A METHOD FOR PRODUCING A COMPOUND COMPRISING A POLYHYDROXYALCANOATE AND CELLULOSE

Abstract

Process for manufacturing a biodegradable compound, said process comprising the steps of, in order: (i) providing an extruder with at least one rotating screw, at least two feeding units suitable for being fed with ingredients, and an extruder die, (ii) feeding the first feeding unit with a PHA polymer and maleic anhydride (MA), (iii) feeding the second feeding unit with cellulosic fibres, (iv) rotating the screw to mix the PHA and maleic anhydride ingredients and graft said maleic anhydride onto said PHA molecules to form PHA grafted with MA (PHA-g-MA) in an amount of 1 to 10%, preferably 1 to 3% of the total content of PHA, and then mixing said PHA-g-MA with cellulosic fibres to form a molten compound of PHA-g-MA and cellulosic fibres, (v) passing said molten compound through said extruder die and shaping said extruded compound into different compound formats.

Claims

1. A process for manufacturing a biodegradable compound, said compound comprising a mixture of cellulosic fibres and at least one type of polyhydroxyalcanoate polymer (PHA), said process comprising the steps of, in order: (i) providing an extruder comprising a heater, at least one rotating screw, at least two feeding units suitable for being fed with ingredients, and an extruder die, the temperature of said extruder being set between 130 C. and 190 C., (ii) feeding the first feeding unit with a PHA polymer and maleic anhydride (MA), wherein the ratio of maleic anhydride to PHA is comprised between 0.1 and 10, (iii) feeding the second feeding unit with cellulosic fibres, said cellulosic fibres being hardwood cellulose fibres having a length of 15 m to 150 m, and having a density of at least 1.0 g/cm3, (iv) rotating the at least one screw to mix the PHA and maleic anhydride ingredients and graft said maleic anhydride onto said PHA molecules to form PHA grafted with MA (PHA-g-MA) in an amount of 1 to 10%, of the total content of PHA, and then mixing said PHA-g-MA with cellulosic fibres to form a molten compound of PHA-g-MA and cellulosic fibres, (v) passing said molten compound through said extruder die, and shaping said extruded compound into, a product selected from the group consisting of: compound pellets, by cutting said extrudate compound cord with a knife system, a compound film or compound plates (in this case, the extruder die takes the form of a cast line), and a compound tridimensional item, by injection moulding or extrusion blow-moulding said extruded compound into a mould.

2. A process according to claim 1, wherein the extruder is a twin-screw extruder.

3. A process according to claim 1, wherein a catalyst is added together with the PHA and the maleic anhydride in the first feeding unit, said catalyst being selected from the group consisting of: dicumyl peroxide (DCP), benzoyl peroxide, dibenzoyl, hydroperoxides and ketone peroxides, and a combination thereof.

4. A process according to the preceding claim 3, wherein the ratio of catalyst to PHA is 0.01% to 5%.

5. A process according to claim 1, wherein a plasticizer is added together with the cellulosic fibres into the second feeding unit, said plasticizer being selected from the group consisting of: beeswax (BW), stearic acid (SA), glycerol monostearate (GMS), and a combination thereof.

6. A process according to the preceding claim 5, wherein the ratio of plasticizer to cellulosic fibre is 0.1% to 10%.

7. A process according to claim 1, wherein said polyhydroxyalcanoate polymer is selected from the group consisting of: poly3-hydroxybutyrate-co-3-hydroxyhexanoate (PHBH), poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV), poly-3-hydroxybutyrate (PHB), poly-3-hydroxyvalerate (PHV), or poly-3-hydroxyhexanoate (PHHx), and derivatives or combinations thereof.

8. A process according to claim 1, wherein the rotation speed of the at least one screw is comprised between 10 rpm and 300 rpm.

9. A process according to claim 1, which further comprises a step of quenching the extrudate compound within a quenching bath.

10. A process according to claim 9, wherein the temperature of said quenching bath (9) is between 5 C. and 50 C.

11. A process according to claim 9, wherein said quenching bath is water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Additional features and advantages of the present invention are described in, and will be apparent from, the description of the presently preferred embodiments which are set out below with reference to the drawings in which:

[0047] FIG. 1 is a schematic diagram view of a manufacturing installation suitable for manufacturing a compound in a process according to the invention;

[0048] FIG. 2 is a diagram view comparing mechanical properties of different compounds comprising: a mixture of non-modified PHA and non-modified cellulose (each 50% of the total), a mixture of non-modified PHA and modified cellulose (each 50% of the total), and a mixture of non-modified cellulose with PHA, a certain fraction of which is grafted with maleic anhydride (PHA-g-MA);

[0049] FIG. 3 is a diagram view comparing mechanical properties achieved by different compounds comprising: a mixture of non-modified PHA (PHBH) with grafted polypropylene (PP-g-MA) and cellulosic fibres, and mixtures of cellulosic fibres with PHA (PHBH), a certain fraction of which is grafted with maleic anhydride in either soluble or powder forms;

[0050] FIG. 4 is a diagram showing comparative mechanical tests for three alternative compounds formed with a process according to the invention (including average value and standard deviation values).

DETAILED DESCRIPTION OF THE INVENTION

[0051] The present invention concerns the compounding of a PHA polymer with cellulosic fibres, particularly with hardwood fibres having preferred length and density characteristics as indicated in the present specification and claims.

[0052] The inventors have discovered that a so-called process of reactive compounding, whereby the PHA polymer is first fed with maleic anhydride into an extruder for grafting of the two to produce a PHA-g-MA, and sequentially thereafter, cellulose fibres are fed in the same extruder for compounding with the PHA-g-MA just produced, is particularly beneficial, not only in terms of industrial and economic efficiency, but also in terms of the improved chemical and mechanical properties of the compound thus obtained.

[0053] As illustrated in the embodiment of FIG. 1, the invention involves a single extruding process with an extruder 1, comprising a casing 2 and a screw 3 located therein. In the embodiment of FIG. 1, the extruder is a dual screw extruder with two screws rotating in opposing directions or in the same direction as indicated with arrows in FIG. 1.

[0054] The extruder further comprises a first feeding unit 4 and a second feeding unit 5. The two feeding units 4, 5 are preferably located at a distance from one another along the extruder length, that is predetermined and sufficient for the ingredients introduced in the first feeding unit to mix properly and react chemically completely inside the extruder, before they reach the location of the second feeding unit. This sufficient time for reaction of the ingredients fed in the first feeding unit can be predetermined appropriately and adjusted depending on the quantities of ingredients. An example of compound preparation is provided in greater details hereafter.

[0055] In the embodiment illustrated in FIG. 1 the second feeding unit comprises a pair of screws 6 for facilitating the introduction of the ingredient towards the extruder. This is particularly helpful when the ingredient is dry, or in a solid particles state which makes it difficult to flow in that case the set of screws facilitates the flow of said ingredient into the extruder.

[0056] When adding fibres in the second hopper, it is possible as alternatives to add the fibres either under the form of fibres or powders, but also alternatively under the form of compressed or pelletized fibres. Furthermore, one can also envisage to use a compatibilizer, and/or wetting or sizing agents.

[0057] The extruder 1 further comprises an extruder die 7 through which a cord 8 of hot extrudate material flows out, in the present embodiment, the extrudate cord is the compound of PHA-g-MA and cellulose fibres that is prepare inside the extruder.

[0058] After flowing out through the die 6, the cord of hot extrudate compound is chilled into a quenching station 9 comprising a water quenching bath (not illustrated in the drawing). The quenching bath is thermoregulated to a temperature of about 20 C., such that the cord of hot extrudate compound which flows out of the extruder in a molten state (i.e. at a temperature which is above the melting point of said compound), reaches a temperature lower than the melting point of the compound within a few seconds. The resulting compound cord comes out of the quenching bath in a solid state, and is then conveyed to a pelletizing station 10. In the pelletizing station 10, the extrudate cord 8 is cut into small pellets 11. The pellets are then packed and can be used as a compound for manufacturing packages with conventional packaging making processes (injection, extrusion-blow-moulding, lamination, compression, etc.).

[0059] In this exemplary embodiment, a PHBH-g-MA is produced as follows: 0.5 g of maleic anhydride (MA), 0.1 g of dicumyl peroxide (DCP), and 9.4 g of poly3-hydroxybutyrate-co-3-hydroxyhexanoate (PHBH) are mixed as grinded powders, or in acetone and subsequently acetone is evaporated. The powder mixture is then fed into the extruder (into the first feeding unit 4, as explained above), and kept in there for 5 minutes (starting when all the material is fed). The temperature of the extruder is set to 175 C.

[0060] After the 5 minutes have elapsed, the extruder is cooled to room temperature. At this stage, a clear color change of the polymer can be noticed, from colorless to yellow, which indicates the formation of PHBH-g-MA (which is of yellow color).

[0061] Prior to compounding with cellulose fibres, the PHBH-g-MA obtained is grinded with liquid nitrogen. Then, cellulose fibres (FC) are introduced into the extruder, through the second feeding unit 5, such that PHBH, FC and PHBH-g-MA are mixed. A lubricant additive (Add.), namely beeswax (BW) is added, the quantity of which is chosen between 3% and 8% by weight of the total compound.

[0062] The processing temperature for the extrusion and hot pressing is set between 175 C. and 180 C.

[0063] Turning to FIG. 2, the inventors have performed a set of comparative mechanical tests for elongation at break, in order to compare various combinations of ingredients and the resulting mechanical properties of the final compound thus obtained. The different alternative formulations tested and reported in FIG. 2 are as follows.

[0064] On the very left-hand side of the diagram, a PHA, not modified with maleic anhydride, is compounded with 50% by weight of cellulose fibers. The resulting compound shows a brittle mechanical behavior, indicated by a low strain in percentage compared to the stress withheld by the material.

[0065] Replacing the cellulose with a chemically modified cellulose (particularly a cellulose modified by AKD reaction according to the technique known in the art), allows to improve compatibility with the polymer, and consequently, the resulting compound displays an increased elongation at break.

[0066] However, the best results are observed (cf. the group of curves in the right-hand side of the diagram) with reactive compounding of PHA with maleic anhydride. In this case, a PHA-g-MA compounded with 50% by weight of the total compound of cellulose fibres, shows the greatest strain in % versus the stress applied to the compound material, i.e. between 2 and 4% of strain for a stress applied which amounts to 300 N.

[0067] As illustrated in FIG. 3, a comparison in strain-stress tests of various compounds in tensile mode, revealed that PHBH-g-MA strongly improves the mechanical behavior of the final compound. For instance, by adding 3% of PHBH-g-MA by weight of the total compound, mechanical properties of the compound thus obtained are increased, versus compounds comprising only unmodified PHBH (not grafted to maleic anhydride) and cellulosic fibres. Whether the beeswax lubricant (BW) is added in solid or solution form does not substantially modify the results.

[0068] From the experiments, it is concluded that the interface between PHBH and cellulose is well mediated by PHBH-g-MA.

[0069] As illustrated in FIG. 4, comparative tests on three different compounds, namely: [0070] PHBH with cellulosic fibres and polypropylene grafted with maleic anhydride (PP-g-MA), [0071] PHBH with cellulosic fibres and PHBH grafted with maleic anhydride (PHBH-g-MA), together with beeswax as lubricant in powder form, [0072] PHBH with cellulosic fibres and PHBH grafted with maleic anhydride (PHBH-g-MA), together with beeswax as lubricant in solution form, [0073] shows that the compounding of PHBH and cellulose fibres with modified PHBH (PHBH-g-MA) improves all the mechanical properties of the final compound, in particular the Young's modulus, the Tensile Strength, and the Elongation at break.

EXAMPLE

[0074] A typical example of a formulation for compounding a modified PHA (especially a PHBH) with cellulose fibres, is given hereafter. The amounts for each ingredient are indicated for each part of the extruder wherein they are introduced: first feeding unit (feeder 1) and second feeding unit (feeder 2).

TABLE-US-00001 Feeder 1 Feeder 2 DCP 0.006 g PHBH 4.8 g MA 0.03 g FC 10 g PHBH 4.564 g BW 0.6 g Total 4.6 Total 15.4

[0075] It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the appended claims.