Preparation and properties of bio-based polyurethane foams from natural rubber and polycaprolactone diol

Bio-based polyurethane foam (PUF) was synthesized by a one-shot polymerization using hydroxyl telechelic natural rubber (HTNR) and polycaprolactone (PCL) diols as a soft segment. The effect of HTNR/PCL diol molar ratio (1/0, 1/0.5, 1/1 and 0.5/1) on the foam formation rate and physical and mechanical properties of the resulting PUF was investigated. The formation of urethane linkage and cross-linked structure were confirmed by FTIR analysis. The foams observed by scanning electron microscope revealed to have almost closed cells. The molar ratio of HTNR/PCL diol affected the foam formation rate, the average diameter of cell, the regularity of cell shape, the elongation at break and the compressive strength. The foam density slightly changed with this molar ratio whereas the specific tensile strength of all samples was in the same range. All PUFs showed relatively high compression set. The biodegradability was assessed according to a modified Sturm test. Low density polyethylene and sodium benzoate were used as a negative and positive control sample, respectively. PUF samples showed an induction time of 33 days in which the percentage of biodegradation was similar to 7-11 %. At the end of testing (60 days), the highest degradation (45.6 %) was found in the sample containing 1/0.5 of HTNR/PCL diol molar ratio.