Modification of Rigid Polyurethane Foams with Straw Additive: Influence of Chemical Treatment and Content on Performance Properties

This work aimed to synthesize rigid polyurethane foams with improved functional properties through modification with the addition of cellulose in the form of straw: unmodified, silanized, and silanized with the addition of fumed silica. The prepared rigid polyurethane foams contained 0.5; 1; and 3 parts by weight of the modifier about the weight of the polyol used. As part of the work, a number of tests were carried out to determine the impact of the modifiers used on the reaction kinetics and on the functional properties of rigid polyurethane foams. Silanization improved thermal stability and interfacial compatibility, while silica further enhanced porosity and surface activity. The optimal properties were obtained at low loadings: 0.5 wt.% provided the best mechanical strength, and 1 wt.% yielded the most uniform cell morphology and density. Higher contents increased porosity, reduced strength, and lowered water resistance. Dynamic mechanical analysis confirmed predominantly elastic behavior, with silica-modified fillers offering the most stable thermomechanical response. Overall, even small amounts of modified straw enhanced mechanical, structural, and water-resistant properties, demonstrating its potential as a sustainable and cost-effective biofiller for eco-friendly polyurethane foams.