radiation on 2800 kGy, there is no significant deterioration of mechanical properties of the composite, and it can retain 98 to 99 % of tensile strength. The future generation aviation and defence industry will be facing a big challenge in terms of recyclability of polymeric composite which is based onthermosetting polymer. Therefore, PEK-PBO fabric composite will certainly be highly complementary for future generation structural application in aircrafts, hypersonic aircrafts. The findings of this project will certainly provide an important contribution in the context of future generation aviation.

Several new applications on PEK based PBO fabric composites are continuing to come to light in new fields that demand material stability at high temperatures. Interestingly, high temperature thermoplastic is gaining enormous importance to various defence missions therefore; the advancement made in this project will not only be highly useful for Unmanned Aerial Vehicle (UAV), missiles, commercial aviation and for hypersonic aviation but also will be contributory to these space missions.

Stress-strain curve of PEK film reveals that elongation of PEK film is about 140 % resulting in significant toughness of PEK film leading to energy absorption. Therefore, combination of PEK with PBO fiber appears to be an excellent combination as an light weight bullet proof material this 10 mm thick composite, consisting of 63 layers of PEK film with 20 layers of PBO fabric can completely stop bullet of 9 mm pistol with a speed of 440 m/sec with back facing signature of 26 to 29 mm and qualified NIJ level 3 A standard shown in figure 13.

Hybrid composite with front facing using silicon foam (2 mm thickness), boron carbide (6 mm thickness), silicon foam (2 mm thickness) and bck facing using PEK-PBO fabric composite with 12 to 15 mm thickness can complete stop hard steel bullet of AK 47 with a speed of 720 m/sec and back facing signature of 20 to 31 mm Therefore, hybrid composite with these combitation is qualified for NIJ level 3+ standard. By optimizing the thickness of hybride composite with same composition, it can be upgrded to NIJ level 4 standard as shown in figure.