The pineapple is an herbaceous perennial monocotyledonous plant. The leaves of pineapple involve the stem and shoots. Adult plants hold up to 80 leaves which vary in shape having length of up to 1.3 meters. They are rigid with waxes in the upper and lower surfaces which reduce perspiration. At the base of the stem older leaves are located having a spear format. The younger leaves are elongated conserving a wider baseline. The pineapple leaf fibers (PALFs) are strong, white and silky fibers extracted from the leaves of pineapple plant.Like other natural fibers PALFs are cellulosic fibers. The composition of PALFs is show in table1. There exist ester linkages between the hemicellulose and the lignin in the fibers. PALFs also contain other minor constituents such as uronic anhydride, pentosan and certain inorganic substances. The length of PALF fibre ranges from 3–8mm, diameter 7–18 μm, ultimate tensile elongation 3.42%, initial tensile modulus 10.2 CN/tex and density 1.543 g/cm 3. On average, about 22 units of pineapple leaf weigh a kilogram. The reported fiber yield is about 2.7 to 3.5% of fibers. The extraction of 100 kg of leaves yielded 3.5 to 4 kg of the PALFs by the process of shredding. The acid coupled steam treatment could be employed before processing the fibers in order to extract nanofibrils. The steam explosion process resulted in the isolation of PALF nanofibers having a width in the range of 5–60 nm. The high-pressure defibrillation gives a unique morphology of the interconnected web-like structure of nanofibers.
PALFs fibre composition
Fat and wax 3.2-4.2%
Properties of PALFs Fibers
Among the various types of natural fibers, PALFs exhibits excellent mechanical properties. The superior mechanical properties of PALFs are associated with their structure due to high cellulose content and low microfibril angle. The fiber properties vary according to their dimensional appearance, length diameter, planting conditions, age and type of leaves. The PALFs are one of the best in terms of fineness indexes among vegetal fibers, which make them suitable for many industrial applications. Due to low lignin content, high fineness index and high aspect ratio PALFs have great potential for many applications. When PALFs like other natural fibers are transformed into nanocellulose, all of their potential defects due to extraction are removed and fibers with very high specific modulus could be obtained. PALFs have poor adhesion properties.
Processing of fiber
PALFs fibers could not be blended either with cotton or with synthetic fibers due to their long length and high fibre weight. In order to impart hydrophobicity, mechanical strength and chemical inertness the PALFs before processing are required to be surface treated. For example, the graft copolymerization onto PALFs could be employed for physicochemical modification and improvement of the textile performance of fibers. As PALFs has poor adhesion properties due to its structure, in order to use this fibre as reinforcement for composite surface adhesion properties must be improved. The treatment with NaOH with the use of coupling agent poly (styrene- co -maleic anhydride) gives better adhesion with the matrix of high impact polystyrene (HIPS) and tensile strength for the composites increases.
Performance of fiber
The superior mechanical properties of PALFs associated with their structure due to high cellulose content and low micro-fibril angle makes them one of the strongest fibers among natural fibers. PALFs derived nano-cellulose can be used to make nano-composites. PALFs nano-sized cellulose fibrils in the polyurethane matrix, especially for medical implants give high tensile strength and high strain to failure with strongly improved modulus. For example, nano-cellulose polyurethane vascular grafts with a wall thickness of 0.7–1.0 mm showed elongation at a break of 800–1200%, and withstood hydraulic pressures up to 300 kPa. The produced nano-cellulose and its composites have a wide range of medical applications including cardiovascular implants, scaffolds for tissue engineering, repair of articular cartilage, vascular grafts, urethral catheters, mammary prostheses, penile prostheses, adhesion barriers and artificial skin. Strong and sustainable textiles can also be produced from PALFs. One such example is Pinatex that can be used in everything from bags to furniture. Even shoe companies like Puma and Camper have made prototypes with the textile of PALFs as an alternative to leather.