Polypropylene is the first stereo regular, industrial-grade polymer. Polypropylene currently occupies the fourth spot after the “big 3” fibre classes. They have since been an integral part of the rapidly growing family of artificial fibres.
What Is Polypropylene?
Thermoplastic polypropylene (PP), is also known as:
It is a linear structure built on the monomer CMH 2n. It is made of propylene gases and titanium chloride as a catalyst. PP is also a by-product of oil refinery processes.
Polypropylene is very crystallized and geometrically regular. Is tactic is opposite to amorphous plastics such as polystyrene or PVC which radicals are placed randomly (i.e. atactic).
It is claimed that PP exhibits an intermediate level in crystallinity, between low-density polyethylenes (LDPE), and high-density polyethylenes (HDPE).
Process of Polypropylene Fibre/Filament Manufacturing:
You can convert polypropylene chips into Polypropylene fibers using traditional melt spinning. However, the operating parameters will need to be adjusted based on the final products. Spunbonded and Melt Blown are both important methods for producing nonwovens.
Figure: Identifiers shown in the figure
Extrusion: L/D=30. The compression ratio is 1:3.5
Metering: Several spinning gear pumps take the molten polymer from the customer and pass it through the spinning box to homogenize and feed the spinning machine at a steady rate.
Spinning: The spinning package consists of three components-the distributor, filters, and the die.
Quenching: The extruded filaments are chilled in a box that distributes 3m 3/min of air.
Finishing: To increase antistatic and reduce friction.
Hot stretching: To improve the physic mechanical properties.
Crimping is used to increase the bulk.
Cut: fibers are cut to 20 to 120mm depending on whether or not they are for the woollen or cotton system.
Biaxially Oriented Polypropylene (BOPP).
Biaxially oriented is polypropylene when it is extruded and stretched both in the machine direction and across the machine. Biaxial orientation increases strength, clarity, and durability. BOPP is a popular packaging material used for products such as fresh produce, snack foods, and confectionery. It is simple to coat, laminate and print to create the desired appearance. This is called converting. It is typically produced in large rolls, which are then cut on a slitting machine into smaller rolls for packaging machines.
There are crystalline as well as non-crystalline areas in polypropylene fibers. The size of the spherulites formed from a nucleus may vary from fractions to a micrometer up to centimeters. The axis of a crystal unit cell’s crystal is aligned in radial directions. The chain axis is uniformly distributed in planes parallel to this radial direction. Each crystal is surrounded by non-crystalline material. The orientation of crystals and amorphous regions can be affected by fiber spinning or drawing. If the extension of spherulite is less than 0.5% then the deformation of the spherulite is elastic and does not cause any disruption to the structure. Otherwise, spherulites will be highly oriented in a force direction and eventually become microfibrils.
Crystallinity Of Pp Fiber :
Depending on processing conditions, PP fibers generally crystallize between 50-60%. Crystallization occurs at the glass transition temperature, Tg, and equilibrium melting points (Tm). PP crystallization is rapid at low temperatures. The crystallization rates of PP decrease with increasing crystallization temperature and decrease with an increase in molecular mass, as illustrated in Figure “3”. The immediate quenching of the extrusion resulted in a paracrystalline structure that had only 45% crystallinity. The quenching of the die further downstream produced a significantly higher crystallinity (62%). Although the drawing orients these crystallites, it might also decrease their crystallinity.