Temperature-Dependent Pyrolysis of Polyamide–Polyethylene Multilayer Films: Yields, Monomer Recovery, and Product Boiling Range

Multilayer plastics
(MLPs) are widely used in packaging
due to
their multifunctional properties. For example, PA (polyamide) offers
excellent oxygen and mechanical barriers, which are critical for demanding
applications. However, the complex structure makes MLP difficult to
recycle conventionally, often leading to its disposal through incineration.
This study focuses on the pyrolysis of PA-6 (polyamide-6)/LDPE (low-density
polyethylene) multilayer film where blends in a range of 3–15
wt % PA-6 were experimentally tested in a temperature range of 500–600
°C in a laboratory-scale pyrolysis unit, with the aim to better
understand how PA-6 in the feedstock behaves and affects properties
such as yield, product composition, and boiling point distribution.
Experimental study revealed that the presence of PA-6 had a small
increase on the condensable yield (maximum yield (92.6 wt %) was achieved
with PA-6 share of 15 wt % and 526 °C). In addition, PA-6 led
to an increase in the CO yield and interacted with temperature with
components such as methane and ethylene. As expected, increasing the
PA-6 share led to a rise in nitrogen (up to 1.5 wt %) and a decrease
in hydrogen concentrations in the products in a nonlinear manner.
In addition, the main degradation product of PA-6, ε-caprolactam,
was steadily increased as a function of PA (up to 5 wt %) but not
affected by the change in temperature. The simulated distillation
curve was modeled after the PCA-R method, which revealed that temperature
and PA-6 square are key factors on dictating the boiling point distribution.