Sandwich panels comprising polyarylene ether sulfone polymers

Abstract

The present invention relates to a sandwich panel comprising an upper top layer (UTL) comprising a polyarylene ether sulfone polymer and a fiber reinforcement, a foam core layer (FCL) comprising a polyarylene ether sulfone polymer, and a lower top layer (LTL) comprising a polyarylene ether sulfone polymer and a fiber reinforcement, wherein the upper top layer (UTL) is joined with the foam core layer (FCL) via a first film (F1) comprising a blend of a polyarylene ether sulfone polymer and a further polymer, and wherein the lower top layer (LTL) is joined with the foam core layer (FCL) via a second film (F2) comprising a blend of a polyarylene ether sulfone polymer and a further polymer. Another aspect of the present invention is a process for the production of the sandwich panel and the use of the sandwich panel as construction parts for aviation industry, and for the construction of rotor blades for wind turbines. Yet another aspect of the present invention is a process for the re-use of the sandwich panel.

Description

[0001] Sandwich panels comprising polyarylene ether sulfone polymers

[0002] Description

[0003] The present invention relates to a sandwich panel comprising an upper top layer (UTL) comprising a polyarylene ether sulfone polymer and a fiber reinforcement, a foam core layer (FCL) comprising a polyarylene ether sulfone polymer, and a lower top layer (LTL) comprising a polyarylene ether sulfone polymer and a fiber reinforcement, wherein the upper top layer (UTL) is joined with the foam core layer (FCL) via a first film (F1) comprising a blend of a polyarylene ether sulfone polymer and a further polymer, and wherein the lower top layer (LTL) is joined with the foam core layer (FCL) via a second film (F2) comprising a blend of a polyarylene ether sulfone polymer and a further polymer. Another aspect of the present invention is a process for the production of the sandwich panel and the use of the sandwich panel as construction parts for aviation industry, and for the construction of rotor blades for wind turbines. Yet another aspect of the present invention is a process for the re-use of the sandwich panel.

[0004] For applications in various industries composite materials are used due to their unique combination of mechanical performance and low density. This allows lightweight constructions in many areas, particularly in the aviation industry or for the construction of rotor blades for wind turbines. The weight reduction generally contributes to the need for CO2-reduction in these applications.

[0005] To meet actual performance challenges, usually different types of materials are combined in one part, which is in contradiction to another society demand, the need for a circular economy. Thus, also for composite materials new end-of-life options are needed.

[0006] A segment where significant amounts of sandwich panels are consumed is the aircraft interior. Sandwich panels are intensively used to manufacture and customize different areas of the interior, like overhead storage compartments, floor panels, roof panels, side panels and cabin walls (E.A. Franco-Urquiza et.al. , Polymers 2021,13, 3258). The growth of air traffic and the continuous need to replace damaged parts or to complete refurbishment from time to time creates a high demand for such materials.

[0007] For the re-use of sandwich panels, it could be an option, to dismantle the whole part from the first application, grind the part and re-use the material in a molding composition together with other thermoplastic materials.

[0008] Such a concept only works if thermoplastic polymers are used as matrix material in the composite. The potential to find high value applications for such regrinds would be even higher, if only one thermoplastic material is used for the different layers of the part, since it is generally known, that most mixtures of polymers are immiscible, which limits their mechanical performance (C. Koning et.al. , Progr. Polym Sci. 23, 707, 1998).

[0009] Actually, most sandwich panels for aircraft interior are based on Honycomb core materials, made out of a polyaramide (Nomex® Honeycomb) which is covered by prepregs of different composition, but usually based on phenolic-resins or epoxyresins. Since the resin forms a 3-dimensional network structure during the curing process, the final part cannot be molten again, which limits the re-use of such parts tremendously.

[0010] Hence, other options for the production of sandwich panels are under discussion. For the production of sandwich panels usually a light core material is assembled with fiber reinforced layers, giving the panel the required bending strength. To replace the expensive Honeycomb structures, as core material thermoplastic foams with a density of 30 to 750 g / l can be used. Since the use in aircrafts requires high flame retardancy (low smoke and heat release), only the high temperature resistant polymer polyetherimide can be used as foam core.

[0011] Fiber reinforced outer layers with thermoplastic matrix materials can be produced by impregnating fibers or fabrics with the matrix polymer by means of solvent impregnation or pultrusion.

[0012] The main challenge for the production of thermoplastic sandwich panels is the lamination of the foam core and the fiber reinforced outer layers.

[0013] For the lamination of the different layers during the panel assembly special solventbased adhesives are necessary, which deteriorate the properties of the regrind significantly. Furthermore, the used solvents can create cracks in the foam core leading to reduced mechanical performance.

[0014] Thus, the objective of the invention was to provide a sandwich panel, wherein the adhesive layer for the lamination is solvent free. The sandwich panel should preferably fulfill the high flame retardancy requirements for the use in aircrafts. Moreover, the sandwich panel should preferably be re-usable after end of life.

[0015] This object is achieved by the sandwich panel comprising an upper top layer (UTL) comprising at least one polyarylene ether sulfone polymer and at least one fiber reinforcement, a foam core layer (FCL) comprising at least one polyarylene ether sulfone polymer, and a lower top layer (LTL) comprising at least one polyarylene ether sulfone polymer and at least one fiber reinforcement, wherein the upper top layer (UTL) is joined with the foam core layer (FCL) via a first film (F1) comprising a blend of at least one polyarylene ether sulfone polymer and at least one further polymer, and, wherein the lower top layer (LTL) is joined with the foam core layer (FCL) via a second film (F2) comprising a blend of at least one polyarylene ether sulfone polymer and at least one further polymer.

[0016] In another embodiment the sandwich panel consist of an upper top layer (UTL) comprising at least one polyarylene ether sulfone polymer and at least one fiber reinforcement, a foam core layer (FCL) comprising at least one polyarylene ether sulfone polymer, and a lower top layer (LTL) comprising at least one polyarylene ether sulfone polymer and at least one fiber reinforcement, wherein the upper top layer (UTL) is joined with the foam core layer (FCL) via a first film (F1) comprising a blend of at least one polyarylene ether sulfone polymer and at least one further polymer, and, wherein the lower top layer (LTL) is joined with the foam core layer (FCL) via a second film (F2) comprising a blend of at least one polyarylene ether sulfone polymer and at least one further polymer.

[0017] Surprisingly, it was found that the sandwich panel according to the invention can be assembled solvent free. The sandwich panel according to the invention has good mechanical properties, good adhesion between the different layers and a good bending strength leading to a good adhesion of the different layers even after bending the sandwich panel.

[0018] It was surprisingly found that a solvent free assembly of polyarylene ether sulfone- based foam cores and reinforced layers can be achieved by using films having a glass transition temperature Tg of at least 5 K below the glass transition temperature Tg of the foam core. By applying temperature and moderate pressure such films provide an excellent adhesion between the core and the reinforced top-layers. It was surprisingly found that a solvent free assembly of a sandwich panel can be achieved by using a polyarylene ether sulfone-based foam core layer (FCL), a polyarylene ether sulfone-based reinforced upper layer (UTL), a polyethersulfone- based reinforced lower layer (LTL) and two films (F1 ; F2), comprising a blend of a polyarylene ether sulfone and a further polymer, having a glass transition temperature Tg at least 5 K below the Tg of the of polyethersulfone-based foam core layer (FCL).

[0019] Surprisingly the sandwich panel according to the invention can be re-used. After grinding, the inventive sandwich panel the ground material can be re-used for high value applications in various industries.

[0020] Polyarylene ether sulfone polymer

[0021] In the sandwich panel according to the invention the top layer (UTL), the foam core layer (FCL), the lower top layer (LTL), the first film (F1), and the second film (F2) comprise each independently from each other at least one polyarylene ether sulfone.

[0022] Polyarylene ether sulfone polymers are high-performance thermoplastics in that they feature high heat resistance, good mechanical properties, and inherent flame retardancy (E.M. Koch, H.-M. Walter, Kunststoffe 80 (1990) 1146; E. Ddring, Kunststoffe 80, (1990) 1149, N. Inchaurondo-Nehm, Kunststoffe 98, (2008) 190).

[0023] Polyarylene ether sulfone polymers can be formed inter alia either via the hydroxide method, wherein a salt is first formed from the dihydroxy component and the hydroxide, or via the carbonate method.

[0024] General information regarding the formation of polyarylene ether sulfone polymers by the hydroxide method is found inter alia in R.N. Johnson et.al., J.Polym. Sci. A-1 5 (1967) 2375, while the carbonate method is described in J.E. McGrath et.al., Polymer 25 (1984) 1827.

[0025] Methods of forming polyarylene ether sulfone polymers from aromatic bishalogen compounds and aromatic bisphenols or salts thereof in an aprotic solvent in the presence of one or more alkali metal or ammonium carbonates or bicarbonates are known to a person skilled in the art and are described in EP-A 297 363 and EP-A 135 130 for example.

[0026] High-performance thermoplastics such as polyarylene ether sulfone polymers are formed by polycondensation reactions which are typically carried out at a high reaction temperature in dipolar aprotic solvents, for example DMF, DMAc, sulfolane, DMSO and NMP. EP 0 412 499 describes a method of forming polyarylene ether sulfone polymers. The dihalogen component used in the method of EP 0412 499 is, for example, 4,4'-di- chlorodiphenyl sulfone or 4,4'-difluorodiphenyl sulfone. The dihydroxy components described in EP 0412 499 include bisphenol A, 4,4'-dihydroxydiphenyl sulfone and 4,4'-dihydroxybenzophenone. The polycondensation described in EP 0412 499 is carried out in the presence of sodium carbonate or sodium bicarbonate.

[0027] In a preferred embodiment the polyarylene ether sulfone polymer comprised in the sandwich panel is obtained by converting a reaction mixture (RG) comprising as components:

[0028] (A1) a dihalogen component comprising not less than 80 wt% of at least one dihalogen compound selected from the group consisting of 4,4‘-dichlorodiphenyl sulfone and 4,4'-difluorodiphenyl sulfone, based on the overall weight of component (A1) in reaction mixture (RG),

[0029] (B1) a dihydroxy component comprising not less than 80 wt% of at least one dihydroxy compound selected from the group consisting of 4,4'-dihydroxy- diphenyl sulfone, bisphenol A, 4,4'-dihydroxybiphenyl and hydroquinone, based on the overall weight of component (B1) in reaction mixture (RG).

[0030] Another object of the present invention, therefore, is a sandwich panel, wherein the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL), the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL), the at least one polyarylene ether sulfone polymer comprised in the lower top layer (LTL), the at least one polyarylene ether sulfone polymer comprised in the first film (F1), and the at least one polyarylene ether sulfone polymer comprised in the second film (F2) are each independently from each other at least one polymer obtained by converting a reaction mixture (RG) comprising as components:

[0031] (A1) a dihalogen component comprising not less than 80 wt% of at least one dihalogen compound selected from the group consisting of 4,4‘-dichlorodiphenyl sulfone and 4,4'-difluorodiphenyl sulfone, based on the overall weight of component (A1) in reaction mixture (RG),

[0032] (B1) a dihydroxy component comprising not less than 80 wt% of at least one dihydroxy compound selected from the group consisting of 4,4'-dihydroxy- diphenyl sulfone, bisphenol A, 4,4'-dihydroxybiphenyl and hydroquinone, based on the overall weight of component (B1) in reaction mixture (RG). The polyarylene ether sulfone polymer comprised in the sandwich panel according to the invention is preferably formed by converting a reaction mixture (RG) comprising the above-described components (A1), (B1), and additionally components (C), and (D).

[0033] Components (A1) and (B1) end up reacting with each other in a polycondensation reaction.

[0034] Component (D) serves as solvent. Component (C) serves as base to deprotonate component (B1) during the condensation reaction.

[0035] So, reaction mixture (RG) is the mixture which is used in the method which the present invention provides for forming the polyarylene ether sulfone polymer. All particulars herein in relation to reaction mixture (RG) thus relate to the mixture which is present before the polycondensation. It is during the method of the present invention that the polycondensation takes place to convert reaction mixture (RG) into the target product, the polyarylene ether sulfone polymer, by polycondensation of components (A1) and (B1). The mixture which is obtained after the polycondensation and comprises the target product, the polyarylene ether sulfone polymer, is also referred to as product mixture (PG).

[0036] In general, the components of reaction mixture (RG) are reacted conjointly. The individual components may be mixed in a preceding step and then reacted. It is also possible to feed the individual components into a reactor, where they are mixed and subsequently reacted.

[0037] In the method of the present invention, the individual components of reaction mixture (RG) are generally converted conjointly. This conversion preferably takes place in a single stage. That is, the deprotonation of component (B1) and the condensation reaction between components (A1) and (B1) take place in a single reaction stage without isolation of intermediates, for example the deprotonated species of component (B1).

[0038] Component (A1)

[0039] Component (A1), which is also referred to as the dihalogen component, is present in reaction mixture (RG) in the form of at least one dihalogen compound. What is meant herein by "at least one dihalogen compound" is precisely one dihalogen compound and also mixtures of two or more dihalogen compounds.

[0040] So, component (A1) may comprise not only a single dihalogen compound but also a mixture of two or more dihalogen compounds. Preferably component (A1) comprises not less than 50 wt% of at least one dihalogen compound selected from the group consisting of 4,4'-dichlorodiphenyl sulfone and 4,4'- difluorodiphenyl sulfone, based on the overall weight of component (A1) in reaction mixture (RG). The weight percentages here in relation to component (A1) further relate to the sum total of the 4,4'-dichlorodiphenyl sulfone used and of the 4,4'- difluorodiphenyl sulfone used. 4,4'-Dichlorodiphenyl sulfone is preferable to 4,4'- difluorodiphenyl sulfone. 4,4'-dichlorodiphenyl sulfone is especially preferred.

[0041] In one embodiment, component (A1) comprises not less than 80 wt%, preferably not less than 90 wt%, and more preferably not less than 95 wt% of at least one dihalogen compound selected from the group consisting of 4,4'-dichlorodiphenyl sulfone and 4,4'- difluorodiphenyl sulfone, based on the overall weight of component (A1) in reaction mixture (RG). The weight percentages here in relation to component (A1) further relate to the sum total of the 4,4'-dichlorodiphenyl sulfone used and of the 4,4'-difluoro- diphenyl sulfone used.

[0042] In one particularly preferred embodiment, component (A1) comprises not less than 50 wt%, preferably not less than 80 wt%, more preferably not less than 90 wt% and especially not less than 95 wt% of 4,4'-dichlorodiphenyl sulfone.

[0043] It is further particularly preferable for reaction mixture (RG) not to contain any further dihalogen compounds in addition to the dihalogen compounds of component (A1).

[0044] In a further particularly preferred embodiment, component (A1) consists of 4,4'- dichlorodiphenyl sulfone.

[0045] Component (B1)

[0046] Component (B1), which is also referred to as the dihydroxy component, is present in reaction mixture (RG) in the form of at least one dihydroxy compound. What is meant herein by "at least one dihydroxy compound" is precisely one dihydroxy compound and also mixtures of two or more dihydroxy compounds.

[0047] So, component (B1) may comprise not only a single dihydroxy compound but also mixtures of two or more dihydroxy compounds.

[0048] In one embodiment component (B1) comprise not less than 50 wt% of at least one dihydroxy compound selected from the group consisting of 4,4'-dihydroxydiphenyl sulfone, bisphenol A (2,2-bis(4-hydroxyphenyl)propane), 4,4'-dihydroxybiphenyl and hydroquinone, based on the overall weight of component (B1) in reaction mixture (RG). The weight percentages here in relation to component (B1) further relate to the total sum of the 4,4'-dihydroxydiphenyl sulfone, bisphenol A (2,2-bis-(4- hydroxyphenyl)propane), 4,4'-dihydroxybenzophenone and hydroquinone used. Of the aforementioned dihydroxy compounds 4,4'-dihydroxydiphenyl sulfone, bisphenol A, and 4,4'-dihydroxybiphenyl are preferable, while 4,4'-dihydroxydiphenyl sulfone is particularly preferable.

[0049] In one embodiment, component (B1) comprises not less than 80 wt%, preferably not less than 90 wt% and more preferably not less than 95 wt% of at least one dihydroxy compound selected from the group consisting of 4,4'-dihydroxydiphenyl sulfone, bisphenol A (2,2-bis(4-hydroxyphenyl)propane), 4,4'-dihydroxybiphenyl and hydroquinone, based on the overall weight of component (B1) in reaction mixture (RG). The weight percentages here in relation to component (B1) further relate to the total sum of the 4,4'-dihydroxydiphenyl sulfone, bisphenol A (2,2-bis-(4-hydroxyphenyl)- propane), 4,4'-dihydroxybiphenyl and hydroquinone used.

[0050] In one particularly preferred embodiment, component (B1) comprises not less than 50 wt%, preferably not less than 80 wt%, more preferably not less than 90 wt% and especially not less than 95 wt% of bisphenol A.

[0051] In one particularly preferred embodiment, component (B1) comprises not less than 50 wt%, preferably not less than 80 wt%, more preferably not less than 90 wt% and especially not less than 95 wt% of 4,4'-dihydroxydiphenyl sulfone.

[0052] In one particularly preferred embodiment, component (B1) comprises not less than 50 wt%, preferably not less than 80 wt%, more preferably not less than 90 wt% and especially not less than 95 wt% of 4,4’-dihydroxybiphenyl.

[0053] It is further particularly preferable for reaction mixture (RG) not to contain any further dihydroxy compounds in addition to the dihydroxy compounds of component (B1).

[0054] In a further particularly preferred embodiment, component (B1) consists of 4,4'- dihydroxydiphenyl sulfone.

[0055] Since reaction mixture (RG) comprises potassium carbonate as component (C), the hydroxyl groups of the dihydroxy compounds used as component (B1) may partly be present in reaction mixture (RG) in deprotonated form.

[0056] Component (C)

[0057] Reaction mixture (RG) comprises potassium carbonate as component (C), which is also known as the carbonate component. The used potassium carbonate is preferably anhydrous. In a preferred embodiment component (C) comprise not less than 90 wt% of potassium carbonate, based on the overall weight of component (C) in reaction mixture (RG).

[0058] In one embodiment, component (C) comprises not less than 80 wt%, preferably not less than 90 wt% and more preferably not less than 98 wt% of potassium carbonate having a volume-averaged particle size of < 50 pm, based on the overall weight of component (B1) in reaction mixture (RG).

[0059] In one particularly preferred embodiment, component (C) consists of potassium carbonate.

[0060] Component (D)

[0061] Reaction mixture (RG) preferably comprises at least one aprotic polar solvent as component (D). What is meant by "at least one aprotic polar solvent" in the present invention is exactly one aprotic polar solvent and mixtures of two or more aprotic polar solvents.

[0062] Useful aprotic polar solvents include for example, anisole, dimethylformamide, dimethyl sulfoxide, sulfolane, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and also mixtures thereof.

[0063] N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and also mixtures thereof are preferable for use as aprotic polar solvent. N-methyl-2-pyrrolidone is particularly preferable for use as aprotic polar solvent.

[0064] In one preferred embodiment, component (D) comprises not less than 90 wt% of at least one solvent selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone, based on the overall weight of component (D) in reaction mixture (RG). N-methyl-2-pyrrolidone is particularly preferable for use as component (D).

[0065] In one preferred embodiment, component (D) consists of N-methyl-2-pyrrolidone. N-methyl-2-pyrrolidone is also known as NMP or N-methylpyrrolidone.

[0066] In a further preferred embodiment, the reaction mixture does not contain any further aprotic polar solvents in addition to the aprotic polar solvents of component (D).

[0067] To form the polyarylene ether sulfone polymer the reaction mixture (RG) is preferably reacted under conditions of the carbonate method. The reaction involved is a polycondensation reaction and is generally carried out at temperatures in the range from 80 to 250°C and preferably at temperatures in the range from 100 to 220°C, the upper limit of the temperature being determined by the boiling point of the aprotic polar solvent (component D) at atmospheric pressure (1013.25 mbar). The reaction is generally carried out at atmospheric pressure. The time interval for the reaction is preferably in the range from 0.5 to 12 hours, especially in the range from 2 to 10 hours.

[0068] The polyarylene ether sulfone polymer obtained according to the present invention may be isolated by precipitating the polymer solution in water or mixtures of water with further solvents, for example alcohols. The precipitated polyarylene ether sulfone polymer may subsequently be extracted with water and thereafter dried. In one embodiment of the invention, the precipitation may also take place in an acidic medium. Suitable acids include, for example, organic or inorganic acids, for example carboxylic acids such as acetic acid, propionic acid, succinic acid or citric acid, and also mineral acids such as, for example, hydrochloric acid, sulfuric acid or phosphoric acid.

[0069] Suitable methods of forming the aforementioned polyarylene ether sulfone polymers are known per se to a person skilled in the art and are described, for example, in Herman F. Mark, "Encyclopedia of Polymer Science and Technology", third edition, Volume 4, 2003, chapter "Polysulfones" on pages 2 to 8 and also in Hans R. Kricheldorf, "Aromatic Polyethers" in: Handbook of Polymer Synthesis, second edition, 2005 on pages 427 to 443.

[0070] Preferred polyarylene ether sulfone polymers comprise at least one of the following building blocks la to Ic as structural repeat units:

[0071] It is also particularly preferable for the polyarylene ether sulfone polymer to be composed essentially of at least one variety of building blocks selected from the group consisting of la, lb and Ic. Particular preference is further given to polyarylene ether sulfone polymers composed of repeat units of formula lb. Polyether sulfone (PESLI) is another appellation for these polyarylene ether sulfone polymers.

[0072] Abbreviations such as PESLI and PSU herein conform to DIN EN ISO 1043-1 (Plastics - Symbols and abbreviated terms - Part 1: Basic polymers and their special characteristics (ISO 1043-1 :2001); German version of EN ISO 1043-1 :2002).

[0073] Particular preference is further given to block or other copolymers constructed of repeat units of formulae la, lb and Ic.

[0074] The weight average molecular weight (Mw) of the polyarylene ether sulfone polymer obtainable by the method of the present invention is generally in the range from 10 000 to 150 000 g / mol, preferably in the range from 15 000 to 120 000 g / mol and more preferably in the range from 18 000 to 100 000 g / mol. The weight average molecular weights (Mw) are measured using gel permeation chromatography (GPC). This measurement is carried out using gel permeation chromatography (GPC). Dimethylacetamide (DMAc) was used as solvent and narrowly distributed polymethyl methacrylate was used as standard in the measurement.

[0075] Preferred are polyarylene ether sulfone polymers with a Viscosity number (V.N.) between 40 and 120 ml / g (measured according to ISO 1628 as 1 wt.% solution in N- methyl-2-pyrrolidone at 23°C). Such polymers are available as Ultrason® E from BASF SE.

[0076] The terminal groups of the polyarylene ether sulfone polymers depend on the reaction conditions and the molar ratios of components (A1) and (B1) and are generally either halogen groups, in particular chlorine groups, or etherified groups, in particular alkyl ether groups. Etherified end groups are obtainable by reacting the terminal OH / phenoxide groups with suitable etherifying agents.

[0077] Examples of suitable etherifying agents are monofunctional alkyl or aryl halides, for example C C6alkyl chlorides, bromides or iodides, preferably methyl chloride, or benzyl chloride, bromide or iodide, or mixtures thereof. The terminal groups of the polyarylene ether sulfone polymer according to the present invention are preferably halogen groups, in particular chlorine, and also alkoxy groups, in particular methoxy, aryloxy groups, in particular phenoxy, or benzyloxy.

[0078] Upper top layer (UTL) / lower top layer (LTL) The upper top layer (UTL) comprises at least one polyarylene ether sulfone and at least one fiber reinforcement. What is meant herein by “at least one polyarylene ether sulfone polymer” is precisely one polyarylene ether sulfone polymer and also mixtures of two or more different polyarylene ether sulfone polymers. Preferably, the upper top layer (UTL) comprises one polyarylene ether sulfone polymer.

[0079] In view of the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL), the above made description, explanations, and preferences in view of the polyarylene ether sulfone polymer hold true accordingly.

[0080] The glass transition temperature Tg of the polyarylene ether sulfone polymer comprised in the upper top layer (UTL) is preferably in the range of 180 to 230 °C, more preferably in the range of from 185 to 228 °C, and most preferred in the range of from 185 to 226 °C. The glass transition temperature Tg is determined by DSC- measurements according to ISO 11357-1 , using a heating rate of 10 K / min.

[0081] The weight average molecular weight (Mw) of the polyarylene ether sulfone polymer comprised in the upper top layer (UTL) is generally in the range from 50 000 to150 000 g / mol, preferably in the range from 52 000 to 120 000 g / mol and more preferably in the range from 53 000 to 100 000 g / mol. The weight average molecular weights (Mw) are measured using gel permeation chromatography (GPC). This measurement is carried out using gel permeation chromatography (GPC). Dimethylacetamide (DMAc) was used as solvent and narrowly distributed polymethyl methacrylate was used as standard in the measurement. In a preferred embodiment the average molecular weight (Mw) of the polyarylene ether sulfone polymer comprised in the upper top layer (UTL) is higher than the average molecular weight (Mw) of the polyarylene ether sulfone polymer comprised in the blend (comprised in the first and second film (F1 ; F2).

[0082] In a preferred embodiment, the upper top layer (UTL) comprises at least one polyarylene ether sulfone polymer selected from the group consisting of polysulfone (PSU), polyether sulfone (PESU) and polybiphenyl sulfone (PPSU).

[0083] In an especially preferred embodiment, the polyarylene ether sulfone polymer comprised in the upper layer (UTL) is polyether sulfone (PESU).

[0084] The upper top layer (UTL), moreover, comprises at least one fiber reinforcement. What is meant herein by “at least one fiber reinforcement” is precisely one fiber reinforcement and also mixtures of two or more fiber reinforcements.

[0085] Suitable fiber reinforcements are, for example, selected from the group consisting of glass fibers and carbon fibers. Usually reinforced thermoplastic laminates (RTLs) are used as upper top layer (UTL). In a preferred embodiment, the upper top layer (UTL) comprises from 25 to 70 wt.-% of the at least one polyarylene ether sulfone polymer and 30 to 75 wt.-% of the at least one fiber reinforcement, based on the total weight of the upper top layer (UTL).

[0086] The preparation of the upper top layer (UTL) is known to the person skilled in the art. The upper top layer (UTL) can, for example, be prepared by impregnation of the at least one fiber reinforcement with the at least one polyarylene ether sulfone polymer in the molten state. Suitable procedures for the preparation of the upper top layer (UTL) are, for example melt pressing of layers of thermoplastic films with layers of fibers in a press to achieve a homogeneous distribution of the thermoplastic material in the RTL. The fiber orientation of the different fiber layers can be adapted to the needs of the particular application and can be 0 / 90 / +45 / -45. The consolidation in a press allows easy processing of the RTLs. RTLs can also be obtained by powder impregnation of fabrics. Details about these processes are given in Valente, M. polymers 2023, 15, 242.

[0087] The upper top layer (UTL), and the lower top layer (LTL) comprised in the sandwich panel preferably independently from each other have a thickness in the range of 0.1 to 0.5 mm. In a preferred embodiment the upper top layer (UTL), and the lower top layer (LTL) comprised in the sandwich panel preferably have the same thickness in the range of 0.1 to 0.5 mm.

[0088] Another object of the present invention, therefore, is a sandwich, wherein the upper top layer (UTL), and the lower top layer (LTL) independently from each other have a thickness in the range of 0.1 to 0.5 mm.

[0089] The upper top layer (UTL), and the lower top layer (LTL) comprised in the sandwich panel preferably independently from each other have an areal weight in the range of 150 to 600 g / m2. In a preferred embodiment the upper top layer (UTL), and the lower top layer (LTL) comprised in the sandwich panel preferably have the same areal weight in the range of 200 to 500 g / m2.

[0090] In another preferred embodiment the upper top layer (UTL), and the lower top layer (LTL) comprised in the sandwich panel comprise the same polyarylene ether sulfone polymer.

[0091] In another preferred embodiment the upper top layer (UTL), and the lower top layer (LTL) comprised in the sandwich panel comprise the same polyarylene ether sulfone polymer and the same fiber reinforcement. In another preferred embodiment the upper top layer (UTL), and the lower top layer (LTL) comprised in the sandwich panel comprise the same polyarylene ether sulfone polymer, the same fiber reinforcement and have the same thickness. In another preferred embodiment the upper top layer (UTL), and the lower top layer (LTL) comprised in the sandwich panel comprise the same polyarylene ether sulfone polymer, the same fiber reinforcement, have the same thickness, and have the same areal weight.

[0092] In another preferred embodiment the upper top layer (UTL), and the lower top layer (LTL) comprised in the sandwich panel comprise the same polyarylene ether sulfone polymer, the same fiber reinforcement, have the same thickness, have the same areal weight and have the same glass transition temperature.

[0093] In an especially preferred embodiment the upper top layer (UTL), and the lower top layer (LTL) are identical.

[0094] In view of the lower top layer (LTL), the above made description, explanations, and preferences in view of the upper top layer (UTL) hold true accordingly.

[0095] The lower top layer (LTL) comprises at least one polyarylene ether sulfone and at least one fiber reinforcement. What is meant herein by “at least one polyarylene ether sulfone polymer” is precisely one polyarylene ether sulfone polymer and also mixtures of two or more different polyarylene ether sulfone polymers. Preferably, the lower top layer (LTL) comprises one polyarylene ether sulfone polymer.

[0096] In view of the at least one polyarylene ether sulfone polymer comprised in the lower top layer (LTL), the above made description, explanations, and preferences in view of the polyarylene ether sulfone polymer hold true accordingly.

[0097] The glass transition temperature Tg of the polyarylene ether sulfone polymer comprised in the lower top layer (LTL) is preferably in the range of 180 to 230 °C, more preferably in the range of from 185 to 227 °C, and most preferred in the range of from 185 to 225 °C. The glass transition temperature is determined as described above.

[0098] The weight average molecular weight (Mw) of the polyarylene ether sulfone polymer comprised in the lower top layer (LTL) is generally in the range from 50 000 to 150 000 g / mol, preferably in the range from 52 000 to 120 000 g / mol and more preferably in the range from 53 000 to 100 000 g / mol. The weight average molecular weights (Mw) are measured using gel permeation chromatography (GPC). This measurement is carried out using gel permeation chromatography (GPC). Dimethylacetamide (DMAc) was used as solvent and narrowly distributed polymethyl methacrylate was used as standard in the measurement. In a preferred embodiment the average molecular weight (Mw) of the polyarylene ether sulfone polymer comprised in the lower top layer (LTL) is higher than the average molecular weight (Mw) of the polyarylene ether sulfone polymer comprised in the blend (comprised in the first and second film (F1; F2). In a preferred embodiment, the lower top layer (LTL) comprises at least one polyarylene ether sulfone polymer selected from the group consisting of polysulfone (PSU), polyether sulfone (PESLI) and polybiphenyl sulfone (PPSLI).

[0099] In an especially preferred embodiment, the polyarylene ether sulfone polymer comprised in the lower layer (LTL) is polyether sulfone (PESU).

[0100] The lower top layer (LTL), moreover, comprises at least one fiber reinforcement. What is meant herein by “at least one fiber reinforcement” is precisely one fiber reinforcement and also mixtures of two or more fiber reinforcements.

[0101] Suitable fiber reinforcements are, for example, selected from the group consisting of glass fibers and carbon fibers. Usually reinforced thermoplastic laminates (RTLs) are used as lower top layer (LTL).

[0102] In a preferred embodiment, the lower top layer (LTL) comprises from 25 to 70 wt.-% of the at least one polyarylene ether sulfone polymer and 30 to 75 wt.-% of the at least one fiber reinforcement, based on the total weight of the lower top layer (LTL).

[0103] The preparation of the lower top layer (LTL) is known to the person skilled in the art. The lower top layer (LTL) can, for example, be prepared by impregnation of the at least one fiber reinforcement with the at least one polyarylene ether sulfone polymer in the molten state. Suitable procedures for the preparation of the lower top layer (LTL) are, those described above for the upper top layer (UTL).

[0104] Foam core layer (FCL)

[0105] The foam core layer (FCL) comprises at least one polyarylene ether sulfone. What is meant herein by “at least one polyarylene ether sulfone polymer” is precisely one polyarylene ether sulfone polymer and also mixtures of two or more different polyarylene ether sulfone polymers. Preferably, the foam core layer (FCL) comprises one polyarylene ether sulfone polymer.

[0106] In view of the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL), the above made description, explanations, and preferences in view of the polyarylene ether sulfone polymer hold true accordingly.

[0107] The glass transition temperature Tg of the polyarylene ether sulfone polymer comprised in the foam core layer (FCL) is preferably in the range of 180 to 230 °C, more preferably in the range of from 185 to 228 °C, and most preferred in the range of from 185 to 225 °C. The glass transition temperature is determined as described above.

[0108] The weight average molecular weight (Mw) of the polyarylene ether sulfone polymer comprised in the foam core layer (FCL) is generally in the range from 50 000 to 150 000 g / mol, preferably in the range from 52 000 to 120 000 g / mol and more preferably in the range from 53 000 to 100 000 g / mol. The weight average molecular weights (Mw) are measured using gel permeation chromatography (GPC). This measurement is carried out using gel permeation chromatography (GPC). Dimethylacetamide (DMAc) was used as solvent and narrowly distributed polymethyl methacrylate was used as standard in the measurement. In a preferred embodiment the average molecular weight (Mw) of the polyarylene ether sulfone polymer comprised in the foam core layer (FCL) is higher than the average molecular weight (Mw) of the polyarylene ether sulfone polymer comprised in the blend (comprised in the first and second film (F1 ; F2).

[0109] In a preferred embodiment, the foam core layer (FCL) comprises at least one polyarylene ether sulfone polymer selected from the group consisting of polysulfone (PSU), polyether sulfone (PESU) and polybiphenyl sulfone (PPSU).

[0110] In an especially preferred embodiment, the polyarylene ether sulfone polymer comprised in the foam core layer (FCL) is polyether sulfone (PESU).

[0111] The preparation of the foam core layer (FCL) is known to the person skilled in the art. The foam core layer (FCL) can, for example, be prepared by extrusion using solvents as foaming agents and special process parameters as described in DE 4207057. Water based mixtures as foaming agents for the preparation of foam core layers (FCL) are described in EP 1333051. If PESU-mixtures with broad molecular weight distribution are used, foaming with water is possible.

[0112] The foam core layer (FCL) comprised in the sandwich panel preferably has a thickness in the range of 0.76 to 50 mm.

[0113] Another object of the present invention, therefore is a sandwich panel, wherein the foam core layer (FCL) has a thickness in the range of 0.76 to 50 mm.

[0114] The foam core layer (FCL) comprised in the sandwich panel has a density in the range of 25 to 200 kg / m3, preferably in the range of a density in the range of 35 to 155 kg / m3.

[0115] Another object of the present invention therefor is a sandwich panel, wherein the foam core layer (FCL) has a density in the range of 25 to 200 kg / m3. In another preferred embodiment the foam core layer (FCL), the upper top layer (UTL), and the lower top layer (LTL) comprised in the sandwich panel comprise the same polyarylene ether sulfone polymer.

[0116] First film (F1) / second film (F2)

[0117] The first film (F1) comprises at least one polyarylene ether sulfone. What is meant herein by “at least one polyarylene ether sulfone polymer” is precisely one polyarylene ether sulfone polymer and also mixtures of two or more different polyarylene ether sulfone polymers. Preferably, the first film (F1) comprises one polyarylene ether sulfone polymer.

[0118] In view of the at least one polyarylene ether sulfone polymer comprised in the first film (F1), the above made description, explanations, and preferences in view of the polyarylene ether sulfone polymer hold true accordingly.

[0119] In a preferred embodiment the at least one polyarylene ether sulfone polymer comprised in the blend has a viscosity number (VN) in the range of 45 to 58 ml / g measured according to ISO 1628, preferably in N-methyl-2-pyrrolidone at 25 °C

[0120] The weight average molecular weight (Mw) of the at least one polyarylene ether sulfone polymer comprised in the blend is preferably in the range from 40 000 to 57 000 g / mol, preferably in the range from 41 000 to 56 000 g / mol and more preferably in the range from 42 000 to 55 000 g / mol. The weight average molecular weights (Mw) are measured using gel permeation chromatography (GPC). This measurement is carried out using gel permeation chromatography (GPC). Dimethylacetamide (DMAc) was used as solvent and narrowly distributed polymethyl methacrylate was used as standard in the measurement.

[0121] In a preferred embodiment, the first film (F1) comprises at least one polyarylene ether sulfone polymer selected from the group consisting of polysulfone (PSU), polyether sulfone (PESLI) and polybiphenyl sulfone (PPSLI).

[0122] In an especially preferred embodiment, the polyarylene ether sulfone polymer comprised in the first film (F1) is polyether sulfone (PESLI).

[0123] The first film (F1), moreover, comprises at least one further polymer. What is meant herein by “at least one further polymer” is precisely one further polymer and also mixtures of two or more further polymers. Preferably the first film comprises one further polymer. Suitable further polymers are, for example, selected from the group consisting of phenoxy polymer, polyethylene oxide polymer and polyvinylpyrrolidone polymer.

[0124] Phenoxy® is a commercially available polymer containing hydroxyl-groups. The structural formula of Phenoxy® PKHH is given below in formula II).

[0125] Formula II

[0126] In formula II n’ is preferably an integer in the range of 10 to 100, preferably in the range of 15 to 90, and more preferably in the range of 20 to 80.

[0127] Phenoxy polymers can be prepared by reacting bisphenol A with epichlorohydrin.

[0128] Preferably as a phenoxy polymer with a Tg in the range of 70 to 100 °C, more preferably in the range of 80 to 98 °C and especially preferred in the range of 85 to 98 °C is used. The glass transition temperature Tg is determined by DSC- measurements according to ISO 11357-1 , using a heating rate of 10 K / min.

[0129] Suitable phenoxy polymers have a number average molecular weight in the range of 2500 to 25 000 g / mol, preferably in the range of 5 000 to 20 000 g / mol. The number average molecular weight is determined as described below for the polyarylene ether sulfone polymers comprised in the upper top layer (UTL).

[0130] Preferably Phenoxy PKHH with a Tg of 97°C is used. The content of Phenoxy PKHH in these blends is between 2 and 40 wt.%, based on the total weight of the film (F1 / F2).

[0131] As further polymer to reduce the Tg of polyarylene ether sulfone polymer, polyethylene oxide can be used. Based on their molecular weight, polyethylene oxides are either liquids or solids. Polyethylene oxides having a number average molecular weight of 200 up to 40000 g / mol can be used. Preferably polyethylene oxides with a number average molecular weight of 600 to 8000 g / mol are used. The content of Polyethylene oxide in these blends comprised in the first film (F1) and / or second film (F2) is between 2 and 40 wt.%, based on the total weight of the film (F1 / F2). Block copolymers of polyarylene ether sulfone and polyethylene oxide can also be employed as material for the film (F1 / F2). The preparation of possible block copolymers is described in EP 2739668 and EP 2992038.

[0132] Furthermore, blends of polyarylene ether sulfone polymer and polyvinylpyrrolidone (PVP) can be used. To retain a good processing, PVP with number average molecular weights between 5000 and 50000 g / mol is preferred. The content of PVP in these blends (F1 / F2) is between 2 and 40 wt.%, based on the total weight of the film (F1 / F2).

[0133] In a preferred embodiment, the blend of the first film (F1), comprises from 97.5 to 65 wt.-% of the at least one polyarylene ether sulfone polymer and 2.5 to 35 wt.-% of the at least one further polymer, based on the total weight of the first film (F1).

[0134] In a more preferred embodiment, the blend of the first film (F1), comprises from 97 to 70 wt.-% of the at least one polyarylene ether sulfone polymer and 3 to 30 wt.-% of the at least one further polymer, based on the total weight of the first film (F1).

[0135] In a particularly preferred embodiment, the blend of the first film (F1), comprises from 96 to 72 wt.-% of the at least one polyarylene ether sulfone polymer and 4 to 28 wt.-% of the at least one further polymer, based on the total weight of the first film (F1).

[0136] The preparation of the first film (F1) is known to the person skilled in the art. The first film (F1) can, for example, be prepared by film extrusion of the blend comprised in the first film (F1). Details about film extrusion are known in the art, e.g. from C. Rauwendaal, “Polymer Extrusion” Hanser, 5thEdition 2014.

[0137] The first film (F1), and the second film (F2) comprised in the sandwich panel preferably independently from each other have a thickness in the range of 0.02 to 0.15 mm. In a preferred embodiment the first film (F1), and second film (F2) comprised in the sandwich panel preferably have the same thickness in the range of 0.02 to 0.15 mm.

[0138] The first film (F1), and the second film (F2) comprised in the sandwich panel preferably independently from each other have a density in the range of 1.15 to 1.36 g / cm3. In a preferred embodiment the first film (F1), and the second film (F2) comprised in the sandwich panel preferably have the same density in the range of 1.16 to 1.35 g / cm3.

[0139] In another preferred embodiment the first film (F1), and the second film (F2) contained in the sandwich panel comprise the same polyarylene ether sulfone polymer.

[0140] In another preferred embodiment the first film (F1), and the second film (F2) contained in the sandwich panel comprise the same polyarylene ether sulfone polymer and the same further polymer. In another preferred embodiment the first film (F1), and the second film (F2) contained in the sandwich panel comprise the same polyarylene ether sulfone polymer, the same further polymer and have the same thickness. In another preferred embodiment the first film (F1), and the second film (F2) contained in the sandwich panel comprise the same polyarylene ether sulfone polymer, the same further polymer, have the same thickness, and have the same density.

[0141] In another preferred embodiment the blend contained in the first film (F1), and the blend contained in the second film (F2) comprised in the sandwich panel comprise the same polyarylene ether sulfone polymer, the same further polymer, have the same thickness, have the same density and have the same glass transition temperature Tg.

[0142] In an especially preferred embodiment the first film (F1), and the second film (F2) are identical.

[0143] Preferably the blend comprised in the first film (F1) has a glass transition temperature Tg at least 5K below the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL) and the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL). The glass transition temperature Tg is determined as described above.

[0144] Therefore, another object of the present invention is a sandwich panel, wherein the blend comprised in the first film (F1) has a glass transition temperature Tg at least 5K below the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL) and the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL).

[0145] More preferably the blend comprised in the first film (F1) has a glass transition temperature Tg at least 5K below the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL) and the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL) and the glass transition temperature Tg of the lower top layer (LTL).

[0146] In case the blend comprised in the first film (F1) has more than one glass transition temperature Tg, reference is made to the upper glass transition temperature Tg.

[0147] In view of the second film (F2), the above made description, explanations, and preferences in view of the first film (F1) hold true accordingly. The second film (F2) comprises at least one polyarylene ether sulfone and at least one further polymer. What is meant herein by “at least one polyarylene ether sulfone polymer” is precisely one polyarylene ether sulfone polymer and also mixtures of two or more different polyarylene ether sulfone polymers. Preferably, the second film (F2) comprises one polyarylene ether sulfone polymer.

[0148] In view of the at least one polyarylene ether sulfone polymer comprised in the second film (F2), the above made description, explanations, and preferences in view of the polyarylene ether sulfone polymer hold true accordingly.

[0149] In a preferred embodiment, the second film (F2) comprises at least one polyarylene ether sulfone polymer selected from the group consisting of polysulfone (PSU), polyether sulfone (PESLI) and polybiphenyl sulfone (PPSLI).

[0150] In an especially preferred embodiment, the polyarylene ether sulfone polymer comprised in the second film (F2) is polyether sulfone (PESLI).

[0151] The second film (F2), moreover, comprises at least one further polymer. What is meant herein by “at least one further polymer” is precisely one further polymer and also mixtures of two or more further polymers. Preferably the first film comprises one further polymer.

[0152] Suitable further polymers are, for example, selected from the group consisting of phenoxy polymer, polyethylene oxide polymer and polyvinylpyrrolidone polymer.

[0153] Phenoxy® is a commercially available polymer containing hydroxyl-groups. The structural formula of Phenoxy® PKHH is given below in formula II).

[0154] Formula II

[0155] Preferably Phenoxy PKHH with a Tg of 97°C is used. The content of Phenoxy PKHH in these blends is between 2 and 40 wt.%, based on the total weight of the film (F1 / F2).

[0156] As further polymer to reduce the Tg of polyarylene ether sulfone polymer, polyethylene oxide can be used. Based on their molecular weight, polyethylene oxides are either liquids or solids. Polyethylene oxides having a number average molecular weight of 200 up to 40000 g / mol can be used. Preferably polyethylene oxides with a number average molecular weight of 600 to 8000 g / mol are used. The content of Polyethylene oxide in these blends comprised in the first film (F1) and / or second film (F2) is between 2 and 40 wt.%, based on the total weight of the film (F1 / F2).

[0157] Block copolymers of polyarylene ether sulfone and polyethylene oxide can also be employed as material for the film (F1 / F2). The preparation of possible block copolymers is described in EP 2739668 and EP 2992038.

[0158] Furthermore, blends of polyarylene ether sulfone polymer and polyvinylpyrrolidone (PVP) can be used. To retain a good processing, PVP with number average molecular weights between 5000 and 50000 g / mol is preferred. The content of PVP in these blends (F1 / F2) is between 2 and 40 wt.%, based on the total weight of the film (F1 / F2).

[0159] In a preferred embodiment, the blend of the second film (F2), comprises from 97.5 to 65 wt.-% of the at least one polyarylene ether sulfone polymer and 2.5 to 35 wt.-% of the at least one further polymer, based on the total weight of the second film (F2).

[0160] In a more preferred embodiment, the blend of the second film (F2), comprises from 97 to 70 wt.-% of the at least one polyarylene ether sulfone polymer and 3 to30 wt.-% of the at least one further polymer, based on the total weight of the second film (F2).

[0161] In a particularly preferred embodiment, the blend of the second film (F2), comprises from 96 to 72 wt.-% of the at least one polyarylene ether sulfone polymer and 4 to 28 wt.-% of the at least one further polymer, based on the total weight of the second film (F2).

[0162] The preparation of the second film (F2) is known to the person skilled in the art. The second film (F2) can, for example, be prepared as described above for the first film.

[0163] Preferably the blend comprised in the second film (F2) has a glass transition temperature Tg at least 5K below the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL) and the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL). The glass transition temperature Tg is determined as described above.

[0164] Therefore, another object of the present invention is a sandwich panel, wherein the blend comprised in the second film (F2) has a glass transition temperature Tg at least 5K below the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the lower top layer (LTL) and the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL).

[0165] More preferably the blend comprised in the second film (F2) has a glass transition temperature Tg at least 5K below the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL) and the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL) and the glass transition temperature of the lower top layer (LTL).

[0166] In case the blend comprised in the second film (F2) has more than one glass transition temperature Tg, reference is made to the upper glass transition temperature Tg.

[0167] Sandwich panel

[0168] The sandwich panel preferably has a thickness in the range of 1.0 to 51.3 mm.

[0169] Therefore, another object of the present invention is a sandwich panel, wherein the sandwich panel has a thickness in the range of 1.0 to 51.3 mm.

[0170] The sandwich panel comprises starting from the upper top layer (UTL) layers in the following order: upper top layer (UTL), first film (F1), foam core layer (FCL), second film (F2), and lower top layer (OTL).

[0171] The sandwich panel in a preferred embodiment comprises at least 80 wt.-%, more preferably at least 85 wt.-% and particularly preferred at least 90 wt.-% of the at least one polyarylene ether sulfone polymer, based on the total weight of polymers in the sandwich panel.

[0172] In another preferred embodiment the sandwich panel comprises only one kind of polyarylene ether sulfone polymer. In a more preferred embodiment, the sandwich panel comprises only one kind of polyarylene ether sulfone polymer, wherein the polyarylene ether sulfone polymer is selected from the group consisting of polysulfone (PSU), polyether sulfone (PESU) and polybiphenyl sulfone (PPSU).

[0173] In an especially preferred embodiment, the sandwich panel comprises only one kind of polyarylene ether sulfone polymer, wherein the polyarylene ether sulfone polymer is polyether sulfone (PESU).

[0174] Therefore, another object of the present invention is a sandwich panel, wherein the at least one further polymer comprised in the blend of the first film (F1) and the at least one further polymer comprised in the second film (F2) are each independently from each other at least one polymer selected from the group consisting of phenoxy polymer, polyethylene oxide polymer and polyvinylpyrrolidone polymer.

[0175] Therefore, another object of the present invention is a sandwich panel, wherein the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL), the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL), the at least one polyarylene ether sulfone polymer comprised in the lower top layer (LTL), the at least one polyarylene ether sulfone polymer comprised in the first film (F1), and the at least one polyarylene ether sulfone polymer comprised in the second film (F2) are each independently from each other at least one polymer selected from the group consisting of polysulfone (PSU), polyethersulfone (PESLI) and polybiphenyl sulfone (PPSLI).

[0176] Therefore, another object of the present invention is a sandwich panel, wherein the upper top layer (UTL), the foam core layer (FCL), the lower top layer (LTL), the first film (F1), and the second film (F2) each comprise the same polyarylene ether sulfone polymer.

[0177] Process for the production of the sandwich panel

[0178] Another object of the present invention is a process for the production of a sandwich panel according to the invention comprising the steps: i) providing the upper top layer (UTL) comprising at least one polyarylene ether sulfone polymer and at least one fiber reinforcement, the foam core layer (FCL) comprising at least one polyarylene ether sulfone polymer, the lower top layer (LTL) comprising at least one polyarylene ether sulfone polymer and at least one fiber reinforcement, ii) placing the first film (F1) comprising a blend of at least one polyarylene ether sulfone polymer and at least one further polymer between the upper top layer (UTL) and the foam core layer (FCL), iii) placing the second film (F2) comprising a blend of at least one polyarylene ether sulfone polymer and the at least one and at least one further polymer between the lower top layer (LTL) and the foam core layer (FLC), to obtain a sandwich comprising starting from the upper top layer (UTL) layers in the following order: upper top layer (UTL), first film (F1) foam core layer (FCL), second film (F2), and lower top layer (LTL), and iv) heating the sandwich obtained step in iii) to a temperature at most 1 K below the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL) and the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL) and the glass transition temperature Tg of the lower top layer (LTL).

[0179] Steps i) to iii) can be carried out in any order. Preferably steps i) to iii) are carried out concurrently. Heating of individual layers by means of IR-radiation before assembly to the panel is also possible.

[0180] In a preferred embodiment in step iv) the sandwich obtained in step iii) is heated to a temperature in the range of 1 to 30 K, more preferably 5 to 25 K and especially preferred 10 to 20 K below the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL) and the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL) and the glass transition temperature Tg of the lower top layer (LTL).

[0181] In another preferred embodiment in step iv) to the upper top layer (UTL) and the lower top layer (LTL) of the sandwich obtained step iii) a pressure in the range of 0.05 to 6 MPa is applied.

[0182] The sandwich panel according to the invention in a preferred embodiment is used as construction part for aviation industry, or for the construction of rotor blades for wind turbines.

[0183] In an especially preferred embodiment, the sandwich panel according to the invention is used as an interior trim for aircraft cabins.

[0184] In another preferred embodiment, the sandwich panel according to the invention is used in aircrafts as parts of the interior, preferably overhead storage compartments, floor panels, roof panels, side panels and cabin walls.

[0185] The sandwich panel according to the invention at the end of its first application can be re-used. Therefore, another object of the present application is a process for the re-use of the sandwich panel according to the invention at the end of its first application comprising the steps: a) crushing the sandwich panel to obtain a ground material b) using the ground material obtained in step a) to produce new products.

[0186] The crushing in step a) can be done be grinding and / or milling. The product produced in step b) is preferably a fiber reinforced polyarylene ether sulfone polymer compound. The present invention is more particularly elucidated by the examples which follow without being restricted thereto.

[0187] Components used:

[0188] Foam core layer (FCL):

[0189] As foam core a polyethersulfone (PESU)-based foam Divinycell F50 with a thickness of 20 mm was used. Tg of the foam is 225°C, as measured by DSC (FCL).

[0190] Upper top layer (UTL) / lower top layer (LTL):

[0191] As inventive upper top layer (UTL) and lower top layer (LTL) a polyethersulfone(PESU)-coated glass fiber fabric with an area weight of 460 g / m2and a polymer content of 155 g / m2was used (UTL / LTLJnv).

[0192] As comparative upper top layer (UTL) and lower top layer (LTL) a polyetherimide(PEI)- coated glass fiber fabric with an area weight of 450 g / m2and a polymer content of 150 g / m2was used (UTL / LTL_comp).

[0193] First film (F1) / second film (F2)

[0194] As comparative first film (F1) and second film (F2) a film extruded out of the polyetherimide Ultem D1010, with a Tg of 217° and a thickness of 98 pm was used (F1 / F2_comp).

[0195] As inventive first film (F1) and second film (F2) a film extruded out of polyethersulfone (PESU) Ultrason E 1010 / Phenoxy PKH 65 / 35-blend, with a Tg1 of 94 and a Tg2 of 218°C and a thickness of 101 pm was applied (F1 / F2_inv1).

[0196] As second comparative film (F1) and second film (F2) a film extruded out of polyethersulfone (PESU) Ultrason E 1010, with a Tg of 224° and a thickness of 97 pm was applied (F1 / F2_comp2).

[0197] As inventive first film (F1) and second film (F2) a film extruded out of polyethersulfone (PESU) Ultrason E 1010 / Pluriol 6000 95 / 5-blend with a Tg of 195° and a thickness of 102 pm was applied (F1 / F2_inv2).

[0198] The sandwich panels were prepared by laminating the foam core layer (FCL) in between two film layers (F1 and F2) and the upper top layer (UTL) and the lower top layer (LTL) in a heated press at 230°C for 20 minutes. The obtained sandwich panels were then evaluated visually and sandwich panels without adhesion between the top layers and the foam core were sorted out. The remaining sandwich panels were tested in a 3-point bending test. The fractured sandwich panels were evaluated regarding the adhesion between the layers (adhesive fracture / cohesive fracture). The results are summarized in table 1.

[0199] Table 1 o: weak adhesion no adhesion

[0200] ++: good adhesaion

[0201] Several sandwich panels (size 60 cm*40 cm) of each composition were molded and then grinded in a mill equipped with a sieving unit to obtain particles with a size below 5 mm. These materials were then characterized by their glass fiber content (char yield, wt.%) and were then compounded in a ZSK 18 Twin screw extruder with PESLI (Ultrason E 1010) to obtain a product with a fiber content of 10 wt.% (corresponding M- product in table 2). The melt temperature during compounding was 365°C, the throughput was 6 kg / h at a screw speed of 250 rpm.

[0202] The obtained granulates were then molded into ISO-bars for Charpy impact tests (ISO 179 1 eU) and samples for tensile tests (ISO 527) at a melt temperature of 360°C and a tool temperature of 150°C. The testing results are summarized in table 2. Table 2

[0203] The sandwich panels with a PESU-content of more than 80 wt.% with respect to the total polymer content deliver fiber reinforced thermoplastic materials with good toughness and strength.

Claims

Claims1. Sandwich panel comprising an upper top layer (UTL) comprising at least one polyarylene ether sulfone polymer and at least one fiber reinforcement, a foam core layer (FCL) comprising at least one polyarylene ether sulfone polymer, and a lower top layer (LTL) comprising at least one polyarylene ether sulfone polymer and at least one fiber reinforcement, wherein the upper top layer (UTL) is joined with the foam core layer (FCL) via a first film (F1) comprising a blend of at least one polyarylene ether sulfone polymer and at least one further polymer, and, wherein the lower top layer (LTL) is joined with the foam core layer (FCL) via a second film (F2) comprising a blend of at least one polyarylene ether sulfone polymer and at least one further polymer.

2. The sandwich panel according to claim 1 , wherein the blend comprised in the first film (F 1 ) has a glass transition temperature Tg at least 5K below the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL) and the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL).

3. The sandwich panel according to claim 1 or 2, wherein the blend comprised in the second film (F2) has a glass transition temperature Tg at least 5K below the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the lower top layer (LTL) and the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL).

4. The sandwich panel according to any of claims 1 to 3, wherein the at least one further polymer comprised in the blend of the first film (F1) and the at least one further polymer comprised in the second film (F2) are each independently from each other at least one polymer selected from the group consisting of phenoxy polymer, polyethylene oxide polymer and polyvinylpyrrolidone polymer.

5. The sandwich panel according to any of claims 1 to 4, wherein the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL), the atleast one polyarylene ether sulfone polymer comprised in the foam core layer (FCL), the at least one polyarylene ether sulfone polymer comprised in the lower top layer (LTL), the at least one polyarylene ether sulfone polymer comprised in the first film (F 1 ) , and the at least one polyarylene ether sulfone polymer comprised in the second film (F2) are each independently from each other at least one polymer obtained by converting a reaction mixture (RG) comprising as components:(A1) a dihalogen component comprising not less than 80 wt% of at least one dihalogen compound selected from the group consisting of 4,4‘-dichloro- diphenyl sulfone and 4,4'-difluorodiphenyl sulfone, based on the overall weight of component (A1) in reaction mixture (RG),(B1) a dihydroxy component comprising not less than 80 wt% of at least one dihydroxy compound selected from the group consisting of 4,4'-dihydroxy- diphenyl sulfone, bisphenol A, 4,4'-dihydroxybiphenyl and hydroquinone, based on the overall weight of component (B1) in reaction mixture (RG).

6. The sandwich panel according to any of claims 1 to 5, wherein the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL), the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL), the at least one polyarylene ether sulfone polymer comprised in the lower top layer (LTL), the at least one polyarylene ether sulfone polymer comprised in the first film (F 1 ) , and the at least one polyarylene ether sulfone polymer comprised in the second film (F2) are each independently from each other at least one polymer selected from the group consisting of polysulfone (PSU), polyethersulfone (PESU) and polybiphenyl sulfone (PPSU).

7. The sandwich panel according to any of claims 1 to 6, wherein the upper top layer (UTL), the foam core layer (FCL), the lower top layer (LTL), the first film (F1), and the second film (F2) each comprise the same polyarylene ether sulfone polymer.

8. The sandwich panel according to any of claims 1 to 7, wherein the sandwich panel has a thickness in the range of 1.0 to 51.3 mm.

9. The sandwich panel according to any of claims 1 to 8, wherein the foam core layer (FCL) has a thickness in the range of 0.76 to 50 mm.

10. The sandwich panel according to any of claims 1 to 9, wherein the upper top layer (UTL), and the lower top layer (LTL) independently from each other have a thickness in the range of 0.1 to 0.5 mm.

11. The sandwich panel according to any of claims 1 to 10, wherein the first film (F1) and the second film (F2) independently from each other have a thickness in the range of 0.02 to 0.15 mm.

12. The sandwich panel according to any of claims 1 to 11 , wherein the foam core layer (FCL) has a density in the range of 25 to 200 kg / m3.

13. A process for the production of a sandwich panel according to any of claims 1 to 12 comprising the steps: i) providing the upper top layer (UTL) comprising at least one polyarylene ether sulfone polymer and at least one fiber reinforcement, the foam core layer (FCL) comprising at least one polyarylene ether sulfone polymer, the lower top layer (LTL) comprising at least one polyarylene ether sulfone polymer and at least one fiber reinforcement, ii) placing the first film (F1) comprising a blend of at least one polyarylene ether sulfone polymer and at least one further polymer between the upper top layer (UTL) and the foam core layer (FCL), iii) placing the second film (F2) comprising a blend of at least one polyarylene ether sulfone polymer and the at least one and at least one further polymer between the lower top layer (LTL) and the foam core layer (FCL), to obtain a sandwich comprising starting from the upper top layer (UTL) layers in the following order: upper top layer (UTL), first film (F1) foam core layer (FCL), second film (F2), and lower top layer (LTL), and iv) heating the sandwich obtained step iii) to a temperature at most 1 K below the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the upper top layer (UTL) and the glass transition temperature Tg of the at least one polyarylene ether sulfone polymer comprised in the foam core layer (FCL) and the glass transition temperature Tg of the lower top layer (LTL).

14. The sandwich panel obtained by process according to claims 13.

15. The use of the sandwich panel, according to any of claims 1 to 12 and 14 as construction part for aviation industry, or for the construction of rotor blades for wind turbines.

16. The process for the re-use of the sandwich panel according to any of claims 1 to 12 and 14 at the end of its first application comprising the steps:a) crushing the sandwich panel to obtain a ground material b) using the ground material obtained in step a) to produce new products.

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