Composition of cellulose ester and plasticizer and related article comprising the same

Abstract

The present invention refers to a cellulose ester composition comprising a cellulose ester and a plasticizing agent, said plasticizing agent comprising at least one vanillin derivative of general formula (I) : wherein : R1 is H or an alkyloxy group C1-C4, linear or branched; - R2 is an alkyloxy group C1-C4, linear or branched; - R3 is OH, vanillate or acetate. The present invention further refers to an article, for example a glasses frame, comprising the aforementioned cellulose ester composition.

Description

[0001] COMPOS ITION OF CELLULOSE ESTER AND PLASTICI ZER AND RELATED ARTICLE COMPRIS ING THE SAME

[0002] Field of the invention

[0003] The present invention falls within the field of cellulose ester-based plastics .

[0004] In particular, the present invention relates to a cellulose ester composition comprising a cellulose ester and a plastici zing agent , wherein said plastici zing agent comprises at least one vanillin derivative .

[0005] Furthermore , the present invention refers to an article comprising the aforementioned cellulose ester composition, particularly a glasses frame .

[0006] Technical background of the invention

[0007] Cellulose esters are generally considered environmentally friendly polymers as they are recyclable , biodegradable and derived from renewable sources . Nevertheless , the use of cellulose esters in plastic compositions has limitations due to their processing di f ficulty .

[0008] In many cases , indeed, cellulose esters are not processable in the molten state because the melting temperature of the cellulose ester is too close to the degradation temperature thereof .

[0009] In order to overcome such issue, using plastici zing agents is known, which reduce the melting temperature of the cellulose ester and increase its Melt Flow Index (MFI ) , which makes the molten cellulose ester processable and, for example , compatible with inj ection molding techniques.

[0010] The plasticizer has further effect on the thermomechanical properties of the material: it decreases the glass transition temperature and the elastic modulus, increases the elongation at break and the impact resistance.

[0011] Among cellulose esters, cellulose acetate is known, a polymer obtained by acetylation of cellulose, whose main field of use is eyewear: for example, glasses frames are obtained by milling from cellulose acetate tablets.

[0012] Other fields of use relate, for example, to fashion accessories, costume jewellery, membranes, and cigarette filters .

[0013] The most commonly used plasticizers to improve the features of cellulose acetate are diethyl phthalate (DEP) and acetyl triethyl citrate (ATEC) , followed by other citric acid and glycerol derivatives.

[0014] It has been observed that introducing these plasticizers into a cellulose acetate polymer matrix in relatively high amount (25-35% by mass with respect to the polymer matrix) and with relatively low molecular weight (<400 g / mol) results in a reduction of the plasticizer concentration time due to its diffusivity in the polymer matrix, resulting in degradation of the polymer material thermomechanical properties and lower durability of the material itself, in addition to the environmental pollution resulting therefrom.

[0015] Furthermore, DEP has a strong affinity for polycarbonate, a material typically used in the production of eyeglass lenses: this prevents the use of polycarbonate lenses in frames made of cellulose acetate plasticized with DEP.

[0016] The ATEC plasticizer is a citric acid derivative; it has the advantage over DEP of remaining longer in the cellulose acetate matrix, having a lower diffusivity coefficient. However, at the same time, ATEC has a lower plasticizing efficiency than DEP: to obtain the same properties, a higher amount of plasticizer is required ( indicatively passing from 28% to 32%) . Furthermore, the production of ATEC has a significantly higher environmental impact than DEP.

[0017] In the prior art, the use of natural-origin plasticizers such as vanillin is known, which represent a promising alternative to DEP and ATEC. Cellulose esters plasticized using vanillin or some derivatives thereof, or ethylvanillin and acetovanillone , are described, for example, in US2016068665A1, US2022162423A1, and US2022118295A1.

[0018] In light of the aforementioned state of the art, there is a need to find further alternative plasticizers for cellulose esters, which combine plasticizing efficiency with low diffusivity and are non-toxic to humans and non-polluting to the environment.

[0019] Summary of the invention

[0020] The Applicant has now found that further vanillin derivatives can be effectively used as plasticizing agents of the cellulose esters. These further derivatives allow to plasticize cellulose esters, resulting in plasticized compositions having thermomechanical and permanence properties of the plasticizing agent in the polymer matrix that are similar to or even higher than those obtained with traditional plasticizers, e.g., DEP, but with the further advantage that such derivatives are substantially non-toxic and environmentally friendly.

[0021] In particular, the vanillin derivatives identified by the Applicant have a diffusivity coefficient lower than that of the vanillin and prior art vanillin derivatives .

[0022] Therefore, an object of the present invention is a cellulose ester composition according to claim 1, comprising a cellulose ester and a plasticizing agent, wherein said plasticizing agent comprises at least one vanillin derivative.

[0023] A further object of the present invention, in accordance with claim 9, is a plastic article comprising the aforementioned cellulose ester composition.

[0024] Further features and advantages of the present invention are described below and are the object of the dependent claims.

[0025] Description of the figures

[0026] Figure 1 shows a transparent film of cellulose acetate plasticized with vanillin isobutyrate.

[0027] Figure 2 presents a tan delta graph as a function of the temperature (DMA) of compositions of cellulose acetate plasticized with DEP or vanillin isobutyrate at different concentrations.

[0028] Figure 3 presents a Tg graph as a function of the plasticizer content for cellulose acetate compositions and various vanillin derivatives.

[0029] Figure 4 presents the diffusivity coefficient values as a function of the plasticizer content for cellulose acetate compositions and various vanillin derivatives .

[0030] Figure 5 presents the diffusivity coefficient value of vanillin isobutyrate compared to those of vanillin, ethylvanillin, and acetovanillone at different plasticizing agent concentrations.

[0031] Detailed description of the invention

[0032] Therefore, according to a first aspect, the present invention refers to a composition comprising at least one cellulose ester and at least one plasticizing agent, wherein said plasticizing agent comprises at least one vanillin derivative having the following structural formula (Formula I) :

[0033] (I) , wherein :

[0034] - R1 is H or an alkyloxy group C1-C4, linear or branched;

[0035] - R2 is an alkyloxy group C1-C4, linear or branched;

[0036] - R3 is OH, vanillate or acetate.

[0037] Without referring to any specific theory, it is believed that the presence of the moderately polar Rl- R3 functional groups in the compounds of general formula (I) promotes interactions between the plasticizing agent and the polymer chains of the cellulose ester, thereby promoting the compatibility of the plasticizer in the polymer matrix and consequently its permanence (low diffusivity) , even when present at high concentrations.

[0038] Examples of alkyloxy groups C1-C4 are: methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy, iso-butoxy, sec-butoxy, and tert-butoxy.

[0039] In a preferred embodiment, the R1 group is selected from: H and alkyloxy C1-C2 (methoxy or ethoxy) .

[0040] Preferably, the group R2 is also an alkyloxy group C1-C2 (methoxy or ethoxy) .

[0041] Vanillate group means the group having the ructural formula:

[0042] According to a particularly preferred embodiment, the vanillin derivatives of general formula (I) are selected from: vanillin acetate, vanillin vanillate, ethyl vanillate, vanillin isobutyrate, ethyl vanillin isobutyrate, and preferably vanillin isobutyrate.

[0043] The vanillin derivatives are obtained through synthesis processes known in the art, starting from natural or synthetic vanillin, and are commercially available .

[0044] In accordance with the present invention, the plasticizing agent can comprise one or more derived plasticizers of general formula (I) .

[0045] The plasticizing agent can also comprise one or more conventional-type plasticizing compounds of the cellulose esters, other than those of general formula (I) •

[0046] In a preferred embodiment, the plasticizing agent does not contain plasticizers other than those of general formula ( I ) .

[0047] The composition according to the present invention comprises at least one cellulose ester. The cellulose ester is preferably selected from C1-C20 aliphatic esters, preferably from cellulose acetate, cellulose propionate, cellulose butyrate, and combinations thereof .

[0048] In a particularly preferred embodiment, the cellulose ester is cellulose acetate.

[0049] In one embodiment, the composition according to the invention comprises a combination of two or more different cellulose esters.

[0050] Cellulose esters are commonly derived from natural cellulose through reactions with organic acids, anhydrides, or acid chlorides.

[0051] Cellulose acetate is an organic ester of great importance due to its wide range of application fields in which it is used; it is prepared with degrees of substitution (DS) ranging from that of hydrolysed and water-soluble monoacetates to that of fully substituted triacetates. In the eyewear field, the degree of substitution is 2.2-2.5, depending on the processing method used. The Tg of a cellulose acetate product used in eyewear is in the temperature range from 100°C to 130°C.

[0052] In one embodiment, the cellulose esters and the plasticizing agent are present in the composition in a weight ratio in the range from 95:5 to 60:40, preferably in a range from 85:15 to 65:35, more preferably in a range between 80:20 and 70:30.

[0053] The composition according to the present invention optionally comprises further conventional additives, such as compatibilizers, dyes, pigments, antioxidants, lubricants, stabilizers, reinforcing substances, inert fillers, etc.

[0054] The plasticized composition according to the present invention can be prepared according to methods known in the art. Generally, the method for preparing the composition comprises mixing the cellulose ester and the plasticizing agent, together with optional additives, in the desired weight ratios to form a paste. Mixing can optionally occur under heat, also in the presence of solvents (e.g., acetone) . The paste can be formed under heat to obtain an article of the desired form or to obtain pellets or sheets. The pellets or sheets can be further processed, for example, by extrusion (pellets) or thermoforming (sheets) .

[0055] In one embodiment, practiced for example in the eyewear field, the plasticizer can be mixed with the cellulose ester, preferably in flake form, in the presence (wet block) or absence (dry block / extrusion) of a solvent, to obtain the paste. In the wet block process, additives such as colouring agents can be added to the obtained paste. The choice of using a solvent in paste preparation is mainly related to the type of desired aesthetic or colour effect. Subsequently, in both processes, the paste is reduced to sheets, which, once overlapping, are thermo-pressed in a mold (e.g., a formwork) to obtain a block of plasticized cellulose ester. The block can be subsequently sliced into dishes, from which temples and fronts can be obtained by mechanical processing (e.g., milling) to be assembled in glasses frames.

[0056] Therefore, according to a further aspect, the present invention refers to an article comprising the cellulose ester composition described above. The articles that can be made by the cellulose ester composition have multiple uses, for example, in the fields of eyewear, automotive, appliances, costume jewellery, cigarette filters, etc.

[0057] The composition according to the present invention, particularly when including cellulose acetate, is especially suitable for making components of a glasses frame, such as temples and fronts. Furthermore, since the vanillin derivatives described here have a characteristic fragrance, if dosed in appropriate amounts, they allow to prepare articles (e.g., glasses frames) capable of releasing a pleasant fragrance.

[0058] The following examples of embodiments are provided solely in order to illustrate the present invention and should not be intended as limiting the scope of protection defined by the appended claims. Examples

[0059] Various vanillin derivatives were tested as plasticizing agents for cellulose acetate. The cellulose acetate (in flake form) and the plasticizing agent were mixed according to the weight ratios reported below until completely dissolved in acetone. The solution was poured onto a glass Petri dish, and the acetone was allowed to evaporate until obtaining a plasticized cellulose acetate film.

[0060] The effectiveness of vanillin derivatives as plasticizers was assessed according to the criteria of:

[0061] - compatibility of the plasticizer with the polymer matrix (transparency of the plasticized film) ;

[0062] - lowering of the glass transition temperature (Tg) of cellulose acetate following the addition of the plasticizer;

[0063] - diffusivity coefficient of the plasticizer in the polymer matrix of cellulose acetate.

[0064] The plasticizer effectiveness was assessed by determining the glass transition temperature (Tg) of the plasticized polymer through experimental Dynamic Mechanical Analysis (DMA) measures according to ISO 6721:2019 and molecular dynamics simulations.

[0065] The simulations were performed using proprietary software to determine the density of the plasticized polymer as a function of the temperature. In order to calculate the glass transition temperature of the plasticized cellulose acetate systems, an annealing process was carried out from 700 K down to 100 K at a constant cooling rate. Every 10 K, a molecular dynamics step of 5 ns is performed, to assess the density of the plasticized acetate system. Once the calculation of the density of the plasticized system at various temperatures is completed, a density data fitting against temperature was performed by a hyperbole. The data fitting procedure by a hyperbole is automated. In this method, the Tg value is defined as the intersection point of the high- and low-temperature asymptotes of the fitting hyperbole.

[0066] Example 1: Cellulose acetate plasticized with vanillin isobutyrate

[0067] The film produced from a composition comprising 70% by weight cellulose acetate and 30% by weight vanillin isobutyrate (percentages referred to the total weight of the dry composition) is transparent (see Figure 1) , thus confirming the high compatibility of the plasticizer with the polymer.

[0068] Figure 2 presents the tan 5 trends of the cellulose acetate plasticized with diethyl phthalate (DEP) and vanillin isobutyrate, at 20% and 30% by weight with respect to the total weight of the dry composition, experimentally determined. It can be noted that the characteristic temperature of the tan 5 peak (Tg) for cellulose acetate plasticized with vanillin isobutyrate is lower than that of the corresponding polymer plasticized with DEP: therefore, for the same weight content, the plasticizing efficiency (lowering Tg) of vanillin isobutyrate is higher than DEP. This result is not attributable to a different molar concentration of the two plasticizers, as they have substantially the same molecular weight.

[0069] Therefore, for the same desired Tg for the plasticized polymer, it is possible to use an amount of vanillin isobutyrate lower than DEP, resulting in benefits of reduced diffusivity of the plasticizer in the polymer and greater material durability.

[0070] Example 2: Cellulose acetate plasticized with vanillin derivatives

[0071] The plasticizing effect of vanillin derivatives according to the present invention on cellulose acetate was assessed using molecular dynamics simulation with the proprietary software and methodology previously described .

[0072] Figure 3 presents Tg data as a function of the plasticizer concentration in cellulose acetate for vanillin (comparative) and the following derivatives thereof: vanillin acetate, vanillin vanillate, ethyl vanillin (comparative) , ethyl vanillate, vanillin isobutyrate, acetovanillone (comparative) , and ethyl vanillin isobutyrate. The Tg data were determined at the following plasticizer concentrations: 20, 25, and 30 wt% with respect to the total weight of the dry composition. It is apparent from Figure 3 that all the examined vanillin derivatives are capable of lowering the Tg of cellulose acetate more efficiently than vanillin.

[0073] Figure 4 presents the diffusivity coefficient values of the same derivatives of Figure 3 as a function of the plasticizer content (20, 25, and 30 wt% with respect to the total weight of the dry composition) , determined through molecular dynamics simulation using the previously described software. The data of Figure 4 show that the diffusivity coefficient of vanillin derivatives according to the invention is lower than that of prior art plasticizers.

[0074] Figure 5 presents the diffusivity coefficient of vanillin isobutyrate upon varying the Tg of the plasticized polymer, at different plasticizer concentrations, compared with the coefficients determined for prior art plasticizers (vanillin, ethylvanillin, and acetovanillone ) at the same concentrations (20, 25, and 30 wt% with respect to the total weight of the dry composition) .

Claims

CLAIMS1) Cellulose ester composition comprising a cellulose ester and a plasticizing agent, said plasticizing agent comprising at least one vanillin derivative of general formula (I) :(I) , wherein :- R1 is H or an alkyloxy group C1-C4, linear or branched;- R2 is an alkyloxy group C1-C4, linear or branched;- R3 is OH, vanillate or acetate.2) Composition according to claim 1, wherein R1 is H, methoxy or ethoxy.3) Composition according to any one of the preceding claims, wherein R2 is methoxy or ethoxy.4) Composition according to any one of the preceding claims, wherein said at least one vanillin derivative of general formula (I) is selected from: vanillin isobutyrate, ethyl vanillin isobutyrate, vanillin acetate, vanillin vanillate, ethyl vanillate and combinations thereof.5) Composition according to claim 4, wherein said at least one vanillin derivative of general formula (I) is vanillin isobutyrate.6) Composition according to any one of the preceding claims, wherein said cellulose ester is a Ci- C20 aliphatic cellulose ester, preferably selected from: cellulose acetate, cellulose propionate and cellulose butyrate .7) Composition according to claim 6, wherein said cellulose ester is cellulose acetate.8) Composition according to any one of the preceding claims, wherein said cellulose ester and said plasticizing agent are present in a weight ratio in the range from 95:5 to 60:40, preferably in a range from 85:15 to 65:35 , more preferably in a range between 80:20 and 70:30.9) Article comprising a cellulose ester composition according to any one of claims 1 to 8.10) Article according to claim 9, said article being a glasses frame or a component thereof.

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