New generation clarifying agents for clear polypropylene offer lower taste and odour, reduce energy costs

Polypropylene is an ideal solution to the challenges of improving the environmental responsibility of plastic packaging. Its low density helps reduce the amount of material needed, overall packaging weight that helps reduce fuel usage during shipping. It also has a low carbon footprint, thanks to fewer emissions released during manufacture. Perhaps most significant, polypropylene is easily recycled in existing waste management systems, allowing the material to be reused indefinitely. Additionally, it does not exhibit undesirable side effects during recycling, such as crosslinking and forming a gel, or off-gassing.
The major limitation of using PP as a packaging material is its lack of transparency. PP is a semicrystalline material with natural haze and is less transparent than polyethylene terephthalate (PET) and polycarbonate (PC), or glass. Technological developments are improving the appearance of polypropylene but challenges remain. PP has higher heat resistance than PET and could serve as a resin for hot-fill containers, without the need for heat-setting. New additives called clarifying agents have been introduced to be incorporated in random copolymer of PP to achieve the desired clarity, haze reduction, easy dispersion of clarifying agents, organoleptics like taste and odour. New levels of clarity in PP resins are said to be achieved with Millad NX8000 introduced by Milliken Chemical Co. Compared to existing products, it is said to offer dramatic haze reduction along with good heat and impact resistance, and is cost-effective as well. This clarifier is derived from a new class of molecules based on nonitol. In addition to optimizing transparency of optics, it helps processors cut temperatures and cycle times. Tunable property of product puts clarity and gloss levels in polypropylene on par with other glass clear polymers and glass itself. The clarifier has much better solubility, and it has food-contact approval from both the Food and Drug Administration (FDA) in the US and the European Food Safety Authority (EFSA) in Europe. Millad® NX8000 series not only sets a new benchmark for clarification, but also enables processors to make substantial improvements in their economics through reduced processing temperatures and shorter cycles. It is believed that no other additive puts clarity and gloss levels in polypropylene on par with other ‘glass clear’ polymers and glass itself. It is equally applicable in products made by injection molding, extrusion-blow molding and injection-blow molding. Processors can also achieve considerable energy savings – the additive can regularly yield cycle time reductions by as much as 15%, while the ability to process at lower temperatures can often cut energy consumption by 15-20%, and in some extreme cases by over 30%. Millad NX8500E is an innovative grade, because of which transparency in extrusion blow molding is no longer limited to PVC or PET. It will allow processors to optimize surface properties as well as bulk haze. It has been designed specifically to provide a step change in optical properties with standard Ziegler-Natta PP EBM resins. Bottles produced with this grade exhibit excellent gloss and transparency and have a fresher look due to a low yellowness index. Improvements are less dependent on processing temperatures than with existing clarifiers. Furthermore, no special mold finishes are required to achieve excellent aesthetics in bottles.
Ciba Specialty Chemicals introduced a clarifier/nucleant for PP that is said to be based on a new chemistry that allows for major cost reduction. Irgaclear XT-386 is based on trisamides rather than sorbitol. It improves optical properties of PP using much lower additive levels than conventional clarifiers. The chemistry of the next-generation additive features high thermal and chemical stability, providing improved organoleptics and less plate-out during processing. The high stability of the clarifier allows it to be used as recyclate or regrind without impacting the final haze and clarity properties. This high-performance clarifier for polypropylene has been approved by the American Food and Drug Administration (FDA) at a new, higher concentration of up to 250 ppm in polypropylene random copolymers and homopolymers. The extended upper limit applies to all conditions of use from high (A) to low temperature (H), as well as to all food contact applications. With its ultra-low migratory system, it is recommended in amounts as small as 150 to 200 ppm. Based on an innovative proprietary clarifying technology, it is not only highly effective in low amounts, in contrast to the older technologies available on the market, which require concentrations of 1500–2000 ppm: it also combines high clarity of polypropylene products with improved organoleptic properties compared to conventional clarifier technologies, making it ideal for clarified polypropylene used in the packaging of food and other sensitive products. Use levels to reduce haze and increase clarity of PP are said to be less than 10% of those for conventional products- 150 ppm vs. 2000 ppm. It is said to be suited to random copolymers for thin-wall injection molding of food containers and stretch-blow molding of bottles. Industrial trials with DVDs and bottles have shown that addition of XT-386 results in significantly shorter cycles.
RiKA International’s RiKACLEAR PC1 is a sorbitol based clarifier that meets all the requirements of the polypropylene industry: clarity, gloss, stiffness, impact strength, heat resistance, organoleptics and low warpage. Its inclusion in homopolymer and random copolymer, including controlled rheology grades shows no signs of chemical degradation and does not affect the organoleptics of the finished article. As a clarifier, it imparts low haze, as well as maintains an excellent impact stiffness balance. These properties are extremely important in thin walled applications such as yoghurt containers and food containers. A concentration study demonstrates that it is a cost-effective product with an optimum dosage that can vary between 1200 and 1600 ppm depending upon the requirements of the final article. Ageing studies show that it is the best long-term clarifier in the market even in high Melt Flow Rate (MFR) grades. Multiple pass data also demonstrate that it may be used in regrind and recycling formulations without any loss of haze and gloss. The excellent balance between transparency and stiffness of this innovative clarifier, its long-term stability, high thermal stability, high efficiency at low dosage and better filling properties demonstrate that the additive addresses the current deficiencies of the polypropylene industry. RiKACLEAR PC1 has been approved by EFSA and the FDA, conditions of use A through H for all foodstuffs up to a maximum concentration of 0.25% by weight of the polymer.
These new clarifiers offer upto 50% improvement in the haze of PP over the current benchmark grade, enabling an increasing number of processors to take advantage of the polymer’s performance and cost advantages. Polypropylene is already the preferred choice for many packaging applications, due to the clarity that can be achieved with the clarifiers, and because of PP’s cost effectiveness, low density, excellent stiffness/Impact balance, and thermal and chemical resistance. Its excellent taste and odour properties have furthermore enabled it to be used in a wide range of food-contact applications. The polymer is also very well suited for squeezable containers. From a sustainability point of view, life cycle analysis shows that the environmental footprint of polypropylene is very favourable relative to other clear packaging options.

SOURCE: PLASTEMART

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