Shape memory polymers, or SMPs, are a class of smart materials that can be programmed into a temporary shape and then recover their permanent, original form when exposed to an external stimulus such as heat, light, or an electrical field. The underlying mechanism involves three steps: the material is deformed above its transition temperature, the deformed shape is fixed by cooling or light exposure, and the original shape is restored upon reapplication of the stimulus. Switching segments within the polymer allow molecular mobility during deformation, while fixed domains created by chemical crosslinking or crystalline structures store the permanent shape. Despite their versatility, neat SMPs suffer from well-known drawbacks, including low thermal conductivity, modest mechanical strength, and a lack of electrical conductivity, all of which limit their usefulness in demanding smart-device applications where uniform heating and fast recovery are essential.

To overcome these limitations, researchers have traditionally turned to synthetic nanofillers such as carbon nanotubes, graphene, and metal nanoparticles. These additives can dramatically improve conductivity, mechanical strength, and recovery rates, but they carry significant environmental and health baggage. They are derived from non-renewable sources, can be potentially toxic, are expensive to produce at scale, and often disperse poorly within polymer matrices, leading to weak interfacial bonding. As global sustainability goals tighten and life cycle assessment becomes a standard metric in product development, the field has been actively searching for greener alternatives. Bio-derived nanofillers such as cellulose nanocrystals, lignin nanoparticles, chitin nanofibers, and starch-derived crystals offer biodegradability, low toxicity, and carbon neutrality, and previous studies have shown they can deliver mechanical and actuation performance comparable to or better than their synthetic counterparts.

In the new study, two biodegradable polymer matrices were used: polycaprolactone, chosen for its low melting point of roughly 60 degrees Celsius and proven shape memory behavior, and polylactic acid, used to evaluate compatibility with lignin fillers. The cellulose nanocrystals were isolated from cellulose pulp through acid hydrolysis with 64 percent sulfuric acid, a process that selectively degrades amorphous regions and leaves behind rigid, rod-like particles measuring 100 to 300 nanometers in length and 5 to 20 nanometers in diameter. The crystals were then dialyzed, centrifuged, and freeze-dried, and their surfaces were modified using TEMPO-mediated oxidation to introduce carboxyl groups that improve aqueous dispersibility and promote hydrogen bonding with the polymer matrix. Lignin nanofibers received a silane treatment with 3-aminopropyltriethoxysilane in an ethanol-water solution, which enhanced their compatibility with the PLA matrix and strengthened interfacial bonding.

The composites were fabricated using three different processing routes: solution casting, in which polymer and dispersed nanofillers were cast into molds and dried; in-situ polymerization, in which silanized lignin was added directly to the lactide monomer during ring-opening polymerization to promote grafting and dispersion; and melt mixing in a twin-screw extruder at 80 to 100 degrees Celsius followed by compression molding. Filler loadings from 1 to 10 percent by weight were investigated, with optimal performance found in the 3 to 5 percent range, where uniform dispersion and mechanical integrity were best balanced. Scanning electron microscopy of fracture surfaces confirmed homogeneous dispersion with no large agglomerates, and a percolated nanonetwork was observed to form at loadings of 3 percent and above, aiding stress transfer and toughening throughout the material.

The mechanical and thermal results were substantial. Dynamic mechanical analysis revealed an increase in storage modulus of up to approximately 25 percent, alongside a shift in viscoelastic transition behavior that confirmed effective filler-matrix interactions. At 3 percent filler loading, Young’s modulus rose by about 20 percent and tensile strength by roughly 10 percent, although elongation at break showed a modest decline, a familiar trade-off in reinforced polymers. Differential scanning calorimetry recorded a modest increase in glass transition temperature of 2 to 3 degrees Celsius and a slight rise in melting temperature with CNC inclusion. Thermogravimetric analysis showed that the onset of thermal degradation was delayed by up to 30 degrees Celsius, confirming that the integrated fillers improved thermal stability, an important consideration for materials that must survive repeated heating cycles.

The shape memory performance itself was impressive and durable. At 5 percent CNC loading, the composites achieved a shape fixity ratio of approximately 97 percent and a shape recovery ratio of about 95 percent, meaning the material both held its programmed temporary shape almost perfectly and returned nearly completely to its original form when reheated. Repeated thermomechanical cycling over ten cycles produced only a slight degradation of less than 3 percent, indicating minimal fatigue. The authors attribute these improvements to increased stiffness and enhanced heat conduction across the matrix-filler interface, which allows the material to heat more uniformly and recover more reliably than neat polymer, which often suffers from uneven heating and delayed response.

The most striking results came from the energy harvesting measurements. The team built a triboelectric nanogenerator, or TENG, using the composite film as one tribo-layer, repeatedly contacting and separating it from a PTFE sheet under cyclic compression at 1 to 2 hertz while capturing voltage and current with a digital oscilloscope. Peak output voltage climbed from roughly 25 volts at 1 percent filler loading to approximately 80 volts at 5 percent loading under 25 percent strain, a more than threefold increase. The gain is attributed to enhanced surface roughness, improved dielectric properties, and a larger effective contact area induced by the CNC incorporation. Triboelectric systems generate charge through contact electrification and electrostatic induction, and the nanofiller network increases both the triboelectric polarity and the real contact area during each deformation cycle.

Crucially, the researchers demonstrated that the intrinsic shape recovery process of the polymer itself could serve as the internal mechanical driving force for electricity generation, removing the need for any external actuation. As the material deforms and recovers, internal stresses and friction at the nanofiller interface drive charge separation and polarization, generating current in connected circuits. Durability testing showed stable output over approximately 500 repetitive deformation cycles, with minor drops after 1000 cycles that were partially recoverable through shape memory reheating, meaning the material can effectively self-restore its electrical performance using the same thermal trigger that powers its actuation. The authors note that the electrical outputs are competitive with systems built on synthetic fillers, yet the composite remains biodegradable and sustainable.

The implications extend across several fast-growing fields. Wearable and flexible electronics demand compact, self-sustaining materials, and an SMP composite that harvests energy from body heat triggered recovery, or from motions like walking, breathing, or typing, offers a route to self-powered sensors and skin-like devices without batteries. In soft robotics and autonomous sensing systems, the same thermo-mechanical-electrical coupling cycle could power onboard electronics while the material performs its actuation function. The work also closes gaps the field has struggled with: it rigorously links filler morphology, dispersion quality, and interfacial bonding to both actuation behavior and energy output, and it evaluates shape recovery, mechanical strength, and electrical generation together in a unified framework. As smart systems increasingly require sustainable, high-performance materials, this demonstration suggests that the future of self-powered devices may be grown in forests and fields rather than synthesized in reactors, with compostable composites quietly converting the physics of shape recovery into usable electricity.

Subject of Research: Biodegradable shape memory polymer composites reinforced with bio-based nanofillers for triboelectric energy harvesting

Article Title: Multifunctional shape memory polymer composites reinforced with bio-based nanofillers for energy harvesting applications

Article References: Multifunctional shape memory polymer composites reinforced with bio-based nanofillers for energy harvesting applications. (n.d.). https://doi.org/10.1007/s44493-026-00006-5

Image Credits: AI Generated

DOI: 10.1007/s44493-026-00006-5

Keywords: shape memory polymers, cellulose nanocrystals, lignin nanofibers, triboelectric nanogenerator, energy harvesting, biodegradable composites, polycaprolactone, polylactic acid, wearable electronics, self-powered sensors, soft robotics, sustainable materials

The motivation is stark. Composite materials such as carbon fibre reinforced plastics and glass fibre reinforced plastics dominate industries from aviation to wind turbine manufacturing because of their exceptional strength-to-weight ratios, yet their end-of-life story is grim. Recycling these composites is expensive and energy-intensive, and enormous volumes of decommissioned wind turbine blades already pile up in landfills worldwide. Even composites made with natural fibres typically fall short of true sustainability because their binding matrices are synthetic polymers that resist degradation. The Mauritian team set out to close that gap by making both components—the fibre and the matrix—fully biodegradable, drawing on a locally abundant plant species that also offers carbon-offsetting benefits while it grows.

The path from leaf to composite began with mechanical extraction. Fibres were harvested from Pandanus utilis leaves, stripped of their cuticle and epidermal layers using a conventional fibre decorticator, and oven dried at 60 degrees Celsius for 24 hours. The researchers then applied mercerization, an alkali treatment with sodium hydroxide at concentrations of 2.5 and 3.0 percent, to prepare the fibre surfaces for bonding with the PLA matrix. Fourier transform infrared spectroscopy confirmed that the treatment worked at the molecular level: characteristic peaks associated with lignin and hemicellulose—those at roughly 1239 and 1730 wavenumbers—flattened noticeably after treatment, while peaks tied to adsorbed water at 1640 and 3400 wavenumbers also diminished. In practical terms, the alkali bath dissolved much of the lignin and hemicellulose that interferes with adhesion, enriched the fibre in cellulose, and reduced its tendency to draw in moisture.

Composite specimens were fabricated by hand lay-up in aluminium-faced moulds, with chopped fibres of 4, 5 and 6 centimetres randomly arranged between two layers of PLA filament, then melted in an oven at 250 degrees Celsius for one hour, compressed, and cooled gradually to prevent cracking. Fibre loadings of 5, 10 and 15 percent by weight were tested against the pure polymer. Differential scanning calorimetry showed textbook PLA behaviour: a glass transition between roughly 50 and 70 degrees Celsius, crystallization peaks near 120 degrees, melting at 171.2 degrees, and thermal decomposition onset around 275 degrees—evidence that the reinforced material remains thermally stable across ordinary service conditions.

The physical tests revealed a familiar trade-off in biocomposites. Water absorption, measured over a 24-hour immersion following the ASTM D570-98 standard, was negligible for pure PLA but climbed to between 2 and 2.75 percent in the composites, rising consistently with fibre content—a statistically significant effect driven by the hydrophilic nature of natural fibres and by microscopic voids at imperfect fibre-matrix interfaces. Fibre length, by contrast, made no statistical difference. The soil burial test, in which specimens spent 30 days in open soil teeming with aerobic bacteria, told a similar story: specimens with 15 percent fibre lost up to 1.6 percent of their mass, compared with only 0.25 percent for plain PLA, confirming that the material genuinely degrades in a biological environment rather than merely fragmenting.

Mechanically, the sweet spot was unambiguous. Both tensile and flexural performance peaked at a fibre loading of 10 percent by weight, where stress distributes more evenly through the structure. The best flexural result—around 270 newtons of load capacity—came from a specimen with 4-centimetre fibres at 10 percent loading, more than double the 110 newtons that plain PLA could bear. Beyond that optimum, at 15 percent fibre content, performance dropped sharply as fibre-to-fibre crowding reduced matrix dispersion and left insufficient adhesive contact, generating stress concentrations and defects. Analysis of variance confirmed that fibre content, though not fibre length, significantly influenced the strength of the unexposed specimens.

The study’s most sobering finding concerns marine conditions, a critical consideration for a material intended for maritime applications. When a full set of reinforced specimens was submerged in seawater for 30 days before tensile testing, the pattern of results inverted: strength now fell with increasing fibre content, dropping from a high of 1400 newtons at 5 percent fibre to a low of 200 newtons at 15 percent. The researchers attribute this to capillary water penetration that progressively undermined the fibre-matrix interface, compounded by the slow hydrolytic degradation of the PLA matrix itself—a reminder that biodegradability, the material’s central virtue, is also its principal vulnerability in wet service environments.

To see failure coming before it happened, the team turned to digital image correlation, a contactless optical technique that tracks a speckled pattern on the specimen surface through a calibrated camera system during tensile loading. The resulting von Mises strain maps revealed localized hot spots of concentrated strain that reliably predicted where each specimen would ultimately fracture in a brittle mode. These hot spots traced back to manufacturing imperfections—randomized void formation, incomplete fibre-matrix adhesion and minor misalignments of the fibres—demonstrating how internal defects, invisible to the naked eye, orchestrate the failure of a composite long before its average material properties would suggest.

Finally, the researchers built a finite element model of the dog-bone tensile specimen in LS-DYNA, meshing it into nearly 75,000 elements with longitudinally aligned fibre bundles and boundary conditions mirroring the physical test. The simulation showed maximum tensile forces of 1400 newtons for the pristine composite and 600 newtons for the seawater-exposed model—at a displacement of 1.5 millimetres, figures that closely matched the experimental data for equivalent specimens. Crucially, the model confirmed that sea exposure cuts the material’s tensile load-bearing capacity roughly in half. With manufacturing defects addressed and fibre loading optimized near 10 percent, the authors conclude, Pandanus-based composites could offer a genuinely sustainable, high strength-to-weight alternative for everyday structural applications—crafted from a tree that grows, quite literally, along the shoreline where these materials may one day serve.

Subject of Research: Development and characterization of biodegradable Pandanus utilis fibre-reinforced PLA composites

Article Title: Biodegradable Pandanus Utilis fibre-reinforced PLA composites: characterization, mechanical behaviour, and fracture analysis

Article References: Dabee, C., Casarejos, E., & Ramful, R. (2026). Biodegradable Pandanus Utilis fibre-reinforced PLA composites: characterization, mechanical behaviour, and fracture analysis. Journal of Materials Science: Polymers, 1(1), Article 17. https://doi.org/10.1007/s44493-026-00019-0

Image Credits: AI Generated

DOI: 10.1007/s44493-026-00019-0

Keywords: Pandanus utilis, PLA, biodegradable composites, natural fibre composites, mercerization, tensile strength, flexural strength, water absorption, soil degradation, digital image correlation, finite element analysis, seawater exposure