FR2765230A1 - COMPOSITION COMPRISING A THERMOPLASTIC MATERIAL AND AN AMYLACEOUS PHASE - Google Patents

Abstract

The invention relates to a composition comprising a thermoplastic material and a starchy phase, a composition the coloring of which is stabilized vis-à-vis the heat treatments used by adding a sulfur compound in the +4 oxidation state. . The invention also relates to the use of this composition for the manufacture of an article and to an article comprising this composition.

Description

-] - Composition comprising a thermoplastic material and a phase

  The invention relates to a composition comprising a material

  thermoplastic and a starchy phase.

  The interest shown by plastic producers and processors in biodegradable or biofragilisable products is growing, especially in view of the environmental advantages they offer. Among these products, the compositions comprising starch or a derivative

  of starch have certain advantages, in particular economic.

  The use of starch, or starch derivative, without simultaneous use

  of thermoplastic material, presents only very limited industrial interests.

  This is due, in particular, to a sensitivity to water, generally undesirable, of the articles thus produced, or even to the inadequacy of the tools usually

  used by processors for such a highly hydrophilic material.

  Other advantages result from the incorporation of starch or starch derivative in the thermoplastic compositions. Among these advantages, it may be mentioned that these starchy compounds provide the products thus

  achieved a certain level of weldability by high frequency current.

  Several compositions comprising a thermoplastic material and a starchy phase have therefore been proposed. Let us cite in particular patent application EP 0 587 216 AI filed in the name of SOLVAY (Société Anonyme) and describing mixtures of polyolefins with a thermoplastic (plasticized) starch and a

ionic compound.

  The use of this type of composition requires at least one step during which the composition is brought to a temperature above the melting temperature (for crystalline or semi-crystalline polymers) or to the glass transition temperature ( for essentially amorphous polymers) of the thermoplastic material. This processing temperature is, in most cases, higher than the processing temperature of compositions

  biodegradable free of thermoplastic material.

  Unfortunately, this step, made necessary for obtaining a good degree of homogeneity of the composition and good mechanical properties of the product produced, results in a change in the coloration of the -2- composition - usually a yellowing or browning that the thermal stabilizers usually used for thermoplastic materials fail to inhibit. This coloring is all the more pronounced as the temperature reached and the residence time at this temperature are high, and does not however seem to come from a conventional thermal degradation of the starchy phase. Curiously, it was found that the intensity of yellowing or browning depended on the temperature of the sample at the time of observation. At high temperature (150 ° C. for example), this coloration is often of low intensity, whereas for the sample cooled to room temperature, the coloration is clearly more intense. This same sample becomes again

lighter if you heat it up.

  In the case of compositions free of dyes or pigments, this coloration can reduce the visual appeal of the product. In the case of intentionally colored articles, their coloration may be affected and depend on the initial composition and on the processing temperature thereof. A larger quantity of pigments or dyes will then be possibly required to mask the coloration due to the implementation step and to guarantee a uniform shade in space and time, which represents a disadvantage to

all the less economical.

  Consequently, the subject of the present invention is a composition comprising a thermoplastic material and a starchy phase, the color development of which is reduced, or even canceled, during and following the subsequent heat treatment (s). The invention therefore relates to a composition comprising a thermoplastic material and a starchy phase, characterized in that it comprises

  in addition to at least one sulfur compound in the oxidation state +4.

  By thermoplastic material is meant any thermoplastic polymer, including thermoplastic elastomers, as well as their mixtures. The term “polymer” denotes both homopolymers and copolymers (binary or ternary in particular), for example random distribution copolymers, block copolymers, block copolymers, graft copolymers, etc. Advantageously, a polyolefin or a mixture of polyolefins is used as the thermoplastic polymer. The term “polyolefin” is intended to denote any olefin homopolymer, any copolymer containing at least two different olefins -3 and any copolymer comprising at least 70% by weight of units

derived from olefins.

  Particularly advantageously, the polyolefin is a polyethylene.

  The term “polyethylene” is intended to denote any homopolymer of ethylene and any copolymer comprising at least 70% by weight of ethylene. In particular, linear low density polyethylenes (LLDPE), very low density polyethylenes (VLDPE), low density polyethylenes (LDPE) and mixtures thereof

  have provided very good results.

  In general, the thermoplastic content of the composition does not

  not more than 95% and preferably not more than 90% by weight.

  This same content is generally not less than 10% and preferably not

less than 20% by weight.

  By starch phase is meant any type of material essentially consisting of one or more starches or modified starches. These starches can be destructured, pregelified, partially depolymerized, come from different plant origins or have any weight ratio between amylose and amylopectin. The starchy phase can also contain various additives specific to starch or its derivatives, such as water and / or plasticizers. Mention may be made, as plasticizers, without limitation, of glycerin, sorbitol, diglycerin, polyglycerins and mixtures thereof. Other additives which facilitate the processing of starch at high temperatures can also

  be used, such as urea and the salts of hydroxycarboxylic acids in particular.

  The addition of ionic, organic or inorganic salts, and / or derivatives

  Ionic starch can also be considered.

  In general, the starch content of the composition does not exceed

  % and preferably not 50% by weight.

  This same content is generally not less than 5% and preferably not

less than 10% by weight.

  The sulfur compound in the +4 oxidation state can be of any type; organic or inorganic, solid, liquid or gas at temperature and pressure

  ambient. Inorganic salts and sulfur dioxide are preferred, however.

  Among the inorganic salts, the bisulfite (or hydrogen sulfite, HSO3-) or the pyrosulfite (or metabisulfite, S2052-) of alkali metal or ammonium have given

interesting results.

  Among the alkali metals, sodium has given excellent results.

  It is preferable to use a concentration of the sulfur compound of at least millimoles per kg of starchy phase. More preferably, the concentration of the sulfur compound is at least 10 millimoles per kg of starchy phase. Likewise, it is preferable to use a concentration of the sulfur compound not exceeding 100 millimoles per kg of starchy phase. More preferably, the concentration of the sulfur compound does not exceed 60 millimoles per

kg of starchy phase.

  The incorporation of the sulfur compound into the composition can be carried out according to any process known to those skilled in the art. A particularly simple process to implement consists of incorporating it, if necessary, into the liquid additives of the starchy phase (plasticizers and / or aqueous solutions of compounds

  facilitating the use of starch).

  The composition may also include a coupling agent, sometimes also called a compatibilizing agent. This coupling agent can be any, but it is however preferable to use one or more coupling agents chosen from polyolefins modified by grafting of maleic anhydride and the copolymers and terpolymers of olefin and maleic anhydride. The terpolymers of ethylene, maleic anhydride and acrylic esters gave very good

results.

  The content of coupling agent (s) generally represents at least 0.5%

  and preferably at least 1% by weight of the composition.

  On the other hand, this content does not generally exceed 30% and, from

  preferably, does not exceed 20% by weight of the composition.

  The composition can also comprise certain usual additives, such as lubricants, stabilizers, pigments, dyes and mineral and / or organic fillers. The composition allows, in a particularly advantageous manner, the manufacture of articles having advantageous characteristics such as, in particular, their absence of yellowing or browning and their weldability by

high frequency current.

  Another object of the invention is, therefore, the use of the composition as

  as described above for the manufacture of an article.

  This manufacturing can be carried out by any method, and can particularly comprise at least one injection, extrusion, coextrusion or calendering step; for example an extrusion-blowing, extrusion-coating step,

  flat die extrusion or related coextrusion techniques.

  Another object of the invention is still an article comprising at least one

  layer consisting essentially of a composition as described above.

  For example, the article may comprise at least one layer of any kind, in particular based on thermoplastic material, and a layer

  essentially consisting of a composition according to the invention.

  The article concerned by the present invention can be of any kind. he can

  be, for example, in the form of a hollow body or a flat product.

  In the case of a flat product, the film or sheet is preferred.

  Said article can be used in various fields. It can be, in particular, an article intended for the fields of packaging, stationery or leather goods. The following practical examples illustrate the invention without limitation (Examples 1R, 4R, 6R and 8R are references, not in accordance with the invention).

IR example

  An internal mixer (type GK5 from the firm WERNER & PFLEIDERER), rotating at 70 rpm. and whose piston pressure is 3 kg / cm2, is used to melt and make macroscopically homogeneous a mixture comprising: 27 parts by weight of native wheat starch, 3 parts by weight of sorbitol, 3 parts by weight of glycerin, 4 , 5 parts by weight of an aqueous solution containing 33% by weight of sodium lactate and 10% by weight of sodium chloride (this solution and the glycerin are mixed before their introduction into the overall mixture),, 5 parts by weight of low density linear polyethylene (LLDPE) ESCORENE type LLN 1004 YB (density: 0.918 g / cm3, MI: 2.8 dg / min. at 190 C and under 2.16 kg), 9 parts by weight of polyethylene low density (LDPE) ESCORENE type LD 100 BW (density: 0.922 g / cm3, MI: 2.0 dg / min. at 190 C and under 2.16 kg), 3 parts by weight of ethylene terpolymer - acrylate butyl maleic anhydride LOTADER type 3210 (91% by weight of ethylene, MI:, 0 dg / min. at 190 C and under 2.16 kg). -6- To this mixture are added another 2 phr of Ca stearate and 1.3 phr of

  LOXIOL G70 lubricant to reduce grip.

  This material is brought to a temperature between 150 and 155 C in less than 3 minutes in this mixer. It is then transferred to a roller mixer (open mixer) of the BERSTORFF brand, conditioned at 130 ° C., with a surface speed of the front and rear cylinders being respectively 21.6 and 25.1 m / min. and an air gap adjusted so as to obtain a pancake 3 mm thick. A sample is taken periodically during this mixing in order to follow

color evolution.

  In this case, the sample taken after 5 minutes of mixing and

refri-oidi is yellow-brown.

Example 2

  The above test is repeated by adding 0.024 parts by weight of sodium bisulfite (NaHSO3) per 100 parts of the overall mixture, ie 6.15 millimoles per kg of plasticized starch (that is to say of starchy phase ). To do this, the bisulfite of

  sodium is added to the premix of glycerin and the aqueous solution.

  The product is not colored when the internal mixer is unloaded and very weakly colored (after cooling) after 5 minutes of mixing on the cylinder mixer. After 10 minutes of this treatment, the color of the sample taken and cooled is similar to that of the sample of example IR, 1 taken

after 5 minutes.

Example 3

  Example IR is repeated by adding this time, in the same way, 0.163 parts of sodium bisulfite per 100 parts of the overall mixture, ie 42.3 millimoles per kg of plasticized starch. After 20 minutes of mixing on the roller mixer, the color of the cooled material did not change significantly.

Example 4R

  Example 3 is repeated (except for the fact that the concentration of LOXIOL G70 is reduced to 0.4 pcr) by first replacing the sodium bisulfite with 0.163 parts of urea, then with 0.163 parts of aspartic acid, then with 0.163 parts of ammonium chloride, and then with 0.244 parts of cysteine. No decrease

  visible from yellowing occurs with respect to the IR example.

- 7-

Example 5

  In 0.1 parts of the composition of Example IR (apart from the fact that the concentration of LOXIOL G70 is reduced to 0.4 pcr), 0.13 parts are incorporated (according to the same procedure as for Examples 2 and 3). sodium bisulfite, or 33.6 millimoles per kg of plasticized starch. The composition is then used on a pilot calendering line comprising the internal mixer described in Example IR, the open mixer described in Example 1R and a 4-cylinder grille of the OLIER brand to produce films of 150 gtm d 'thickness. The operating conditions of the internal mixer and of the open mixer are maintained as in Example 1R. For the grille, the temperatures of

  cylinders 1, 2, 3 and 4 are respectively 141 C, 141 C, 137 C and 128 C.

  The speed differences between each pair of successive cylinders are equal to 10%, 10% and 13%. The average residence time of the material at high temperature (between 135 and 155 C, in the two mixers and on the calender) is 7 minutes. The line speed, measured at cylinder 4, is 6 m / min. The film obtained remains

colorless after cooling.

Example 6R

  Example 5 is repeated, with the exception that sodium bisulfite is not added. The films obtained are brown to beige, with a tint varying according to the

  residence time in the open mixer.

Example 7

  A mixture is produced comprising - 26.5% (by weight) of waxy maize starch partially hydrolysed by the acid route (FLUITEX 880), - 10.5% of a mixture of sorbitol (3%), glycerin (3% ), water (2.5%), sodium lactate (1.5%), and sodium chloride (0.5%), - 3.0% of LOTADER 3210 terpolymer, - 60% of linear low density polyethylene DOWLEX 2035E (density: 0.919 g / cm3, MI: 6.0 dg / min. At 190 C and under 2.16 kg), 0.13 parts (by weight) of sodium bisulfite per 100 parts of the components

  previous (i.e. 33.6 millimoles per kg of plasticized starch or starchy phase).

  This material is kneaded for 10 minutes in an internal laboratory mixer BRABENDER W50, conditioned beforehand at 150 ° C., with a rotation speed of 50 revolutions / min. and 75 rpm. for the slow cam and the fast cam (respectively) and under a closing pressure of 1 kg / cm2. The final temperature of the mixture reaches 159 C. A sample of this material is then brought to 140 C for 21/2 min. , then subjected to a pressure of 75 bars, at the same temperature, for 21/2 min. to obtain a film 250 gm thick. After cooling to room temperature, maintaining the

  same pressure, the film is not colored.

Example 8R

  The formulation of Example 7, without adding sodium bisulfite, provides a

  yellow-brown film after the same thermomechanical treatment.

-9-

Claims (7)

CLAIMS I - Composition comprising a thermoplastic material and a starchy phase, characterized in that it also comprises at least one sulfur compound in the +4 oxidation state.   2 - Composition according to claim 1 wherein the sulfur compound is bisulfite or pyrosulfite of alkali metal or ammonium.   3 - Composition according to any one of the preceding claims in   which the concentration of the sulfur compound is at least 5 millimoles per kg of starchy phase.   4 - Composition according to any one of the preceding claims in   which the concentration of the sulfur compound is at most 100 millimoles per kg of starchy phase.   - Composition according to any one of the preceding claims in   which the thermoplastic material comprises at least one polyolefin.   6 - Composition according to claim 5 wherein at least one polyolefin is a polyethylene.   7 - Composition according to any one of the preceding claims   further comprising a coupling agent.   8 - Use of a composition according to any one of claims   for the manufacture of an article.   9 - Article comprising at least one layer consisting essentially of a   composition according to any one of claims 1 to 7.   - Article according to claim 9, in the form of film or sheet.