Polyurethane pre-polymer, method of obtention and uses thereof

Abstract

The present disclosure relates to a low toxicity and high biobased content polyurethane pre-polymer, method of obtention and uses thereof. It is described a polyurethane pre-polymer comprising: a 30 to 60 %(w / w) of a polyol; a 55 to 90% (w / w) bio-based carbon content, up to 0.1% (w / w) of free monomer, wherein the free monomer is a diisocyanate.

Description

D E S C R I P T I O NPOLYURETHAN E PRE-POLYMER, METHOD OF OBTENTION AND USES THEREOFTECHNICAL FIELD

[0001] The present disclosure relates to a low toxicity and high biobased content polyurethane pre-polymer, method of obtention and uses thereof.

[0002] In particular, the present disclosure relates to a pre-polymer composition of polyurethane with a monomer-free content of up to 0.1%, offering several advantages over conventional pre-polymers, including improved safety, enhanced performance and environmental compliance.BACKGROUND

[0003] Prior art in the field of polyurethane prepolymers, particularly as they relate to the development and application of stoppers, spans several important aspects, including material composition, processing techniques, and specific applications. Stoppers, used widely in various industries such as pharmaceuticals, laboratory environments, and beverage industries, require materials that ensure tight seals, chemical resistance, and durability. Polyurethane, due to its versatility and excellent performance characteristics, has been a material of choice for these applications.

[0004] Initially, polyurethane prepolymers were developed and used primarily for their excellent mechanical properties such as flexibility, toughness, and abrasion resistance. These materials were synthesized from reactions between polyols and polyisocyanates, where the formulation could be adjusted to yield different properties, tailored to specific needs. For stoppers, particularly those used in pharmaceutical applications, the polyurethane's non-reactivity and ability to form airtight seals made it highly favorable. Over time, formulations were optimized to enhance these properties, focusing on reducing the free monomer content to minimize potential leaching of harmful substances.

[0005] In response to environmental and health concerns, advancements in polyurethane prepolymer technology incorporated the use of more environmentally friendly and safer ingredients. This led to the development of prepolymers with lower volatile organic compound (VOC) emissions and reduced toxicity. The innovation included the introduction of bio-based polyols, which not only addressed environmental concerns but also contributed to the sustainability of polyurethane production. These bio-based polyols are derived from renewable sources such as plant oils, sugar fermentation and have gradually been integrated into the synthesis of polyurethane prepolymers for stoppers.

[0006] Further innovations in the field targeted the enhancement of the physical properties of the polyurethane stoppers. This included the development of microcellular foams or solid elastomers tailored for better compression set characteristics, enhanced chemical and thermal stability, and improved barrier properties. These properties are crucial for maintaining the integrity and efficacy of the contained substances, especially in medical and food applications. Techniques such as reaction injection molding (RIM) facilitated the production of complex-shaped stoppers with precise dimensions and properties, enhancing the seal quality and performance in application.

[0007] Recently, the focus has also shifted towards the development of polyurethane prepolymers with improved biodegradability and recycling capabilities, driven by the global push towards sustainable manufacturing practices. Innovations have led to prepolymers that can degrade more easily under industrial composting conditions, or that can be reprocessed more effectively. For stoppers, this means that after their useful life, they can be disposed of in a more environmentally friendly manner or recycled into new products, thereby reducing waste and the environmental impact associated with the disposal of polymeric materials.

[0008] The document EP4375208A1 discloses a binder consisting of 65% to 77% by mass of a vegetable oil fraction and 23% to 35% by mass of an aliphatic isocyanate fraction, wherein said vegetable oil fraction comprises at least 1% by mass of grape seed oil. The technology also relates to agglomerated cork stoppers comprising said binder. The binder finds particular application in the cork area, both in the productionof agglomerated cork stoppers and in the production of other composites comprising cork.

[0009] The document EP2677030A1 discloses to a polyurethane rigid and flexible foam, which is obtainable from wood origin raw materials - tall oil derived polyols or lignin, said foams being used as support for immobilization of microorganisms, which produce ligninolytic enzymes.

[0010] These facts are disclosed in order to illustrate the technical problem addressed by the present disclosure.GENERAL DESCRIPTION

[0011] The present disclosure relates to a low toxicity and high biobased content polyurethane pre-polymer, method of obtention and uses thereof.

[0012] The present disclosure discloses a pre-polymer composition of polyurethane with a monomer-free content of up to 0.1%. The pre-polymer is synthesized through a controlled reaction process that significantly reduces the presence of unreacted monomers, particularly isocyanates, resulting in a safer and more stable product.

[0013] The polyurethane pre-polymer with a monomer-free content of up to 0.1% offers several advantages over conventional pre-polymers, including improved safety, enhanced performance and environmental compliance.

[0014] The solution of the present disclosure allows a decrease in toxic exposure risk, making the handling and application of the pre-polymer considerably safer for workers and end-users.

[0015] Regarding the improved safety, the polyurethane pre-polymer comprising a low monomer content reduces the risk of exposure to toxic isocyanates, making the prepolymer safer for handling and use. Isocyanates, commonly used in the production of polyurethane pre-polymers of the prior art, are known for their reactive nature and potential health hazards. These monomers can cause respiratory irritation, skin sensitization, and, in severe cases, occupational asthma. The presence of residual isocyanates in polyurethane pre-polymers presents significant risks during handling,processing, and application. The polyurethane pre-polymer disclosed in this description comprises a monomer-free content of up to 0.1%, significantly lowering the concentration of free isocyanates. This reduction in free isocyanate content directly correlates with a decrease in toxic exposure risk, making the handling and application of the pre-polymer considerably safer for workers and end-users.

[0016] In many jurisdictions, strict regulations govern the permissible exposure levels of isocyanates due to their associated health risks. These regulations, set by agencies such as the Occupational Safety and Health Administration (OSHA) in the United States and the European Chemicals Agency (ECHA) in Europe, mandate lower exposure limits for workplace safety. By reducing the monomer content up to 0.1%, the polyurethane pre-polymer not only meets but often exceeds the safety requirements set by these regulatory bodies. This compliance helps manufacturers and employers mitigate the risk of health-related incidents and potential liabilities associated with isocyanate exposure.

[0017] In industrial settings where polyurethane pre-polymers are used, such as in the production of coatings, adhesives, and sealants, workers are frequently exposed to fumes and airborne particles containing residual monomers. High levels of free monomers can lead to acute and chronic health problems, necessitating the use of extensive personal protective equipment (PPE) and engineering controls. The polyurethane pre-polymer now disclosed, with its significantly reduced monomer content, diminishes the likelihood of harmful exposure, allowing for a safer working environment. While PPE and other safety measures are still recommended, the reduced risk associated with lower monomer content can lead to a reduction in the severity and extent of these precautions, enhancing overall workplace safety.

[0018] Along this description, it is considered that a free monomer is a single, relatively small molecule that serves as a fundamental building block, capable of chemically bonding with other monomers to form larger, repeating structures called polymers. The term "free" emphasizes that these are individual, unlinked units, as opposed to being part of a larger polymer chain.

[0019] Products made from polyurethane pre-polymers, such as coatings and elastomers, are often applied in environments where end-users may come into contactwith the material. In these scenarios, the presence of free monomers can pose health risks not only to the workers applying the products but also to the general public who may be exposed to off-gassing or residual chemicals. The polyurethane pre-polymer now disclosed, with up to 0.1% free monomer content, mitigates these risks by ensuring that the final product releases minimal or no hazardous isocyanates during and after application. This improvement in product safety is particularly important in sensitive applications, such as in indoor environments, automotive interiors, or consumer goods, where human exposure must be minimized.

[0020] In addition to the direct health benefits, the reduced monomer content also offers environmental safety advantages. Isocyanates are classified as hazardous air pollutants (HAPs) under various environmental regulations, and their release into the atmosphere is strictly controlled. By minimizing the monomer content, the technology now disclosed aligns with environmental regulations aimed at reducing hazardous emissions. This not only supports manufacturers in meeting environmental compliance but also contributes to broader public health and environmental protection goals by reducing the release of toxic substances into the air and water during manufacturing and application processes.

[0021] In the manufacturing and transportation of chemicals, materials classified as hazardous require special handling, storage, and disposal procedures, often leading to increased costs and operational complexities.

[0022] The low monomer content of the polyurethane pre-polymer reduces the material's classification as a hazardous substance, simplifying logistics and handling. This reduction in hazard classification can lower costs related to transportation, storage, and waste management, while also decreasing the risk of accidents or environmental contamination.

[0023] The absence of free monomers in the polyurethane pre-polymer now disclosed also leads to improved mechanical properties, such as tensile strength and elongation, in the final polyurethane product.

[0024] The use of polymeric isocyanates with low free monomer wherein the purification step with vacuum distillation or solvent extraction or molecular sieving is also less toxic than monomeric isocyanates .

[0025] The incorporation of raw materials of biological origin into polymeric isocyanates also increases the sustainability and the biobased content of polyurethane prepolymers.

[0026] Polymeric isocyanates can have various synthetic chemistries, Biuret, Isocyanurate, Allophanate, Uretidinedione, Carbodiimide, Polyurethane prepolymer and Polyurea prepolymer.

[0027] Allophanate aliphatic polymeric isocyanates with low free monomer, have low toxicity and can have a significant biobased content, this is very useful for the sustainability polyurethane prepolymer (Fig2).

[0028] The innovation of polyurethane prepolymers is based on environmental concerns and the sustainability of polyurethane production, the use of raw materials of biological origin derived from renewable sources.

[0029] The biotechnology industry, using renewable raw materials (1st, 2nd, 3rd, 4th and 5th generation) and genetically modified micro-organisms, for produced various chemical monomers for the polymer industry.

[0030] The biobased 1,3-propanediol monomer produced by the biotechnology industry using renewable raw materials is polymerised by polycondensation or ring opening polymerisation reactions to produce polyether polyols 100% biobased for the synthesis of polyurethane prepolymers (Fig. 1).

[0031] Biobased polyether Polyols produced with biobased 1,3-Propanediol have neutral organoleptic properties that is useful for the polyurethane prepolymer, agglomerated cork stoppers with polyurethane prepolymer of the invention are organoleptically neutral.

[0032] Biobased polyester polyols produced with biobased 1,3-propanediol and biobased succinic acid are 100% biobased for the synthesis of polyurethane prepolymers . Biobased polyester polyols can help to achieve a very specific physical properties of polyurethane polymers.

[0033] Biobased reactive plasticisers like biobased alcohols, are very important for obtaining polyurethane polymers with flexibility and elasticity and contribute to the sustainability of the polyurethane prepolymer.An aspect of the disclosure comprises a polyurethane pre-polymer comprising: a 30 to 60 %(w / w) of a polyol; a 55 to 90 %(w / w) bio-based carbon content, up to 0.1% (w / w) of free monomer, wherein the free monomer is a diisocyanate.

[0034] In an embodiment, the free monomer of the polyurethane pre-polymer ranges from 0.001 to 0.1% (w / w), preferably from 0.01 to 0.1% (w / w), more preferably from 0.03 to 0.1% (w / w).

[0035] In an embodiment, the molecular weight of the polyol of the polyurethane prepolymer ranges from 500 to 10,000 Daltons, preferably from 1000 to 6000 Daltons, more preferably from 1000 to 4000 Daltons.

[0036] In an embodiment, the polyol of the polyurethane pre-polymer is polyether polyols from the polycondensation or ring opening polymerization reaction of biobased 1,3-propanediol with different molecular weights.

[0037] In an embodiment, the free monomer of the polyurethane pre-polymer is selected from a list consisting of methylene diphenyl diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, pentamethylene diisocyanate and combinations thereof.

[0038] In an embodiment, the polyurethane pre-polymer comprises a isocyanate that is an allophanate polymeric isocyanate based on Hexamethylene diisocynante with low free monomer and 32% biobased content and or an allophanate polymeric isocyanate based on hexamethylene diisocyanate with low free monomer and or an Isocyanurate trimer based on hexamethylene diisocyanate with low free monomer and or an isocyanurate trimer based on pentamethylene diisocyanate of biological origin with low free monomer and or an hexamethylene diisocyanate polyurethane prepolymer with low free monomer.

[0039] In an embodiment, the polyurethane pre-polymer comprises at least one reactive plasticiser, preferably at least one reactive plasticiser selected from a listconsisting of biobased alcohols, oleyl alcohol, decyl alcohol, heptanol, cardanol, and their combinations thereof.

[0040] In an embodiment, the bio-based carbon content of the polyurethane prepolymer is selected from a list consisting of lignocellulosic biomass, algae, recycled plant waste, starches, sugars and combinations thereof.

[0041] It is also disclosed the use of the polyurethane pre-polymer in the formulation of adhesives, production of elastomers, manufacture of sealants and production of cork stoppers, production of elastomers or durable coatings, biodegradable automotive and aerospace parts and medical devices.

[0042] It is also disclosed a polyurethane product prepared by curing the polyurethane pre-polymer described.

[0043] It is also disclosed a cork stopper prepared by agglomerated and curing the polyurethane pre-polymer.

[0044] In an embodiment, the cork stopper comprises a torsion strength when an angular momentum is applied that ranges from 50 daN. cm to 85 daN. cm, preferably from 55 daN. cm to 80 daN. cm, more preferably from 60 daN. cm to 75 daN. cm.

[0045] In an embodiment, the cork stopper comprises a torsion angle, when an angular momentum is applied, that ranges from 55° to 85°, preferably from 60° to 80°, more preferably from 65° to 75°.

[0046] In an embodiment, the cork stopper comprises a compressive strength ranging from 1200 N to 2400 N, preferably from 1350 N to 2150N, more preferably from 1450 N to 2000 N.

[0047] In an embodiment, the cork stopper comprises a relaxation force ranging from 100 N to 900 N, preferably from 250 N to 750N, more preferably from 350 N to 650 N.It is also disclosed a method for preparing a polyurethane pre-polymer, comprising the following steps: reacting a polyol component with an excess of a diisocyanate component at a temperature ranging from 20°C to 90°C.

[0048] In an embodiment, the step of reacting a polyol component with an excess of a diisocyanate component in the method is done at an inert atmosphere.

[0049] In an embodiment, the purification step of the method comprises vacuum distillation.

[0050] In an embodiment, the purification step of the method comprises solvent extraction.

[0051] In an embodiment, the purification step of the method comprises molecular sieving.

[0052] In an embodiment, the reacting temperature of the first step of the method ranges from 20°C to 120°C, preferably from 40°C to 100°C, more preferably from 60°C to 90°C.BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The following figures provide preferred embodiments for illustrating the disclosure and should not be seen as limiting the scope of invention.

[0054] Figure 1: Schematic representation of 1,3-propanediol Polyol

[0055] Figure 2: Schematic representation of allophanate polymeric aliphatic isocyanates with 32% Biobased content.

[0056] Figure 3: Table of the reagents used in the preparation of the disclosed polyurethane prepolymer.

[0057] Figure 4A to 4E: - Al;A2;A3;A4;A5;A6;A7;A8;A9;A10;All;A12;A13;A14:Schematic representation of formulations of the various polyurethane prepolymer.

[0058] Figure 5: Photographic representation of the disclosed polyurethane prepolymer and of a cork stopper agglomerated with said polyurethane prepolymer.

[0059] Figure 6: Illustration of results table.

[0060] Figure 7: Illustration of ATR-FTIR analyses.

[0061] Figure 8: Illustration of GPC analyses.DETAILED DESCRI PTION

[0062] The present disclosure relates to a polyurethane pre-polymer, method of obtention and uses thereof.

[0063] The polyurethane pre-polymer now disclosed comprises a monomer-free content of up to 0.1%, as determined by High-performance liquid chromatography(HPLC) or an equivalent analytical method. This determination was made using a 'Knauer'® chromatographic system consisting of a Smartline 1050 pump, a Smartline 5050 quaternary degasser / gradient former, a Smartline 2060 DAD detector and a Smartline 2300 refractive index detector. The sample is introduced using an Hta® HT350L automatic sampler with an automatic valve equipped with a 30uL loop. The chromatograms were acquired and processed using Clarity software version 5.0.0.323 from DataApex Lda®. The compounds are separated on a Thermo® BDS HYPERSIL C18 column protected by a Phenomenex® C8 pre-column. Both column and pre-column are kept at constant temperature in an Eldex® model CH50 column oven. The samples are weighed on an analytical balance with sensitivity to the tenth of a milligram.

[0064] The polyurethane pre-polymer disclosed in the present disclosure is surprisingly able to reduce toxic exposure risk, making the handling and application of the prepolymer considerably safer for workers and end-users, while maintaining the physical and mechanical proprieties and also the organoleptic neutrality in the case of use in cork.

[0065] It is described a polyurethane pre-polymer comprising: a 30 to 60 %(w / w) of a polyol; a 55 to 90% (w / w) bio-based carbon content, up to 0.1% (w / w) of free monomer, wherein the free monomer is a diisocyanate.

[0066] In an embodiment, the free monomer of the polyurethane pre-polymer varies from 0.001 to 0.1% (w / w), preferably from 0.01 to 0.1% (w / w), more preferably from 0.03 to 0.1% (w / w), for better results.

[0067] In an embodiment, the molecular weight of the polyol used in the polyurethane pre-polymer ranges from 500 to 10,000 Daltons, preferably from 1000 to 6000 Daltons, more preferably from 1000 to 4000 Daltons, for better results.

[0068] In an embodiment, the polyol of the polyurethane prepolymer is selected from a list consisting of polyether polyols from the polycondensation reaction of biobased 1,3-propanediol, polyester polyols from the reaction of biobased 1,3-propanediol with biobased succinic acid, and combinations thereof, to obtain better results.

[0069] In an embodiment, the free monomer of the polyurethane pre-polymer is selected from a list consisting of methylene diphenyl diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, pentamethylene diisocyanate and combinations thereof, for better results.

[0070] In an embodiment, the isocyanate is an allophanate polymeric isocyanate based on Hexamethylene diisocynante with low free monomer and 32% biobased content and or an allophanate polymeric isocyanate based on Hexamethylene diisocynante with low free monomer.

[0071] In an embodiment, the isocyanate is an Isocyanurate trimer based on Hexamethylene diisocyanate with low free monomer and or an Isocyanurate trimer based on Pentamethylene Diisocyanate of biological origin with low free monomer and or an Hexamethylene diisocyanate polyurethane prepolymer with low free monomer.

[0072] In an embodiment, the polyurethane pre-polymer comprises at least one biobased reactive plasticiser, preferably at least one reactive plasticiser selected from a list consisting of are biobased alcohols, oleyl alcohol, decyl alcohol, heptanol, cardanol and their combinations thereof. These biobased reactive plasticisers can help a lot to have the ideal physical characteristics for the final application, such as a cork stopper, and also help to increase the biobased content of the product of the invention, as they are alcohols from biobased sources.

[0073] In an embodiment, the bio-based carbon content of the polyurethane prepolymer is selected from a list consisting of lignocellulosic biomass, algae, recycled plant waste, starches, sugars and combinations thereof, for better results.

[0074] It is also disclosed the use of the polyurethane pre-polymer in the formulation of adhesives, production of elastomers, manufacture of sealants, production of cork stoppers and automotive parts.

[0075] It is also disclosed a polyurethane product prepared by curing the polyurethane pre-polymer.

[0076] It is also disclosed a cork stopper prepared by agglomerated and curing the polyurethane pre-polymer.

[0077] In an embodiment, the cork stopper comprises a torsion strength when an angular momentum is applied that ranges from 50 daN. cm to 85 daN. cm, preferably from 55 daN. cm to 80 daN. cm, more preferably from 60 daN. cm to 75 daN. cm, for better results.

[0078] In an embodiment, the cork stopper comprises a torsion angle, when an angular momentum, is applied that varies from 55° to 85°, preferably from 60° to 80°, more preferably from 65° to 75°, to obtain the best results.

[0079] In an embodiment, the cork stopper comprises a compressive strength ranging from 1200 N to 2400 N, preferably from 1350 N to 2150N, more preferably from 1450 N to 2000 N, for best results.

[0080] In an embodiment, the cork stopper comprises a relaxation force ranging from 100 N to 900 N, preferably from 250 N to 750N, more preferably from 350 N to 650 N, for best results.

[0081] The above results from compressive strength and relaxation force were measured using the Compression Test Method NP 2803-3:2017 - Cork stoppers - physical tests. This Test Method is a standardized procedure used to determine the compressive strength of materials, particularly construction products such as concrete, mortars, and similar composites. It establishes the conditions for specimen preparation, dimensions, alignment, and loading rate to ensure reliable and reproducible results. The method involves applying a gradually increasing compressive load to a test specimen until failure occurs, with the maximum load sustained by the specimen recorded and expressed as compressive strength. This test is widely employed for quality control, performance assessment, and comparative analysis of materials, providing essential data for structural design, safety, and compliance with technical specifications.

[0082] It is also disclosed a method for preparing a polyurethane pre-polymer comprising the following steps: reacting a polyol component with an excess of a diisocyanate component at a temperature ranging from 20°C to 90°C.

[0083] In an embodiment, the step of reacting a polyol component with an excess of a diisocyanate component of the method is done at an inert atmosphere, for better results and to prevent unwanted side reactions.

[0084] In an embodiment, the purification step of the method comprises vacuum distillation, for better results and to remove unreacted monomers.

[0085] In an embodiment, the purification step of the method comprises solvent extraction, for better results and to remove unreacted monomers.

[0086] In an embodiment, the purification step of the method comprises molecular sieving, for better results and to remove unreacted monomers.

[0087] In an embodiment, the reacting temperature of the first step of the method varies from 20°C to 120°C, preferably from 40°C to 100°C, more preferably from 60°C to 90°C, for better results.

[0088] The purified pre-polymer is characterized by its viscosity, molecular weight distribution, and monomer-free content. The final product is a stable, low-toxicity prepolymer suitable for use in various polyurethane-based applications. In an embodiment, the viscosity of the purified pre-polymer ranges from 5 Pa.s to 15 Pa.s, preferably from 6 Pa.s to 14 Pa.s, more preferably from 7 Pa.s to 12 Pa.s. In an embodiment, the molecular weight of the purified pre-polymer ranges from 1000 to 20000 Daltons, preferably from 2000 to 18000 Daltons, more preferably from 3500 to 15000 Daltons.

[0089] Viscosity is a parameter that strongly influences the behaviour of the purified pre-polymer. The influence of the viscosity was therefore tested using the Brookfield Viscometer DV-I Prime, not excluding similar ones, with the following analysis conditions: viscometry mode controlled by a shear rate ramp between 0.1 s1and 100 s-1; cone / plate geometry (31 mm); 25 °C temperature and; humidity trap (to prevent evaporation of the suspension during measurement).

[0090] Molecular weight distribution is a parameter that strongly influences the behaviour of the purified pre-polymer. The influence of the molecular weight distribution was therefore tested using gel permeation chromatography (GPC) measurements of polymers were carried out on a Malvern Omnisec Resolve / Reveal instrument equipped with three porous styrene divinylbenzene copolymer columns from Malvern (one T3000 and two T1000) operating in THF with BHT at a temperature of 40°C. A refractive index detector (RID) was used for the analysis of the polymers. A conventional calibration curve was plotted with ten polystyrene standards ranging from 162 to 87200 g / mol (Mp) and was used to calibrate the instrument. For the measurements, the polymers were weighed out accurately and dissolved in eluent such that the concentrations were known.

[0091] The presence of residual monomers, particularly isocyanates, in polyurethane pre-polymers can negatively impact the mechanical properties of the final polyurethane material. High levels of unreacted monomers can lead to incomplete polymerization or undesirable side reactions during the curing process, resulting in a final product with inferior mechanical strength, lower tensile strength, reduced elasticity, and diminished durability. The pre-polymer described in this invention, with its monomer-free content of less than 0.1%, ensures a more complete and controlled polymerization process. This leads to the formation of a more uniform polymer network with enhanced mechanical properties.

[0092] The low monomer content contributes to higher tensile strength in the cured polyurethane product. This makes the material more resistant to stretching and breaking under load, which is particularly beneficial in applications requiring high- performance elastomers or durable coatings.

[0093] The reduction in residual monomers helps in achieving better elongation properties, allowing the final product to stretch more before breaking. This is crucial in applications where flexibility and resilience are essential, such as in sealants.

[0094] The improved polymer network formed due to the reduced monomer content also enhances the tear resistance of the material. This is particularly advantageous in protective coatings, gaskets, and other applications where the material must withstand mechanical wear and tear over time.

[0095] Polyurethane pre-polymers are often used in adhesives and sealants, where the quality of adhesion and cohesion is critical to performance. Residual monomers can interfere with the formation of strong adhesive bonds by either reacting unpredictably or by remaining as unreacted entities within the polymer matrix, leading to weaker bonds.

[0096] The polyurethane pre-polymer of the present disclosure, with its low monomer content, enables the formation of strong, stable bonds at the molecular level. This results in improved adhesion and enhanced cohesion. The polymer adheres more effectively to a wide range of substrates, including metals, plastics, wood, and textiles, leading to superior bonding strength. This is particularly important in high-stress environments, such as automotive or aerospace applications, where adhesion failure can lead to significant safety issues. The internal strength of the adhesive itself is also improved, reducing the likelihood of the material breaking down or delaminating over time. This contributes to the longevity and reliability of the bonded assemblies.

[0097] Polyurethane materials are often exposed to various chemicals, solvents, oils, and other aggressive substances in their end-use environments. Residual monomers can create weak points in the polymer structure, making the material more susceptible to chemical attack. The polyurethane pre-polymer with up to 0.1% (w / w) free monomer content exhibits a more tightly cross-linked polymer network, which enhances its chemical resistance. This makes the material more suitable for use in harsh chemical environments, such as in industrial coatings, automotive parts, and protective barriers, where exposure to corrosive substances is common.

[0098] Residual monomers, especially isocyanates, can volatilize from the prepolymer, leading to the release of harmful vapors during processing and curing. This not only poses health risks but can also affect the consistency and quality of the final product. With a monomer-free content of up to 0.1%, the polyurethane pre-polymer reduces the risk of volatile emissions, leading to several performance benefits, namely consistent curing and improved surface finish.

[0099] Environmental factors such as UV radiation, moisture, and temperature fluctuations can degrade polyurethane products over time. The presence of residual monomers can accelerate this degradation, leading to premature failure of thematerial. The polyurethane pre-polymer's low monomer content contributes to a more stable polymer structure that is better able to resist environmental stressors. This leads to improved UV stability, enhanced moisture resistance and thermal stability.

[0100] The final product exhibits better resistance to UV radiation, reducing the risk of yellowing, cracking, or loss of mechanical properties over time. This is essential for outdoor applications, such as in coatings, sealants, and construction materials.

[0101] The more complete polymerization reduces the material's susceptibility to hydrolytic degradation, making it more resistant to moisture and humidity. This is particularly important in applications such as waterproofing membranes, insulation materials, and marine products.

[0102] The improved polymer network provides greater thermal stability, allowing the material to perform reliably across a wider range of temperatures. This is crucial in automotive, aerospace, and industrial applications where materials are exposed to extreme temperature conditions.

[0103] All the aforementioned performance enhancements contribute to the overall durability and longevity of the final polyurethane product. The reduced monomer content ensures that the material maintains its structural integrity and performance characteristics over a longer period, leading to reduced maintenance costs and increased product reliability.

[0104] The term "comprising" whenever used in this document is intended to indicate the presence of stated features, integers, steps, components, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0105] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof. The above-described embodiments are combinable.

[0106] The following dependent claims further set out particular embodiments of the disclosure.

Claims

C L A I M S1. A polyurethane pre-polymer comprising: a 30 to 60 %(w / w) of a polyol; a 55 to 90 %(w / w) bio-based carbon content, up to 0.1% (w / w) of free monomer, wherein the free monomer is a diisocyanate.

2. The polyurethane pre-polymer according to the previous claim, wherein the free monomer ranges from 0.001 to 0.1% (w / w), preferably from 0.01 to 0.1% (w / w), more preferably from 0.03 to 0.1% (w / w).

3. The polyurethane pre-polymer according to any of the previous claims, wherein the molecular weight of the polyol ranges from 500 to 10,000 Daltons, preferably from 1000 to 6000 Daltons, more preferably from 1000 to 4000 Daltons.

4. The polyurethane pre-polymer according to any of the previous claims, wherein the polyol is polyether polyols from the polycondensation or ring opening polymerization reaction of biobased 1,3-propanediol with different molecular weights.

5. The polyurethane pre-polymer according to any of the previous claims, wherein the free monomer is selected from a list consisting of methylene diphenyl diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, pentamethylene diisocyanate and combinations thereof.

6. The polyurethane pre-polymer according to any of the previous claims, comprising an isocyanate that is an allophanate polymeric isocyanate based on Hexamethylene diisocynante with low free monomer and 32% biobased content and or an allophanate polymeric isocyanate based on hexamethylene diisocyanate with low free monomer and or an Isocyanurate trimer based on hexamethylene diisocyanate with low free monomer and or an isocyanurate trimer based onpentamethylene diisocyanate of biological origin with low free monomer and or an hexamethylene diisocyanate polyurethane prepolymer with low free monomer.

7. The polyurethane pre-polymer according to any of the previous claims, comprising at least one reactive plasticiser, preferably at least one reactive plasticiser selected from a list consisting of biobased alcohols, oleyl alcohol, decyl alcohol, heptanol, cardanol, and their combinations thereof.

8. The polyurethane pre-polymer according to any of the previous claims, wherein the bio-based carbon content is selected from a list consisting of lignocellulosic biomass, algae, recycled plant waste, starches, sugars and combinations thereof.

9. Use of the polyurethane pre-polymer described in any of the previous claims 1 to 8 in the formulation of adhesives, production of elastomers, manufacture of sealants and production of cork stoppers, production of elastomers or durable coatings, biodegradable automotive and aerospace parts and medical devices.

10. A polyurethane product prepared by curing the polyurethane pre-polymer described in any of the previous claims 1 to 8.

11. A cork stopper prepared by agglomerated and curing the polyurethane prepolymer described in any of the previous claims 1 to 8.

12. The cork stopper according to the previous claim, comprising a torsion strength when an angular momentum is applied that ranges from 50 daN. cm to 85 daN. cm, preferably from 55 daN. cm to 80 daN. cm, more preferably from 60 daN. cm to 75 daN. cm.

13. The cork stopper according to any of the previous claims 11 to 12, comprising a torsion angle, when an angular momentum is applied, that ranges from 55° to 85°, preferably from 60° to 80°, more preferably from 65° to 75°.

14. The cork stopper according to any of the previous claims 11 to 13, comprising a compressive strength ranging from 1200 N to 2400 N, preferably from 1350 N to 2150N, more preferably from 1450 N to 2000 N.

15. The cork stopper according to any of the previous claims 11 to 14, comprising a relaxation force ranging from 100 N to 900 N, preferably from 250 N to 750N, more preferably from 350 N to 650 N.

16. A method for preparing a polyurethane pre-polymer described in any of the previous claims 1 to 8, comprising the following steps: reacting a polyol component with an excess of a diisocyanate component at a temperature ranging from 20°C to 90°C.

17. The method according to the previous claim, wherein the step of reacting a polyol component with an excess of a diisocyanate component is done at an inert atmosphere.

18. The method according to the any of the previous claims 16 to 17, wherein the purification step comprises vacuum distillation.

19. The method according to the any of the previous claims 16 to 18, wherein the purification step comprises solvent extraction.

20. The method according to the any of the previous claims 16 to 19, wherein the purification step comprises molecular sieving.

21. The method according to the any of the previous claims 16 to 20, wherein the reacting temperature of the first step ranges from 20°C to 120°C, preferably from 40°C to 100°C, more preferably from 60°C to 90°C.

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