Use of fatty acid esters of glycerol formal as processing oils for producing synthetic elastomers, elastomer compositions and tire treads

Abstract

The invention relates to the use of fatty acid esters of glycerol formal as processing oils for producing synthetic elastomers, elastomer compositions and tire treads. The present invention provides the use of C8-C18 fatty acid esters of glycerol formal as processing oils for the production of synthetic elastomers. The invention also provides its use in the production of tire treads as well as medical devices such as condoms and medical gloves, which can provide better performance characteristics. Furthermore, the invention relates to elastomer compositions comprising these fatty acid esters, and to tire treads comprising such elastomer compositions.

Description

TECHNICAL FIELD

[0001] The present invention relates to the use of fatty acid esters of glycerol formal as processing oil in the production of elastomers, in particular in the production of tire treads. BACKGROUND

[0002] The most widespread use of elastomers is in the manufacture of automobile tires. Other applications include the automotive industry, household appliances, construction, textiles and biomedical applications.

[0003] Elastomers (elastomeric polymers) are distinguished from plastic bodies (plastic polymers, so-called plastics) on the basis of the behavior of suitable test specimens when subjected to tension. Elastomers undergo considerable deformation at relatively moderate stresses, while plastic polymers have much lower elongation even when the stress reaches the tensile strength. From a functional point of view, the characteristic of plastic polymers is their flexibility, while the characteristic of elastomers is their elasticity.

[0004] The main components of the compounds used to produce synthetic rubber are elastomeric polymers, reinforcing fillers, processing oils (also known as rubber processing oils, extenders, plasticizers), vulcanizing agents. Other additives such as stabilizers and antioxidants are present in smaller amounts.

[0005] Reinforcing fillers are incorporated into the compositions used to produce synthetic rubber to increase rigidity and mechanical strength. In the past, carbon black has been widely used in tire production, but in recent years, precipitated silica has largely replaced carbon black. However, fillers increase the viscosity during processing, which can cause serious problems in the rubber manufacturing process, so it is necessary to add diluents.

[0006] Processing oils are mainly added to improve the dispersibility of the fillers and to reduce the viscosity of the compound, which not only allows the uniform distribution of the fillers and other components, but also reduces the entanglement of long polymer chains, thus allowing the chain to be improved. expandability. Due to its property of unraveling the entanglement between polymer chains, processing oil is also known as an extender. In addition, a more reasonable chain distribution allows the process of vulcanization or crosslinking with sulfur of the double bonds contained in the polymer chains of the elastomer to be optimized.

[0007] Aromatic petroleum oils are widely used as processing oils due to their compatibility with styrene butadiene rubber (SBR) and other unsaturated polydiene rubbers. The most common are residual aromatic extracts (RAE), treated distillate aromatic extracts (TDAE), mild or medium solventate extracts (MES). Naphthenic oils are also used.

[0008] Because nitrile elastomers have a higher polarity than styrene elastomers, phthalate-based plasticizers such as dioctyl phthalate (DOP) are widely used as a substitute for aromatic petroleum because they have a higher polarity. However, in recent years, there has been a tendency to replace phthalates with carboxylic diesters, as endocrine disruptors phthalates have been shown to be associated with obesity, insulin resistance, asthma and attention deficit hyperactivity disorder. Some of the most commonly used diesters are dioctyl adipate and dibutyl sebacate.

[0009] According to the European Parliament and Council Regulation on REACH (EC 18 / 09 / 2006), high aromatic oils containing polycyclic aromatic hydrocarbons (PAHs) have been banned since January 1, 2010. The limit of PAHs in process oil should be less than 3% by mass, measured according to the IP346 method. Manufacturers of rubber process oils have provided some environmentally friendly alternative process oils with low PAH content, such as TDEA and MES. However, to date, few studies have been published on the possible adverse effects of oils with low aromatic content.

[0010] Of particular concern is the problem of the dispersion of elastomer particles in the environment, caused by the wear of the tread of motor vehicle tires on asphalt pavements. According to the Mordor Intelligence website, 3.52 million tons of rubber process oil were produced in 2023, and it is expected that production will reach 4.07 million tons by 2028. However, almost all of the plasticizer of the tires is present in the tread, which gradually wears away over time due to the friction between the rolling tire and the asphalt pavement. Since the tire is replaced almost completely worn out, it can be assumed that at least 50% of the oil in the plasticizer will be dispersed into the environment.

[0011] It should also be remembered that the molecules of petroleum with aromatic structures are not soluble in water and are difficult to biodegrade, so the dust generated by wear tends to accumulate in the environment over the years. If we also consider that the oil usually represents about 15% by weight of the tread, the amount of dust emitted each year due to tire wear can exceed 20 million tons / year. In addition, the finest particles deposited on asphalt pavements are easily raised by passing vehicles, thus forming so-called fine particulate matter, polluting the environment of large cities.

[0012] Therefore, due to the health and environmental problems caused by aromatic oils used as process oils, there is an increasing demand for renewable, safe, sustainable and environmentally friendly alternative oils.

[0013] As a renewable source alternative to fossil process oils, the patent literature mainly reports soybean oil, sunflower oil and palm plant oil as a partial or complete replacement of aromatic oils.

[0014] Vegetable oil-based process oils used commercially in tire tread production are added to improve low-temperature flexibility. However, vegetable oils can usually be added in modest amounts, only partially replacing aromatic oils, or in cases of complete replacement, requiring the use of other adjuvants to impart the desired properties.

[0015] For example, patent application US2014 / 0135437 proposes the use of soybean oil in combination with certain resins. As for esters, EP3251872 A1 describes certain fatty acid esters that lower the glass transition temperature and thus reduce the performance of elastomers in winter.

[0016] However, vegetable oils and carboxylic acid esters have low compatibility with the diene polymers that make up most commercial elastomers. Therefore, if the oil or ester concentration in a composition exceeds the compatibility limit, the oil molecules will bleed to the elastomer's outer surface, causing it to feel sticky to the touch and giving it a greasy appearance. Over time, this continued migration of the ester or oil can lead to an irreversible loss of the material's elastic properties.

[0017] Regarding the use of elastomers in biomedical applications, particularly in medical gloves and condoms, it is well known that natural rubber latex, due to its molecular structure, is a highly flexible and stretchable cross-linked polymer material. It is important to note that the molecular structure that provides the material with flexibility inherently and necessarily confers permeability to some substances. This flexibility stems from a certain degree of molecular mobility, meaning that certain substances, depending on their atomic or molecular size and affinity for the latex components, are able to pass through this molecular structure. This diffusion process is naturally time-dependent. Most procedures that rely on the barrier function of latex are short enough in duration that this diffusion process is not of practical concern. However, of some clinical importance, contact with certain chemicals may enhance this diffusion process through swelling or other processes.

[0018] Therefore, plasticizers are not currently used in the production of nitrile or latex gloves, nor in the production of condoms. Summary of the Invention

[0019] The primary purpose of the present invention is to convert C6-C 22 The esters obtained by the esterification of fatty acids with glycerol formal (abbreviated as GFE) are used as processing oils in the production of elastomeric materials such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), polyurethane and acrylic elastomers, polyesters, etc. They can improve the dispersion of compound components in the production process of synthetic rubber and improve the elastic properties of the finished material.

[0020] A second object of the invention is to use these esters in the production of tire treads in order to improve road performance at low temperatures or to reduce tread wear by modifying the crosslink density.

[0021] A third object of the present application is to use these esters for the production of medical gloves and condoms made of elastomers such as natural rubber and nitrile rubber, with improved elastic properties, thus also forming a better barrier against microorganisms. DETAILED DESCRIPTION

[0022] Automotive tires must perform well in terms of wear resistance, rolling resistance, wet grip and retention of elasticity at low temperatures (winter performance). It is difficult to improve all the performances at the same time by replacing the current aromatic oils with other types of processing oils, since the above-mentioned performances are interrelated, an improvement in one parameter usually leading to a deterioration in another.

[0023] When a tire rolls on asphalt, a form of friction is generated due to the rolling. This can be explained as a continuous deformation of the elastomer from the moment the polymer chain molecules come into contact with the ground (compression) to the instant they detach from the ground (expansion). Since the compression-expansion mechanism is not perfectly elastic, heat is generated. This energy loss of the elastomer is called hysteresis.

[0024] In order to have a good rolling resistance (reduction in fuel consumption), the elastomer must provide a good elastic behavior and low hysteresis. Conversely, in order to obtain good wet performance (improvement in safety), the elastomer must have a high degree of hysteresis.

[0025] Surprisingly, it was found that the use of esters obtained by esterification of fatty acids with glycerol formal (called GFE) instead of other extenders significantly improves some important performance characteristics of the elastomer and there are no signs of any ester bleeding on the surface of the elastomer.

[0026] Due to the increase in rubber elasticity, the use of this tire tread material makes it possible to obtain better performance in winter driving, where low temperatures cause an increase in the modulus of elasticity of the elastomer.

[0027] Among the improvements achieved when using GFE as processing oil, of particular importance is the decrease in the modulus of elasticity of the elastomer in compositions of the same formulation compared to conventional petroleum. This means greater elasticity, measured by elongation at the same force, and therefore the use of GFE in tire treads provides better performance in winter driving, where low temperatures cause an increase in the modulus of elasticity of the elastomer, which in turn causes a loss of flexibility and hardening of the tire. In this way, of course, the safety in driving the vehicle in winter is also improved.

[0028] Alternatively, by exploiting this same property of conferring a lower modulus of elasticity to the elastomer, it is possible to obtain an increase in the wear resistance of the tyre by increasing the amount of vulcanizing agent when producing standard use tyres for roads in less cold climates or possibly with snowfall.

[0029] GFE is a fatty acid ester of glycerol formal, is in liquid state, has a boiling point between 190-195°C and is chemically a lipid. The illustration of the two isomers of the 6-atom and 5-atom dioxolane is as follows:

[0030]

[0031] The chemical name is oleic acid, 1,3-dioxan-5-yl ester or oleic acid, (1,3-dioxolan-4-yl)methyl ester or isomer and the molecular formula is C 22 H4O4.

[0032] The fatty acids that make up the acid part of the GFE ester are produced industrially by the hydrolysis reaction of vegetable oils, from which the components of the triglyceride are obtained: glycerol and fatty acids. Table 1 below shows the percentage composition of the main fatty acids in rapeseed oil, soybean oil and palm oil.

[0033] Table 1. Comparison of the main fatty acids in some vegetable oils

[0034]

[0035]

[0036] The fatty acid ester of glycerol formal can be obtained by direct esterification of the fatty acid with glycerol formal or by transesterification of the fatty acid methyl ester (FAME for short) with glycerol formal.

[0037] The production method is a typical method of this type of esterification. The method using titanates as catalyst is carried out at 220°C with a reaction time of 6-8 hours, depending on the excess alcohol used to promote the kinetics of the reaction.

[0038] GFE derived from vegetable oils such as soybean oil, rapeseed oil, palm oil, sunflower oil can advantageously replace petroleum-based process oils or other extenders such as phthalates in elastomers such as SBR and NBR rubbers, thus achieving an improvement in the flexibility of the finished product. In fact, from the experimental data on the stress-strain properties of SBR and NBR plasticized elastomers, it seems that GFE offers a lower modulus at all elongations compared to other reference oils.

[0039] In SBR rubbers, the significantly higher elongation at break measured for the GFE compound confirms a very good elastomeric effect of the GFE compound on the rubber compound compared to the standard MES oil.

[0040] A very important application consequence of this improved performance of GFE compared to petroleum is the excellent winter performance in the formulation of vulcanized diene rubber compositions for tire treads, when GFE is substituted for petroleum and the same amount is used, in the formulation.

[0041] Despite the lower modulus, in the same formulation (recipe), GFE is able to maintain the same tensile strength as the reference MES, while having a higher elongation at break. This makes it possible to achieve certain performance goals by changing the formulation of the mixture. In particular, by increasing the amount of sulfur and other cross-linking agents in the composition of the tread, it is possible to increase the degree of cross-linking of the elastomer and thus reduce tire wear while keeping other performances at appropriate values.

[0042] In NBR rubber applications, the performance of GFE is even better than that of plasticizers such as dibutyl sebacate or dioctyl adipate.

[0043] For the above reasons, medical authorities have established test methods to evaluate the ability of medical gloves and condoms to protect against the penetration of microorganisms. In Europe, the ISO 166040:2004 standard uses the bacteriophage Phi-X174 as a penetration probe for medical gloves. In particular, as will be shown in the examples, the introduction of GFE in the components of the elastomer improves the protection of the user against the penetration of viruses and bacteria.

[0044] According to the present application, it is possible to provide an elastomeric composition for tires, in which the amount of elastomer can vary between 20% and 90% wt and the amount of C8-C10 18 The amount of the ester of the formol of the fatty acid is between 10% and 80% wt, preferably between 20% and 70% wt of the fatty acid, more preferably 50% wt of the fatty acid.

[0045] For latex gloves and condoms, preferably, the composition comprises between 1% and 60% wt, more preferably between 5% and 50% wt of the ester, and between 40% and 99% wt of the elastomer.

[0046] Application Examples

[0047] The following examples show the results of experimental studies on the performance characteristics of elastomers such as SBR and NBR. These studies were carried out in comparison with some reference plasticizers in their respective fields of application.

[0048] Example 1. Tire Tread

[0049] In this example, the difference in tire performance was compared by replacing the petroleum-based processing oil with the GFE ester of the present application. The GFE made from rapeseed oil was used, while the MES aromatic oil was chosen as a typical reference oil. To this end, an experimental test was performed on a typical tread composition for a passenger car tire, as shown in Table 2. The formulation (recipe) was based on a mixture of elastomers consisting of dry styrene-butadiene rubber (S-SBR) with 25% styrene and 64% vinyl, high-cis-1,4-polybutadiene (Nd-BR) obtained by a neodymium-based catalyst, and natural rubber of the SIR-10 type (cis-1,4-polyisoprene). The fillers were Ultrasil 7000 silica and ASTM N375 standard grade carbon black. The other components were all typical elastomer vulcanization additives in the composition of this example. The relative amounts are expressed in parts by weight per 100 parts of total elastomer (phr). For example, the reference plasticizer, the GFE and the MES each had a concentration of 34.5 parts, with respect to 100 parts by weight of total elastomer (which is the sum of the fractions of S-SBR + Nd-BR + natural rubber = 102.5 parts). These quantities are expressed in parts per hundred rubber (phr) as a unit of measurement.

[0050] Furthermore, it can be seen from the following experimental data that the glass transition temperature of the tread obtained with the composition of the present application is lower than -70°C, and has a viscous modulus lower than 11 MPa at -20°C. Other characteristics are related to the ratio E” / E’ at -20°C (which is less than 0.2), the ratio E” / E’ at 0°C (which is less than 0.15), and the breaking strength after aging (which is greater than 11.00 Mpa), as shown in the experimental data reported below.

[0051] Table 2. Rubber composition for the tread

[0052] Ingredients GFE (phr) MES (phr) S-SBR FX5000 Arlanxeo 52.5 <------ Nd-BR (Europrene BR40) 35.0 <------ Natural Rubber 15.0 <------ Ultrasil 7000 Silica 65.0 <------ Carbon Black N375 22.0 <------ Fatty Acid Ester GFE 34.5 Aromatic Hydrocarbon MES 34.5 Silane Si-69 7.0 <------ ZnO 4.0 <------ Stearic Acid 2.0 <------ Paraffin Wax 1.0 <------ 6PPD 1.5 <------ CBS 1.8 <------ DPG 1.8 <------ Sulfur 1.5 <------ Total PHR 244.6 <------

[0053] Preparation of Rubber Compositions

[0054] The composition of the rubber to be tested was prepared in a 1.5 liter mixer using a two-step process. In the first phase, the elastomers, the fillers and the plasticizers were introduced into the mixer and the mixture was mixed at a temperature of 150°C to 180°C in order to optimize the distribution of the fillers in the elastomer chain mixture. In the second step, the elastomer crosslinking reaction was performed. The mixture was cooled to a temperature lower than 110°C, then the necessary components for crosslinking were introduced.

[0055] Test Methods

[0056] Rheological curves were recorded on an oscillating disc rheometer (ODR) at 175°C for 6 minutes according to the general rules of ISO 3417:2008. The stress-strain properties and final properties of the elastomer test specimens were tested according to ISO 37:2017 test method. The stress-strain properties after aging were determined for elastomer test specimens aged in an oven for 3 days at 100°C. The measurement of Shore A hardness was performed according to ISO 7619-1 :2010. The viscoelastic properties were measured on a Mettler-Toledo Star 1 DMA machine on which dynamic mechanical analysis (DMA) measurements were performed. The measurements were performed with a heating rate of 2°C / min in a temperature scan range from -100 to +100°C. The Tan Delta curve was determined according to ASTM E1640-13 (2018) test method.

[0057] Torque after crosslinking

[0058] Table 3 shows some characteristic data measured by rheometer during the vulcanization of the elastomers having the compositions shown in Table 2. MH represents the maximum torque reached by the rheological curve at the end of the crosslinking reaction, while ML is the minimum torque before the start of the vulcanization.

[0059] Table 3. Rheological test - torque data

[0060] Torque at 175°C x 6 min GFE MES ML (dNm) 16.62 16.42 MH (dNm) 61.62 68.97 MH-ML (dNm) 45.00 52.55

[0061] ML provides an indication of the viscosity of the unvulcanized rubber compound, and there is no evidence of a significant difference between the GFE oil and the reference MES oil. MH is related to the modulus of elasticity at the end of crosslinking. MH-ML is related to the crosslinking density, and this value is the lowest for the GFE, about 14% lower than the MES oil.

[0062] Hardness

[0063] The hardness of the elastomers was measured by a Shore A hardness tester. The higher the number on the Shore A hardness scale indicates a stronger resistance to penetration by a specific foot, and thus the material is harder. The lower the number indicates a lower strength and softer material. Just after vulcanization, the hardness provided by the GFE is the same as the MES oil. After aging, the MES oil exhibits an increase of +3 Shore A units, in contrast the GFE increases only by +2 units (Table 4).

[0064] Table 4. Shore A hardness

[0065] Shore A Hardness GFE MES After crosslinking 71 71 Cure at 100°C for 3 days 73 74

[0066] Mechanical properties after crosslinking

[0067] Table 5 shows the modulus, tensile strength and elongation at break after crosslinking.

[0068] Table 5. Stress-strain properties after crosslinking

[0069] Tensile strength Unit GFE MES Stress at 50% elongation Mpa 2.36 2.57 Stress at 100% elongation Mpa 3.76 4.41 Stress at 200% elongation Mpa 7.17 9.01 Stress at 300% elongation Mpa 11.17 13.36 Breaking tensile strength Mpa 14.8 14.9 Breaking elongation ％ 397 323

[0070] In general, compounds with low modulus provide higher elongation and lower tensile strength, while rubbers with GFE as process oil show high elongation at break, and their tensile strength is practically equal to that with MES as process oil, compared to MES + 33%.

[0071] Mechanical properties after aging

[0072] Table 6 shows the stress, stress at break and elongation at break at different degrees of elongation for the elastomer samples after aging at 100°C for 3 days.

[0073] Table 6. Stress-strain properties after aging

[0074]

[0075]

[0076] After aging, the stress-strain properties of GFE are further improved compared to MES. The experimental results show that the tensile strength and elongation at break are 23% and 46% higher, respectively, compared to MES.

[0077] Dynamic mechanical properties unaged

[0078] Dynamic mechanical analysis (DMA) can provide a practical evaluation of the main properties required for the tread compound.

[0079] The elastic modulus E' (also known as the storage modulus) provides an indication of the rolling resistance: the higher its value, the lower the elongation of the elastomer at the same force, and therefore the lower the consumption of elastic energy during calendering. On the other hand, the viscous modulus E" (also known as the loss modulus) gives an indication of the heat generated when the tire is rolling on asphalt. In order to obtain good wet grip performance, the tread must have high hysteresis, and therefore a high E" value.

[0080] From the DMA curve of the tire tread composition at -100°C to +100°C, the elastic modulus (E'), the loss modulus (E") and the mechanical hysteresis tan delta (E" / E' ratio) can be extracted. The elastic modulus at -20°C is used to evaluate the winter performance, and the mechanical hysteresis at 0°C, +30°C and +60°C are used to evaluate the wet traction, dry traction and rolling resistance, respectively.

[0081] The following Table 7 shows a general summary of the dynamic properties of the rubber tire tread compositions in this example, comparing the use of GFE as processing oil to replace MES.

[0082] Table 7. Dynamic Mechanical Analysis

[0083]

[0084]

[0085] The comparison of the DMA data shows that GFE is an excellent extender for winter tires, as its glass transition temperature is -75°C, much lower than the -68°C of MES, and its tan delta (E" / E' ratio) at -20°C is 0.18, also significantly lower than the 0.28 of MES. The tan delta data at 0°C, used to evaluate wet grip, shows that GFE (tan delta = 0.14) provides better results than MES (tan delta = 0.17). The tan delta data at 30°C, used to evaluate dry grip strength, shows that GFE (tan delta = 0.11) provides comparable results to MES (tan delta = 0.12). The tan delta data at 60°C, used to evaluate rolling resistance, shows that GFE (tan delta = 0.11) provides lower results than MES (tan delta = 0.09).

[0086] Wear loss

[0087] Wear resistance has been measured according to ISO 4649.2017. The test shows that the loss for GFE is 127 mm 3 , compared to 122 mm 3 for MES. The loss for GFE is slightly higher than for MES, and the difference between the two values is not significant in terms of percentage, being about 4%. Wear resistance is greatly influenced by the elastic modulus: the lower the elastic modulus, the greater the deformation, as the energy dissipation due to internal friction between the molecules is greater and is directly proportional to the degree of stretching of the polymer chains. However, it must be remembered that this comparison is made with the same composition. As described below, increasing the degree of crosslinking can improve wear resistance while maintaining good elastic properties.

[0088] Conclusion

[0089] The results of the comparative tests performed on elastomeric compounds having a typical composition for tire treads with MES oil show that, at the same amount used in the composition, GFE significantly improves the road adhesion properties at low temperatures, however, the parameters that provide an indication of the rolling resistance and wear resistance are worsened, although not significantly in the case of the latter.

[0090] The loss in rolling resistance is 22% in percentage terms, which means a 2-3% increase in energy consumption. On the other hand, the increase in the elastic properties of the elastomer inevitably leads to an increase in the elastic energy loss, since the heat dissipation energy is proportional to the square of the elongation; at the same force, the elongation increases proportionally as the modulus of elasticity decreases. However, the small increase in energy consumption fully justifies the safety improvement brought about by the use of tyres containing plasticizers that provide sufficient flexibility to the tyre under low temperature conditions. Even if the degree of wear of the tyre increases slightly due to wear, it is largely offset by the improvement in driving safety.

[0091] It should be considered that the comparison between GFE and MES was made with the same formulation. Therefore, a change in the concentration of process oil, filler or vulcanizing agent would lead to a corresponding change in the performance parameters. It can be observed that the torque is reduced when using GFE, which means that there is less crosslinking, probably because GFE reduces the sulphur fraction. Therefore, for example, by increasing the amount of sulphur and accelerators, the degree of crosslinking of the compound can be increased, which leads to an increase in the modulus of elasticity, which in turn improves the rolling resistance and wear resistance.

[0092] With the formulation (recipe) according to the application, GFE provides an elongation at break after ageing of 316%, while MES provides an elongation at break of only 216%; this improvement is very significant, equal to 46%. In addition, it was found that the tensile strength of GFE is 12.8 MPa, while that of MES is 10.4 MPa. These data are influenced by the ability of the plasticizer to promote the disentanglement of the polymer chains, making the distribution and orientation of the chains more efficient, but also by the dispersion ability of the fillers (carbon black and / or silica). If GFE enables higher values of elongation at break and tensile strength, it means that an increase in the degree of crosslinking is likely to significantly improve the rolling resistance and wear resistance without excessively affecting the winter performance.

[0093] Example 2. NBR elastomer, comparison with aromatic oil MES

[0094] Nitrile rubber (NBR) is an unsaturated random copolymer of acrylonitrile and butadiene. The application of NBR varies depending on the acrylonitrile content and the molecular weight of the polymer. The polar nature of NBR is provided by the acrylonitrile component. The higher the proportion of acrylonitrile, the higher the polarity of the polymer.

[0095] NBR elastomers are widely used in the automotive and oil industries for engine oils and fuel transport equipment, machinery, pumps, etc., but the greatest use of NBR is for the production of medical gloves.

[0096] Nitrile rubber has been considered a very durable glove compound, more durable than vinyl gloves, and has become more popular as such. Nitrile has been around for a while, but until recently its price has become more affordable; thus, it is becoming more popular in medical, food, cleaning, and other industries. Some important properties that nitrile gloves offer include their higher puncture resistance than any other glove material. In addition, nitrile rubber gloves fit snugly, leaving the wearer comfortable while working. Nitrile gloves are used as a precaution against natural rubber allergies. This makes them suitable for medical applications in work environments that can come into contact with bodily fluids, microorganisms, and chemicals. Other industries that use nitrile gloves include automotive, general industry, wood industry, roofing, and the like. They typically use gloves coated with a durable, slip-resistant nitrile coating that provides chemical resistance and water resistance.

[0097] Table 8 below shows a typical composition for producing an elastomer based on nitrile rubber. The reference oil in the second column from the left is GFE obtained from soybean oil, while the third column is MES aromatic oil. The percentage content, measured in parts per hundred of the polymer itself (phr), is the same for both.

[0098] Table 8. Nitrile rubber composition

[0099]

[0100] The compounds were prepared in a laboratory mixer using a two-stage mixing procedure. The polymer was introduced first, followed shortly by the processing oil, carbon black, stearic acid, and all other components, except for sulfur and accelerators, and CBS, which were added after 5 minutes. The tensile strength and tear strength of the samples were determined according to ISO 37:2017 and ISO 34-1 :2015. Hardness measurements were determined according to DIN ISO 7619-1 :2009 (Shore A hardness).

[0101] A Shore A hardness tester is a device used to measure the hardness of a polymer. The higher the number on the Shore A scale indicates a stronger resistance to penetration by a specific indenter, and thus the material is harder. The lower the number indicates a lower strength and softer material. Compression set (CS) values were determined according to DIN ISO 815-1 2020. Aging tests were performed by keeping the samples at 60 °C for 500 hours, and at the end of the treatment, tensile strength, hardness, compression measurements were taken again to evaluate their changes.

[0102] Table 9 below shows the rheological data. MH is the torque after vulcanization at 175 °C for 10 minutes.

[0103] Table 9. Torque

[0104]

[0105] Table 10 below shows the values of tensile strength, elongation at break, tear strength and Shore A hardness.

[0106] Table 10. Mechanical properties

[0107] Parameters GFE MES Tensile strength (MPa) 16 13 Breaking strain (%) 590 480 Tear strength (N / mm) 9.8 7.3 Shore A hardness (num) 53 50 Compression set (%) 10 8

[0108] From Table 10, it can be seen that the replacement of MES with GFE resulted in an increase of 23% in tensile strength, 23% in elongation at break and 34% in tear strength.

[0109] Table 11 below shows the mechanical property results of GFE after aging at 60°C for 500 hours. It can be seen that even after aging, GFE exhibits better retention of mechanical properties.

[0110] Table 11. Data after 500 hours of thermal oxidative aging at 60°C

[0111] Parameters GFE MES Tensile strength (MPa) 15 12.5 Compression set (%) 8 6 Shore A hardness (num) 60 60

[0112] The results show that after thermal oxidative aging, there is only a slight and insignificant deterioration in the performance characteristics except for Shore A hardness.

[0113] Example 3. NBR elastomer, comparison with dicarboxylic acid ester

[0114] In this example, the difference in tire performance was compared by replacing the dicarboxylic acid ester process oil with the GFE ester of the present application. GFE made from soybean oil was used, while dioctyl adipate (DOA) and dibutyl sebacate (DBS) were chosen as typical reference ester plasticizers. To this end, experimental tests were carried out on a typical formulation (recipe) of an oil-resistant conveyor belt shown in Table 12. The formulation was based on a mixture of the following elastomers: a) KUMHO KNB 40M, which is characterized by an acrylonitrile (ACN) content of 41% and a Mooney viscosity of 60; it is suitable for various technical articles requiring good processability as well as very high oil and fuel resistance; b) Europrene N OZO 7028, which is a 70 / 30 NBR / PVC blend and the NBR is characterized by an ACN content of 19.5%. The Mooney viscosity is 75. It is characterized by having excellent processability, high oil resistance and outstanding fire protection. This grade represents the best balance between ozone resistance and low temperature performance. The filler was carbon black N772. The other components were typical elastomer vulcanization additives in the composition of this example. The relative amounts are expressed in parts by weight (phr) per 100 parts of total elastomer. For example, with reference to 100 parts by weight of total elastomer, the plasticizers each had a concentration of 30 parts. In Table 12, the samples are labeled with the initial letters of the extender contained therein.

[0115] Table 12. Nitrile rubber compositions

[0116]

[0117]

[0118] Preparation of Rubber Compositions

[0119] The compositions of the rubbers to be tested were prepared in a 1.5 liter mixer using a two-step process. In the first stage, the elastomer, filler and plasticizer were introduced into the mixer and the mixture was mixed at a temperature of 150°C to 180°C in order to optimize the distribution of the filler in the elastomer chain mixture. In the second step, the elastomer crosslinking reaction was carried out. The mixture was cooled to a temperature below 110°C before the necessary components for crosslinking were introduced.

[0120] Test Methods

[0121] The rheological curves were recorded on an oscillating disc rheometer (ODR) at 175°C for 6 minutes according to the general rules of ISO 3417:2008. The stress-strain properties and the final properties of the elastomer test specimens were tested according to the test method of ISO 37:2017. The stress-strain properties after aging were determined on elastomer test specimens aged in an oven for 3 days at 100°C. The measurement of the Shore A hardness was carried out according to ISO 7619-1 :2010.

[0122] Table 13 shows some characteristic data measured by rheometer during the vulcanization of the elastomers having the compositions shown in Table 12. MH represents the maximum torque reached by the rheological curve at the end of the crosslinking reaction, while ML is the minimum torque before the start of the vulcanization.

[0123] Table 13. Rheological test - torque data

[0124] Torque at 175°C x 6 min DBS DOA GFE ML (dNm) 3.88 3.71 4.43 MH (dNm) 45.60 37.50 41.79 MH-ML (dNm) 41.72 33.79 37.36

[0125] ML provides an indication of the viscosity of the unvulcanized rubber compound, and there is no evidence of a significant difference between the GFE oil and the reference DBS and DOA esters. MH is related to the modulus of elasticity at the end of crosslinking. MH-ML is related to the crosslinking density, and this value is the lowest for DOA, but not much different from GFE (about 10%).

[0126] Hardness

[0127] The hardness of the elastomers was measured by a Shore A hardness tester. The higher the number on the Shore A hardness scale indicates a stronger resistance to penetration by a specific indentor, and thus a harder material. The lower the number indicates a lower strength and softer material.

[0128] As can be seen from Table 14 below, the rubber using GFE has a hardness comparable to the reference before aging and the hardness of GFE experiences a similar increment to DOA after aging.

[0129] Table 14. Shore A hardness

[0130] Shore A Hardness DBS DOA GFE After crosslinking 61 63 62 Cure at 100°C for 3 days 70 64 65

[0131] Mechanical properties after crosslinking

[0132] Table 15 shows the modulus, tensile strength and elongation at break after crosslinking.

[0133] Table 15. Stress-strain properties after crosslinking

[0134] Unit DBS DOA GFE Modulus at 50% elongation Mpa 1.4 1.3 1.2 Modulus at 100% elongation Mpa 2.4 2.3 2.0 Modulus at 200% elongation Mpa 4.7 4.6 3.8 Modulus at 300% elongation Mpa 7 7.1 5.6 Breaking tensile strength Mpa 11.1 11.8 11.9 Breaking elongation ％ 460 474 730

[0135] In general, elastomers with low modulus provide higher elongation and lower tensile strength, while rubber with GFE as process oil shows high elongation at break and slightly better tensile strength at break than DOA and DBS, compared to DOA + 54%.

[0136] Mechanical properties after aging

[0137] Table 16 shows the modulus, stress and elongation at break at different degrees of elongation after 3 days of aging at 100°C for the elastomer samples.

[0138] Table 16. Stress-strain properties after aging

[0139] Tensile strength Unit DBS DOA GFE Force at 50% elongation Mpa 2.6 1.7 1.0 Modulus at 100% elongation Mpa 4.6 3.0 1.8 Modulus at 200% elongation Mpa 9.3 6.6 3.6 Modulus at 300% elongation Mpa 13.7 10.8 5.5 Breaking stress Mpa 14.3 11.5 10.9 Breaking elongation ％ 314 320 568

[0140] Also, after aging, GFE maintains a lower Young's modulus and a higher elongation than DBS and DOA. The elongation at break of GFE is 77% higher than DOA, a value even better than that obtained for the unaged elastomer. The tensile strength at break is slightly lower than DOA, but this is not too important because the energy consumed in breaking is equal to work = force x displacement and even after aging, GFE has a much higher elongation than the other two extenders.

[0141] Example 4. Butyronitrile and latex gloves

[0142] When it is desirable to increase the flexibility of medical gloves, better disperse fillers such as calcium carbonate, reduce the penetration of chemical substances or pathogenic organisms (GFE esters have a destructive effect on them), GFE esters can be introduced into the components of medical gloves.

[0143] However, the mixing of GFE with the elastomer modifies the mechanical properties of the material that makes up the glove, so it is necessary to verify that the tensile strength remains within acceptable limits.

[0144] In this example, a hand-shaped ceramic mold, into which a nitrile or latex medical glove was inserted, was immersed in a container containing GFE ester for 1 minute. It was then removed and placed in an oven kept at 60°C for 30 minutes. The mold (referred to as "dip former" in industrial practice) was hung by a hook on the top of the oven, so as to let the liquid not absorbed by the glove drip off. At the end of the treatment, the glove was weighed.

[0145] The ester with which the treatment was carried out was either the ester obtained by esterification of glycerol formal with soybean fatty acids, referred to as GFE-A, or the same ester in which the double bonds were partially epoxidized, referred to as GFE-B. The gloves appeared dry and showed no signs of surface greasiness, which indicated that the ester was absorbed by the polymeric material. The degree of GFE absorption was evaluated by measuring the difference in weight of the glove before and after the treatment.

[0146] The values are shown in Table 17 below. From the weight increase of the gloves it was observed that, under the same treatment conditions (dipping time and oven holding time), it seems that the GFE-B sample has a better absorption capacity in nitrile rubber, while GFE-A is better absorbed in latex.

[0147] Table 17. Weight variation of the gloves after absorption

[0148]

[0149] The breaking force of the samples taken from the gloves was measured according to the method specified in paragraph 5.2 of the EN 455-2-2015 standard "Medical gloves for single uses - Requirements and testing for physical properties". Dumbbell-shaped test pieces were prepared from the palm area, using a cutter, as far as possible avoiding the textured areas, and in the longitudinal direction of the glove, as specified above.

[0150] Table 18. Mechanical parameters after absorption of GFE by dipping

[0151]

[0152] It can be seen that, in this example, after the introduction of glycerol formal fatty acid ester in the amounts indicated, the tensile strength is still higher than the minimum acceptable limit for gloves or surgical gloves, i.e. 14 MPa, as checked in the ISO D3578 2002 standard.

[0153] From this example, it can be concluded that GFE esters whose double bonds are partially epoxidized exhibit greater compatibility in polar elastomers such as NBR, based on the amount of ester absorbed in the same absorption time.

[0154] Example 5. Penetration test of natural rubber

[0155] To evaluate the resistance of nitrile and latex gloves with GFE additives to viral penetration, we used the method described in the publication “PCR-Based Method for Detecting Viral Penetration of Medical Exam Gloves” (J Clin Microbiol. 2002 Aug; 40(8): 2725-8. Broyles, O'Connell, Korniewicz) Phage Penetration Test: Latex gloves fresh from the packaging were compared to latex gloves to which the plasticizers designated GFE-A and GFE-B from the previous example had been added.

[0156] The method for conducting this test is described in the "Materials and methods" section of the aforementioned publication and is provided below.

[0157] A polypropylene beaker was filled with 200 ml of sterile nanopure water. For proof-of-principle testing, an 18-gauge needle was used to prick each finger of the glove five times. The glove was then placed over a beaker filled with water and a solution containing phage (10 μl in sterile H2O) was injected into the glove. 5 to 10 6 PFU / ml), ensuring that all five fingers are filled. The glove is placed in a beaker filled with water and left at room temperature for 30 minutes, after which samples are drawn from the inside and outside of the glove. The sample is serially diluted in 10-fold increments and tested for the presence of phage by co-culturing with a bacterial host in top agar. The diluted sample (100 μl) is mixed with Escherichia coli (E. coli) and top agar, then poured onto NB medium plates. The plates are then incubated at 37°C for 3 to 4 hours, after which plaques are counted.

[0158] In our tests, to make the differences more apparent, we prepared samples containing a concentration of approximately 10 8 Table 19 below shows the results of phage penetration of punctured latex gloves.

[0159] Table 19. Latex Glove Penetration Results

[0160]

[0161] It can be seen that both GFE esters completely prevent the penetration of the virus through the material. This property of making the elastomer completely waterproof is very important in the production of condoms, as it ensures the absolute protection of the user against viruses and sexually transmitted bacteria, in particular AIDS.

Claims

1. C8-C of glycerol formal 18 Use of fatty acid esters as process oils for the production of synthetic elastomers.

2. The use of the ester according to claim 1, wherein The fatty acid is selected from the group consisting of caprylic acid, lauric acid, myristic acid, stearic acid, palmitic acid, oleic acid, linoleic acid, linolenic acid, ricinoleic acid, and mixtures thereof.

3. Use of the ester according to claims 1 and 2, wherein The elastomer is selected from styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), butadiene rubber (BR), natural rubber (NR), isoprene rubber (IR), polyurethane rubber and mixtures thereof.

4. Use of the ester according to claims 1 to 3, wherein The double bonds are partially epoxidized and used to produce synthetic polar elastomers such as nitrile rubber and polyurethane rubber.

5. Use of the esters according to claims 1 and 3 for producing tire treads, enabling the elastomer to have a glass transition temperature Tg of less than -74°C and a viscous modulus at -20°C of less than 11 MPa.

6. Use of the esters according to claims 1 to 3 and 5 in an elastomeric composition for producing automobile tire treads, wherein the composition comprises from 20 to 90% by weight of a functionalized styrene-butadiene rubber (SBR) and optionally from 10 to 80% of at least one rubber chosen from polybutadiene rubber (BR), natural rubber (NR), polyisoprene rubber (IR) and mixtures thereof.

7. Use of the esters according to claims 1 and 4 in elastomeric compositions for the production of medical devices such as condoms and medical gloves.

8. An elastomeric composition for a tire comprising an elastomer in an amount of 20 to 90% by weight and a C8-C60 compound of at least one glycerol in an amount of 10 to 80% by weight. 18 Formal esters of fatty acids.

9. The elastomer composition according to claim 8, wherein After aging, the tensile strength at break is greater than 11.00 MPa, preferably greater than 12.00 MPa.

10. Tire tread comprising the elastomeric composition according to claim 6 or 7, wherein the glass transition temperature is lower than -70°C, the ratio E" / E' at -20°C is less than 0.2 and the ratio E" / E' at 0°C is less than 0.

15.

11. An elastomeric composition for condoms and medical gloves comprising a C8-C10-C12-C16 elastomer in an amount of 40% to 99% by weight of an elastomer and 1% to 60% by weight of glycerol. 18 Formal esters of fatty acids.

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