Polymer material based on polylactic acid

Abstract

The invention relates to a polymer material comprising a mixture of: a base polylactic acid (PLA) polymer formed by between 60 wt.-% and 85 wt.-% L units and between 15 wt.-% and 40 wt.-% D units or between 60 wt.-% and 85 wt.-% D units and between 15 wt.-% and 40 wt.-% L units; and a plasticizer selected from the group containing citric acid esters, glycerin esters and derivatives, poly(alkylene ethers), oligomers of lactide or derivatives of lactic acid, fatty acid esters and epoxidized oils, representing between 10 wt.-% and 40 wt.-% in relation to the total weight of the polymer material.

Claims

1. A laminated assembly according, comprising: at least two substrates, and an interposed film of impact- and tear-resistant polymer material comprising a mixture (i) of a base polylactic acid polymer comprising 15% to 30% by weight of a D structural unit and 70% to 85% of an L structural unit; and (ii) a plasticizer in a content of from 15% to 20% by weight based on a total weight of the impact- and tear-resistant polymer material, wherein one of the at least two substrates is a glass substrate, wherein the interposed film lies between the at least two substrates, wherein the plasticizer is n-tri-butyl citrate, and wherein a Young's modulus of the interposed film is from 2 to 56 MPa.

2. The laminated assembly according to claim 1, wherein an elongation at break of the interposed film is 350% to 620%.

Description

EXAMPLES

(1) In all the following examples the polymer materials with the base PLA, in which plasticisers, cross-linking agent and other additives are incorporated, are prepared in the following manner.

(2) The base PLA is introduced into a Brabender kneader (volume of mixing chamber=55 cm.sup.3) at a temperature of 190 C. After mixing for 5-10 min. the plasticiser is incorporated at contents varying between 10% and 40% by weight in relation to the total weight of the base PLA polymer. The whole mixture is mixed at this temperature for 10 min. to obtain a homogeneous polymer material. This is then thermoformed at 190 C. under a pressure of 130 bar to obtain discs that are 10 cm in diameter and 0.5 mm thick.

(3) The polymer materials that comprise a cross-linking agent in addition to the plasticiser are prepared in the following manner.

(4) 3% by weight of cross-linking agents (or cross-linkers), Joncryl ADR 4368-CS from BASF and DCP respectively, are incorporated before adding the plasticiser and after introducing the base PLA as above. The whole mixture is mixed for about 5 min. and the plasticiser is then incorporated. The subsequent steps are those described above. In the case where two different cross-linking agents are added, 1.5% by weight of the first cross-linking agent is incorporated and mixed for 5 min. and 1.5% of the second cross-linking agent is incorporated followed by mixing for 5 min.

(5) The synthesis of base PLA having a proportion of PDLA isomers in the range or between 15% and 40% by weight is conducted with two samples of polymer grade lactides, one being a lactic acid dimer, L isomers, the other being a racemic mixture of lactic acid dimers, L and D isomers. Contents varying between 15% and 40% by weight of D structural units are obtained, depending on the respective quantity of each sample. A catalyst/primer system composed of tin ethylhexanoate, triphenylphosphine and octanol (lactide/tin ethylhexanoate=4500, lactide/octanol=420, tin ethylhexanoate/triphenylphosphine=1) is used in the presence of toluene. The mixture is heated under reflux at 190 C. for 35 min. The residual lactide and the low oligomers are eliminated by precipitation in methanol and the base PLA is then dried in vacuum at 60 C. to completely eliminate the solvent.

(6) Base PLAs with a proportion of PDLA isomers of less than 15% were selected from the industrial grades available from Natureworks. The relative proportion of L-lactide and D-lactide determines the optical purity of the base PLA.

(7) The quantities of additives added are expressed in percentages by weight of the total for each formulation mentioned in the following examples.

Example 1

(8) A formulation of polylactic acid (PLA), to which a plasticiser, n-tri-butyl citrate (TBC), has been added to a content of 20% (Sample A), is studied. It has a proportion of D structural units of 30%.

(9) A Sample B characterised by a proportion of D structural units of 12% and comprising a proportion of TBC of 5% was studied for comparison.

(10) Table 1 indicates the development of the Tg of the formulations and the mechanical properties thus obtained.

(11) By way of example, Table 1 also includes the values of these properties for PVB.

(12) TABLE-US-00001 TABLE 1 Tg E Sample % D Plasticiser ( C.) (MPa) (MPa) (%) A 30 20% 15.9 25 18 419 TBC B 12 5% 49.1 2362 46 33.4 (comparative) TBC PVB 18.8 3 30 460

(13) The results of Table 1 clearly indicate that the optical purity of the PLA and the content of plasticiser according to the invention allow the Tg values to be reduced and it is evident that for Sample B (comparative), the composition of which is outside the invention, the values obtained are too high in terms of the Young's modulus (E) and too low for elongation at break ().

Example 2

(14) A formulation of polylactic acid (PLA), to which a plasticiser, n-tri-butyl citrate (TBC) has been added, wherein the base PLA has been cross-linked (J=joncryl ADR 4368-CS), is studied.

(15) The following Table 2 shows the characteristics of the polymer materials: plasticiser content, proportion of D structural units, cross-linking agent content, as well as data relating to the mechanical properties of these materials.

(16) TABLE-US-00002 TABLE 2 Cross- linking Tg E Sample % D Plasticiser agent ( C.) (MPa) (MPa) (%) C 30 20% 3% 11.9 3 8 500 TBC (J + DCP; 50/50) D 20 20% 3% J 15.3 56 16 350 TBC E 30 15% 3% 21.1 2 10 620 TBC (J + DCP; 50/50) F 20 17% 3% 21.7 15 16 400 TBC (J + DCP; 50/50) G 12.1 5% 3% J 48.2 2210 45 6 (compar- TBC ative)

(17) The results of Table 2 indicate that in the case of Samples C to F according to the invention the desired properties for these materials are obtained, in contrast to Sample G outside the invention where the properties are not satisfactory.

Example 3

(18) Ageing tests enable the stability of the formulations produced to be characterised. A series of tension test pieces was thus subjected to ageing at 100 C. for one night and the thermo-mechanical properties were re-evaluated.

(19) A formulation of polylactic acid (PLA), to which a plasticiser, n-tri-butyl citrate (TBC) has been added, wherein the base PLA has possibly been cross-linked (J=joncryl ADR 4368-CS), is studied.

(20) The following Table 3 shows the characteristics of the polymer materials: plasticiser content, proportion of D structural units, cross-linking agent content, as well as data relating to the mechanical properties of these materials before and after the ageing step (the values after ageing are given in italics) and also indicates if a fusion peak was observed during the DSC measurement, this showing the presence of a crystalline phase in the polymer material.

(21) TABLE-US-00003 TABLE 3 Cross- % linking Tg E Crystalline Sample PDLA Plasticiser agent ( C.) (MPa) (MPa) (%) phase A 30 20% 15.9 25 18 419 no TBC 9.2 11.5 8 500 no C 20 20% 3% 11.9 3 8 500 no TBC (J + DCP; 16.4 4.8 5 420 no 50/50) H 1.4 20% 3% DCP 16 36 24 230 no (comparative) TBC 24.6 810 28 12 yes I 12.1 20% 18 45 29 430 no (comparative) TBC 19 200 20 190 yes J 12.1 20% 3% J 18.9 15 27 500 no (comparative) TBC 20.7 70 28 350 yes K 12.1 20% 3% 17 15 14 330 no (comparative) TBC (J + DCP; 24 187 10 37 yes 50/50)

(22) Samples A and C exhibit satisfactory properties before and after ageing.

(23) In contrast, in the case of Samples H to K outside the invention the appearance of a crystalline phase is observed during ageing at high temperature, which results in unsatisfactory thermo-mechanical properties, as well as opacification of the material, which makes it unsuitable for the envisaged applications.

Example 4

(24) Contact adhesion tests were conducted on films of polymer material of several different compositions either including anti-blocking agents or not (for comparison). Kieselguhr supplied commercially by Merck has a grain size of less than 0.1 mm. The type of erucamide used is a cis-13-docosenamide supplied commercially by Sigma-Aldrich.

(25) These tests were conducted as follows:

(26) Two films obtained from the described formulations were placed in contact, hydroflated by a weight of 94 g, then placed in an oven at 30 C. or 60 C. for 24 hours. After their removal from the oven an attempt is made to separate the films. If separation of the films is possible (result OK), there is no problem with contact adhesion. However, if the films cannot be separated (result KO), there is clearly a problem with contact adhesion.

(27) The following Table 4 shows the characteristics of the tested polymer materials: plasticiser content, proportion of D structural units, cross-linking agent content, as well as data relating to the mechanical properties of these materials before and, if applicable, after the ageing step (the values after ageing are given in italics), and gives the adhesion results.

(28) TABLE-US-00004 TABLE 4 Cross- Anti- linking blocking Tg E Adhesion Sample % D Plasticiser agent agent ( C.) (MPa) (MPa) (%) test L.sub.0 12 20% 17.8 45 28 430 60 C.: KO TBC L.sub.1 12 20% 2% 21.1 168 30 383 60 C.: OK TBC kieselguhr L.sub.2 12 20% 4% 20.2 180 29 321 60 C.: OK TBC kieselguhr L.sub.3 12 20% 3% 4% 20.6 15 15 282 60 C.: OK TBC (J + DCP; kieselguhr 50/50) M.sub.0 12 20% 16.2 14 26 420 30 C.: KO TBC M.sub.1 12 20% 0.5% 20.2 24 25 521 30 C.: OK TBC erucamide M.sub.2 12 20% 3% 0.5% 21.5 15 15 326 30 C.: OK TBC (J + DCP; erucamide 50/50) N.sub.1 30 20% 0.5% 17.2 3 5 465 30 C.: KO TBC erucamide 15.6 32 10 390 N.sub.2 30 20% 3% J 0.5% 9 3 3 515 30 C.: OK TBC erucamide 15.4 7 7 495 N.sub.3 30 20% 1.5% 0.5% 16.4 3 7 500 30 C.: OK TBC J + erucamide 17.3 10 9 460 0.5% DCP)

(29) The results of this table generally show the advantage of adding kieselguhr or erucamide to a polymer material comprising a polylactic acid (PLA) polymer, a plasticiser and possibly a cross-linking agent to be able to reduce the contact adhesion of the polymer material.

(30) The N group of samples shows that when 0.5% erucamide is added, this advantage of reducing contact adhesion is evident for PLAs with a high proportion of D, primarily when a cross-linking agent is also present in the polymer material.