Nucleation of PE Cuts Cycle Times and Boosts Performance
Polyolefins, including polypropylene (PP) and polyethylene (PE), are the most widely used plastics in the world, and are essential to the packaging industry. Many trends, from consumers’ desire for improved aesthetics to manufacturers’ drive to cut costs, have led to improvements in the appearance, performance and processing efficiency of polyolefins.
Specifically, PP has been successfully modified through nucleation and clarification to improve aesthetics, physical properties, warpage control and processing speed. In contrast, although nucleation of PE has been studied for some time, a number of technical issues prevented success. Recently, however, a new nucleation technology was developed, offering the flexible packaging industry significant improvements in barrier performance coupled with enhanced productivity and aesthetics.
By utilizing nucleated PE, film converters can reduce cycle times and take advantage of down-gauging opportunities (through barrier improvements) to lower system costs, while packaging manufacturers can achieve better barrier performance for extended product shelf life, improve optical quality and gain new freedom to create novel designs.
Another important advantage of nucleation is environmental responsibility. By improving the value and cost-effectiveness of PE, nucleation has the potential to expand the use of this easily recycled material and replace other plastics that may not be as sustainable. Down-gauging also offers new possibilities for reducing total packaging amounts.
Nucleation BenefitsNucleation is the process that occurs in the initial formation of a crystal. During cooling of molten PE, the molecules become arranged in a crystalline pattern. Without a nucleating agent, this pattern tends to be random and the crystals tend to be larger, reflecting more light and producing a lower level of clarity.
But a new nucleating agent on the market positively impacts the crystallization process in several ways: First, it decreases the size of the PE crystals for improved optical performance in butane gas-phase linear low-density polyethylene (LLDPE) blown film. Second, it promotes a controlled and uniform crystal orientation that increases barrier performance, and it raises the peak crystallization temperature and significantly increases the rate of crystallization (half time is decreased) to shorten cycle times.
The optical improvement of LLDPE blown film (particularly C4 gas phase), creates opportunities for film converters to reduce the amount of low-density PE (LDPE) – in cases where Low-density polyethylene (LDPE) is used for optical quality and not melt strength – used in typical LLDPE-rich blends, resulting in the potential for cost savings.
Due to the specific crystalline orientation that the new nucleating agent imparts, called Hyperform HPN-20E, a passive barrier mechanism is created, significantly reducing permeation for a wide range of permeants, including water, oxygen, solvents, hydrocarbons and grease. Better barrier performance translates into cost and quality benefits. Thanks to the 20 percent to 40 percent improvement in barrier properties in high-density PE (HDPE) blown film applications that is achievable with nucleation, companies have the choice of two desirable results: increasing the shelf life of products with a film of existing thickness, or using a thinner-gauge film (down-gauging by as much as 20 percent) to maintain current shelf life.
Improved barrier performance also cuts costs by reducing evaporative loss. By changing to nucleated PE, personal care product manufacturers would no longer need to overfill packages to compensate for volume loss due to the permeation of water vapor or solvents, nor would they need to add more fragrance to ensure a long-lasting presence.
For converters, nucleation technology cuts cycle times to lower system costs. A higher peak crystallization temperature results in an earlier onset of crystallization, thus decreasing the frost line height, which can be then be offset by increasing output in blown film.
Nucleated PE for Film PackagingNucleation of PE is particularly appropriate for blown film, among other applications. For blown film, there are significant effects in a wide range of PE types (LLDPE, mLLDPE, HDPE), as well as enhancements in physical and barrier performance. This additive offers improved clarity and gloss, particularly in C4 gas phase LLDPE. It also allows for a broader processing window for LLDPE and LLDPE/ LDPE blended films, leading to higher output rates. In LLDPE/LDPE blends, LDPE amounts can be reduced when used for optics. Typical applications are cereal and dry food packaging (barrier performance) as well as fruit and vegetable multilayer bags (optical performance).
The advent of new nucleation technology has removed a longstanding roadblock to broader use of PE in the packaging industry. Nucleation of PE provides benefits to converters – cost savings through reduced cycle times and down-gauging – and to packagers – enhanced barrier performance and optical improvements. However, it also has wider implications, particularly for the environment. Down-gauging provides the opportunity to reduce overall packaging volume to conserve resources, and the expanded use of easily recycled PE helps to relieve the burden on landfills. This technology promises to make a major impact on the future of flexible packaging.