Stability of the hottest mixed polyurethane rubber

The stability of mixed polyurethane rubber

mixed polyurethane rubber (sometimes called mixed rubber) is prepared from polyester and polyether polyols, supplemented by aromatic, aliphatic diisocyanates and chain extenders. Compared with other polyurethane compounds, polyurethane (PU) rubber has the properties of rubber. In many high standard practical applications, polyester polyurethane rubber is required to have hydrolysis resistance. In other applications, polyether polyurethane rubber is required to maintain the transparency or color fastness of the material after heating or ultraviolet radiation. As a rubber formulation engineer, we are mainly looking for suitable stabilizers to improve the hydrolysis resistance and performance stability of rubber after heating and lighting. We hope that these additives have good solubility in polyols to improve the efficiency of the production process; Or it is easy to weigh and can be easily mixed into the raw materials as a matching material

hydrolytic stability of polyester polyurethane

hydrolytic stabilizers are carbodiimide products, which are divided into monomers, liquid oligomers and polymers. This kind of anti hydrolysis stabilizer is added to polyester polyurethane rubber to maintain the Mooney viscosity of the rubber during storage. The mold made of polyurethane rubber with stabilizer can inhibit the hydrolysis of water or acidic substances. The properties of anti hydrolysis stabilizers used in this study are listed in Table 1

for polyester polyurethane rubber, three anti hydrolysis stabilizers are very useful. Due to the low molecular weight of carbodiimide monomer (cdi-m), it can move to the surface of the material, improve the stability of polyurethane rubber or polyurethane masterbatch, and prolong their storage time. Liquid hydrolytic stabilizers, such as carbodiimide oligomer (cdi-o), are soluble in polyester polyols. Therefore, it can directly add liquid anti hydrolytic stabilizers to polyester polyols before polymerization, so as to improve production efficiency. The carbodiimide content of polymer anti hydrolysis stabilizer is high, which can inhibit hydrolysis for a long time

the decomposition of polyester part of polyurethane rubber is shown in Figure 1. We can see that water molecules attack the carbonyl group of polyester, splitting it into an alcohol and an acid, and these products will react with the polyester junction, thereby further degrading the polyester. In this process, polyurethane rubber will gradually degrade and gradually lose its rubber properties. Molds without hydrolysis stabilizer will continue to suffer from this hydrolysis reaction. Generally speaking, this part will gradually lose its hardness and eventually soften into a paste

the role of hydrolysis stabilizer is like a scavenger who uses computer to carry out the experimental process and dynamically display the experimental curve of water and acid reaction, generating urea derivatives with stable properties. This mechanism is shown schematically in Figure 2. Table 2 describes an example of the role of carbodiimide in maintaining polyurethane stability. From table 2, we can see that one part (1%) of carbodiimide can still maintain the viscosity of the polymer after 136 days of aging under the temperature and humidity conditions in Florida

the comparison of monomer and polymer effects of carbodiimide is shown in Table 3. The rubber used is polyester polyurethane au5004. These data show that rubber composites soaked in boiling water show good performance stability

content level of carbodiimide

high content level of carbodiimide can prolong the water resistance and hydrolysis resistance of the material, although this protection will eventually fail. Table 4 shows the effect of adding 0 part, 1 part, 2 parts and 5 parts of carbodiimide monomer (cdi-m) to polyester polyurethane au5004 on the material properties. These data show that carbodiimide can not only improve the water resistance and hydrolysis resistance of materials, but also improve the thermal stability and compression deformation value of materials. When a part of carbodiimide monomer is added to the composite, these properties have been significantly improved, and with the increase of carbodiimide monomer content, the properties of the composite will be further improved. In the boiling water immersion test, the material with high content of carbodiimide monomer shows great advantages, which can better maintain the performance of the material

the content of carbodiimide in the composite determines the durability of the water resistance of the material. The change of tensile strength of polyester blended polyurethane au5004 composite containing 0, 2 and 4 parts of carbodiimide monomer after aging for 90 days at 70 ℃ and 95% relative humidity. The data showed that the mechanical properties of the composite without stabilizer decreased by more than 60% after 30 days of aging at high temperature and high humidity, and the mechanical strength was completely lost after 60 days. After adding two parts of carbodiimide monomer, the mechanical properties of the same composite are still more than 80% after 60 days of aging, but the mechanical properties begin to decline significantly after 90 days. The mechanical properties of the composite containing 4-component carbodiimide monomer decreased by about 14% at the beginning of the 90 day test period, and then basically remained unchanged

in the water immersion test of the same composite aged at 70 ℃ for 84 days, the decline curve of the mechanical properties of the materials is similar to that of the materials without carbon addition and with the focus on improving their practical ability to use different materials. After 84 days, the tensile strength of the composite containing 2 parts and 4 carbodiimide monomers decreased significantly, but the tensile strength of about 15MPa was retained after the first rule

long term data

the research results show that au5004 mixed polyester polyurethane rubber containing 5 parts of carbodiimide polymer (cdi-p) still has excellent stability after being exposed to water at room temperature for one year. From the change data of the stress-strain properties of the composite after 0, 6 and 12 months, we can see that the stress-strain properties of the composite have hardly changed. Of course, the inhibitory effect of carbodiimide will eventually be lost due to its reaction with water, but when the material is in contact with water or in a humid environment, the appropriate addition of carbodiimide is an effective blending method

effect of stearic acid on the hydrolysis process of polyester polyurethane

for mixed polyurethane, stearic acid is a very effective spacer, which is often added in a small amount to mixed polyurethane to prevent the latter from adhering to the mixing equipment. However, when it is added to polyester polyurethane, the hydrolysis resistance of the material will be reduced, especially when the content of stearic acid is high. The research data showed that after peroxide vulcanization and silicon filled polyester polyurethane au5004 rubber composite was soaked in 100 ℃ water for 70 hours, the decrease of hardness increased with the increase of stearic acid content

thermal aging stability

blended polyurethane is made from polytetrafluoroethylene glycol (PTMEG) maintained by the host of universal testing machine. It is well known that aliphatic dicyclohexylmethane-4.4 'diisocyanate (h12md1) has good photostability, but it is easy to be oxidized. The light stability and oxidation stability can be improved by adding antioxidants and UV stabilizers. In the process of storage, processing and final use, polyether polyurethane often degrades, which is mainly due to the combined effect of thermal oxidation and UV exposure

the degradation mechanism of the bond between polyether and polyester can be found in the literature, which is described here in Figure 3 and Figure 4. The degradation of polyether is mainly due to the free radical mechanism of oxidation and circulation. Oxidation is mainly caused by energy sources, such as thermal action, UV radiation, mechanical action, electronic magnetic field and so on. These energies break the hydrocarbon bond and the carbon carbon bond link, producing free radicals (r-). The residual catalyst accelerates the oxidative decomposition process. Once in the form of free radicals, they can attract hydrogen atoms from Alfa carbon, turn into hydrogen peroxide (ROOH) and another carbon free radical, and then continue this cycle. When hydrogen peroxide is decomposed into two free radicals, the process of oxidative decomposition will be accelerated. The two free radicals decomposed are alkoxy (ro-) and hydroxyl (oh-). In polyether based blended polyurethane rubber, this oxidative decomposition process will lead to chain breaking, and the hardness and tensile strength will decrease

polyurethane protectants are usually divided into three categories, including initial antioxidants, UV absorbers, and amine and light blocking agents. Initial antioxidants, often spatially hindered phenolic antioxidants such as ao-10, inhibit the formation of free radicals. UV absorbers and amine blocking and anti light agents can prevent the oxidation of polyurethane caused by UV light

the polyurethane rubber used in this study is made of aliphatic diisocyanate. However, the decomposition mechanism shown in Figure 4 still applies and points out the necessity of using UV stabilizers. Ultraviolet radiation can also break nitrogen carbon bonds and carbon oxygen bonds to form free radicals. These free radicals continue to react, leading to the decomposition of polyurethane rubber, resulting in chain breakage and reduced physical properties

aliphatic polyether polyurethane eu97 is widely used in occasions where transparent materials are required. The cured part of the polymer after proper mixing looks transparent to the naked eye. Transparent compounds of course cannot have any UV protectants, such as carbon black or titanium dioxide. This makes them very vulnerable to ultraviolet light and outdoor weather. During the aging process, the compound will also appear slight yellowing, which is mainly caused by heating. Many studies have been carried out on improving aging performance

the basic formula used in this study is shown in Table 5. Foamed silica is used as a high toughening additive in the formula, which will not affect the transparency of the product, and the isobutyrate degdma (diethylene glycol 3,4-isobutyrate) is also used as a peroxide additive. These basic composites do not have any protective agents and have good transparency, just like the effect of just curing. Even if they are accelerated at 70 degrees in the oven for 5 to 10 days, the transparency will not be affected. Unfortunately, studies have shown that aging these compounds without adding protective agents over a longer period of time and at a lower temperature will cause a certain degree of decomposition; However, even if antioxidants are added to protect the polymer, the product will still turn yellow. If the cured product is exposed to ultraviolet radiation in the open air, it will obviously cause decomposition. Therefore, it is a challenge to develop an anti degradation compound to protect the polymer from oxidation, weathering and yellowing

the performance evaluation of several antioxidants and two substances containing UV stabilizer added to polyether blended polyurethane eu97 is shown in Table 5. The mixture was cured into thin sheets conforming to ASTM standards, and then the samples were exposed to 70 degrees in an oven with circulating hot air for 5 and 10 days. The data shows that the samples without antioxidants have the best resistance to yellowing, but even the most yellowing samples show slight yellowing for transparent samples

the sample was weathered for 8 weeks in Florida (latitude 27 degrees 52 minutes, west longitude 82 degrees 41 minutes). The data showed that there was no or only 0.1 phr of hindered phenolic antioxidant ao-10 in the complex, and the surface crack appeared at 2 weeks. The samples with higher content of antioxidants but no UV stabilizer appeared after 4 weeks