Title of Invention

PINEAPPLE LEAF FIBRE ( PALF) / GLASS REINFORCED POLYPROPYLENE COMPOSITES

Abstract

Pineapple Leaf fibers (PALF) reinforced Polypropylene (PP) composites and PALF/Glass fiber reinforced PP hybrid composites were fabricated using melt blending followed by injection moulding. Maleated Polyolefin (MAPP) was used as a coupling agent to improve the adhesion between the hydrophilic fibers and hydrophobic PP matrix. The degree of mechanical reinforcement that can be achieved by the introcuction of glass fibers in PALF fiber reinforced PP composites has been assessed experimentally. By incroporating upto 20 weight% of glass fibers into PALF-PP composites at 20 weight% of PALF-PP composities. The sorption behaviour and effects of environmental ageing on tensile properties were also deramatically reduced with incroporation of glass fibers. SEM micrographs further confirms improved interfacial adhesion in case of PALF/Glass fiber PP hybrid composites with considerably lesser fiber pull out and gaps between the fibers and the PP matrix. Thus it is concluded that the mechanical performance and the durability of PALF fiber reinforced PP composites can be enhanced by hybridization with the addition of glass fibers for use in high performance engineering applications.

Full Text

The present invention relates to hybrid composites comprising polypropylene (PP), natural and synthetic fibers, and more particularly referring to a low-cost pineapple leaf-fiber (PALF) based polypropylene composite with material hybridization with glass fibers and material layout for improved behavior that leads to enhanced mechanical properties resulting in lower cost and reduced environmental impact. Fiber reinforced polymer (FRP) composites have surpassed their initial target applications in the aerospace industry to become a viable alternative material in the sporting goods, automotive, and construction industries. High performance FRP composites made with synthetic fibers such as carbon, glass or aramid embedded in polymeric matrices provide the advantages of high stiffness and strength to weight ratio and increased chemical inertness compared to conventional construction materials, i.e., wood, clay, concrete and steel. However, despite the aforementioned advantages, the widespread use of synthetic FRP composites has been limited. Common impediments are high initial material costs, non-efficient structural forms, difficulties in processing and moreover their environmental impact. Increased environmental awareness and the interest in long-term sustainability of construction materials have thus challenged the development of natural-fiber-reinforced polymer (NFRP) composites. However, unlike synthetic fiber reinforced FRP's, the use of NFRP's has been limited to non-primary, or non-load-bearing applications due to their lower strength and stiffness compared with synthetic FRP composites (Biswas et al., "Development of Natural Fibre Composites in India", Proceedings of the Composites Fabricators Association's Composites, Tampa, Fla. (2001)). Recent developments, however, have shown that the properties of the NFRP's can be tailor made and desired performance can be attained by hybridization with synthetic fiber i.e. glass fibers. Furthermore, the surface of the fiber can also be suitably modified with coupling agents to obtain improved physico-mechanical properties than that of virgin polymer martix as well as economical, and environmentally conscious alternative to E-glass fiber reinforced composites (the most common synthetic fiber composite) without sacrificing performance. Natural fibers embedded in a natural or synthetic polymeric matrix, have gained recent interest because of their low material and manufacturing costs, light weight, high specific modulus (elastic modulus over density), and environmentally friendly appeal (Mohanty et al., Journal of Applied Polymer Science, Vol. 94, 1336 (2004)). Lignocellulosic natural fibres can be broadly classified into two categories, particulates & fibres. Particulates have an aspect ratio of approximately one, wherein no significant strengthening is expected although the elastic modulus & some other properties may be improved. Wood floor, ground rice hulls, ground corn cob etc. fall under this category. Fibres can be considered to be short when the aspect ratios vary between that of the particulate & continuous fibres. Wood fibres are the most widely used short fibres but can also be obtained from agro bases of different parts of the plant such as bast (jute, abaca , flax, hemp, kenaf), leaf (pineapple, sisal, screw pine), seed or fruit fibre (coir, cotton, oil palm) grasses & reeds (bamboo, sugarcane) etc. These fibres come from the xylem of angiosperm (hardwood) and gymnosperm (softwood) trees. Examples include maple, yellow poplar and spruce. Typical mechanical properties of these fibers together with E-glass fibers are given in Table 1. All natural fibers are ligno-cellulosic in nature with the basic components being cellulose and lignin. The density of natural fibers is about half that of E-glass (Table 1), which makes their specific strength quite comparable, while the elastic modulus and specific modulus is comparable or even superior to E-glass fibers. Table I Mechanical Properties for Selected Natural Fibers and E-Glass Fiber 2/29 Consideration of NFRP's for load-bearing, or structural applications has been neglected due to their low stiffness and strength as compared with other high performance materials and only limited research and development projects have considered potential structural uses. However, hybridization of natural fiber with stronger and more corrosion-resistant synthetic fiber, for example, glass or carbon fiber, can also improve the stiffness, strength, as well as moisture resistance of the composite. Using a hybrid composite that contains two or more types of different fibers, the advantages of one type of fiber could complement what are lacking in the other. As a consequence, a balance in performance and cost could be achieved through proper material design. However, only a few studies on the mechanical properties of natural and synthetic fiber reinforced polymer matrix hybrid composites are available to date and in most cases durability issues are not addressed (R. Mohan et al. Jute-glass sandwich composites. J Reinforced Plastic Comp. 1985;4:187-9, N. Chand, et al. The toughness of sunhemp-carbonfiber- polyester hybrid composite. Polym Composites 1987;28:146-8. C. Pavithran et al. Coir-glass intermingled fiber hybrid composites. J Reinforced Plastic Comp. 1991:1091-3). Out of all thermoplastics, Polypropylene (PP) is preferred as the most suitable matrix for reinforcement as it possess outstanding properties like low density, high vicat softening point, good flex life, sterilizability, good surface hardness, scratch resistant, good abrasion resistant and excellent electrical property. Wherever a more pronounced mechanical performance is required, PP is reinforced with glass. However, most of the automobile parts made of PP, when exposed to natural environment, changes are expected in the thermal behaviour and mechanical property and surface morphology of the products. The present invention thus focuses on natural fiber-glass hybrid composites that can suitably complement the impediments in the natural fiber composites as well serve as a sustainable alternative to various synthetic load-bearing applications. In particular, the present invention reports the use of PALF natural fiber-glass-polypropylene hybrid composites with improved mechanical performance. In an embodiment, the effects of PALF fiber loading, PALF to glass ratio and coupling agent has been reported. In another embodiment the sorption behaviour and retention in mechanical properties of the composites after ageing have also been reported. The aforementioned hybrid composites can be used in multi applications (e.g., building walls, floors and roofs, bridge and ship decks, aircraft floors) with tailorable integrated multi-functions (i.e., stiffness, strength, thermal insulation, fire protection, and user friendliness). The sustainability and social acceptance of the proposed components, stemming from its large constituency on rapidly renewable resources, will pioneer the use of agricultural commodities in markets aimed at load-bearing materials and structures. It is therefore an object of the present invention to provide novel hybrid composites which can be used in load bearing applications, particularly that can be used in engineering applications while exposed to exterior environments. Further, it is an object of the present invention to provide composition of the PP, PALF and glass fibers and coupling agent in the hybrid composites to achieve improved mechanical performance and ageing characteristics. In particular, a substantial need exists for the utilization of PALF fiber waste that becomes abundant in India. Further, it is an object of the present invention to provide hybrid composites, which are easily and economically fabricated. The mechanically stable polypropylene based PALF and glass fiber hybrid composites of the present invention comprise: (a) at least one polypropylene material present in an amount in the range of about 60% to 70% by weight of the composite (b)at least one cellulosic material derived from pineapple leaves present in an amount within the range of about 15% to 20% by weight of the composite, (c) at least one synthetic fiber, preferably E-glass fibers present in an amount within the range of about 15% to 20% by weight of the composite, and (d) at least one maleated polyolefin used as a coupling agent present in an amount in the range of about 1% to 3% by weight of the composite. The present invention also includes a method of making the above-describe composites. The composites of the present invention have a mechanical strength that exceeds that of virgin PP material alone as well as PP/PALF composites. The inventive composite material may utilize waste pineapple leaf cellulosic material that is produced in excess of 200 million kilograms annually. 3/29 It is an aspect of the invention to provide compositions for the purposes described which are inexpensive, dependable and fully effective for their intended purposes. These and other aspects of the present invention will become readily apparent upon further review of the following specification and charts. FIG. 1A illustrates a) Tensile Strength b) Tensile Modulus of PALF fiber PP composites with PALF contents ranging from 0 to 40% by mass. FIG. 1B illustrates stress strain curves of the PALF fiber PP composites FIG. 2A illustrates a) Flexural Strength b) Flexural Modulus of PALF fiber PP composites with PALF contents ranging from 0 to 40% by mass. FIG. 2B illustrates load deflection curves of the PALF Fiber PP composites FIG. 3 illustrates Impact Strength of PALF fiber PP composites with PALF contents ranging from 0 to 40% by mass. FIG. 4 illustrates a) Tensile Strength b) Tensile Modulus of PALF/glass fiber PP hybrid composites with variation in PALF/glass contents by mass. FIG. 5 illustrates a) Flexural Strength b) Flexural Modulus of PALF/glass fiber PP hybrid composites with variation in PALF/glass contents by mass. FIG. 6 illustrates Impact Strength of PALF/glass fiber PP hybrid composites with variation in PALF/glass contents by mass. FIG. 7 illustrates SEM micrographs of tensile fracture specimens of PALF fiber PP composites at 40 weight % PALF by mass FIG. 8 illustrates SEM micrographs of tensile fracture specimens of PALF/glass fiber PP composites at 20:20 weight % ratio of PALF/glass by mass. FIG. 9 illustrates SEM micrographs of tensile fracture specimens of PALF fiber PP composites at 40 weight % PALF by mass and 2 weight % MAPP FIG. 10 illustrates SEM micrographs of tensile fracture specimens of PALF/glass fiber PP composites at 20:20 weight % ratio of PALF/glass by mass and 2 weight % MAPP FIG. 11 Sorption behaviour of PALF fiber PP composites at 40 weight% of PALF by mass, PALF-glass fiber PP composites at 20:20 weight % ratio of PALF: glass by mass with and without 2 weight % MAPP FIG. 12 a, b SEM micrographs of PALF fiber PP composites at 40 weight % of PALF after aging at 25. Degree.C for 520 hrs and 1200 hrs FIG. 13 SEM micrographs of PALF fiber PP composites at 40 weight % of PALF with 2% MAPP after aging at 25. Degree.C for 1200 hrs FIG. 14 SEM micrographs of PALF-glass fiber PP composites at 20:20 weight % ratio of PALF: glass by mass after aging at 25. Degree.C for 1200 hrs FIG. 15 SEM micrographs of PALF-glass fiber PP composites at 20:20 weight % ratio of PALF: glass by mass with 2% MAPP after aging at 25. Degree.C for 1200 hrs The actual data for FIGS. 1, 2, 3, 4, 5 and 11 are in Tables II through V. The present invention is an improved PP hybrid composite material employing PALF and glass fibers as a component and a method of making the PP hybrid composite material. The resulting hybrid composite material provides improved tensile modulus and mechanical stability. It has been discovered that the sorption behaviour of the hybrid composite material is substantially better than the PALF fiber PP composite material. It is preferred that the PALF cellulosic material(s) is/are present in an amount in the range of about 15% to about 20% by weight of the inventive composite. It is also preferred that glass fibers present in an amount in the range of from about 15% to about 20% by weight of the composite It is preferred that the total of polypropylene material(s) be present in an amount in the range of from about 60% to about 70% by weight. It is preferred that the total of polypropylene material(s) include polar modified polypropylene material(s) present in amount in the range of from about 1% to about 3% by weight of the composite. 4/29 hlxpi The composition of the present invention is characterized by comprising a polypropylene(PP) matrix resin (a); a natural fiber PALP but not limited to other materials selected from i) particulates i.e. wood flour; ground rice hulls; ground com cob etc. ii) bast fibers i.e jute, abaca, flax, hemp, kenaf; leaf fibers i.e sisal, screw pine; seed or fruit fibers i.e. coir, cotton, oilpalm; grasses and reeds i.e. bamboo, sugarcane; wood fibers from the xylem of angiosperm (hardwood) and gymnosperm (softwood) trees, maple, yellow poplar and spruce etc. (b), glass fibers (c) and functionalized polyolefin as coupling agent (d). a)Polypropylene Homopolymers or statistical copolymers or block copolymers of propylene with one or several olefins such as ethylene and linear and/or branched C.sub.4 to C.sub.10 1-olefins are used as polypropylenes. It is practical to use polypropylene homopolymers and block copolymers with a low ethylene content The preferred component a) is a isotactic polypropylene with a melt-flow index of 11g/10min. (23O.degree. C./2.16 kg) and with a density of 0.9 g/ccm b) Natural fiber As employed herein, the term "natural fiber" means a fiber obtained, directly or indirectly, from a source in nature. Included within the term, but not limited there to, are pineapple leaf fiber (PALF) and agricultural fibers such as wheat straw, flax, hemp, kenaf, nut shells, and rice hulls. Preferably, the natural fiber is selected from the group consisting of starch or cellulosic material such as cotton fibers, wood pulps, leaf, stem or vegetable fibers, wood flours, starch, waste papers, cartons, or cellulosic cloth. More preferably, the natural fiber is PALF, wood fiber, hemp, flax, or kenaf. PALF is obtained from the leaves of the plant anannus cosmosum belonging to the family bromelliacese, largely cultivated in tropical countries like India and has over 87200 hectares(estimated) of land under pine apple cultivation. PALF is multicellular and lignocellulosic like Jute fiber, containing cellulose and hemi cellulose, it also contains other minor constituents such as fat wax, pectin uronic anhydride, pentosan, and in organic substance. PALF is finer then jute but 10 times coarser than cotton fiber. PALF has a ribbon like structure and is cemented together by lignin pentosan like materials, which contribute to the strength of the fiber. After the harvesting of the pineapple fruit, the leaves and the plant itself is either abandoned till the next plantation or let the rest for cattle feeding. Previous studies show that if the leaves are properly decorticated to extract the fibers, one hectare of pineapple plants can produce up to 3.000 kg of fibers. In terms of 33.000 to 44.000 plants occupy one hectare. PALF seems to be an important fiber for building up agro-based industry but this potential source of fiber has not been properly utilized because of the lack of adequate information about its physicochemical properties. Fiber levels in the range of from about 10 to about 65 weight % can be used. Fiber levels in the range of from about 10 to about 40 weight % are most preferred. c) Glass fibers The reinforcement fibers also include glass fibers preferably and advantageously comprises glass fibers such as chopped glass strands having a length of 1/8 to 1 inch (about 3.2 to 25.4 mm), milled glass fibers which generally have a length of about 1/32 to 1/8 inch (about 0.79 to 3.2 mm) and mixtures thereof. The glass fibers are advantageously heat cleaned generally comprise from about 15 to about 20 weight percent of the composite. The most preferable ones are the E-glass fibers in the present invention. d) Coupling agent Among the polar modified materials, which can be used in the making of the inventive composite compounds, is maleated polypropylene. Examples of this maleated polypropylene (MAPP) include Epolene E-43 and Epolene G-3003 produced by Eastman Chemical Company . These are polypropylene polymers with molecular weight ranging from 15000 g/mol to 50,000 g/mol reacted with maleic anhydride to produce MAPP containing a maximum of 10 mol percent maleic anhydride. Other suppliers of MAPP are Uniroyal Chemical company under the name Polybond 3002 and DuPont chemical company under the name Fusabond MD 511D. Common commercial lubricants known in the plastics processing industry, both internal and external, can also be used in carrying out the injection moulding process. Examples of lubricants, which can be used in 5/29 the practice of the present invention, include calcium stearate, paraffin wax, and amide wax, for example, Honeywell AC-6 polyethylene wax or amide wax or Calford Wax 106 from Blachford Company. The wax serves to facilitate the molding process and provide lubrication during injection molding. This lubrication reduces energy consumption and minimizes fiber breakage during molding of specimens. The composite material can be conveniently made by mixing the polypropylene resin with the lubricants, and any process aids in a conical twin screw extruder having counter-rotating screws, the mixing being carried out at a temperature of about 200.degree. C. The mixed material may then be pelletized for further molding specimens as per ASTMD standards. In a preferred embodiment, the natural fiber (PALF) is first scoured in hot detergent solution (2%) at 70 .degree. C for one hour to remove dirt and core material were dried in vacuum oven at 104.degree. C, cut to 6mm length using an electronic fibre cutting machine. The PALF fibers are dried to between about 0.5% to 3% by weight in moisture content by weight, and preferably from about 1% to about 2% moisture content by weight. The glass fibers of approx. 6 mm in length were obtained by cutting from continuous fiber roving using an electronic fiber cutting machine. These short glass fibers were also dried in oven at 104.degree. C. EXAMPLE 1 A PALF/glass fiber polypropylene hybrid composites is fabricated as follows: Polypropylene resin was combined with 5 phr lubricants with and without 1-3 phr polar modified polypropylene coupling agents. The polypropylene resin used was obtained from M/s Reliance Industries Ltd and injection moulding grade . The dry blend was then fed into the hopper of a intermeshing counter rotating twin screw extruder (Haake Rheocord 9000, Germany). The detergent treated PALF fibers and glass fibers were introduced at the melting zone to minimize fiber degradation. The extruder melts and mixes the components to produce a homogeneous mixture at high pressure and produces a strand of composite material that is subsequently palletized (cut into small pieces) using a special rotating knife. The first two stages of the extruder were heated to about 22O.degree. C. The last two stages, which are located after the vent, were heated to about 200.degree. C. The die temperature was also at about 200.degree. C. The screw temperature was about 200.degree. C. Vacuum was applied to the vent to further reduce the moisture in the extrudate. The resulting pellets from the twin screw extruder were fed to an 80T injection moulding machine (ES330/80HL, ENGEL Austria) that melted the pellets and applied high pressure on the melt to feed it into moulds of the final product shape. The pellets were molded as per ASTMD standards for mechanical property evaluation. The temperature of the injection molding was within the range of 180 degrees C. to 200 degrees C. The macro-scale properties of the material systems were studied through ASTM material testing procedures for short fiber reinforced plastics. The evaluated properties were: tensile strength and modulus (D638), flexural strength and modulus (D790) by Universal Testing Machine (LR 100K, Lloyds UK), and impact strength (D256) by Impactometer (Ceast, Italy). Five replicate specimens were tested at 23.Degree.C and 55% RH for each of the tests, and the mean values were reported. Corresponding standard deviation along with the uncertainty values for the data showing maximum deviation are reported. EXAMPLE 2 A particular benefit anticipated from these composites is the generation of a hybrid composite system with significantly improved mechanical performance and ageing phenomenon in the composites. 6/29 EXAMPLE 3 Referring to FIG.1 and Table II, increase in PALF fiber content from 0 to 40% increases the tensile properties of PP in PALF fiber PP composites without MAPP. Typical stress strain curves of the composite samples were nonlinear. Usually, a linear behaviour is displayed upto 0.28% strain and the curve begins to level off at about 0.8% strain. The strain at maximum tensile stress ranged from about 1.59 to 1.67%. At higher PALF content beyond 40 wt, there was a substantial decrease in the tensile strength due to poor adhesion between the fibers & PP. However, tensile modulus showed a steady increase due to reinforcing effect of PALF. An increase of 41.18% in tensile strength and 169.5% in modulus of PP matrix was obtained in PALF fiber PP composites with 40 wt% of PALF. The results are shown in the table below. Table II Mechanical Properties of the PALF fiber PP composites of the invention j a Uncertainty values as per A2LA Guidelines, *S.D = Standard Deviation EXAMPLE 4 Referring to FIG. 2 and Table II, it is evident the flexural strength and modulus also increased with the increase in PALF content from 0 to 40 wt%. An increase of 35.8% in flexural strength & 86.8% in modulus of PP matrix was obtained in PALF fiber PP composites at 40 wt% of PALF. Typical load deflection curves of the composites shows that the flexure strain ranged from 1.31 and 1.76 % and damage in the form of matrix cracking initiated from the tensile side of the specimen and propagated through the thickness of the specimen causing failure. EXAMPLE 5 Referring to FIG. 3 and Table II, there is also a sequential increase in the impact with the increase in PALF content from 0 to 40 wt%. An increase of 28.7% in impact strength of PP matrix was obtained in PALF fiber PP composites at 40 wt% of PALF. However beyond 40 wt% of PALF there is a substantial decrease in impact strength due to incompatibility between the fibers and matrix resulting in void formation during processing leading to microcracks in the composites. EXAMPLE 6 Referring FIG.s. 4, 5 and 6, and Table III, it is evident that replacing PALF fiber by glass fiber to the tune of 20 wt% by mass results in a substantial increase in the mechanical properties as compared with PP matrix as well as PALF fiber PP composites prepared at 40 wt% by mass of PALF. This is due to hybridization of the PALF fiber with glass fibers which results in the improved material performance. The tensile, flexural and impact strength increased to the tune of 24.5%, 40.1% and 23.8% at PALF:Glass ratio of 20:20 as compared with PALF fiber PP composites at 40 wt% of PALF. A substantial increase in the tensile and flexural modulus to 62.3% and 22.5% was also obtained. 7/29 Table III Mechanical Properties of the PALF/Glass fiber hybrid PP composites of the invention EXAMPLE 7 The influence of varying the amount of coupling agent, MAPP (maleated polypropylene G3003 from Eastman Chemicals) on final mechanical properties of the composites containing about 40 weight % of PALF fibers, 20:20 wt ratio of PALF:Glass and PP with and without MAPP is illustrated in Table IV. The composites were prepared according to the procedures of EXAMPLE 1, above, and contained 2 phr polyethylene wax. It is clear that increasing the polar maleated polypropylene (MAPP) content increases the mechanical strength of the composite material. More particularly, the improvement in the mechanical performance of the hybrid composites at 20:20 wt ratio of PALF:Glass with 2 wt% of MAPP was significant. This is because PALF and glass fibers do not adhere well to the PP matrix as a consequence of their chemical structures; the fibers are hydrophilic while PP is hydrophobia MAPP acts as a coupling agent, as maleic anhydride group (CH3CO)2O) can be strongly bonded to the OH groups of the PALF fiber surface and the SiO group of the glass fiber resulting in an improved interfacial adhesion. Table IV Mechanical Properties of the PALF/Glass fiber hybrid PP composites with MAPP of the invention REFERENCE EXAMPLE It can be concluded from the test results (See FIGS. 1-6 and Table II, III and IV) that the use of the PALF/glass fiber hybrid PP composites allows for improved properties with reduced cost compared to PP. Referring FIG's. 7 and 8, it is observed that the fiber matrix adhesion is relatively poor with large gaps 8/29 between the PALF fibers and PP matrix revealing incompatibility between the two phases (FIG. 7) in PALF fiber PP composites without MAPP at 40 weight % by mass of PALF. Similarly in case of PALF /glass fiber hybrid PP composites at 20:20 ratio of PALF:glass (FIG. 8), without MAPP, the SEM micrographs also revealed more pulled out glass fibers with dissociated fiber-matrix morphology on the tensile fractured surface of the samples. This further confirms poor interfacial adhesion and incompatibility between fiber and matrix phases. REFERENCE EXAMPLE Referring FIG. 9, it is evident that addition of MAPP, improved adhesion between PALF fiber and the matrix polymer. The fractured surfaces of the failed samples shows that in some areas the fibers are still bonded to the PP-MAPP matrix. Similar bonding characteristics were also observed in case of PALF /glass hybrid PP composites at 20:20 ratio of PALF: glass, with 2 weight % of MAPP (FIG. 10) EXAMPLE 8 Sorption Behaviour Tensile dumbels prepared as per EXAMPLE 1 were immersed in water at 25. Degree. C for 1600 hrs and mass change was calculated at regular intervals. The moisture uptake is calculated as Mo and Mt are the mass of the specimens before and after ageing. REFERENCE EXAMPLE Referring FIG. 11, the sorption curves of PALF fiber PP composites at 40 weight % of PALF by mass and PALF-glass fiber hybrid PP composites at 20:20 ratio of PALF:glass, with and without MAPP, it is evident that water uptake plotted as a function of soaking time shows typical Fickian behavior with a saturation level after about 1600 hours. The saturation level was about 14% for PALF fiber PP composites at 40 weight % of PALF which was comparatively higher than PALF /glass hybrid PP composites at 20:20 ratio of PALF:glass, without MAPP. This is predominantly because of presence of glass fibers within the matrix, which reduces water uptake. However, addition of MAPP substantially reduces water uptake in the both the samples , which confirms improved interfacial adhesion that reduces water accumulation in the interfacial voids and prevents water from entering the fibers. REFERENCE EXAMPLE Referring to Table V, the degradation in the mechanical properties of the PALF fiber PP composites at 40 weight % of PALF by mass and PALF/glass hybrid PP composites at 20:20 ratio of PALF:glass, with and without MAPP after aging in water at 25. Degree. C for 520 hours and 1200 hrs, it is observed that tensile property retention in the hybrid composites with and without MAPP was better as compared with the PALF fiber PP composites at 40 weight % of PALF by mass. In general the hybrid composites outperform the PALF fiber PP composites at 40 weight % of PALF by mass and addition of MAPP in these hybrid composites further accelerates the mechanical performance. Table V Percent reduction in Tensile Strength of PALF fiber PP composites at 40 weight % of PALF by mass and PALF/glass fiber hybrid PP composites at 20:20 ratio of PALF:glass, with and without MAPP 9/29 % EXAMPLE 9 SEM micrographs of tensile fractured surfaces of the PALF fiber PP composites at 40 weight % of PALF by mass without MAPP after aging in water at 25. Degree. C for 520 hours and 1200 hrs is illustrated in FIGs. 12 a and b. It is evident that with the influence of moisture the fibers split into thinner fibrils and the fiber surface becomes rougher as compared with the micrographs in FIG. 7. Fine threads appeared on surface of the specimen which is believed to be the result of polymer dissolution. However, addition of MAPP as well hybridization reduces such phenomenon which is confirmed in FIGs. 13, 14 and 15. Thus durability of natural fiber composites can be tailored by employing appropriate amount of PALF/glass fibers for various engineering applications. In addition to cost-performance balance, a balance between environmental impact and performance could also be achieved by design according to service requirements. It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims. 10/29 We claim 1. A hybrid composite, comprising polypropylene(PP) matrix resin (a); selected from the group consisting of leaf fiber i.e PALF but not limited to other natural fibers such as jute, coir, bamboo, flax, kenaf, sisal etc. (b), glass fibers (c) and functionalized polyolefin, MAPP as a coupling agent (d). 2. The hybrid composite of claim 1 wherein the PALF /glass fibers is employed at a ratio of 15:15 to about 20:20 weight % and MAPP at 2 weight % based on the weight of the total formulation of the composite. 3. The hybrid composite of claim 2 wherein the PALF /glass fiber hybrid composites at PALF/glass ratio of 20:20 and 2 weight % MAPP exhibits optimum mechanical performance with an increase in tensile, flexural and impact strength to the tune of 124.8%, 138.7% and 105.6% and tensile and flexural modulus to about 457% and 202.8% respectively as compared with PP matrix. 4. The hybrid composite of claim 2 wherein the PALF /glass fiber hybrid composites at PALF/glass ratio of 20:20 and 2 weight % MAPP exhibits optimum mechanical performance with an increase in tensile, flexural and impact strength to the tune of 59.2%, 75.7% and 59.4% and tensile and flexural modulus to about 106.7% and 62.1% respectively as compared with PALF fiber PP composites at 40 weight% of PALF. 5. The hybrid composite as claimed in claims 2 and 3 wherein the PALF /glass fiber hybrid composites at PALF/glass ratio of 20:20 and 2 weight % MAPP exhibits improved fiber matrix interfacial adhesion with lesser fiber pull outs and improved wettability 6. The hybrid composite of claim 5 wherein the PALF /glass fiber hybrid composites at PALF/glass ratio of 20:20 and 2 weight % MAPP exhibits Fickian like behaviour at 25 Degree. C to up to 1600 hrs 7. The hybrid composite of claim 6 wherein the sorption characteristics of PALF /glass fiber hybrid composites at PALF/glass ratio of 20:20 and 2 weight % MAPP is substantially less saturation level due to improved interfacial adhesion that prevent accumulation of water in the voids. 8. The hybrid composite of claim 7 wherein the retention in tensile strength of PALF /glass fiber hybrid composites at PALF/glass ratio of 20:20 and 2 weight % MAPP after ageing in water at 25 Degree. C at 520 and 1200 hrs is better than PALF fiber PP composites at 40 weight% of PALF which is also confirmed with improved morphology. 9. The hybrid composite claimed in claim 8, wherein the durability of natural fiber composites can be tailored by employing appropriate amount of PALF/glass fibers in addition to cost-performance balance, a balance between environmental impact and performance could also be achieved by design according to service requirements. 11/29 Pineapple Leaf fibers (PALF) reinforced Polypropylene (PP) composites and PALF/Glass fiber reinforced PP hybrid composites were fabricated using melt blending followed by injection moulding. Maleated Polyolefin (MAPP) was used as a coupling agent to improve the adhesion between the hydrophilic fibers and hydrophobic PP matrix. The degree of mechanical reinforcement that can be achieved by the introcuction of glass fibers in PALF fiber reinforced PP composites has been assessed experimentally. By incroporating upto 20 weight% of glass fibers into PALF-PP composites at 20 weight% of PALF-PP composities. The sorption behaviour and effects of environmental ageing on tensile properties were also deramatically reduced with incroporation of glass fibers. SEM micrographs further confirms improved interfacial adhesion in case of PALF/Glass fiber PP hybrid composites with considerably lesser fiber pull out and gaps between the fibers and the PP matrix. Thus it is concluded that the mechanical performance and the durability of PALF fiber reinforced PP composites can be enhanced by hybridization with the addition of glass fibers for use in high performance engineering applications.

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