PHOSPHORUS-CONTAINING CELLULOSE ESTERS, METHOD FOR THEIR PREPARATION, USE AND FLAME RETARDANTS

Description

[0001] The invention relates to cellulose esters whose ester groups are at least partially phosphorus-containing and are based on unsaturated carboxylic acids and on reactive phosphorus components, the latter preferably being phosphorus derivatives of sugar alcohols or tartaric acid derivatives. The invention also relates to processes for the production of the new phosphorus-containing cellulose esters and their use as flame retardants for plastics.

[0002] The high flammability of most plastic materials is a disadvantage that must be overcome or mitigated for numerous applications using flame retardants. Besides mineral additives and polyphosphates, which usually have to be added in considerable quantities and often impair material properties, and special flame retardant additives with limited applications, halogenated flame retardants are of great importance because they are efficient, cost-effective, and less detrimental to material parameters. However, the latter can pose health risks—especially due to the release of toxic gases during a fire—and cause environmental problems, not least during the disposal of the plastics containing them.This particularly applies to combinations of halogenated flame retardants with the synergist antimony(III) oxide, which are widely used in engineering plastics and polyolefins.

[0003] Desirable are flame retardants that do not exhibit these disadvantages and can ideally be produced from renewable raw materials. As an alternative to halogenated flame retardants, special organophosphorus compounds, which are less problematic from an ecological and health perspective, have become important. The use of such phosphates, phosphinates, and phosphonates as flame retardants on their own is known, as is their use as components of flame retardant mixtures or synergistic flame retardant systems, e.g., in combination with 1,3,5-triazine compounds or polyphosphates.

[0004] Macromolecular organophosphorus compounds, when used as flame retardants, have the advantage of producing less of a plasticizing effect compared to corresponding low-molecular-weight phosphorus compounds. This plasticizing effect is often undesirable due to the deterioration of material properties, and they exhibit little tendency to migrate from the material. The use of macromolecular phosphorus compounds as flame retardants for plastics is already established.

[0005] WO 2009 / 109347 A1 describes a linear phosphorus-containing polyester based on itaconic acid and ethylene glycol, obtained by Phospha-Michael addition of DOPO to itaconic acid or itaconic acid derivatives, followed by polycondensation with ethylene glycol. This polyester softens or melts at relatively low temperatures, which is disadvantageous for its incorporation into plastics.

[0006] German patent DE 10 2013 101 487 A1 describes phosphorus-containing thermosets. These thermosets have a polyacrylate core structure and are also obtained via a two-step process. First, a suitable phosphorus component, e.g., 9,1O-dihydro-9-oxa-1O-phosphaphenanthrene-10-oxide (DOPO), is added to multifunctional acrylates via Phospha-Michael addition, whereby the stoichiometric ratio is chosen such that, on average, more than one free acrylate group remains per molecule. Subsequently, the remaining acrylate functionalities are converted by radical polymerization, leading to cross-linking and the formation of the thermoset. These macromolecular flame retardants are only suitable for specific applications. In addition to macromolecular properties, a high proportion of bio-based structural components is increasingly desired for phosphorus-containing flame retardants.

[0007] One of the starting materials of the phosphorus-containing polyester described in WO 2009 / 109347 A1 - itaconic acid - is bio-based, but the other two are not, so the proportion of renewable raw materials is relatively small.

[0008] Furthermore, phosphorus-containing flame retardants based on cellulose, starch, lignin, oligomeric sugars, castor oil, etc., were synthesized and tested.

[0009] Furthermore, flame retardants were produced in which some of the starting materials, such as pentaerythritol, specific phenols, or other raw materials, were derived from renewable resources. While the former flame retardants have disadvantages compared to conventional, non-bio-based flame retardants with regard to their thermal stability, material compatibility, etc., and are therefore hardly suitable for high-performance polymers, the latter usually have only a moderate bio-based content, especially when considering the synthetic chemicals required for their production.

[0010] The following review article provides an overview of current developments in bio-based flame retardants: Sonnier R., Taguet A., Ferry L., Lopez-Cuesta JM. (2018) Flame Retardant Biobased Polymers. In: Towards Bio-based Flame Retardant Polymers. SpringerBriefs in Molecular Science. Springer, Cham (DOI https: / / doi.org / 10.1007 / 978-3-319-67083-6-1; Online ISBN 978-3-319-67083-6; Print ISBN 978-3-319-67082-9).

[0011] L. Yan et al. describe in Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 46, 3306-3313 (2008) the graft copolymerization of 2-methacryloyloxyethyl phosphorylcholine to cellulose in homogeneous media using atom transfer radical polymerization to obtain new hemocompatible coating materials.

[0012] The object of the present invention, compared to the prior art, was to provide macromolecular flame retardants for plastics, which are largely bio-based and suitable for various plastics, including engineering plastics. These novel flame retardants are intended to provide a high level of flame protection without adversely affecting the material properties of the plastics. An efficient method for the production of these bio-based flame retardants is to be developed.

[0013] This task is accomplished with respect to a cellulose derivative having the features of claim 1, with respect to a manufacturing process of the cellulose derivative having the features of claim 5, with respect to the use of the cellulose derivative having the features of claim 10, and with respect to a flame retardant composition having the features of claim 11.

[0014] as well as with respect to a plastic composition with the features of claim 13. The respective dependent claims represent advantageous further developments.

[0015] The present invention thus relates to a cellulose derivative of general formula I where The substance is the same or different in each occurrence and is selected from the group consisting of hydroxyl groups, residues of general formula II and residues of general formula III. where R 1< is the same or different in each occurrence and is selected from the group consisting of phosphorus-containing substituents, and R 2< is the same or different in each occurrence and is selected from the group consisting of linear or branched alkyl groups with 1 to 36 carbon atoms, linear or branched arylalkyl groups with 7 to 36 carbon atoms, with the proviso that in formula I at least one group R is a group according to formula II.

[0016] In the compounds shown above according to Formula II and Formula III, the wavy line represents the point of attachment of the respective molecular fragment to the cellulose backbone according to the general Formula I. These definitions also apply to all other formulas underlying the present application.

[0017] Surprisingly, it was found that cellulose derivatives containing phosphorus groups also exhibit excellent flame-retardant properties, especially for plastic compositions.

[0018] One advantage of the new phosphorus-containing flame retardants is their macromolecular structure, which is increasingly required for flame retardants. However, the most important advantage of the flame retardants according to the invention is their high proportion of bio-based structural components.

[0019] This is achieved by using cellulose for the polymer backbone, which is particularly advantageous because cellulose is the most widely available and abundant bio-based substance and has a structure favorable for effective flame retardancy. Furthermore, cellulose is very cost-effective. The use of sugar alcohols or tartaric acid derivatives for the phosphorus-bearing groups is preferred for the particularly high bio-based content. Sugar alcohols such as erythritol, xylitol, and mannitol are now available in large quantities and increasingly at low cost, but the use of their phosphorus derivatives in flame retardants is not yet known. Moreover, the structure of the flame retardants, especially that of the phosphorus-bearing groups, can be adapted to the specific application, thus opening up areas of use for which bio-based flame retardants are not currently suitable.It is also advantageous that an efficient synthesis sequence for the production of the new flame retardants is provided according to the invention. Finally, it is advantageous that the substances according to the invention differ structurally significantly from known flame retardants and thus represent a new class of flame retardants.

[0020] The phosphorus-containing cellulose esters according to the invention can be used as sole flame retardants or as a component of flame-retardant mixtures in combination with other flame retardants or substances that enhance the flame-retardant effect in plastics.

[0021] According to the invention, in the cellulose derivative, it is provided that in general formula II the residue R 1< is selected from the group consisting of residues according to general formula IV where the variables are either the same or different in each occurrence and R 3< is selected from the group consisting of hydrogen or linear or branched alkyl groups with 1 to 36, preferably 1 to 6, carbon atoms, R4< and R5< are independently selected from the group consisting of alkyl groups, aryl groups, alkylaryl groups, arylalkyl groups, O-alkyl groups, O-aryl groups, O-alkylaryl groups, N-alkyl groups, N-aryl groups, N-arylalkyl groups, N-alkylaryl groups, where R4< and R5< as well as the phosphorus atom may also be part of heterocyclic ring systems, which may be single- or multi-membered, and n0 is an integer from 1 to 3.

[0022] Furthermore, it is advantageous if the heterocyclic ring system is selected from the group consisting of the following groupings. where R 6< is selected independently from the group consisting of alkyl groups, aryl groups, alkylaryl groups, arylalkyl groups, O-alkyl groups, O-aryl groups, O-alkylaryl groups, N-alkyl groups, N-aryl groups, N-arylalkyl groups and N-alkylaryl groups; preferably alkyl groups with 1 to 12 carbon atoms or alkylryl groups with 7 to 14 carbon atoms.

[0023] It is also preferred that R 2< is the same or different in each occurrence and is selected from the group consisting of linear or branched alkyl groups with 1 to 12 carbon atoms, linear or branched arylalkyl groups with 7 to 14 carbon atoms.

[0024] With regard to the substitution pattern, it is advantageous if, with respect to all residues R, the molar fraction of the residues according to formula II is at least 2 mol%, preferably 5 to 100 mol%, further preferably 15 to 95 mol%, particularly preferably 40 to 90 mol%, of the residues according to formula III is 0 to 98 mol%, preferably 0 to 95 mol%, further preferably 5 to 85 mol%, particularly preferably 10 to 90 mol% and / or of the hydroxy groups is a maximum of 50 mol%, preferably 0 to 50 mol%, preferably 0 to 20 mol%, particularly preferably 0 to 10 mol%.

[0025] The present invention also relates to a method for producing the cellulose derivative according to the invention, by a) Esterification and / or transesterification reaction followed by the addition of at least one compound containing a phosphorus-containing substituent, wherein in a first step cellulose is at least partially esterified with at least one esterification reagent which esterifies the hydroxyl groups of the cellulose to form residues R', where R' is a residue of the general formula V wherein R 7< is a reactive functionality towards the compound containing at least one phosphorus-containing substituent, or a cellulose ester of general formula I as defined above, provided that R is the same or different in each occurrence and is selected from the group consisting of residues of general formula III, at least partially with at least one transesterification reagent that transesterifies the residues according to general formula III to residues of general formula V, or a mixed cellulose ester of general formula I as defined above, provided that R is the same or different in each occurrence and is selected from the group consisting of hydroxyl groups and residues of general formula III, wherein the mixed cellulose ester comprises both hydroxyl groups and residues R of general formula III, with at least one reagent,that the hydroxyl groups of the mixed cellulose ester are esterified to residues of general formula V and / or the residues according to general formula III are transesterified to residues of general formula V, and in a subsequent second step at least one compound containing a phosphorus substituent is added to the reactive functionality R 7< of general formula V, or b) by esterification or transesterification, wherein cellulose is at least partially esterified with at least one esterification reagent that esterifies the hydroxyl groups of the cellulose to residues R as defined above, wherein, with respect to the total cellulose, at least one hydroxyl group is esterified to an ester group according to formula II, or a cellulose ester of general formula I as defined above, with the proviso that R is the same or different in each occurrence and is selected from the group consisting of residues of general formula III,at least partially with at least one transesterification reagent that transesterifies the residues according to general formula III to residues of general formula II, or a mixed cellulose ester of general formula I as defined above, provided that R is the same or different at each occurrence and is selected from the group consisting of hydroxyl groups and residues of general formula III as defined above, wherein the mixed cellulose ester comprises both hydroxyl groups and residues R of general formula III, with at least one reagent that transesterifies the hydroxyl groups of the mixed cellulose ester to residues of general formula I as defined above and / or transesterifies the residues according to general formula III to residues of general formula I,wherein, with respect to the entire cellulose derivative, at least one hydroxyl group is esterified to an ester group according to formula II and / or at least some of the residues are transesterified according to general formula III to residues of general formula II.

[0026] The production of the cellulose derivative according to the invention thus comprises two variants. In variant a) described above, the production is carried out in two stages, wherein cellulose is first esterified or a cellulose ester is transesterified, followed by the addition of a compound containing a phosphorus substituent. In variant b) as described above, the esterification or transesterification is carried out with a compound already containing a phosphorus substituent. In variant a) or in the production of the compound containing a phosphorus substituent according to variant b), the addition can be carried out, for example, by a phosphorus-Michael addition. In particular, variant a) can be carried out by phosphorus-Michael addition of organophosphorus compounds, which bear a reactive hydrogen atom on the phosphorus atom, to cellulose esters which bear activated alkenyl groups.

[0027] The Phospha-Michael addition of the phosphorus compounds to the activated alkenyl groups of the cellulose esters can be carried out with the aid of a base, such as triethylamine, under conditions known to those skilled in the art for Phospha-Michael additions.

[0028] A preferred embodiment of the variants of the method according to the invention provides that in the a) Esterification and / or transesterification reaction followed by the addition of at least one compound containing a phosphorus substituent in the first step, the at least one esterification reagent, the at least one transesterification reagent or the at least one reagent, at least one compound selected from the compounds of the general formula Vla and / or VIb includes or consists of, where in formula Vla R' is the same or different at each occurrence and is selected from residues according to the general formula Vlla and Vllb and residues R 2< as defined above. where R 3< is defined as above, with the proviso that at least one residue R' is according to formula VIIa or VIIb, and m is 0, 1 or 2, and in formula VIb R' is selected from residues according to general formula VIIa and VIIb, and in the subsequent second step the at least one compound containing a phosphorus substituent is selected from the group consisting of compounds of general formula VIII wherein R 4< and R 5< are defined as in claim 2, or b) in the esterification or transesterification in the first step the at least one esterification reagent, the at least one transesterification reagent or the at least one reagent at least one compound selected from the compounds of the general formula Vla and / or VIb includes or consists thereof, wherein in formula VIIIa R is the same or different at each occurrence and is selected from residues according to the general formula IV as in claim 2 and residues R 2< as defined above, and in formula VIIIlb R is selected from residues according to the general formula IV as defined above.

[0029] It is further advantageous if, in variants a) or b), 0.1 to 20, preferably 0.5 to 10, particularly preferably 1.0 to 5.0 mol equivalents of the at least one esterification reagent, the at least one transesterification reagent or the at least one reagent are used, based on the totality of the hydroxy groups of the cellulose, ester groups of the cellulose ester or hydroxy groups and the ester groups of the mixed cellulose ester.

[0030] In variant a), it is advantageous if, in relation to the amount of residues of the general formula V produced in the first reaction step, 0.05 to 10, preferably 0.1 to 5, particularly preferably 0.25 to 1.0 mol equivalents of the compound containing at least one phosphorus-containing substituent are used.

[0031] Esterification / transesterification is particularly preferably carried out in the presence of transesterification or esterification catalysts.

[0032] Furthermore, the present invention relates to the use of a cellulose derivative according to formula I where The substance is the same or different in each occurrence and is selected from the group consisting of hydroxyl groups, residues of general formula II and residues of general formula III. where R 1< is the same or different in each occurrence and is selected from the group consisting of phosphorus-containing substituents, and R 2< is the same or different in each occurrence and is selected from the group consisting of linear or branched alkyl groups with 1 to 36 carbon atoms, linear or branched arylalkyl groups with 7 to 36 carbon atoms, with the proviso that in formula I at least one group R is a group according to formula II. as a flame retardant, preferably for plastics, especially for thermoplastics such as unfilled and filled or reinforced polyesters, polyamides, polyolefins, polycarbonates, PMMA, polystyrene, styrene block polymers such as ABS and SBS, for cellulose esters such as cellulose acetate, cellulose propionate and cellulose butyrate, as well as for polyurethanes and epoxy resins.

[0033] Furthermore, the present invention relates to a flame retardant composition comprising a cellulose derivative according to formula I where The substance is the same or different in each occurrence and is selected from the group consisting of hydroxyl groups, residues of general formula II and residues of general formula III. where R 1< is the same or different in each occurrence and is selected from the group consisting of phosphorus-containing substituents, and R 2< is the same or different in each occurrence and is selected from the group consisting of linear or branched alkyl groups with 1 to 36 carbon atoms, linear or branched arylalkyl groups with 7 to 36 carbon atoms, with the proviso that in formula I at least one group R is a group according to formula II. and includes or consists of at least one other flame retardant that differs from the cellulose derivative of general formula I.

[0034] In particular, in the flame retardant composition according to the invention, it is advantageous if the at least one further flame retardant, which differs from the cellulose derivative of general formula I, is selected from the group consisting of metal hydroxides, melamine derivatives, nitrogen bases, phosphates, phosphonates, phosphinates, pyrophosphates, polyphosphates, siloxanes, pentaerythritol and derivatives of these compounds, preferably magnesium hydroxide, aluminum hydroxide, boehmite, melamine polyphosphate, ammonium polyphosphate, melamine cyanurate, zinc pyrophosphate, piperazine pyrophosphate and piperazine polyphosphate, 1,3,5-tris(2-hydroxyethyl)isocyanurate and mixtures and combinations thereof.

[0035] Furthermore, the present invention relates to a plastic composition comprising or consisting of a cellulose derivative composition or a flame retardant composition according to the invention.

[0036] The process according to the invention can in particular be carried out by the esterification of cellulose with anhydrides or anhydride mixtures, preferably using a strong acid, preferably concentrated sulfuric acid, or zinc chloride as a catalyst. Reaction scheme 1

[0037] In reaction scheme 1, the substituents R' and R are defined as above. The substituent R" corresponds to a group formed by the esterification of a free OH group of the cellulose with the esterification reagent according to formula Vla, or—in the case that not all OH groups of the cellulose are esterified—to a free OH group. Normally, no free OH groups remain after esterification with anhydrides (unlike esterification with acid chlorides), which is advantageous for the intended use, as OH groups can interfere with its use as a flame retardant additive. The substituent R' is therefore an acrylate functionality according to formula Vlla (see above) or a di-, tri-, or tetraalkylate functionality according to formula VIIb (see above).

[0038] The latter have the advantage of increasing the melting point and solubility of the cellulose esters and can be formed in situ during the esterification of cellulose by acid-catalyzed dimerization or trimerization of acrylic acid. A key advantage here is that the amount of diacrylate or triacrylate substituents in the cellulose esters of formula I can be controlled by varying the reaction conditions according to reaction scheme 1. If the esterification is carried out at moderate temperatures (up to approximately 55°C), only very small amounts of diacrylate or triacrylate groups are introduced. In contrast, at somewhat higher reaction temperatures and longer reaction times, cellulose esters with a significant proportion of such substituents are formed. The anhydrides of formula Vla can be efficiently produced by reacting acrylic acid with acetic anhydride, whereby the resulting acetic acid is continuously distilled from the reaction mixture and, for example,A polymerization inhibitor—preferably phenothiazine—is present. This reaction can be carried out in the presence of a suitable catalyst, such as trifluoromethanesulfonic acid, or without a catalyst. The principle of this "manhydridization" is known from the literature and / or has been described in patents (DE3037301A1; EP0231689B1; US009969670). In a preferred embodiment of the invention, in contrast to known methods of "manhydridization," the aim is not to obtain a uniform product—for example, acrylic anhydride—but rather a mixture of different anhydrides. Upon reaction according to reaction scheme 1, these anhydrides yield products of general formula Ia, each with the desired substitution pattern. These products then undergo Phospha-Michael addition to produce phosphorus-containing cellulose esters of formula I, whose structural properties are adapted to the respective application.The desired ratio between the anhydrides can be achieved by appropriately selecting the reaction conditions during the "manhydridization" (ratio of starting materials, reaction time and temperature, catalyst). During the "manhydridization," the introduction of di- or triacrylic groups can also be selectively induced or largely suppressed (the latter is the case with "manhydridization" without a strongly acidic catalyst and at a moderate reaction temperature). This process has the further advantage that the entire reaction sequence, from the generation of the anhydride mixture and the esterification of the cellulose to the phospho-Michael addition, can be carried out in the same reaction apparatus, thus enabling efficient processing. Acetic acid is the only byproduct.

[0039] Further anhydrides, such as propionic anhydride, butyric anhydride, and methacrylic anhydride, or mixtures of such anhydrides, can be added to the anhydride mixture obtained after the "unmanhydridization" to introduce propionate, butyrate, or methacrylate groups during the esterification of the cellulose. The introduction of such groups further improves the solubility of the cellulose esters. In addition, these ester groups positively influence important properties of the flame retardants according to the invention, such as improved compatibility with the flame-retardant polymers and reduced water absorption.

[0040] Alternatively, the process according to the invention can preferably be carried out by transesterification of cellulose alkyl esters, e.g. of cellulose acetate or cellulose triacetate, with activated alkenyl group-bearing carboxylic acids - for example with acrylic acid - in the presence of suitable transesterification catalysts and polymerization inhibitors, wherein the freed carboxylic acid is distilled from the reaction mixture by distillation in partial vacuum (reaction scheme 2). Reaction scheme 2

[0041] In reaction scheme 2, the residues R stand for R 3< as defined above. The residue R" corresponds to a grouping that is formed by transesterification of an ester group R of the cellulose with the esterification reagent according to formula VIb, or - in the case that not all ester groups of the cellulose are transesterified - an ester group R 3< .

[0042] The present invention will be explained in more detail with reference to the following examples, without limiting the subject matter to the embodiments shown. Example 1: Synthesis of an anhydride mixture of acrylic acid and acetic anhydride:

[0043] The reaction apparatus, consisting of a 500 ml two-necked flask with a nitrogen supply and a thermally insulated distillation column, a Liebig condenser with a thermometer, and a receiving flask connected to a pressure-controlled diaphragm pump, was vacuum-dried and filled with nitrogen. Acetic anhydride (1.50 mol; 153 g), anhydrous acrylic acid (3.00 mol; 216 g), and phenothiazine (1.0 g) were then added to the two-necked flask, which was immersed in an oil bath preheated to 55°C. After the nitrogen supply was stopped, the target oil bath temperature was increased to 92°C over the course of one hour, and the pressure was reduced to 115 mbar, whereupon the distillation of the acetic acid began (head temperature approximately 62–64°C at 115 mbar; corresponding to the expected boiling point of acetic acid at this pressure). The distillation was continued for 6 hours, during which the oil bath temperature was increased to 95°C and the pressure was reduced to 108mbar.The apparatus was then filled with nitrogen. After adding another 35 g of acrylic acid, stopping the nitrogen supply, and reducing the pressure to 103 mbar, the distillation was continued for two hours (oil bath temperature 96°C), with the pressure gradually reduced to 90 mbar. The apparatus was then refilled with nitrogen, and another 75 g of acrylic acid and 0.5 g of phenothiazine were added. Heating under partial vacuum was continued for another 6 hours, with the oil bath temperature at 95–97°C and the pressure gradually reduced to 75 mbar. A total of approximately 180 g of distillate, consisting mostly of acetic acid (analyzed by NMR spectroscopy), was collected in the receiving flask. After changing the receiving flask, the excess acrylic acid was distilled off under further pressure reduction. An almost colorless residue remained, which had the following composition (determined by NMR spectroscopy): Acrylic anhydride ((AcS) 2 A): approx.82%; mixed acrylic acid-acetic anhydride (AcSESA): approx. 8%; acetic anhydride: approx. 2%; acrylic acid: approx. 3%; acetic acid: 1%; anhydrides of oligomeric acrylic acids: approx. 4%.

[0044] The amount of anhydride mixture obtained in this way was approximately 205 g.

[0045] This anhydride mixture was subjected to vacuum distillation using a short column. After the foreshots (approx. 25 g), obtained at a pressure of 25 mbar, the product fraction was distilled under further pressure reduction to 4 mbar. 165 g of the product fraction were obtained, containing approximately 90% (AcS)₂A, 6% AcSESA, approximately 1% acetic anhydride, and approximately 2% acrylic acid (1% each of acetic acid and oligomeric acrylic anhydrides). About 15 g of distillation residue remained, consisting mainly of oligomeric acrylic anhydrides. Example 2: Synthesis of a cellulose acrylate acetate from cellulose and the anhydride mixture of Example 1

[0046] 3.0 g of cellulose wadding were placed in a 250 ml three-necked flask equipped with a mechanical stirrer (PTFE stirring blade, PTFE-coated stirring shaft). The apparatus was then dried under vacuum and subsequently filled with nitrogen. Next, 20 g of the distilled anhydride mixture obtained in Example 1, 34 g of acrylic acid, approximately 0.3 g of sulfuric acid, and approximately 100 mg of phenothiazine were added. Vigorous stirring was carried out to distribute the reagents as evenly as possible over the cellulose wadding, which absorbed the entire amount of reagents. Stirring continued for 20 minutes at room temperature. Over the next 20 minutes, the temperature was increased to 50°C and then gradually raised to 58–60°C (over the course of 15 minutes). During heating, the wadding became more compact and formed clumps that gradually disintegrated. A liquid phase formed, the volume of which increased.Approximately 150 minutes after the addition of the reagent, the reaction mixture was almost homogeneous, relatively thin, and pale yellow. Stirring was continued for 2 hours at 58–60°C, after which the oil bath was removed. The still-warm contents of the flask were stirred into 300 mL of cyclohexane. Stirring was continued at room temperature for 45 minutes, and then the crude product was isolated by filtration through a G3 glass frit. The crude product was then transferred to a round-bottom flask and dried under a fine vacuum with gentle warming. Meanwhile, the lumps were crushed (the flask had been previously filled with nitrogen). 60 mL of toluene and 50 mg of phenothiazine were then added. The mixture was stirred for approximately 40 minutes at about 50°C (under nitrogen). After cooling, the mixture was decanted. The remaining residue was stirred a second time in toluene (40 ml, 50°C, 45 min) and, after decanting, washed twice with 10 ml and 5 ml of toluene respectively. The residue was then processed under vacuum (approx.The solution was heated (0.1 mbar) to 100°C over 3 hours, yielding a light brown powder (approximately 3 g yield). The proton NMR spectrum of the resulting cellulose acrylate acetate showed complete conversion of the OH groups. The spectrum revealed that approximately 70% of the OH groups were acrylated (R1: CH=CH2) and approximately 28% were acetylated (R1: CH3) (diacrylate group fraction ≤ 3%). Example 3: Synthesis of a cellulose-acrylate-acetate-propionate diacrylate from cellulose, the anhydride mixture of Example 1, and propionic anhydride

[0047] 3.3 g of cellulose wadding were placed in a 250 ml three-necked flask equipped with a mechanical stirrer (PTFE stirring blade, PTFE-coated stirring shaft). The apparatus was then dried under vacuum and subsequently filled with nitrogen. Next, 20 g of the distilled anhydride mixture obtained in Example 1, 1.5 g of propionic anhydride, 37 g of acrylic acid, approximately 0.3 g of sulfuric acid, and approximately 100 mg of phenothiazine were added countercurrently under nitrogen. The wadding absorbed the entire liquid mixture of reagents. The reaction mixture was stirred at room temperature for 10 minutes and then heated to 58°C in an oil bath, while continuously stirred and covered with nitrogen. Approximately 1.5 hours after reaching the reaction temperature, the wadding had dissolved almost completely, leaving only a few lumps. About one hour later, the reaction mixture was homogeneous, low-viscosity, and orange in color.The mixture was stirred for a total of 4.5 hours at an oil bath temperature of 58–63°C. After cooling to approximately 40°C, the majority of the liquid components were distilled under vacuum into a cold trap (approximately 8 mbar). During distillation, the temperature was increased to 50°C. Distillation was stopped when the viscosity had increased significantly. The viscous liquid was transferred countercurrently under nitrogen, with stirring, into a flask containing 200 mL of cyclohexane, whereupon the product precipitated as a solid. Stirring continued for approximately 30 minutes at room temperature, followed by approximately 15 minutes at 45°C. After cooling to room temperature, the mixture was filtered through a G3 glass frit (non-inert). Subsequently, the product was transferred to a flask, and 40 mL of toluene and 50 mL of methyl tert-butyl ether were added. This mixture was stirred under nitrogen for 30 minutes at 50°C. The resulting suspension was then filtered through a G3 glass frit.The product was then transferred back into a round-bottom flask and fermented for another 30 minutes in 50 ml of methyl chloride. tert -butyl ether was stirred at 50°C under nitrogen. It was then filtered again through a G3 glass frit (non-inert). The filter residue was treated twice with 20 ml of methyl- tert -butyl ether washed. The product was dried at 40°C under fine vacuum (yield 3.5 g).

[0048] The proton NMR spectrum of the resulting cellulose-acrylate-acetate diacrylate showed complete esterification of the OH groups. The spectrum showed that approximately 50% of the OH groups were esterified with acrylate groups (R 7 : CH=CH 2 ) and diacrylate groups (R 7 : CH 2 -CH,-O-COCH=CH 2 ), approximately 15% of the OH groups were esterified with acetate groups (R 7 : CH 3 ), and approximately 35% with propionate groups (R 7 : CH 2 -CH 3 ). Example 4: Synthesis of a cellulose acrylate acetate by transesterification of cellulose acetate with acrylic acid

[0049] In a vacuum-dried distillation apparatus equipped with a three-necked flask, heavy magnetic stirrer, Liebig condenser, nitrogen supply line, and a cooled receiving flask connected to a bubble counter, 50 g of anhydrous acrylic acid, 10 g of cellulose acetate, and the stabilizer (4-methoxyhydroquinone; 0.25 g) were placed. The nitrogen flow was then switched on to superimpose nitrogen on the reaction mixture. Since the stabilizer requires oxygen to be active, approximately 20 ml of ambient air was introduced into the flask through a septum using a syringe at 15-minute intervals. The oil bath was then heated to 105°C using a heating magnetic stirrer and positioned so that the contents of the flask were approximately 1 cm below the level of the oil. The contents of the flask were stirred vigorously during this process.Once all the cellulose acetate had dissolved in the acrylic acid, 0.3 g of trifluoromethanesulfonic acid and then 0.5 g of anhydrous aluminum chloride were added. The mixture was stirred for 4.5 h at an oil bath temperature of 105°C, with a weak stream of nitrogen passing through the apparatus. During this time, the reaction mixture turned dark.

[0050] After slightly cooling the reaction mixture (oil bath temperature 100°C), approximately 100 mg of the stabilizer phenothiazine was added. Then, most of the unreacted acrylic acid and the acetic acid produced during the reaction were distilled, starting at a pressure of approximately 400 mbar, which was reduced in 50 mbar increments to approximately 150 mbar. The distillate was condensed in a flask cooled with liquid nitrogen. NMR spectroscopy of the distillate showed that it consisted of acrylic acid and acetic acid.

[0051] The distillation residue was dissolved in 100 ml of dichloromethane. The solution was stirred with 200 ml of an 18% ammonium bicarbonate solution (carbon dioxide release). After the carbon dioxide release subsided, the aqueous phase was separated in a separatory funnel. After adding [something], the separatory funnel was gently shaken. The dichloromethane phase was dried over anhydrous magnesium sulfate. After removing the drying agent (filtration), the dichloromethane was removed by rotary evaporator. To remove any remaining dichloromethane residue, the solid was then dried under vacuum. A light brown solid was obtained (yield 8.8 g), the NMR spectroscopy of which showed that approximately one-third of the acetate groups had been replaced by acrylate groups. Example 5: Synthesis of a phosphorus-containing cellulose ester from the cellulose acrylate acetate of Example 2 and 9,10-dihydro-9-oxa-10-phosphaphenathrene-10-oxide (DOPO)

[0052] Into a carefully vacuum-dried, nitrogen-filled Schlenk flask containing a heavy stir bar, 1 g of cellulose acrylate acetate from Example 2 and approximately 30 mg of 4-methoxyhydroquinone (MEHQ) were added, followed by 8 ml of dry tetrahydrofuran and 1.5 ml of triethylamine. The mixture was then heated to approximately 50°C, and 1.4 g of DOPO was added countercurrently in a nitrogen atmosphere. The reaction mixture was stirred under a nitrogen atmosphere.

[0053] The mixture was stirred for 3 hours at 50°C under a nitrogen atmosphere, during which a solid precipitated. This was isolated by decantation and first heated with toluene (15 ml) to approximately 90°C while stirring, and then stirred into acetonitrile (10 ml, approximately 70°C) (decanting each time). To dry the resulting product, it was heated under vacuum (approximately 0.1 mbar) with stirring for 4 hours to 125°C, and then heated to 145°C for 30 minutes. After drying, a phosphorus-containing (DOPO-functionalized) cellulose ester was obtained as a brownish-white powder (1.8 g). The in Figure 1 The 31< P-NMR spectrum shown (measured in DMSO-d 6 ) demonstrates the high purity of the phosphorus-containing (DOPO-functionalized) cellulose ester. Example 6: Synthesis of a phosphorus-containing cellulose ester 1 from the cellulose acrylate acetate propionate diacrylate of Example 3 and 9,10-dihydro-9-oxa-10-phosphaphenathrene-10-oxide (DOPO)

[0054] A 100 ml Schlenk flask equipped with a heavy magnetic stir bar was heated under vacuum to remove any traces of moisture and then filled with nitrogen. Then, 1.2 g of the cellulose-acrylate-acetate-propionate diacrylate obtained in Example 3, 15 ml of dry acetonitrile, and 1.5 ml of dry triethylamine were added countercurrently with nitrogen. This mixture was heated to 60°C using an oil bath and magnetic heating stirrer with vigorous stirring. After the starting material had dissolved, 1.5 g of DOPO was added countercurrently with nitrogen.

[0055] The temperature of the oil bath was then increased to 78°C. After 2.5 hours at the same temperature, another portion of DOPO (0.27 g) was added. The mixture was stirred for another hour at 78°C under a nitrogen atmosphere. After cooling, the tightly sealed flask was stored overnight in the refrigerator. A gel-like sediment had precipitated out. After warming to room temperature, the supernatant was removed. Then, 25 ml of toluene were added, and the mixture was heated to boiling with vigorous stirring. After cooling the contents of the flask, the toluene solution was decanted. The heating with toluene was repeated with half the amount of solvent.

[0056] The resulting solid (product) was dried under vacuum (approx. 0.1 mbar). Stirring was carried out to break up any solid particles. The product was initially dried at room temperature, then heated to 90°C for 4 hours, and finally dried at 115°C for 4 hours. After drying, a phosphorus-containing (DOPO-functionalized) cellulose ester was obtained as a white powder (1.9 g).

[0057] The in Fig. 2a The ¹H NMR spectrum of the product (measured in CDCl₃) shown here demonstrated complete conversion of the acrylate and diacrylate groups as well as complete removal of solvent and amine traces. The Fig. 2b The 31< P-NMR spectrum shown (measured in CDCl 3 ) confirms the high purity.

[0058] The in Figure 2c The thermogram (TGA curve) shown demonstrates good thermal stability of the product. Example 7: Synthesis of a phosphorus-containing cellulose ester from cellulose-acrylate-acetate-propionate-diacrylate and phosphorylated anhydroerythritol (PAHE)

[0059] The phosphorylated anhydroerythritol (PAHE) required for this synthesis was prepared from erythritol and dimethyl phosphite using a synthesis method known from the literature (G. Lapienis, St. Penczek, Journal of Polymer Science: Part A: Polymer Chemistry, 1990, 28, 1743-1762).

[0060] A 100 ml Schlenk flask equipped with a heavy magnetic stir bar was heated under vacuum to remove any traces of moisture and then filled with nitrogen. Then, in a nitrogen countercurrent, 1 g of the cellulose-acrylate-acetate-propionate diacrylate obtained in Example 3, 5 ml of dry acetonitrile, and 1.5 ml of dry triethylamine were added. This mixture was heated to 70°C using an oil bath and a magnetic stir bar with vigorous stirring. After dissolving the starting material, a solution of 0.65 g PAHE in 5 ml of acetonitrile was added in a nitrogen countercurrent over 45 min through a septum while stirring. After 4 h at 75°C and subsequent cooling of the solution, it was stirred into 40 ml of toluene, whereupon the product precipitated. After decanting the toluene, the resulting solid was dried under vacuum (approx. 0.1 mbar) for 4 hours at room temperature, 3 hours at 80°C and 2 hours at 100°C.A PAHE-functionalized cellulose ester was obtained as a white powder (1.2 g). The in . Fig. 3 The 31< P-NMR spectrum shown (measured in CDCl 3 ) confirms the high purity. Example 8 Synthesis of a cellulose-acrylate-acetate propionate from cellulose and an anhydride mixture synthesized according to Example 1

[0061] In a dry 500 ml three-necked flask equipped with a KPG stirrer (PTFE-coated stirrer shaft, PTFE stir plate), 15 g of cellulose (biocellulose) were placed. The flask was then dried under vacuum and filled with nitrogen. Next, 100 mg of phenothiazine were added. This was followed by 150 g of anhydrous acrylic acid, and the mixture was stirred gently for 3 minutes. Then, 87 g of acrylic anhydride synthesized according to Example 1, along with 4.5 g of propionic anhydride, were added and stirred for a few minutes until the cotton wool was well wetted. Finally, 1.25 g of concentrated sulfuric acid was added, resulting in a yellow coloration. The cellulose absorbed almost all of the reagents. The mixture was then stirred for 10 minutes at room temperature, and the temperature was gradually increased to approximately 57–58°C over about 40 minutes, while stirring continuously. The cotton ball disintegrated as soon as it was heated and gradually began to dissolve or disintegrate.Approximately 100 minutes after the addition of the reagent, only a small amount of suspended solid remained. After another hour, the reaction mixture was largely homogeneous and relatively thin. However, it still contained some solid. The color was light brown. Stirring at 56–59°C was continued for another 2 hours, resulting in a solution that was homogeneous except for minimal turbidity (still pale brown). The oil bath was then removed.

[0062] Immediately afterwards, the flask was equipped with a distillation bridge and a receiver cooled by liquid nitrogen. First, the more volatile components of the solution were distilled under vacuum using a diaphragm pump (minimum pressure approx. 5 mbar) and then under fine vacuum, with the oil bath temperature being increased to approximately 55°C. A distillate was collected and analyzed by NMR spectroscopy. The analysis revealed that this distillate consisted of >99% acrylic acid and acrylic anhydride.

[0063] The distillation residue was mixed with approximately 400 ml of cyclohexane without cooling and stirred under a nitrogen atmosphere. After the gel had suspended in the cyclohexane, stirring continued for approximately 30 minutes, during which time the oil bath temperature was increased to 55°C. The crude product precipitated as a fine-grained solid, which was filtered off using a large G3 glass frit. The brownish filter cake was returned to the flask, and approximately 300 ml of methyl tert-butyl ether was added. The mixture was heated to approximately 55°C while stirring. The oil bath was then removed, and the mixture was allowed to cool for a few minutes. The product was then filtered off using the G3 glass frit. This step was repeated three times (each time with approximately 200 ml of methyl tert-butyl ether). Filtering was faster after each treatment with methyl tert-butyl ether because the product effluxed.The first methyl tert-butyl ether filtrate was distinctly yellow and slightly cloudy, the second was paler yellow and clear, and filtrates 3 and 4 were almost colorless.

[0064] After the fourth treatment with methyl tert-butyl ether, the product was transferred to a 500 ml flask and dried for 30 min in a fine vacuum at an oil bath temperature of max. 60°C. A flour-colored powder was obtained, which was analyzed by NMR spectroscopy. The product was then subjected to a further treatment with methyl tert-butyl ether, filtered again using the G3 frit, and then dried in a fine vacuum at max. approximately 55°C. Spectra of the resulting product were recorded in deuterochloroform and deutero-DMSO, showing that approximately 70% of the OH groups of the cellulose were esterified with acrylate groups.

[0065] The remaining OH groups were mostly esterified with propionate groups and to a lesser extent with acetate groups. Small amounts of diacrylate groups were also introduced. No free OH groups remained. 25 g of the product were obtained as a white powder. Example 9 Synthesis of a cellulose-acrylate-acetate propionate from cellulose and an anhydride mixture synthesized according to Example 1 using zinc chloride as a catalyst

[0066] In a dry 100 ml three-necked flask equipped with a magnetic stir bar, 1.2 g of cellulose (biocellulose from cotton fibers) was placed. The flask was then dried under vacuum and subsequently filled with nitrogen. 10 mg of phenothiazine was then added. Next, 12 g of acrylic acid were added and stirred gently for 3 minutes. Then, 7 g of the acrylic anhydride synthesized according to Example 1 and 0.36 g of propionic anhydride were added and stirred for a few minutes, ensuring good wetting of the cotton. At room temperature, 0.25 g of zinc chloride was then added (flask under nitrogen). The cellulose absorbed almost the entire amount of reagents. The mixture was stirred for 10 minutes at room temperature, and then the temperature was increased to 57 °C over 40 minutes. Ten minutes later, the temperature was increased to 63 °C. One hour later, the temperature was increased to 75 °C.After adding another 0.3 g of zinc chloride, the temperature was increased to 85 °C. More and more liquid formed, and the cotton wool gradually diminished. The reaction mixture remained under these conditions for another hour and a half. The mixture was then heated to 87 °C, at which point it became homogeneous. After two hours, the temperature was increased to 90 °C and remained at this temperature for approximately 40 minutes before the heating was switched off.

[0067] The reaction mixture was stirred into 80 ml of cyclohexane at 50 °C, whereupon the product precipitated as a brownish solid. It was then decanted. Next, 80 ml of methyl tert-butyl ether were added to the product, and this mixture was heated to 55 °C with vigorous stirring. Once this mixture had cooled, it was decanted again. This process was repeated three more times before the product was dried under fine vacuum at 55 °C for approximately two hours.

[0068] 1.3 g of cellulose acrylate acetate propionate were obtained, the NMR spectra of which are almost identical to those of the product of Example 8 (approx. 70% of the OH groups esterified with acrylate groups, remaining OH groups were esterified with propionate and acetate groups). Example 10 Synthesis of a phosphorus-containing cellulose ester from the cellulose acrylate acetate propionate of Example 8 and phosphorylated anhydroerythritol (PAHE)

[0069] The phosphorylated anhydroerythritol (PAHE) required for this synthesis was prepared from erythritol and dimethyl phosphite using a synthesis method known from the literature (G. Lapienis, St. Penczek, Journal of Polymer Science: Part A: Polymer Chemistry, 1990, 28, 1743-1762).

[0070] A 250 ml Schlenk flask equipped with a heavy stir bar was sealed with a septum and connected to the Schlenk line. A vacuum was then applied using a rotary vane pump, and the flask was heated with a hot air gun to remove any traces of moisture. The flask was then filled with nitrogen. This process was repeated three times before 9 g of the cellulose ester from Example 8 and approximately 0.05 g of phenothiazine were added to the flask in a countercurrent nitrogen flow. 75 ml of acetonitrile were then added through the septum, and this mixture was heated to 60°C under strong stirring and nitrogen in an oil bath with a magnetic stirrer. Most of the starting material dissolved. Then, 12 ml of triethylamine were added, and the temperature was further increased to 70°C.When the oil bath reached 70°C, a slightly warmed solution of 7.68 g PAHE and approximately 24.7 g acetonitrile was added through the septum using a syringe and cannula over a period of 40 minutes. After the entire mixture had been added, the oil bath temperature was increased to 78°C. The reaction mixture remained under these conditions for 70 minutes. By this time, the mixture was almost completely clear and its color had changed to pale yellow. Then, a solution of 1.5 g PAHE in 3.7 g acetonitrile was added, and the mixture was stirred for another three hours under unchanged conditions. The solution was then stirred for a further one hour under unchanged conditions. After this, the oil bath was removed, the nitrogen flow and the stirring magnet were switched off, and the flask was tightly sealed and stored at room temperature for 12 hours.

[0071] A portion of the volatile components (approximately 35 ml) was then distilled into a cold trap, gently warmed in the process. The oily distillation residue was stirred vigorously with a syringe into 225 ml of dry toluene (argon atmosphere) over 25 minutes, with the mixture being heated to approximately 50°C (oil bath temperature) at the end. A few minutes after the addition was completed, the oil bath was removed. A small amount of solid, which remained in the flask that had previously contained the product solution, was not added. By the end of the addition, a viscous, reddish-brown sediment had formed. This was decanted from the toluene phase. The crude product was then dissolved in 35 ml of dry acetonitrile under heat (oil bath 60°C). The resulting viscous solution was added in portions via syringe to 125 ml of dry toluene (under nitrogen) over 20 minutes, with vigorous stirring. A third and fourth precipitation were carried out in the same manner.The resulting product was heated to 100°C for 1.5 hours under a fine vacuum. Heating was interrupted twice to break up any lumps. After about an hour, a powder was obtained, which was then vigorously stirred. Drying was then continued at an oil bath temperature of 130°C for two and a half hours. Finally, the product was dried for another 30 minutes at 135°C under a fine vacuum.

[0072] In the 31< P-NMR spectrum of the product thus obtained, the product signal comprises approximately 96 mol% of the ³¹P compounds (see Fig 4 The proton spectrum showed a conversion of the acrylate functionalities of ≥ 95%.

[0073] 14.5 g of a white powder were obtained (12 g were sent to Hamm-Lippstadt University of Applied Sciences). The isolated yield is approximately 84% (theoretical yield: approximately 17.3 g).

[0074] The thermal analysis of this product shows that decomposition begins at approximately 250°C (see Fig. 5 , measured three times). Example 11 Synthesis of a phosphorus-containing cellulose ester from the cellulose acrylate acetate propionate of Example 8 and DOPO

[0075] A 500 ml three-necked Schlenk flask equipped with a KPG stirrer was heated under vacuum to remove any traces of moisture and then filled with nitrogen. Then, in a nitrogen countercurrent flow, 8.7 g of the cellulose-acrylate-acetate propionate obtained in Example 8, approximately 100 mg of phenothiazine, 120 ml of dry acetonitrile, and 12 ml of dry triethylamine were added. This mixture was heated to 70–75°C using an oil bath and a magnetic heating stirrer with vigorous stirring.

[0076] Then, a solution of 12 g DOPO in acetonitrile was added via syringe over 45 minutes in a nitrogen countercurrent atmosphere while stirring. The mixture was stirred for two hours under a nitrogen atmosphere at 75°C, during which time the product precipitated.

[0077] An NMR sample of the precipitated product showed that approximately 97.5% of the phosphorus components belonged to the product and the conversion of the acrylate functionalities was almost complete (≥ 97%).

[0078] The crude product was boiled twice with acetonitrile and then dried under fine vacuum, being heated to 135°C. 12 g of the DOPO-functionalized cellulose ester were obtained, the thermal analysis of which showed an onset of decomposition at approximately 300°C (see TGA curve in [reference]). Fig. 6 , measured three times). Example 12 Synthesis of a phosphorus-containing cellulose ester from the cellulose acrylate acetate propionate of Example 9 and phosphorylated anhydroerythritol (PAHE)

[0079] In a nitrogen-filled flask, 2g of PAHE were dissolved in 8ml of dry acetonitrile.

[0080] A 100 ml Schlenk flask equipped with a heavy stir bar was sealed with a septum and connected to the Schlenk line. A rotary vane pump was then used to create a vacuum, and the flask was heated with a hot air gun to remove any traces of moisture. The flask was then filled with nitrogen. This process was repeated three times before 1 g of the cellulose acrylate acetate propionate from Example 9 and 10 mg of phenothiazine were added to the flask under countercurrent nitrogen. The flask was then sealed again, a vacuum was reapplied, and it was filled with nitrogen. Finally, 12 ml of acetonitrile and 1.3 ml of triethylamine were added through the septum, and this mixture was heated to 70°C under strong stirring and nitrogen in an oil bath using a magnetic stirrer.Once the oil bath reached 70°C, 4.12 g of the previously prepared PAHE solution was added through the septum using a syringe and needle over a period of 40 minutes. After the entire mixture had been added, the oil bath temperature was increased to 78°C. The reaction mixture remained under these conditions for 4.5 hours. The oil bath was then removed, and the mixture was stored at room temperature for 12 hours.

[0081] A portion of the volatile components (approximately 10 ml) was then distilled into a cold trap and gently warmed. After the reaction mixture had cooled slightly, it was carefully transferred (along with the solid formed during the reaction) in a nitrogen-countercurrent process, with vigorous stirring, into a Schlenk flask containing 25 ml of toluene (which was heated to 50°C using an oil bath). A brown solid precipitated out. The solvent above the solid was then decanted, and the solid was dissolved again in 4 ml of acetonitrile. Once dissolved, the mixture was carefully transferred in a nitrogen-countercurrent process, with vigorous stirring, into a Schlenk flask containing 25 ml of toluene (which was heated to 50°C using an oil bath). The solvent above the solid was then decanted. This process was repeated once more.The product was dried for 4 hours under a fine vacuum, gradually heated to 155°C. The product was obtained as a white powder. The 31< P-NMR spectrum ( Fig. 7 ) this phosphorus-containing cellulose ester and its 1H-NMR spectrum ( Fig. 8 The samples showed very good purity. Thermal analysis revealed the onset of decomposition at approximately 275°C. Example 13 Flame retardancy tests:

[0082] The PAHE-functionalized cellulose ester obtained in Example 10 and the DOPO-functionalized cellulose ester obtained in Example 11 were incorporated into polyamide 11 (from Sigma-Aldrich) and the partially bio-based polyamide RX 2298 (a product of BASF SE) using a microextruder. The extrusion temperature was 220°C in both cases. UL94-V fire-resistant rods (1.6 mm) were injection-molded from the resulting granules, and the test rods were subjected to a fire test according to DIN EN 60695-11-10. For comparison, flame-retardant-free specimens of the same dimensions were also produced and tested in the same manner. When using the PAHE-functionalized cellulose ester, the flame retardant concentration (loading) was 18% by mass, and when using the DOPO-functionalized cellulose ester, it was 20% by mass.

[0083] In addition, the DOPO-functionalized cellulose ester was incorporated into polyethylene terephthalate (BISNEINEX; product of the company Equipolymers) in an analogous manner (extrusion temperature 260°C).

[0084] Prior to extrusion, the polymer granules were milled using a Retsch cryogenic mill. This involved grinding the granules at cryogenic temperatures for 5-10 minutes at a frequency of 30 Hz. A Thermo Scientific HAAKE MiniLab II small extruder was used for extrusion. The Thermo Scientific HAAKE MiniJet PRO was used to produce the UL94 test specimens. The Atlas HVUL2 fire chamber was used to determine the flame resistance.

[0085] The flame retardant additives and the polymer powders obtained after milling were dried in a vacuum before the extrusion process.

[0086] The UL94-V tests yielded the following results: polymer Additive Additive concentration (mass%) Burning duration of 1st and 2nd firing (s) Burning dripping UL94-V classification RX 2298 - - 1. 2-9 Yes V2 2. 4-11 RX 2298 Example 8 18 1. ≤ 0,5 No V0 2. ≤ 0,5 RX 2298 Example. 20 1. ≤ 1,0 Yes V2 10 2. ≤ 1,0 PA 11 - - 1. 1-3 Yes V2 2. 2-3 PA 11 Example. 20 1. ≤ 0,5 No V0 10 2. ≤ 0,5 PET - - 1. 2-3 Yes V2 2. 3-4 PET Page 10 10 1. ≤ 0,5 No V0 2. ≤ 0,5

[0087] These tests demonstrate the good flame-retardant effect of the flame-retardant additives according to the invention. The best possible flame-retardant classification V0 was achieved in all three polymers.

Claims

1. A cellulose derivate of the general Formula I wherein R being the same or different on each occurrence and being selected from the group consisting of hydroxyl groups, moieties of the general formula II and moieties of the general formula III R1 being identical or different on each occurrence and being selected from the group consisting of phosphorus-containing substituents, and R2 being identical or different on each occurrence and being selected from the group consisting of linear or branched alkyl moieties having 1 to 36 carbon atoms, linear or branched arylalkyl moieties having 7 to 36 carbon atoms, with the proviso that in formula I, at least one moiety R is a moiety according to formula II, characterized in that in the general formula II, the moiety R1 is selected from the group consisting of moieties according to the general formula IV wherein the variables are the same or different at each occurrence and R3 is selected from the group consisting of hydrogen or linear or branched alkyl moieties having 1 to 36, preferably 1 to 6 carbon atoms, R4 and R5 are independently selected from the group consisting of alkyl moieties, aryl moieties, alkyl aryl moieties, arylalkyl moieties, O-alkyl moieties, O-aryl moieties, O-alkyl aryl moieties, N-alkyl moieties, N-aryl moieties, N-arylalkyl moieties, N-alkyl aryl moieties, wherein R4 and R5 and the phosphorus atom can also be part of heterocyclic ring systems, which can be single or multi-membered, and n is 0 or an integer from 1 to 3.

2. The cellulose derivate according to the previous claim, characterized in that the heterocyclic ring system is selected from the group consisting of the following moieties: wherein R6 is independently selected from the group consisting of alkyl moieties, aryl moieties, alkyl aryl moieties, arylalkyl moieties, O-alkyl moieties, O-aryl moieties, O-alkyl aryl moieties, N-alkyl moieties, N-aryl moieties, N-arylalkyl moieties and N-alkyl aryl moieties; preferably alkyl moieties having 1 to 12 carbon atoms or alkyl aryl moieties having 7 to 14 carbon atoms.

3. The cellulose derivative according to any one of the preceding claims, characterized in that R2 is identical or different on each occurrence and is selected from the group consisting of linear or branched alkyl moieties having 1 to 12 carbon atoms, linear or branched arylalkyl moieties having 7 to 14 carbon atoms.

4. The cellulose derivative according to any one of the preceding claims, characterized in that based on all moieties R, the molar proportion of the moieties according to formula II is at least 2 mol%, preferably 5 to 100 mol%, more preferably 15 to 95 mol%, particularly preferably 40 up to 90 mol%, of the moieties according to formula III, is 0 to 98 mol%, preferably 0 to 95 mol%, more preferably 5 to 85 mol%, particularly preferably 10 to 90 mol% and / or the hydroxyl groups is a maximum of 50 mol%, preferably 0 to 50 mol%, preferably 0 to 20 mol%, particularly preferably 0 to 10 mol%.

5. A method for producing a cellulose derivate according to any one of the preceding claims, by a) esterification and / or transesterification reaction followed by an addition of at least one compound containing a phosphorus-containing substituent, in a first step • cellulose being at least partially reacted with at least one esterification reagent which esterifies the hydroxyl groups of the cellulose to form moieties R', R' being a moiety of the general formula V R7 being a functionality that is reactive toward the compound containing at least one phosphorus-containing substituent, or • a cellulose ester of the general formula I as defined in claim 1, with the proviso that R is the same or different on each occurrence and is selected from the group consisting of moieties of the general formula III, at least partially with at least one transesterification reagent which transesterifies the moieties according to general formula III to form moieties of general formula V, or • a mixed cellulose ester of the general formula I as defined in claim 1, with the proviso that R is the same or different on each occurrence and is selected from the group consisting of hydroxyl groups and moieties of the general formula III, the mixed cellulose ester comprising both hydroxyl groups and moieties R of the general formula III, with at least one reagent which esterifies the hydroxyl groups of the mixed cellulose ester to form moieties of the general formula V and / or transesterifies the moieties according to the general formula III to form moieties of the general formula V, and in a subsequent second step, at least one compound containing a phosphorus-containing substituent is added to the reactive functionality R7 of the general formula V, or b) by esterification or transesterification, • cellulose being at least partially reacted with at least one esterification reagent which esterifies the hydroxyl groups of the cellulose to form moieties R as defined in claim 1, at least one hydroxyl group being esterified to an ester group according to formula II based on the total cellulose, or • a cellulose ester of the general formula I as defined in claim 1, with the proviso that R is the same or different on each occurrence and is selected from the group consisting of moieties of the general formula III, at least partially with at least one transesterification reagent which transesterifies the moieties according to general formula III to form moieties of general formula II, or • a mixed cellulose ester of the general formula I as defined in claim 1, with the proviso that R is the same or different on each occurrence and is selected from the group consisting of hydroxyl groups and moieties of the general formula III as defined in claim 1, wherein the mixed cellulose ester comprising both hydroxyl groups and moieties R of the general formula III, with at least one reagent which esterifies the hydroxyl groups of the mixed cellulose ester to form moieties of the general formula I as defined in claim 1 and / or transesterifies the moieties according to the general formula III to form moieties of the general formula I, wherein, based on the entire cellulose derivative, at least one hydroxyl group is esterified to an ester group according to formula II and / or the moieties according to general formula III are at least partially transesterified to form moieties of general formula II.

6. The method according to the preceding claim, characterized in the in the a) esterification and / or transesterification reaction followed by an addition of at least one compound containing a phosphorus-containing substituent in the first step, the at least one esterification reagent, the at least one transesterification reagent or the at least one reagent contains or consists of at least one compound selected from the compounds of the general formula Vla and / or VIb, wherein in Formula VIa R' is the same or different on each occurrence and is selected from moieties according to the general formula VIIa and VIIb and moieties R2 as in claim 1 wherein R3 is as defined in claim 2, with the proviso that at least one moiety R' is according to formula Vlla or Vllb, and m is 0, 1 or 2, and in formula Vlb R' is selected from moieties according to the general formula VIIa and Vllb, and in the subsequent second step, the at least one compound containing a phosphorus-containing substituent is selected from the group consisting of compounds of the general formula VIII wherein R4 and R5 are as defined in claim 2, or b) in the esterification or transesterification in the first step, the at least one esterification reagent, the at least one transesterification reagent or the at least one reagent contains or consists of at least one compound selected from the compounds of the general formula Vla and / or VIb, wherein in Formula VIIIa R is the same or different on each occurrence and is selected from moieties according to the general formula IV as in claim 2 and moieties R2 as defined in claim 1, and in Formula VIIIb R is selected from moieties according to the general formula IV as defined in claim 2.

7. The method according to any one of the two preceding claims, characterized in that in variants a) or b), based on the totality of the hydroxyl groups of the cellulose, ester groups of the cellulose ester or hydroxyl groups and the ester groups of the mixed cellulose ester, 0.1 to 20, preferably 0.5 to 10, particularly preferably 1.0 to 5.0 mol equivalents of the at least one esterification reagent, of the at least one transesterification reagent or the at least one reagent can be used.

8. The method according to any one of claims 5 to 7, characterized in that in variant a), based on the amount of moieties of the general formula V, 0.05 to 10, preferably 0.1 to 5, particularly preferably 0.25 to 1.0 mol equivalents of the at least one compound containing a phosphorus substituent can be used.

9. The method according to any one of claims 5 to 8, characterized in that the esterification / transesterification is carried out in the presence of transesterification or esterification catalysts.

10. A use of a cellulose derivative according to the general formula I wherein R being the same or different on each occurrence and being selected from the group consisting of hydroxyl groups, moieties of the general formula II and moieties of the general formula III R1 being identical or different on each occurrence and being selected from the group consisting of phosphorus-containing substituents, and R2 being identical or different on each occurrence and being selected from the group consisting of linear or branched alkyl moieties having 1 to 36 carbon atoms, linear or branched arylalkyl moieties having 7 to 36 carbon atoms, with the proviso that in formula I, at least one moiety R is a moiety according to formula II, as a flame retardant, preferably for plastics, in particular for thermoplastics, such as unfilled and filled or reinforced polyesters, polyamides, polyolefins, polycarbonates, PMMA, polystyrene, styrene block polymers such as ABS and SBS, for cellulose esters such as cellulose acetate, cellulose propionate and cellulose butyrate and for polyurethanes and epoxy resins.

11. A flame retardant composition comprising or consisting of at least one cellulose derivative of the general formula I wherein R being the same or different on each occurrence and being selected from the group consisting of hydroxyl groups, moieties of the general formula II and moieties of the general formula III R1 being identical or different on each occurrence and being selected from the group consisting of phosphorus-containing substituents, and R2 being identical or different on each occurrence and being selected from the group consisting of linear or branched alkyl moieties having 1 to 36 carbon atoms, linear or branched arylalkyl moieties having 7 to 36 carbon atoms, with the proviso that in formula I, at least one moiety R is a moiety according to formula II, and at least one further flame retardant differing from the cellulose derivative of the general formula I.

12. The flame retardant composition according to the previous claim, characterized in that the at least one further flame retardant differing from the cellulose derivative of the general formula I is selected from the group consisting of metal hydroxides, melamine derivatives, nitrogen bases, phosphates, phosphonates, phosphinates, pyrophosphates, polyphosphates, siloxanes, pentaerythritol and derivatives of these compounds, preferably magnesium hydroxide, aluminum hydroxide, boehmite, melamine polyphosphate, ammonium polyphosphate, melamine cyanurate, zinc pyrophosphate, piperazine pyrophosphate and piperazine polyphosphate, 1,3,5-tris(2-hydroxyethyl) isocyanurate and mixtures and combinations thereof.

13. A plastic composition comprising or consisting of at least one plastic, preferably at least one thermoplastic, and at least one cellulose derivative of the general formula I according to any one of claims 1 to 4 or a flame retardant composition according to any one of claims 11 or 12.