Driven by the growing demand for sustainable packaging and the
upcoming European Packaging and Packaging Waste Regulation, which will
require all packaging to be recyclable “at scale” by 2035.
Fiber-based materials are emerging as a highly promising alternative to
fossil-based plastics. Among fiber-based solutions, plastic combined with
fiber enable a multi-material packaging with desire functional properties.
However, plastic and paper do not integrate well together in recycling
streams, undermining circularity. 
Three-dimensional molded pulp technology has gained significant
attention in both research and industry, enabling the production of
lightweight, high-surface-quality fiber objects with excellent mechanical
performance. However, a major limitation of molded fiber products remains
their poor mechanical stability under wet conditions. Traditional
wet-strength agents, such as polyamideamine-epichlorohydrin (PAE), can
improve wet strength but at the cost of recyclability and with associated
toxicity concerns.
Polycarboxylic acids (PCAs) offer a promising, sustainable alternative to
PAE. PCA-based plastics have proven to be a renewable and biodegradable
option to polyolefins, with complete circularity enabled through enzymatic
recycling. Inspired by PCA-plastic work, by reacting with cellulose to form
ester bonds, PCAs could impart water resistance while maintaining the
possibility of recycling via hydrolysis. In this project, we investigate the
use of PCAs, particularly dicarboxylic acids as cross-linkers for
lignocellulosic substrate in molded fiber applications. Notably, the
resulting ester linkages are known to be cleavable under enzymatic catalysis,
which further supports recyclability of the treated fibers. By taking
advantage of the high temperature and pressure conditions inherent to the
thermoforming step in 3D-molded pulp production, we successfully integrated
PCAs into the process, achieving a wet-to-dry strength ratio of 60% without
the addition of any catalyst under industrially relevant process
conditions.
The flexibility of this method, combined with the sustainable sourcing of
raw materials, paves the way for the development of new classes of
recyclable, high-performance fiber-based packaging solutions, offering a
viable alternative to plastics even in demanding application environments.
Moreover, this approach helps advance a circular ecosystem in which new
plastics and paper-based composites works synergistically to enable
innovative applications for fiber-based materials that were previously
attainable only with plastics.