Issue 03 – October 2012 Material challenges
An evaluation of the materials typically used for the production of food and beverage containers - including polyethylene terephthalate (PET), polystyrene (PS), homopolymer polypropylene (hPP) or random copolymer PP (RCP) - reveals the following conclusions: PET provides good clarity but exhibits poor heat resistance. As a result, PET containers cannot be used for hot beverages or used in a microwave, as they may warp. PET is also difficult for masterbatch dispersion and cannot be used long-term, re-filled or re-used.
PS can either be transparent or coloured and offers good processability, but it has poor heat resistance and inadequate impact and tear resistance, especially at low temperatures. While hPP offers good heat resistance and broad food contact compliance, it lacks flexibility. This can result in unsatisfactory detail and incomplete forming or cracking during manufacture, leading to higher rejection rates than with other materials. It also exhibits low impact resistance during transportation and can be brittle at low temperatures.
RCP can be a more expensive option than hPP but while it provides good clarity and flexibility, its impact resistance remains inadequate at low temperatures.
To improve flexibility, a “three-in-one” polymer formulation may be pursued. Comprising 15 percent low density polyethylene (LDPE), 15 percent high density polyethylene (HDPE) and 70 percent PP, such a combination can improve flexibility during processing, but reduce clarity. Incorporating a fourth ingredient, a nucleating or clarifying agent, can improve clarity but it also can introduce a problem of odour during processing.
New possibilities with Vistamaxx™ Vistamaxx™
Better products Vistamaxx™
propylene-based
elastomers can offer two solutions with regard to flexibility: For applications requiring a balance of impact resistance, clarity and stiffness, a dry blend formulation of 5-10 percent Vistamaxx™
3020 propylene-based
elastomer with PP can be used. This has been proven to reduce cup breakage during production and transportation. As an alternative solution, a low dosage of Vistamaxx™ 6102 propylene-based elastomer can be added to PP. This improves impact resistance and maintains clarity, while avoiding die cutting issues, at low cost.
More efficient processing Vistamaxx™
can easily be blended
with hPP and RCP. Compatibility with polypropylene, combined with improved flexibility and elasticity, results in a simpler moulding process which is important for complex shapes, such as deep-draw cups. Compounders can target the flexibility that is best-suited for the application, giving them a broader choice than the original hPP or RCP grades.
The lower melt temperature and higher flow of Vistamaxx™
propylene-
based elastomers allow the processing temperature to be reduced and the processing rate to increase. This can reduce energy consumption and improve processing efficiency.
Its flexibility helps to increase the draw ratio resulting in fewer flow marks, better product quality and lower scrap rate. The scrap rate can also be reduced because the elastomer shrinks less than PP, making the production process easier to control and die cutting more accurate, for improved cup and lid matching.
can cost-effectively
improve overall product quality for attractive packaging with more customer appeal. It helps to maintain clarity, colour dispersion and reduces or eliminates stress whitening to maintain the colour and quality of the part. This is important for cups and other containers, such as sheets, trays, hinges and profiles. Enhanced impact strength enables downgauging opportunities for lower material usage and costs.
Breakage during storage and handling is minimised, and cups are less prone to collapse when stacked, making transportation easier. Even at low temperatures, Vistamaxx™ propylene-based elastomers help to improve the impact strength of PP due to a glass transition temperature of -28°C (-18.4°F).
Low seal initiation temperatures and excellent heat-sealing characteristics can lead to energy savings and reduced costs. For applications that require a greater degree of slip resistance, such as sheets, grips, and cups, it can be used to increase the coefficients of friction. This results in better traction, so that products are less likely to slip during use.
Complying with US and EU food contact regulations, Vistamaxx™ is creating new possibilities for thermoformed cups and other food packaging applications.
Further information on Vistamaxx™ propylene-based elastomers can be found at:
www.exxonmobilchemical.com Vistamaxx™
is a trademark of Exxon Mobil Corporation.
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