Compositions comprising tetrahydrofurfuryl and alkoxylated alkyl esters as plasticisers for biodegradable resins

Abstract

The present invention refers to a composition comprising tetrahydrofurfuryl and alkoxylated alkyl esters and their use as plasticizers in biodegradable resins, more in particular, in a biodegradable aliphatic polyester resin comprising polylactic acid. In a preferred embodiment the composition comprises a tetrahydrofurfuryl butyldiglycolate ester. The invention also refers to a biodegradable resin composition, more in particular, comprising homo- or co-polymers of polylactic acid and comprising such compositions.

Claims

1. A composition comprising: a) a biodegradable resin; and b) a plasticiser of aliphatic dicarboxylic acid esters of formula (II) and of formula (I) or (III)
R.sup.1—OC(O)—X—[C(O)O—R.sup.1]  (I)
R.sup.1—OC(O)—X—[C(O)O—R.sup.2]  (II)
R.sup.2—OC(O)—X—[C(O)O—R.sup.2]  (III) wherein R.sup.1 is a tetrahydrofurfuryl group, or a substituted tetrahydrofurfuryl group; R.sup.2 is an alkoxylated alkyl group, or a substituted alkoxylated alkyl group, different from R.sup.1; R.sup.2 is butyldiglycolate; and X is an alkyl group or a hydroxyl-substituted alkyl group comprising from 1 up to 4 C-atoms.

2. A biodegradable aliphatic polyester resin composition comprising a composition comprising: a) a biodegradable resin; and b) a plasticiser of aliphatic dicarboxylic acid esters of formula (II) and of formula (I) or (III)
R.sup.1—OC(O)—X—[C(O)O—R.sup.1]  (I)
R.sup.1—OC(O)—X—[C(O)O—R.sup.2]  (II)
R.sup.2—OC(O)—X—[C(O)O—R.sup.2]  (III) wherein R.sup.1 is a tetrahydrofurfuryl group, or a substituted tetrahydrofurfuryl group R.sup.2 is an alkoxylated alkyl group, or a substituted alkoxylated alkyl group, different from R.sup.1; and X is an alkyl group or a hydroxyl-substituted alkyl group comprising from 1 up to 4 C-atoms.

3. The biodegradable aliphatic polyester resin composition of claim 2, wherein the biodegradable aliphatic polyester resin is at least one member selected from the group consisting of resins obtained by condensation of hydroxycarboxylic acid(s) and resins obtained by condensation of aliphatic dicarboxylic acid(s) and aliphatic diols.

4. The biodegradable aliphatic polyester resin composition of claim 2, comprising a homo- or copolymer of a polylactic acid and/or a polybutylene succinate.

5. The biodegradable aliphatic polyester resin composition of claim 2 includes a polylactic acid.

6. A composition comprising: a) a biodegradable resin; and b) a plasticiser of aliphatic dicarboxylic acid esters of formula (II) and of formula (I) or (III)
R.sup.1—OC(O)—X—[C(O)O—R.sup.1]  (I)
R.sup.1—OC(O)—X—[C(O)O—R.sup.2]  (II)
R.sup.2—OC(O)—X—[C(O)O—R.sup.2]  (III) wherein R.sup.1 is a tetrahydrofurfuryl group, or a substituted tetrahydrofurfuryl group; R.sup.2 is an alkoxylated alkyl group, or a substituted alkoxylated alkyl group, different from R.sup.1; and X is an alkyl group or a hydroxyl-substituted alkyl group comprising from 1 up to 4 C-atoms wherein the composition is obtained by esterification of an aliphatic dicarboxylic acid with a mixture of tetrahydrofurfuryl alcohol and one or more alcohols selected from the following: butoxyethoxyethanol, butoxyethoxyethoxyethanol, methoxyethoxyethoxyethanol, and butoxypropoxypropanol.

7. The composition of claim 6, wherein the aliphatic dicarboxylic acid includes succinic acid.

8. A biodegradable aliphatic polyester resin composition comprising the composition of claim 1.

9. The biodegradable aliphatic polyester resin composition of claim 8, wherein the biodegradable aliphatic polyester resin is at least one member selected from the group consisting of resins obtained by condensation of hydroxycarboxylic acid(s) and resins obtained by condensation of aliphatic dicarboxylic acid(s) and aliphatic diols.

10. The biodegradable aliphatic polyester resin of claim 8, comprising a homo- or copolymer of a polylactic acid and/or a polybutylene succinate.

11. A biodegradable aliphatic polyester resin composition comprising the composition of claim 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The characterising feature of the composition according to the present invention is the presence of aliphatic polycarboxylic acid esters that comprise on the one hand a tetrahydrofurfuryl group or a substituted tetrahydrofurfuryl group, and on the other hand an alkoxylated alkyl group, or a substituted alkoxylated alkyl group.

(2) These esters are referred to as ‘asymmetrical esters’ as will be clarified hereinafter. These esters may be present in the composition according to the invention, along with esters that comprise either tetrahydrofurfuryl groups or substituted tetrahydrofurfuryl groups alone, or alkoxylated alkyl groups, or substituted alkoxylated alkyl groups alone.

(3) These esters are referred to as ‘symmetrical esters’ as will be clarified hereinafter. The compositions according to the present invention are thus characterised by the joint presence of specific symmetrical as well as asymmetrical esters.

(4) According to a preferred embodiment, the polycarboxylic acid esters are obtained by esterification of either dicarboxylic acids, or tricarboxylic acids.

(5) The compositions of the invention can be prepared by esterification of the aliphatic polycarboxylic acid with a selected mixture of different alcohols, wherein at least one alcohol comprises a tetrahydrofurfuryl group or a substituted tetrahydrofurfuryl group.

(6) The term symmetrical ester in the context of the present invention is to be understood as an ester derived from a polycarboxylic acid, wherein all carboxylic acid groups are esterified with the same kind of alcohol.

(7) An asymmetrical ester in the context of the present invention is to be understood as an ester derived from a polycarboxylic acid, wherein not all carboxylic acid groups are esterified with the same kind of alcohol.

(8) In the case of a dicarboxylic acid such as e.g. succinic acid, glutaric acid or adipic acid, both carboxylic acid groups are esterified with the same alcohol in case of a symmetrical ester, and are esterified with a mixture of at least 2 different alcohols in case of an asymmetrical ester.

(9) When the aliphatic polycarboxylic acid is an aliphatic dicarboxylic acid, the preparation method set forth supra yields on the one hand symmetrical esters, i.e. esters comprising a tetrahydrofurfuryl group or a substituted tetrahydrofurfuryl group at either side, or an alkoxylated alkyl group, or substituted alkoxylated alkyl group at either side, and on the other hand asymmetrical esters, comprising a tetrahydrofurfuryl group or a substituted tetrahydrofurfuryl group at one side and an alkoxylated alkyl group, or substituted alkoxylated alkyl group at the other side.

(10) In the case of a tricarboxylic acid, such as e.g. citric acid or trimellitic acid, the asymmetrical ester is obtained by esterification of one carboxylic acid group with one type of alcohol, and both of the other carboxylic acid groups are esterified with the other type of alcohol.

(11) Application:

(12) The composition of the present invention is in particular useful as plasticiser, more preferably as plasticiser for biodegradable polyester resins.

(13) The term biopolymers in the context of the present invention should be understood as comprising polymers that are manufactured in a synthetic manner from monomers of biological origin. More in particular, the succinate, according to the invention, can be used as plasticiser in such biodegradable polymers on the basis of aliphatic polyesters, as well homo- as copolyesters. Still more in particular, the succinate can be used as plasticiser in biopolymers on the basis of polylactic acid (PLA).

(14) The term polylactic acid, as used in the context of the present invention, relates to a polymer or copolymer comprising at least 50 mol % of lactic acid monomer units.

(15) Examples of such polylactic acids comprise, but are not restricted to:

(16) (a) a homopolymer of polylactic acid, (b) a copolymer of lactic acid with one or more aliphatic hydroxycarbon acids, different from lactic acid, (c) a copolymer of lactic acid with an aliphatic polyhydric alcohol and an aliphatic polycarboxylic acid, (d) a copolymer of lactic acid with an aliphatic polycarboxylic acid, (e) a copolymer of lactic acid with an aliphatic polyhydric alcohol, and (f) a mixture of two or more of (a)-(e) as above mentioned. Examples of lactic acid comprise L-lactic acid, D-lactic acid, a cyclic dimer hereof (L-lactide, D-lactide or DL-lactide) and mixtures hereof. Examples of the hydroxycarboxylic acid that can be used in the above-mentioned copolymers (b) and (f) comprise, but are not restricted to, for example: glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxyhexanoic acid and hydroxyheptanoic acid, as well as combinations hereof.

(17) Furthermore, the biodegradable or bio-renewable thermoplastic materials wherein the succinate according to the invention might be used as plasticiser, may consist of a single thermoplastic material such as a polymer (for example polylactic acid alone), but they might also consist of a mixture of polylactic acid with at least one additional thermoplastic material. In such a preferred embodiment, the biodegradable or bio-renewable thermoplastic material may comprise a blend or mixture of polylactic acid with one or more aliphatic polyesters or copolyesters like polybutylene succinate, polyhydroxy alkanoates (PHA), starch, cellulose or another polysaccharide or combinations hereof.

(18) In still another preferred embodiment the biodegradable or bio-renewable material may comprise a blend or mixture of polylactic acid with at least one aliphatic polyester (e.g. polybutylene succinate) or copolyester, a mixture of polylactic acid with at least one polyhydroxy alkanoate (PHA), or a blend of polylactic acid with another biopolymer such as starch, cellulose or another polysaccharide. In a still more preferred embodiment, the biodegradable or bio-renewable thermoplastic material may comprise a mixture of polylactic acid, at least one PHA and at least one starch. In some embodiments, the thermoplastic material may be present in about 5 to about 95% by weight, calculated on the basis of the total weight of the composition. In some embodiments, the amount of polylactic acid, as compared to the total amount of thermoplastic material in the composition, is comprised between approximately 15 to approximately 100% by weight, and, in other embodiments, is comprised between approximately 30 to approximately 100% by weight calculated in relation to the total weight of thermoplastic material.

(19) Mode of Preparation:

(20) The composition and the esters according to the invention may be prepared according to the process described hereinafter.

(21) As a first step, a mixture is prepared of the alcohols selected in the appropriate concentration, depending on the intended application, and wherein at least one of the alcohols comprises a tetrahydrofurfuryl group. This group may be substituted. These alcohols are introduced into a reactor, followed by heating up to approx. 90° C. and addition of the aliphatic polycarboxylic acid or the corresponding anhydride in an amount such that the ratio of the carboxylic acid over the alcohol mixture is approximately 1:2 in case a dicarboxylic acid is used, and to approximately 1:3 in case a tricarboxylic acid is used.

(22) The use of an excess amount of alcohol and the use of a dehydrating agent or azeotropic agent may be of advantage to finish the reaction.

(23) (A dehydrating agent is to be understood as an auxiliary compound that serves to remove the excess water obtained as by-product during the esterification. This is not an additive for the resin composition, only an auxiliary compound in this process step during the esterification.)

(24) As a catalyst, use can be made e.g. of a strong acid, such as sulphuric acid.

(25) The reaction is considered to be finished when no water is formed any more. After neutralization of the catalyst, the possible excess amount of alcohol is removed by distillation. The mixture may be washed to remove possible impurities. As a supplementary step, the ester can be discoloured by means of discoloration techniques known per se, such as: the use of active carbon, oxidation with hydrogen peroxide, hydrogenation with hydrogen, . . . . Finally, the product is dried by heating at increased temperature (80 up to 150° C.) under vacuum.

(26) An alternate mode of preparation for the process described above, namely the esterification of a carboxylic acid and an alcohol, is the reaction of the carboxylic acid with a different functional group such as an alkyl chloride.

Effects of the Invention

(27) The most surprising effect of the compositions according to the invention is the low volatility in polyester resins, in particular those comprising or based upon polylactic acid, as compared to e.g. a symmetric ester of a polycarboxylic acid such as dibutoxyethoxyethyladipate, in spite of a higher vapour pressure of this compound. Moreover, when the compositions of the invention are used as plasticiser in e.g. polylactic acid, in particular when used in film products, significantly improved properties are observed, such as e.g. the absence of smell and the absence of greasiness on the film surface.

(28) Although the inventors cannot give an assurance as to the scientific exactness of this phenomenon, they believe that this surprising effect is resulting from an improved compatibility of this plasticiser with the hydrophilic, polar nature of polylactic acid.

(29) By way of example, hereinafter is set forth a specific compound that may be present in the compositions of the invention.

(30) Tetrahydrofurfuryl-butoxyethoxyethyl-succinate (THFBEES), molecular weight 346.

(31) ##STR00002##

(32) This compound may also be denoted as tetrahydrofurfuryl-butyldiglycol-succinate.

(33) The mixtures of alcohols suitable for use in the present invention may comprise, apart from tetrahydrofurfurylalcohol, as such or substituted, one or more alkoxylated alcohols, such as butoxyethoxyethanol, butoxyethanol, methyltriglycolether as well as isomers and mixtures of these compounds.

(34) The process of ethoxy- or propoxylation is known as such for the person skilled in the art.

(35) The ethoxylation or propoxylation process yields alcohols whereby the corresponding esters are more polar and as such are more compatible with polar polymers, such as some biodegradable aliphatic polyester resins.

(36) Ethyleneoxyde, polyethyleneoxyde, propyleneoxyde or polypropyleneoxyde have an average chain length of 2 to approx. 8 mol of oxygen per mol of alcohol.

(37) An extra benefit resulting from the addition of an oxygen is the increase of the molecular weight and a substantial reduction of the VOC in combination with the increase in compatibility with the biodegradable polymer.

(38) The ester, according to the invention, is in particular suitable for use as plasticiser in various polymers, and more specifically in biopolymers. Examples of polymers wherein the ester can be used as plasticiser are aliphatic polyester resins (for example polylactic acid and polybutylene succinate), cellulose esters, polyvinylchloride, polyvinylbutyral, polar rubbers, polyurethanes and acrylate polymers such as poly(methyl methacrylate).

(39) Aliphatic polyesters may be produced according to the dehydration-polycondensation reaction of one or more aliphatic hydroxycarboxylic acids or their dehydrated cyclic analogues (lactones and lactides). Examples of hydroxycarboxylic acids are L-lactic acid, D-lactic acid, glycolic acid, hydroxy-butyric acid, hydroxy-valeric acid, hydroxy-pentanoic acid, hydroxy-hexanoic acid, hydroxy-heptanoic acid, . . . .

(40) According to an alternative method the aliphatic polyesters may be manufactured by a dehydration-polycondensation reaction of a mixture comprising an aliphatic polycarboxylic acid and an aliphatic diol, such as polybutylene succinate. Examples of such compounds are mentioned in the already cited PCT publication WO 2013/148255.

(41) The term polylactic acid, as used in the context of the present invention, relates to a homopolymer of lactic acid or a copolymer of lactic acid with a hydroxycarboxylic acid or a polymer composition containing either the homopolymer of lactic acid or a copolymer of lactic acid with a hydroxycarboxylic acid. By the presence of a chiral core in lactic acid, the molecular structure of lactic acid in the polylactic acid can be either L-lactic acid or D-lactic acid, or a mixture of both in various possible concentrations. The choice of the cyclic monomer used in the polymerization reaction to produce polylactic acid determines, together with the choice of the plasticiser, the concentration of the plasticiser in the polymer and the processing conditions for incorporation of the plasticiser in the polymer, the final properties of the polymer. For the polymerization reaction to polylactic acid, use is, preferably, made of lactide, i.e., the cyclic monomer comprising two molecules of lactic acid that are dehydrated. This lactide can be either L,L-lactide (2 molecules of L-lactic acid), as well as D,D-lactide (2 molecules of D-lactic acid) or meso-lactide (1 molecule of L-lactic acid and 1 molecule of D-lactic acid).

(42) The average molecular weight of the polylactic acid is, preferably, from about 10 000 up to 1 000 000, more preferably, from about 30 000 to about 600 000, and still more preferably, from about 50 000 to about 400 000. Polylactic acid, with an average molecular weight between the above-mentioned limits, has usually a sufficient mechanical strength and a good process ability.

(43) Examples of commercially available polylactic acids are “Ingeo” of Natureworks,“Purasorb” from Corbion Purac, “Lacty”, marketed by Shimadzu Corp., “Lacea”, marketed by Mitsui Chemicals Inc., “Terramac”, marketed by Unitika Ltd., “eco-PLA” marketed by Cargill-Dow LLC, USA, “Ecologe”, marketed by Mitsubishi Plastics Inc.

(44) When used as plasticiser, the ester according to the present invention usually functions as primary plasticiser. According to a more specific embodiment, other plasticisers may be added to the biopolymer, whereby the ester, according to the invention, may then function either as primary or secondary plasticiser.

(45) According to a preferred embodiment of the present invention, the amount of polylactic acid in the plastic composition is at least 50% of the total weight of the composition, and according to a still more preferred embodiment, at least 60%.

(46) So as to obtain a sufficient level of mechanical strength, impact resistance and flexibility, the amount of ester in the plastic composition, according to the present invention, amounts to 2 to 50%, more preferably from 2 to 20%. In more durable consumption products such as the housing or casing of electrical appliances and automotive parts, the amount should preferably not exceed 25%. In products that require a high degree of flexibility such as films for use in agricultural applications or for packaging, the amounts are preferably comprised between 5 and 40%.

(47) The resin composition, according to this invention, may, apart from the plasticiser, comprise one or more other ingredients such as, for example, inorganic fillers and silicates, such as talc, china clay, montmorillonite, silica, magnesium oxide, titanium oxide, calcium carbonate, magnesium hydroxide, fibre glass, carbon fibers, graphite powder, etc.

(48) The resin composition according to this invention may apart from the plasticiser also comprise one or more other ingredients added so as to optimize the resin composition in view of the anticipated application. These ingredients may comprise flame retardants, hydrolysis-retardants, a lubricant, an antistatic agent, antifogging agents, light stabilizers, UV-absorbers, fungicidal additives, antimicrobial additives, foaming agents, . . . .

(49) Preparation of the Resin Composition:

(50) An amount of polylactic acid Ingeo 2003D (extrusion quality) grains were dried during 24 hours in an oven at 70° C. and subsequently introduced in a Brabender-mixing device. The amount of PLA was chosen so as to obtain an amount of 55 g of resin material. PLA was then heated at a temperature of around 190° C. and stirred at a speed of 50 revolutions per minute.

(51) After 5 minutes the plasticiser was added, and the mixture was further stirred for a total duration of 15 minutes. Afterwards, the mixture was cooled.

(52) Preparation of Films (10 cm*10 cm*450 μm)

(53) Films were prepared by means of an Agila PE20 hydraulic press. 7.5 g of the resin composition containing the ester compound, as previously described, was pressed at a temperature of 170° C. The contact time was initially 4 minutes, followed by 3 minutes 20 seconds at 10 bar and 2 minutes 30 seconds at 150 bar with two degassing cycles; after this, cooling with water took place at 50 bar for the period of 3 minutes.

(54) Evaluation of the ester mixture as plasticiser for PLA by means of DSC:

(55) Analysis conditions: Equilibration at −20° C. for 2 min; First heating cycle from −20° C. to 200° C. at a speed of 10° C./min; Cooling from 200° C. to −40° C. at a speed of 10° C./min; Second heating from −40° C. to 200° C. at a speed of 10° C./min.

(56) Evaluation of the films took place on the basis of a visual inspection, odour, greasy appearance of the film surface, weight loss at 60° C. after 7 days.

(57) For the evaluation, the following codes were used:

(58) 1=total absence;

(59) 2=little;

(60) 3=noticeable by visual inspection;

(61) 4=clearly visible by visual inspection;

(62) 5=large amounts visible.

(63) TABLE-US-00001 TABLE Evaluation of PLA 2003D with plasticiser Film evaluation Weight DSC Greasy loss Plasticiser Conc Tg (° C.) Visual odour surface (%) none 61.8 transparent 1 1 0.25 Di(butyldiglycol)adipate 15% 30.3 transparent 4 2 1.64 Di(butyldiglycol)succinate 15% 30.0 transparent 4 2 0.22 Di(tetrahydrofurfuryl)succinate 15% 30.2 transparent 2 1 0.33 Tetrahydrofurfuryl-butyldiglycol- 15% 26.2 transparent 1 1 0.30 succinate Di(benzyl)succinate 15% 31.5 transparent 4 5 0.50 Tetrahydrofurfuryl-butyldiglycol-citrate 15% 29.5 transparent 1 1 0.97

(64) From the above tests it is clear that the use of the new compounds according to the invention, i.e. tetrahydrofurfuryl-butyldiglycol-succinate and tetrahydrofurfuryl-butyldiglycol-citrate, yield significantly improved results as compared to the results resulting from the use of the comparative compounds.