Manufacturing of tapes:
The granules of polypropylene bags are fed to the extruder hopper, where they are plasticized and the melt flow is passed through a T-die. Film thus produced is slit into the form of tapes. These strips are then oriented by stretching them under heated condition at a predetermined ratio. Finally the tapes are wound on cheese winders. It is also possible to produce films by blown film process, instead of T-die extrusion. The compounding ingredients used along with polypropylene and HDPE are generally CaCO3 and master batch.
Weaving of tapes into fabrics:
The tapes so obtained are fed to circular looms/ flat looms and woven into tubular or flat fabric respectively.
Lamination or extrusion coating:
This step is not necessary for all types of polypropylene bags as in case of jute sacks. Therefore, calculations were made without taking into account the energy/emission in this process. Fabric produced may require to be coated. HDPE woven sacks are laminated with LLDPE/LDPE while in case of polypropylene bags; lamination is done by lamination grade polypropylene.
Fabric roll is mounted on unwinding roll from where it passes through two rolls over which T-die connected to the extruder is located. The melt of the material, which is to be coated on the fabrics comes through the T-Die as an extrudate and coats the woven fabric. It is then cooled under pressure and wound.
Cutting and stitching of polypropylene bags:
In the next stage the unlaminated fabric as produced earlier is cut, reversed manually, and the bottom is stitched. Then it is printed as per the requirement of the customer.
Primary properties of polypropylene used in producing woven sacks are their chemical inertness and inertness to metabolic processes.
Polypropylene used for the manufacturing of polypropylene bags meets the requirements stipulated in BIS standard IS 10910. The grade of additives incorporated in polypropylene complies with the FDA: CFR title 21, 177.1520 olefin polymers. Additive incorporated in polypropylene also conform to the positive list of constituents as prescribed in BIS standard IS: 10909.