As mentioned before, bonding processes used for bonding the fibrous web falls into one of three broad categories : mechanical bonding , thermal bonding , or chemical bonding
Mechanical bonding method is based on the frictional forces between fibres, as increasing the frictional engagement of fibres increases the tensile properties of the fabric.
This method is achieved by passing the loose web under banks of rapidly reciprocating barbed needles pointing down, which penetrate through the web and entrap bundles of fibres forcing them downward through the web, forming numerous small loci of fibre entanglement. As the needles are withdrawn , the tangled bundles stay in place . (53)
Thermal bonding ( also called melt or heat bonding) process, is often applied to low – melting thermoplastic fibres, especially polypropylene and polyethylene . Thermal bonding is achieved by passing the fibrous web between heated metal cylinders, which fuse and bond fibres mainly at their crossing points where the pressure is greatest . (48) But if the melting temperature of the web fibres is high ,bonding additives such as powder can be used to bond the fibres together.
3-Chemical bonding – In the chemical bonding process , which is used the least in geotextiles , a cementing medium such as glue , latex or resin is added to bind the filaments or short fibres together . The impregnated web is then cured and / or calendered. (4)
In this research, both mechanical bonding process ( using needle punching machine) and thermal bonding process ( using heated calendars) were used.
A novel technique for web bonding was also used using a woven fabric bonded to the nonwoven web using needle punching technique in order to improve the stability of the produced samples.