Sustainable Plastics - May/June 2020 - 29

collaboration

BOPE explained
no film breaks. Achieving those requires low gel resins and a wide process window for orientation, which
Nova's solution phase resins are
ideal for.

Why is it only now possible to
produce HD-BOPE, while BOPE
has been made with LLDPE for
some time now? Traditional HDPE
typically lacks the elasticity to be
stretched to any extent while LLDPE
is inherently easier, especially biaxially (in the machine and transverse
direction). The resin technology that
Nova Chemicals has developed enables a biaxial stretch ratio comparable to BOPP.
The technical explanation is that
LLDPE is more amorphous and
has better elasticity which makes
it much easier to stretch, while the
higher crystallinity of HDPE makes
it a much harder material to orient
with a dramatically smaller orientation window compared to LLDPE.
What are the important properties for biaxial orientation
of HDPE? The desired properties
of the film are stiffness, heat resistance, low tear and good optics.
HDPE provides better heat resistance and stiffness which is why it is
preferred over LLDPE. The key processing characteristics are extrusion
output and reliable production with

Multilayer films have important
barrier properties, with barrier
layers that are often of a different material than the structural layers. Does HD-BOPE offer
the same performance? As with
many other flexible film applications,
polyethylene offers a monomaterial
solution for many applications that
can't be achieved with any other
single polymer. BOPE is no different.
While there are limitations to oxygen
barrier performance of high-density
polyethylene, HD-BOPE film structures can be metalized, coated with
thin barrier lacquers or laminated to
other polymers when necessary.
What is the advantage of HDBOPE over BOPP? The most significant benefit is easier recyclability. Many packaging applications
require multiple materials to provide
the required performance unless
they utilize an all-PE film structure,
especially due to the outstanding
seal properties of PE. In addition,
polypropylene is harder to recycle
(due to lack of recycling streams) in
some regions of the world including much of the North America. Essentially, HD-BOPE is an important
building block to help brand owners
reach their packaging sustainability
goals.
What about punctures and
tears: is it as strong as BOPP?
HD-BOPE has comparable performance to BOPP including stiffness
and toughness while demonstrating
low tear for easy opening.

What are the differences for
the converter? Film manufacturers such as Polivouga who produce HD-BOPE provide the convertor another building block to
create monomaterial, recyclable
flexible packaging. For example,
a traditional mixed material laminate such as PET/PE can now be
replaced with HD-BOPE/PE. Additionally, the enhanced properties
of biaxially stretched film can allow
converters to downgauge existing
packages. The convertor will need
to optimise their packaging lines
as HD-BOPE will require new settings compared to BOPP or PET
materials.
Can recycled material be used?
At this stage, recycled material
is not being used in BOPE films.
Highly specialized resins that offer
extremely low gels and lot-to-lot
consistency are required due to the
processability requirement for defect-free film. However, BOPE enables downgauging vs. blown film
applications - another sustainability
benefit.
Besides this, recycled content can
be incorporated into a blown-film
partner web if the final structure is
a laminate.
What about the price of HDBOPE? HD-BOPE is a high value
film for companies that are looking
to advance the circular economy.
However, it's also a relatively new
substrate for flexible packaging and
time will tell how the pricing dynamics take shape. These are new
times with new challenges and new
drivers and it is through collaboration that the true value will be established.

May/June 2020

Sustainable Plastics - May/June 2020

Table of Contents for the Digital Edition of Sustainable Plastics - May/June 2020