Hemp shives, the woody core of the hemp stem left over after bast fibers are harvested, are an attractive raw material. They are lightweight, highly porous, and offer thermal conductivity around 0.048 W/m·K, making them excellent candidates for insulation panels. When bonded with gelatinized potato starch, hemp-shive composites have previously achieved thermal conductivities in the range of 0.06 to 0.07 W/m·K and impressive moisture-buffering values above 2.6 g/(m²·%RH). But the same porosity that makes them good insulators also makes them vulnerable. Water seeps into the open pore network, the hydrophilic starch binder swells, and over time the material can lose dimensional stability, mechanical integrity, and resistance to biological growth.

Earlier attempts to fix this weakness have relied on thermal modification of fibers, silane treatments, hot-water extraction, or synthetic hydrophobic coatings. These approaches work, but they add processing steps, energy demands, costs, and sometimes environmentally questionable chemistry. The new study takes a different route: instead of chemically altering the plant material, the researchers simply dispersed finely ground natural calcium carbonate throughout the matrix. The mineral powder, milled from Champagne-region limestone and composed of 94.6 percent calcium carbonate, was treated not as a passive filler but as a functional additive that reshapes the composite’s internal architecture.

Because the performance of such composites depends on several competing variables, the team avoided trial-and-error formulation. They applied Response Surface Methodology using a Central Composite Design, varying two parameters, the starch-to-fiber ratio and the calcium-carbonate-to-fiber ratio, across eleven experimental runs including replicated center points. Four responses were tracked simultaneously: bulk density, thermal conductivity, water absorption, and compressive strength. Quadratic regression models fitted to the data achieved coefficients of determination between 0.83 and 0.94, and analysis of variance confirmed that both factors and their interaction significantly shaped every property measured.

The models revealed a fascinating tug-of-war inside the material. Increasing starch raised water uptake, as expected from its hydroxyl-rich chemistry, but calcium carbonate pushed hard in the opposite direction, blocking capillary pathways and reducing the accessible internal surface. A significant negative interaction term showed that the mineral partially counteracts the binder’s hydrophilic tendency. Meanwhile, both components boosted compressive strength, with starch dominating through inter-particle bonding and calcium carbonate acting as a micro-reinforcement that stiffens the matrix and fills residual micropores. Density and thermal conductivity rose moderately with both additives, a predictable consequence of replacing trapped air with solid matter.

Multi-objective optimization using desirability functions converged on a formulation with a starch-to-fiber ratio of 0.30 and a calcium-carbonate-to-fiber ratio of 0.39. Validation experiments matched the predictions closely, with individual errors of 0.93 to 6.46 percent and an average deviation of just 3.72 percent, yielding a global desirability of 80 percent. The optimized composite reached a bulk density of 221 kg/m³, a thermal conductivity of 0.056 W/m·K, water absorption of 22 kg/m², and a compressive strength of 0.68 MPa, a compelling balance of insulation, strength, and moisture resistance.

Microscopy and porosimetry explained why the formulation works so well. Scanning electron micrographs of the reference material showed a heterogeneous, poorly bonded structure with large voids and smooth, uncoated hemp particles. In the optimized composite, calcium carbonate microspheres were embedded throughout the matrix, the binder film became continuous and evenly distributed, and fiber-matrix interfaces appeared far more cohesive. Mercury intrusion porosimetry quantified the transformation: total intrusion volume fell from 2.635 to 1.577 mL/g, total porosity dropped from 73.5 to 66.0 percent, and the median volumetric pore radius shrank from 0.452 to 0.401 micrometers. Ultrasonic pulse velocity nearly doubled, rising from 273 to 446 m/s, confirming dramatically improved internal cohesion.

The hydric results were equally striking. Capillary water absorption at long exposure times fell by roughly 29 percent compared with the references, from more than 30 kg/m² to 22 kg/m², and the wetting front penetrated only about 5 centimeters into the optimized panel. Surface wettability improved as well: the initial water contact angle climbed from around 50 to 54 degrees for the references to 87.26 degrees for the optimized composite, and the starch-calcium-carbonate binder gel itself showed a higher contact angle than pure starch gel. Crucially, the material did not become a vapor barrier. Water vapor permeability remained in the same range as other plant-fiber insulators, and the moisture buffer value actually reached the classification of excellent, meaning the wall material can still absorb and release humidity to regulate indoor air, while resisting liquid water ingress.

Acoustic and thermal stability tests rounded out the picture. Sound absorption curves for all formulations showed a characteristic peak near 1000 Hz, and the weighted absorption coefficient slightly improved from 0.30 to 0.36 with the mineral addition, indicating that pore refinement did not destroy the interconnected network responsible for acoustic dissipation. Thermogravimetric analysis showed the optimized composite retained 37.1 percent residual mass at 600 °C, compared with under 21 percent for the references, thanks to the mineral fraction and the endothermic decarbonation of calcium carbonate near 770 °C. Infrared spectroscopy confirmed the diagnostic carbonate bands in the optimized sample and suggested interfacial interactions, possibly hydrogen bonding, between the mineral surface and the hydroxyl-rich organic matrix.

The broader significance is that a mineral available almost anywhere, requiring no chemical synthesis, can deliver durability improvements that previously demanded elaborate surface treatments. The researchers caution that long-term service performance, including freeze-thaw cycling, wet-dry aging, biological attack, and fire behavior, still requires dedicated testing, and a full life-cycle assessment remains to be done. But the demonstration that ground limestone can simultaneously strengthen a hemp-starch insulation panel, cut its water uptake by nearly a third, preserve its breathability and moisture buffering, and even modestly improve its acoustic and thermal stability marks a meaningful step toward insulation materials that store carbon, breathe with the building, and survive decades of real-world weather.

Subject of Research: Multi-objective optimization of hemp-shive and starch biocomposites reinforced with natural calcium carbonate for moisture-resistant building insulation

Article Title: Natural CaCO₃ improves the moisture resistance and mechanical performance of hemp-starch biocomposites: A multi-objective optimization study

Article References: Balti, S., Maalouf, C., Moussa, T., Bliard, C., Lachi, M., Rousse, C., Alsedeh, O., Vazquez, P., Bogard, F., & Polidori, G. (2026). Natural CaCO₃ improves the moisture resistance and mechanical performance of hemp-starch biocomposites: A multi-objective optimization study. Case Studies in Construction Materials, 25, Article e06574. https://doi.org/10.1016/j.cscm.2026.e06574

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06574

Keywords: hemp shives, calcium carbonate, potato starch, bio-based insulation, response surface methodology, moisture resistance, thermal conductivity, compressive strength, porosity, moisture buffering, sustainable construction, biocomposites

Salecan is not an ordinary hydrocolloid. Produced by microbial fermentation, it was approved as a novel food additive by the U.S. FDA in 2020 and by China’s National Health Commission in 2021. Structurally, it is a linear, unbranched glucan built from a repeating unit of seven beta-1,3-linked and two alpha-1,3-linked glucose residues, with purity exceeding 90 percent. That linearity matters enormously. Most familiar anionic polysaccharides, from xanthan gum to carrageenan and pectin, carry highly branched backbones and heterogeneous branch distributions, features that create steric hindrance and thermodynamic incompatibility with starch chains. Salecan’s naked backbone can align and entangle directly with starch molecules, while its uniformly distributed carboxyl groups from succinyl and pyruvyl substituents provide consistent negative charge across the entire chain. As a fermentation product, it is also immune to the seasonal and geographic constraints that complicate plant- and seaweed-derived gums.

To test whether Salecan’s behavior depends on starch structure, the research team led by Wanping Xiong and Xianggui Chen at Sichuan University paired two starches that sit at opposite ends of the botanical spectrum. Potato starch, a tuber starch, features large oval granules of 15 to 100 micrometers, negatively charged monophosphate ester groups on its molecular chains, a B-type crystalline pattern and a highly cross-linked granular architecture. Corn starch, the cereal archetype, presents small polygonal granules of 5 to 20 micrometers, a nearly neutral surface, an A-type crystalline pattern and a substantially higher amylose content of 25 to 28 percent with a lower degree of polymerization. Every major structural determinant of polysaccharide-starch interaction therefore differs between the pair, making it an ideal contrast model.

The divergent results began immediately. When Salecan was added at concentrations from 0.5 to 2 percent by starch dry weight, both starches showed delayed gelatinization, with pasting curves shifted to the right and peak times significantly prolonged, findings confirmed by differential scanning calorimetry. But the viscosity story split cleanly along charge lines. In potato starch, Salecan dramatically reduced peak, trough and final viscosity, and at 2 percent addition the consistency coefficient fell by 81.56 percent. The authors attribute this to electrostatic repulsion between the negatively charged potato starch and the anionic polysaccharide, which confines Salecan to the granule surface as a barrier that blocks water ingress and amylopectin leaching. Corn starch behaved in the opposite way: Salecan increased its peak viscosity, breakdown strength and final viscosity, with the consistency coefficient surging by 332.9 percent at 2 percent addition, because the neutral granules allowed Salecan to disperse through the paste and leached amylose supplied abundant hydroxyl groups for hydrogen bonding and chain entanglement.

Rheological measurements reinforced the split. All composite pastes displayed shear-thinning pseudoplastic behavior, but Salecan reduced the apparent viscosity and shear stress of potato starch systems while raising those of corn starch. Frequency sweep tests showed that Salecan depressed the storage and loss moduli of potato gels yet elevated the moduli of corn gels in a concentration-dependent fashion. For food engineers, this duality is a gift. High-viscosity tuber pastes used in sauces, custards and dessert gels become easier to pump and process without sacrificing final gel integrity, while cereal-based soups, gravies and bakery fillings gain viscosity and thermal stability exactly where hot filling and cooling demand them.

The second half of the study tackled retrogradation, the costlier enemy of shelf life, and here Salecan proved a unifying remedy. Storing gels at 4 degrees Celsius for up to 21 days, the researchers tracked gel hardness with texture analysis, water mobility with low-field nuclear magnetic resonance, crystallinity with X-ray diffraction, molecular order with Fourier transform infrared spectroscopy and microstructure with scanning electron microscopy. Every technique converged on the same conclusion: at 1 percent addition, Salecan significantly slowed the aging of both starches, cutting gel hardness by 33.63 percent for potato starch and 31.19 percent for corn starch relative to controls.

The water-migration data are particularly striking. During storage, bound water progressively escapes the starch matrix and becomes free water, a process that culminates in syneresis, the unappetizing pooling of liquid that ruins chilled desserts and fillings. Free water appeared in plain corn starch gel after only three days and in potato starch gel after fourteen days. At 1 percent Salecan, the free water fraction after 21 days fell from 3.75 percent to 0.54 percent in potato gels and from 15.81 percent to 6.31 percent in corn gels. X-ray diffraction showed that Salecan did not change the crystal type formed during aging but significantly lowered relative crystallinity, while infrared ratios revealed suppressed short-range molecular order and reduced double-helix formation at the same optimal dosage. Interestingly, both hardness and structural indices followed a U-shaped dose curve, first falling and then rebounding at high concentrations, because Salecan’s intense water-holding capacity ultimately concentrates amylose in the remaining solvent and promotes renewed association.

The proposed mechanism weaves these observations together. During short-term retrogradation, Salecan’s linear backbone entangles with amylose and sterically blocks chain re-association, delaying initial network formation. During long-term storage, it disrupts the hydrogen-bond reformation needed for double-helix nucleation, impedes the ordered alignment of amylopectin side chains, and physically retains water within the gel network. Scanning electron microscopy captured the microstructural fingerprints of these effects: Salecan produced smaller, more orderly pores and tighter matrix interconnection in potato gels, while in corn gels it preserved a smoother, looser honeycomb structure by resisting the dehydration shrinkage that normally crumples high-amylose networks. No new covalent bonds were detected, confirming that the interactions are dominated by hydrogen bonding and physical entanglement.

Perhaps the most surprising results came from simulated digestion. Freshly gelatinized starch with Salecan was hydrolyzed more slowly by alpha-amylase and amyloglucosidase, because the additive suppresses complete gelatinization and its dense composite network shields enzyme binding sites on starch molecules, a finding that points toward low-glycemic-index versions of instant porridges, steamed rice alternatives and gluten-free breads. Yet after seven days of retrogradation, the pattern inverted: Salecan-containing gels were digested faster than highly crystallized plain retrograded gels, precisely because Salecan had prevented the formation of enzyme-resistant crystalline domains. That inversion doubles as independent mechanistic evidence, confirming from a nutritional angle that Salecan suppresses resistant crystal formation during aging. The authors caution that their structural-dependence conclusions rest on just two contrasting starches, and that broader starch panels will be needed to validate generality. Still, the prospect of a single clean-label, fermentation-produced ingredient that simultaneously tames viscosity where it runs too high, boosts it where it falls short, prevents staling, stops syneresis and reshapes glycemic response is exactly the kind of multifunctional tool the clean-label food industry has been searching for.

Subject of Research: Modulation of potato and corn starch gelatinization, retrogradation and digestibility by the anionic polysaccharide Salecan

Article Title: Structure-dependent modulation of potato and corn starch gelatinization and retrogradation by Salecan

Article References: Xiong, W., Hu, L., Ni, C., Zhao, J., Huang, Y., Yang, X., Chen, P., & Chen, X. (2026). Structure-dependent modulation of potato and corn starch gelatinization and retrogradation by Salecan. Food Chemistry: X, 39, Article 104470. https://doi.org/10.1016/j.fochx.2026.104470

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104470

Keywords: Salecan, starch gelatinization, starch retrogradation, potato starch, corn starch, food hydrocolloids, rheology, X-ray diffraction, water migration, in vitro digestion, low glycemic index, clean label