PP has been increasingly used in rigid packaging with products like disposable cups for water or food products, where aesthetics on account of clarity and gloss are of prime considerations. In the automotive segment, particularly in applications like bumpers, enhanced toughness, along with rigidity as well as higher softening temperatures are considered to be of great advantage.

It is well known that semicrystalline PP can never match the crystal clarity of PET, but the newer developments of metallocene PP reduce haze by almost half compared to the conventional Z-N catalyzed PP grades. Infact it is heartening to know that mhomoPP (metallocene PP homopolymer) with clarifiers could have haze value as low as 6-8. The random metallocene PP with clarifiers could even reach the level of 2-3 haze value after stretching, almost comparable to that of PET.

In addition to the basic PP grades, the newer nucleators as well as clarifiers have helped PP grades to have better clarity, rigidity and productivity due to reduced cycle time in injection moulding process. Some of the recently developed nucleators such as organophosphate salts/esters or Norbornane Carboxylic acid esters have shown to improve crystallization temperatures by 15-17°C and flex modulus by 250-300 Mpa.

These advanced nucleators are required to be used at a much lower level (0.1 - 0.15%) compared to the conventional nucleators like Sodium Benzoate, etc. Of course, the advanced nucleators cost about US$30-35/kg compared to US$2.50-3.00/kg of the traditional nucleators. Such advanced nucleators are presently available from Asahi Denka, Japan. They offer 2 essential grades; ADKSTAB NA-11 and ADKSTAB NA-21. ADKSTAB NA-21 is more efficient than NA11 and provides better clarity.

Milliken Chemical, a primary supplier of third generation Sorbitol based clarifier Millad 3899, has recently introduced Norbornane Carboxylic acid ester called HPN 68 advanced nucleator. These advanced nucleators provide better clarity compared to the traditional Sodium Benzoate/Talc but possibly cannot match the clarity imparted by Sorbitol based clarifiers. Of Course ADKSTAB NA-21 comes very close to the clarity of clarifiers. ADKstab NAll as well NA-21 are marketed by Ciba in specific regions.

Clarifiers have also seen several developments, particularly in the areas of decomposition temperatures and odour levels. The most well accepted third generation clarifier, Millad3988 has decomposition temperatures as high as 200°C or beyond. Besides Millad3988, the benchmark of PP clarifier, Ciba and Mitsui offer second generation but improved clarifiers called Ingaclear and NC4. These clarifiers, because of their organic nature, are easier to disperse in PP matrix compared to the advanced nucleators based on inorganic components. The dispersion can certainly be improved by enhanced mechanical mixing.

While Millad 3988 has become a benchmark for rigid packaging applications, the advanced nucleators have been found to enhance rigidity of impact copolymers along with low temperature impact characteristics required for automotive applications.