Zoran S. Petrović

Polyurethanes from Vegetable Oils

Vegetable oils are excellent but very heterogeneous renewable raw materials for polyols and polyurethanes. This review discusses the specific nature of vegetable oils and the effect of their structures on the structure of polyols and polyurethanes. One section is dedicated to polyols for rigid and flexible foams and methods of their preparation such as direct oxidation of oils, epoxidation followed by ring opening, hydroformylation, ozonolysis, and transesterification. The next section deals with preparation and structure‐property relationships in polyurethanes from different groups of polyols, different isocyanates, and different degrees of crosslinking. The final section covers the environmental aspects of bio‐based polyurethanes, i.e., thermal stability, hydrolytic stability, and some aspects of biodegradability.

Thermal stability of polyurethanes based on vegetable oils

A series of polyurethanes from polyols derived from soybean, corn, safflower, sunflower, peanut, olive, canola, and castor oil were prepared, and their thermal stability in air and nitrogen assessed by thermogravimetric analysis, FTIR, and GC/MS. Oil-based polyurethanes generally had better initial thermal stability (below 10% weight loss) in air than the polypropylene oxide-based polyurethane, while the latter was more stable in nitrogen at the initial stage of degradation. If weight loss at a higher conversion is taken as the criterion of stability, then oil polyurethanes have better thermal stability both in air and in nitrogen.

Structure and properties of polyurethane–silica nanocomposites

Nanocomposites with different concentrations of nanofiller were prepared by adding nanosilica filler to the single-phase polyurethane matrix. A control series was prepared with the same concentrations of micron-size silica. The nanosilica filler was amorphous, giving composites with the polyurethane that were transparent at all concentrations. The nanocomposites displayed higher strength and elongation at break but lower density, modulus, and hardness than the corresponding micron-size silica-filled polyurethanes. Although the nanosilica showed a stronger interaction with the matrix, there were no dramatic differences in the dielectric behavior between the two series of composites.

Rigid polyurethane foams based on soybean oil

Both HCFC- and pentane-blown rigid polyurethane foams have been prepared from polyols derived from soybean oil. The effect of formulation variables on foam properties was studied by altering the types and amounts of catalyst, surfactant, water, crosslinker, blowing agent, and isocyanate, respectively. While compressive strength of the soy foams is optimal at 2 pph of surfactant B-8404, it increases with increasing the amount of water, glycerin, and isocyanate. It also increases linearly with foam density. These foams were found to have comparable mechanical and thermoinsulating properties to foams of petrochemical origin. A comparison in the thermal and thermo-oxidative behaviors of soy- and PPO-based foams revealed that the former is more stable toward both thermal degradation and thermal oxidation. The lack of ether linkages in the soy-based rather than in PPO-based polyols is thought to be the origin of improved thermal and thermo-oxidative stabilities of soy-based foams.

Structure and properties of halogenated and nonhalogenated soy‐based polyols

Four polyols intended for application in polyurethanes were synthesized by oxirane ring opening in epoxidized soybean oil with hydrochloric acid, hydrobromic acid, methanol, and hydrogen. The structures of the polyols were characterized by spectroscopic, chemical, and physical methods. The brominated polyol had 4.1 hydroxy groups, whereas the other three polyols had slightly lower functionality. The densities, viscosities, viscous-flow activation energies, and molecular weights of the polyols decreased in the following order: brominated > chlorinated > methoxylated > hydrogenated. All the polyols were crystalline solids below their melting temperature, displaying multiple melting peaks. The methoxylated polyol was liquid at room temperature, whereas the other three were waxes.

Polyols and Polyurethanes from Hydroformylation of Soybean Oil

This paper compares physical and mechanical properties of polyurethanes derived via the hydroformylation approach and is a part of our study on the structure–property relationships in polyurethanes created from vegetable oils. The double bonds of soybean oil are first converted to aldehydes through hydroformylation using either rhodium or cobalt as the catalyst. The aldehydes are hydrogenated by Raney nickel to alcohols, forming a triglyceride polyol. The latter is reacted with polymeric MDI to yield the polyurethane. Depending on the degree of conversion, the materials can behave as hard rubbers or rigid plastics. The rhodium-catalyzed reaction afforded a polyol with a 95% conversion, giving rise to a rigid polyurethane, while the cobalt-catalyzed reaction gives a polyol with a 67% conversion, leading to a hard rubber having lower mechanical strengths. Addition of glycerine as a cross-linker systematically improves the properties of the polyurethanes. The polyols are characterized by DSC. The measured properties of polyurethanes include glass transition temperatures, tensile strengths, flexural moduli, and impact strengths.

Epoxidation of soybean oil in toluene with peroxoacetic and peroxoformic acids - kinetics and side reactions

The kinetics of the epoxidation of soybean oil and the extent of side reactions were studied at 40, 60, and 80 °C. Epoxidation was carried out in toluene with “in situ” formed peroxoacetic and peroxoformic acid and in the presence of an ion exchange resin as the catalyst. The reaction was found to be first-order with respect to the double bond concentration. At higher temperatures and at higher conversions a deviation from the first-order kinetics was observed. The rate constants for the epoxidation with peroxoacetic acid were 0.118 (h−1) at 40 °C, 0.451 (h−1) at 60 °C and 1.278 (h−1) at 80 °C, while those for peroxoformic acid were 0.264, 0.734, and 1.250 (h−1). The activation energy was found to be 54.7 kJ/mol for the epoxidation with peroxoacetic acid and 35.9 kJ/mol for that with peroxoformic acid. Three factors indicated that side reactions did not occur on a large scale: The absence of an OH band in the IR spectra, the formation of less than 2% of higher molecular weight products from gel permeation chromatography and the selectivity values between 0.9 and 1.

Structure and properties of polyurethanes based on halogenated and nonhalogenated soy–polyols

Four polyols were prepared by a ring opening of epoxidized soybean oil with HCl, HBr, methanol, and by hydrogenation. Two series of polyurethanes were prepared by reacting the polyols with two commercial isocyanates: PAPI and Isonate 2143L. Generally, the properties of the two series were similar. The crosslinking density of the polyurethane networks was analyzed by swelling in toluene. Brominated polyols and their corresponding polyurethanes had the highest densities, followed by the chlorinated, methoxylated, and hydrogenated samples. The polyurethanes with brominated and chlorinated polyols had comparable glass transition and strength, somewhat higher than the polyurethane from methoxy containing polyol, while the polyurethane from the hydrogenated polyol had lower glass-transition and mechanical properties.

Structure and physical properties of segmented polyurethane elastomers containing chemical crosslinks in the hard segment

Two series of segmented polyurethanes, one containing 50% soft segments and the other with 70% soft segments were synthesized. Chemical crosslinks were introduced through the hard segment in a controlled way. Chemical polyurethane networks were characterized by swelling. The effect of the degree of crosslinking on properties was examined. It was found that chemical crosslinks in the hard segment reduce the mobility of the soft phase and destroy the crystallinity of the hard phase, but they improve heat stability of the hard domains.

Effect of Nano-and Micro-Silica Fillers on Polyurethane Foam Properties:

Two series of rigid and flexible polyurethane foams were prepared with two types of silica fillers. The density of the flexible foams was 60 kg/m 3 and that of rigid 30 kg/m3. The fillers were micro-silica of the average particle size of 1.5 mm and nano-silica of the average particle size of 12 nm. The concentration of fillers varied from 0–20%. The micro-silica filler did not show any significant effect on density of either rigid or flexible foams. Nano-silica increased the density of both types of foams only at concentration above 20%. Nano-silica lowered the compression strength of both types of foams at all concentrations while micro-silica exhibited the same effect at concentrations above 10%. The hardness and compression strength in flexible polyurethane foams with nano-silica was increased and the rebound resilience decreased. Reduced density of foams was not changed by nano-silica concentrations up to 20%. It is assumed that the nano-filler, as an additional physical crosslinker, increased modulus of the flexible segment in the polyurethane matrix, resulting in increased hardness and compression strength. The micro-filler in flexible foams lowered hardness and compression strength, but increased rebound resilience. Wide angle X-ray scattering (WAXS) showed amorphous morphology of both flexible and rigid foams filled with nano-silica. WAXS of the micro-silica filled foams showed the presence of randomly oriented crystalline quartz particles and the amorphous structure of the polymeric matrix.