1. Polyurethane modified with cellulose/lignin/bark
Biodegradable polymeric materials synthesized from cellulose, lignin, chitin, etc. are on rise due to fact that their raw materials are a renewable resource and are completely biodegradable.
Using lignin as a polyol for synthesis of PU, a material with high stress and low ultimate strain was obtained. Add 18% polyethylene glycol (PEG) to provide soft segment structure; it reacts with diphenylmethane diisocyanate (MDI) to improve hardness of PU, but it also reacts with toluene diisocyanate (TDI), hardness of resulting product remains high. .
Using tetrahydrofuran as a solvent, lignin, MDI and polyoltriol as raw materials, polymerizing at room temperature for 8 hours, resulting PU can be converted into a transparent and fairly uniform film. With a molar ratio of -NCO/-OH of 1.2 and a mass fraction of lignin of 10-15%, physical and mechanical properties (Young's modulus, tensile strength and tensile strength) of prepared polyurethane material are better than those of polyester alone. Characteristics of material synthesized with trihydric alcohol in as hydroxyl component, even better.
Using acetonitrile as a solvent, react phenylisocyanate and catechin under nitrogen at 30°C for 24 hours. According to different molar ratios of two, three types of reaction products are obtained: tautomerism 3'-o-phenylaminocarbonylcatechol , 4' -o-phenylaminocarbonyl catechin (excess catechin), 3',4'-di-o-phenylaminocarbonyl catechin (excess isocyanate).
Filling polyurethane with plant components (syrup, lignin, wood powder filler, coffee powder, etc.) improves its thermodynamic properties and biodegradability. The botanical component is dispersed or dissolved in PEG or polyethylene sebacate (PES) and then mixed with MDI at room temperature to form a pre-cured product, which is then hot pressed to form a PU sample. If a plasticizer, surfactant and catalyst (dibutyltin dilaurate) are added and foamed with water before adding MDI, polyurethane foam can be obtained. The DSC spectrum and TG spectrum of PU showed that with an increase in mass fraction of plant components, Tg of polymer also increases, as well as its physical and mechanical properties. When mass fraction of plant components reached 20%, enhancement effect was most significant. The degradability of PU plant components, measured by soil incorporation method, is: mass loss rate of PU coffee powder reaches 5-10% after 9 months, and mass loss rate of PU syrup reaches 15% after 12 months.
Lignin and catechin have been successfully incorporated into polyurethane as degradable components, but extraction process has been extremely difficult. If bark containing these components is used directly as hydroxyl component, process can be simplified. Bark (BK) is processed into 80 mesh particles, dissolved or suspended in PEG or PES, stirred at 80°C for 5.5 hours, additives and diisocyanate are added after cooling, mixed and polymerized at a speed of 700 rpm for polyurethane foam. With an increase in amount of bark, compressive strength and elasticity of obtained PU increase linearly. In addition, strength factor of PU increases rapidly and very rigid foam can be obtained (see table). The biodegradability test of this foam shows that as bark content increases, rate of weight loss increases and elasticity also decreases.
Preparation and properties of biodegradable polyurethane foam
2. Polyurethane modified with monosaccharides or disaccharides
Someone did a thermodynamic analysis and mechanical testing of a mixture of glucose/fructose/sucrose and PEG-DI. In this experiment, 1,4-diazobicyclo(2,2,2)octane dissolved in diethylene glycol was used as a catalyst, and a mixture of PEG 200/PEG 400 was used as PEG. After prepolymerization at room temperature for 10 minutes at 120 Vulcanize at ℃ within 25 hours. With a mass fraction of glucose and fructose of 8% or a mass fraction of fructose of 14%, a film with uniform plasticity can be obtained. The DSC test found that Tg of obtained PU increases with an increase in mass fraction of sugar component, and melting temperature decreases accordingly. The DMA test also showed that with an increase in content of sugar component, elastic modulus and loss factor y increase, breaking stress increases and tensile strain decreases, which indicates that with an increase in mass fraction of sugar component, elasticity of resulting sample increased and viscosity decreased.
3. Polyurethane modified with starch
Chemical modification of polyurethane with cornstarch results in a highly absorbent foam. Reaction of TDI and polyester in a three neck flask at 80-90°C for 1-2 hours to obtain a prepolymer. The content of -NCO was analyzed by method of dipropylamine-hydrochloric acid to monitor reaction. Add to prepolymer corn starch, dried to constant weight, and quickly mix at a temperature of 70-90°C for 1-2 hours to obtain starch prepolymer. Add diluent (xylene:dibutyl phthalate molar ratio 5:1), water, catalyst and surfactant to mixture of prepolymer and starch-prepolymer, mix at high speed for 2-3 seconds, then pour into a mold and foam until polyurethane foam is obtained. The mechanical properties of this polyurethane foam, except that elasticity is reduced, rest of properties are equal or superior to those of ordinary polyurethane foam. When mass fraction of corn starch reaches 50%, water absorption capacity is almost 20 times higher than polyurethane foam without starch. According to analysis of infrared spectrum, structure of resulting polymer is -NHCO-OCH3-starch.
Add modified esterified tapioca starch (degree of substitution 0.05-0.07) to polyester polyurethane prepolymer and then further crosslink to form a polyurethane elastomer. The results show that when amount of tapioca esterified starch filler is 6-30%, except for elongation at break, mechanical properties of polyurethane elastomers are significantly improved, as well as thermal aging resistance is improved.
A biodegradable polyurethane elastomer has been synthesized using starch as a polyol.The degree of crosslinking of obtained elastomer increased, and tensile strength increased with increase in ratio , large, and decreased with increase in mass fraction of starch, and obtained elastomers had good elasticity. After being buried in soil for one month, compared with starch-free polyurethane elastomer, strength loss rate of former reaches 20-40%, and a large number of mold spots appear on surface, indicating its good biodegradability. .
The anti-vibration material obtained by modifying polyurethane with lactic acid has a weight loss rate of 50% after 40 days.