A novel highly functional plant oil-based polyols, Methoxylated Sucrose Soyate Polyols (MSSP), were cross-linked with isocyanate to formulate MSSP-based polyurethane (PU) thermosets. The degree of cure or conversion was studied using differential scanning calorimetry (DSC). Compression molding process was used to make composite panels out of MSSP-based polyurethane and flax fiber reinforcement of about 50 vol %. The MSSP-based PU resin reinforced with 50 vol % unidirectional E-glass fiber mats was tested as a reference. The composites were cured at 150°C for 60 minutes. Properties of the MSSP-based PU thermosets and its corresponding flax/glass-fiber reinforced thermoset composites were assessed by tensile strength and modulus, flexural strength and modulus, interlaminar shear strength (ILSS), nanoindentation test, and impact strength. Specific tensile modulus and strength of the flax fiber composites were found to compare with those of glass/MSSP-based PU. The glass/MSSP-based PU composite exhibited superior mechanical properties compared to both bio-based and petroleum-based composites used in previous studies. Compared to soybean oil based composites used in previous studies, bio-based composites based on MSSP showed 70 % and 101 % increase in flexural strength and modulus respectively, 102 % and 93 % increase in tensile strength and modulus respectively, and 56 % increase in ILSS. Compared to petroleum-based PU/glass composites used in previous studies, bio-based composites based on MSSP showed 60 % and 40 % increase in flexural strength and modulus respectively, 102 % and 78 % increase in tensile strength and modulus respectively, 50 % increase in ILSS. Higher mechanical properties in MSSP-based PU composites can be attributed to high functionality, rigid and compact chemical structures of MSSP oligomers in polyol resin.

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