Comparison of different Polypropylenes
Homopolymer is used for hot fill applications. Generally preferred grade is Repol H110 MA. However, Homopolymer has lesser impact strength. Random Co-polymers are used where better gloss and clarity are desired. Air tight containers are made with tight fitting lids moulded out of LDPE/LLDPE.
high Density Polyethylene is also used to mould houseware items like kitchen containers, mugs and buckets. Buckets made out of HDPE have better impact strength than those made out of
Homopolymer has excellent integral hinge properties.
Impact Co-polymers are used where
enhanced impact properties are required. Flip top lids are made out of Polypropylene because of its hinge properties. Grades used will depend upon the number of impressions in the mould. Multi-cavity moulds need grades of higher flow. Controlled rheology grades of PP are effective in giving warpage free mouldings. When stress- is applied, like flexing at the hinge, the stressed area, i.e. hinge becomes white, when impact Co-polymer is used. This phenomenon
is known as stress whitening.
LDPE, LLDPE & HDPE are also used to mold closures
. PP closures give good dimensional
stability. LDPE/LLDPE is used if flexibility is required in lids.
Homopolymers form a major
component of furniture mouldings. Homopolymers have high in imparting stiffness to furniture. This can further be enhanced
with addition of mineral fillers like talc or calcium carbonate improve upon impact strength, Impact Copolymers are added. keeping in view the end properties required for the furniture.
to the tune of 10 to 15%. To The blend ratio is determined
Design also plays a significant part in determining the blend. Preferred Homopolymer grade is H110MA and Copolymer is B030MG or B120 MA.