EP2553012A2

EP2553012A2 - Novel thermoplastic composite material

Info

Publication number: EP2553012A2
Application number: EP11730996A
Authority: EP
Inventors: Laurent Bedel
Original assignee: Norske Skog Golbey SAS
Current assignee: BEDEL, LAURENT; Norske Skog Golbey SAS
Priority date: 2010-03-26
Filing date: 2011-03-25
Publication date: 2013-02-06
Also published as: FR2957927B1; US9334397B2; US20130245193A1; WO2011117484A2; FR2957927A1; WO2011117484A3

Abstract

The present invention relates to the field of thermoplastics, the synthesis thereof and the use thereof. It describes in particular the integration of light ash resulting from the combustion of waste from the paper-making industry into thermoplastic matrices. It describes in particular the manufacture and use of novel thermoplastic composite materials containing a thermoplastic resin and light ash resulting from the combustion of waste from the paper-making industry. The present invention also describes a novel filler material capable of being combined with a thermoplastic resin in the manufacture of a thermoplastic composite material.

Description

NEW THERMOPLASTIC COMPOSITE MATERIAL

The present invention relates to the field of thermoplastic materials, their synthesis and their use. It notably describes the integration of light ash resulting from the combustion of production waste from the paper industry into thermoplastic matrices. In particular, it describes the manufacture and use of novel thermoplastic composite materials containing a thermoplastic resin and light ash from the combustion of production waste of the paper industry. The present invention also discloses a novel filler material capable of being combined with a thermoplastic resin in the manufacture of a thermoplastic composite material.

A thermoplastic composite material, also called thermoplastic composite, is typically formed of a thermoplastic base resin also called thermoplastic matrix, one or more fillers and, optionally, one or more plasticizers and additives. The thermoplastic base resin consists of crude polymers, copolymers or polymer blends. The charge or fillers are typically used in the form of powder and intended to reduce the cost of manufacturing the parts to be manufactured or to improve certain mechanical properties. The filler may be of mineral origin (talc, clay, kaolin, silica, etc.), organic (wood flour, fruit bark flour, cellulose pulp, starch, etc.), or metallic (glitter powder aluminum, copper, zinc, etc.); the filler may also be fibrous (glass fiber, basalt fiber, carbon fiber, etc.), non-fibrous (glass beads or equivalent) or else intended to promote recycling (clay, cereals, flax, etc.). The charge is generally present in large or very large quantities; it can even be largely in the majority. The plasticizer (s) are present in a variable quantity according to the nature of the thermoplastic matrix. Examples of plasticizers include phthalates, adipates, phosphates, polyesters, etc. The additives are generally intended to modify a specific property of the thermoplastic material and are present in small amounts.

There are many materials, including thermoplastic materials, whose synthesis provides the use of ash of different kinds as a load. Indeed, ashes are bulky, inexpensive materials, resulting from the combustion of different raw materials and / or secondary, and often considered as waste therefore not exploited. In addition, said ashes are generally produced in large quantities. Indeed, other materials commonly used as a filler such as talc or kaolin are expensive because they require extraction and treatment before use.

Patent application WO 1998/042779 describes a composition based on black ash and a thermoplastic polymer and its potential uses. Black ash is a by-product of the chemical pulp industry. The residues forming this black ash are saline residues from the combustion of black liquors generated by the production of chemical pulps. According to the applicants themselves, these residues are considered environmentally hazardous, particularly because of their high sodium sulphide content, the hydrolysis of which can lead to the formation of hydrogen sulphide which is commonly considered a poison broad spectrum with a toxicity threshold of 14 mg / m ³ (International Program for the Safety of Chemical Substances). In this thermoplastic composition, black ash is used as swelling agent, filler or stabilizer. In addition, this black ash with a high level of salt residues is sensitive to moisture (hydrolysis of salts) and chemically reactive. This specific behavior is also put forward by the applicants who describe the reaction of the carbonate salts present with an acid (tartaric or citric acid) leading to the formation of a release of carbon dioxide. This release of carbon dioxide allows the expansion of plastics in the molten state thus leading to foam parts whose structure is not homogeneous. This inevitably affects the mechanical properties of these plastics. It should be noted that a release can also be obtained without using the use of acid. Indeed, carbonates can degrade thermally and generate carbon dioxide. For use of this material in the field of plastics, the formation of cells can be an advantage if the objective is the search for relief. Most often, the formation of cells is a disadvantage because of a degradation of the mechanical properties of the part and its appearance with bubbles visible to the naked eye. Moreover, during their use for the manufacture of objects or materials, the thermoplastic materials are heated beyond their threshold of plasticization. This very generally results in a release of water more or less in the form of water molecules trapped in the polymer network. The black ash described by applicants containing a large proportion of chemically reactive salts, hydrolysis thereof is expected. This will inevitably generate reactive compounds capable of degrading the thermoplastic resin according to the invention described by the applicants. This composition based on black ash and thermoplastic polymer therefore has many disadvantages including the reduction of its mechanical properties and its aesthetic quality due to the presence of cells, as well as the risk of production of toxic compounds.

Patent FR 75 01268 describes a structural material made of a mixture of at least one thermoplastic resin and at least one filler of mineral and / or organic nature. The weight share of the load is at least equal to the weight share of the thermoplastic resin in the total mixture. The thermoplastic material contains low density polyethylene alone or in combination with other thermoplastics. This invention particularly describes the incorporation of various wastes industrial waste incineration plants, including ashes, as fillers in this thermoplastic material. The ashes described here are from the combustion of household waste (organic materials, plastics, etc.) unsorted and therefore of all kinds. As detailed above, these ashes are therefore likely to give rise to different chemical reactions that can lead to an alteration of the mechanical properties and aesthetic qualities of the thermoplastic material thus obtained.

The patent application WO 2005/072188 describes a polymer composite material containing, among other things, ash from the combustion of coal, as a filler. The ashes described are indifferently light in nature or heavy in that the desired properties are those of an inorganic material in particulate form. Again, these ashes are likely to give rise to different chemical reactions that can lead to an alteration of the mechanical properties and aesthetic qualities of the thermoplastic material thus obtained. US Pat. No. 6,916,863 and US Pat. No. 6,695,902 describe composite polymers containing fillers of two different natures, at least one of which consists of ash resulting from the combustion of coal and of a given particle size distribution. All these patents use only ash from the combustion of coal and do not describe any other nature of ash because the desired properties are only filling properties or grain size.

The patent application WO 2008/094529 describes composite materials based on thermoplastic polymer resins combined with natural mineral fillers including volcanic ash or ash from the combustion of coal. Composite materials exhibit increased mechanical performance especially in terms of flexural properties and thermal stability. Preferred resins are polyolefins. Volcanic ash contains in particular fine particles of rocks and minerals, but also metal particles. As mentioned above, the nature of the ashes described by this patent application is particular and is likely to give rise to different chemical reactions that can lead to an alteration of the mechanical properties and aesthetic qualities of the thermoplastic material thus obtained.

Finally, US Pat. No. 5,759,258 describes the recycling of mineral pigments resulting from the combustion of de-inking sludge. It details in particular the use of ash resulting from the combustion of de-inking sludge which is collected and then dissolved in water in the presence of calcium hydroxide (Ca (OH) ₂ ). This results in obtaining a sludge containing ash in which is then circulated a gaseous mixture containing carbon dioxide. This results in the formation of precipitated calcium carbonate (PCC). This PCC is likely to be reused in the manufacture of recycled paper as a mineral pigment. It is not intended to use these as fillers in the production of thermoplastic composites. In addition, this process involves an integrated recycling system for sludge combustion, ash collection, sludge production and treatment.

The present invention describes the use of particular ashes which are light ash from the combustion of production waste of the paper industry. In fact, the paper industry produces different types of paper pulp used as a base for different types of media such as newsprint, cardboard, printing and writing paper, etc. In general, the preparation of paper pulp consists in isolating cellulosic fibers contained in hardwood and softwood or other ligneous plants (for example wheat straw, kenaf, bagasse), while preserving as much as possible their mechanical properties. To do this, there are two main processes that produce two main types of paper pulp: chemical pulp and mechanical pulp. The mechanical pulp is obtained by separating the wood fibers by a mechanical action. Abrasive grinding wheels (also known as shredders) are used to grate wood logs previously debarked, or discs equipped with plates structured in rotation between which pass calibrated wood chips from the debarking and cutting of logs. This represents the stage of refining the wood. In order to reduce the energy consumption and the mechanical degradation of the wood fibers, it is possible to add to this procedure before refining a preheating phase of the platelets with steam. The function of the steam is to soften the lignin that constitutes the cement of the wood fibers. The separation of the cellulosic fibers and the lignin is thus carried out with a minimum of damaged fibers. This produces a thermomechanical pulp (TMP) having improved mechanical characteristics. If, in addition to the steam, chemical agents such as sodium hydroxide (NaOH) and sulfur dioxide (SO ₂ ) are introduced, chemo-thermomechanical pulp (CTMP) is obtained. Mechanical pulp is mainly used for the manufacture of low-resistance products such as newsprint and some cardboard. Chemical pulp is made by burning wood at high temperatures in chemical digesters to dissolve lignin and release cellulose fibers. Chemical paper pulps are used for the manufacture of papers that offer high mechanical strength such as printing and writing papers, papers for sanitary and domestic use and some paper and cardboard packaging.

The production of newsprint generally involves the use of mechanical or thermomechanical pulp and / or deinked pulp from the recycling of old newspapers, magazines or advertisements. These old newspapers, magazines and advertisements come from the selective sorting of household collection and / or industrial collection formed by printing waste and unsold press. This sorting is done by specialized companies. In the activities of the plaintiff, the recovered papers typically represent 60% of the raw materials used for the production of newsprint. On average, this rate is higher in Europe and Asia. Recycling paper recovered in white paper is done by implementing a process in different stages, the most of which important is the separation of the ink from the mixture constituted by the cellulosic fibers and the mineral fillers. This separation step or deinking step essentially consists of suspending the cellulose fibers in water and a deinking step for the removal of inks and dyes. In Europe, the most used de-inking process is the flotation deinking process, and in the American continent, the washing deinking process is the most common. Whatever the process used, at the end of the deinking procedure inks, dyes, cellulose fiber residues and mineral fillers form sludge. The flotation process has a relatively low yield in that it causes the loss of a very large amount of material, of the order of 20%, which represents up to 148,000 T / year. This sludge is thickened to a dryness of 67%. Once isolated and dried, the dry content of these sludges consists of 50% mineral fillers (carbonates, talc, kaolin, silicates, titanium oxides ...) and 50% organic matter in the form of fibers and Cellulosic fragments as well as latex, polymers, etc. These sludges are called de-inking sludge. This dry matter, considered as a terminal waste of the paper industry, is generally used as fuel. One of the principles of recovery of these de-inking sludge is therefore the exploitation of their thermal properties. However, the combustion of these de-inking sludges leads to the production of two main residues: the secondary ash which is dense or coarse ash removed at the beginning of the flue gas circuit, and the primary or light ash which is separated from the flue gas by through a filter. In fact, to increase the lower calorific value of the de-inking sludge, and thus facilitate their incineration, it can be added to them bark and wood end-of-life crushed, or even natural gas. These additional fuels have little influence on the nature of the light ash obtained after combustion of the deinking sludge. Indeed, their combustion produces denser ash that is easily separated from light ash by systems well known to those skilled in the art. By Moreover, the fuel mixture described above can also be supplemented by sludge from the wastewater treatment plant of paper production site, and this has no impact on the quality of the light ash obtained. Indeed, the composition of these sludges from the purification plant of the papermaking plant is very close to that of the deinking sludge. The combustion of these mixtures leads to the production of heavier ashes and also to the production of bottom ash which is a very heavy and non-combustible combustion residue consisting of ferrous and non-ferrous waste.

The Applicant is particularly interested in light ash having a regular geometry from the combustion of waste production of the paper industry, especially de-inking sludge, and has shown a significant improvement in the qualities of a material. thermoplastic containing said ash. The present invention describes the integration of light ash having a regular and spherical geometry, resulting from the combustion of production waste of the paper industry as a filler in thermoplastic matrices. The present invention more particularly describes the integration of light ash having a regular and spherical geometry, resulting from the combustion of de-inking sludge as a filler in thermoplastic matrices. Indeed, it has been surprisingly observed that the integration of light ash having a regular and spherical geometry according to the invention makes it possible on the one hand to increase the mechanical properties of the thermoplastic matrix thus formed, but also to modify its rheological properties by providing additional fluidity in the molten state. This use also makes it possible to transform the ultimate waste of the paper industry into a secondary raw material.

In the present invention, the term "de-inking sludge" is pure de-inking sludge as described above, or a fuel mixture containing a significant proportion of de-inking sludge from the paper industry; said fuel mixture being contain other sludge from a wastewater treatment plant in the paper industry as well as bark and wood residues. The deinking inks of the present invention will typically contain from 60% to 100% de-inking sludge and from 0% to 40% other fuels.

The light ash used in the present invention is obtained by burning a fuel mixture containing deinking sludge at a minimum temperature of 850 ° C for two seconds to prevent the formation of dioxins. These particular conditions cause a physical and chemical transformation of the mineral charges of the fuel, and in particular a decarbonation. These light ashes have no reactivity due to the presence of carbonates. In addition to leading to a very significant decrease in the chemical reactivity of ash, particularly because of the decarbonation described above, the very high temperature used in the incineration cycle also leads to a change in the morphology of fly ash. issued. Indeed, these light ashes have a regular and spherical geometry. The combination of this particular geometry and the particle size of the ashes is responsible for the surprising rheological behavior changes of the molten polymers obtained from said ashes. A scanning electron microscope (SEM) photograph of light ash according to the present invention is reproduced in FIG. 6. It has been established by our researchers that the small size of ash particles and their spherical morphology induced by a heat treatment at very high temperature allow them to be placed between the polymer chains and thus to act on them. as the balls of a ball bearing when the polymer matrix (or base resin) is in the supercooled state and subjected to shear stresses. This is detailed in Example 4 below. The light ashes used in the present invention have a regular and spherical shape.

The present invention relates to a thermoplastic composite material containing a thermoplastic base resin combined with light ash of regular and spherical shape, from the combustion of production waste in the paper industry. In a preferred embodiment, the present invention describes a thermoplastic composite material containing a thermoplastic base resin combined with light ash of regular and spherical shape, resulting from the combustion of deinking sludge.

The thermoplastic composite materials according to the invention have as a base resin a thermoplastic resin selected from polyolefins (polypropylene (PP), polyethylene (PE), etc.), polyamides (PA), ethylenic polyterephthalates (PET) and butylenic ( PBT), polycarbonates (PC), phenylene polyoxides (PPO), polyoxymethylenes (PO), polyamide-imide (PAI), polyetherimide (PEI), polyether-sulfone (PES) and polyether- ether-ketone (PEEK). These thermoplastic resins are used in the molten state and are therefore likely to flow under the action of a stress, particularly mechanical stress. This allows their shaping by means of techniques well known to those skilled in the art such as thermoforming, extrusion or injection molding.

In a particular embodiment, the thermoplastic material according to the invention contains a filler consisting of light ash at a rate of 1% to 99% by weight, preferably 10% to 50% by weight and even more preferably at a rate of 30% to 40% by weight. % by mass.

The nature of the base resin used for the manufacture of the thermoplastic material according to the invention is determined according to the object to be produced, the technique to be used or production criteria such as the production yield. Depending on the use for which the thermoplastic composite material according to the invention is intended, the latter preferably contains a base resin which is a polyolefin. In fact, the thermoplastic materials based on polyolefins have very interesting properties such as a high chemical inertness and a high hydrophobicity. These qualities allow their common use in the food industry. Among the polyolefins, a particular embodiment of the The present invention uses polypropylene (PP) as a thermoplastic resin and a preferred embodiment uses polyethylene (PE).

In another embodiment, the thermoplastic composite material according to the invention contains a base resin which is a polyamide (PA). Polyamides are very common especially in textile fibers, for example nylon, but also for the manufacture of various plastic objects.

Figures 1 to 6 illustrate the particular mechanical and rheological properties of composite materials according to the invention. The results of the corresponding experiments are described in the examples below.

Fig.-1 describes a granulometric analysis of the light ash used for the realization of the samples that will be tested for their mechanical and rheological properties.

Fig. 2 describes the evolution of the tensile modulus of the composite materials according to the invention as a function of their light ash content.

Fig. 3 describes the evolution of flexural modulus of the composite materials according to the invention as a function of their content of light ash.

Fig. 4 describes the evolution of the melt flow rate MFR of the composite materials according to the invention as a function of their content of light ash.

Fig. 5 illustrates the evolution of the complex dynamic viscosity (Eta *) of composite materials according to the invention as a function of their content of light ash.

Fig. Figure 6 shows a scanning electron microscope (SEM) photograph of the light ashes used in the present invention.

The thermoplastic composite material according to the invention can be manufactured industrially according to methods well known to those skilled in the art. An example of a standard manufacturing method is the combination of polymeric resin or matrix with the filler, and optionally the other constitutive elements such as the plasticizer (s) and / or the additive (s), by a mixing means commonly used in the plastics industry such as Banbury® mixers or kneaders . The filler is in the form of ash and the polymeric resin is in the form of powder, flakes or granules. The temperature at which the mixing operation is carried out is adapted according to the resin used and the possible presence of plasticizers and / or additives. Once the mixture is homogeneous and the different ingredients evenly distributed in the mixture, the material can be exploited. The thermoplastic material obtained is used in the molten state in an extrusion or injection step for example.

The improvement of the properties of the thermoplastic composite material according to the invention essentially relates to the increase in melt flowability. This allows in particular to produce very thin plastic parts and / or very small because the shear stresses are reduced. This also allows a productivity gain because a better fluidity makes it possible to produce parts of constant section more quickly. The present invention also has the advantage of making it possible to increase the melt flowability of recycled polymers. Indeed, recycled polymers generally have very low fluidity indices and this is a major problem in the context of industrial recovery of these recycled polymers. The shrinkage performance observed during molding steps are also improved with the thermoplastic composite material according to the invention. This is illustrated in Example 1 below. The melt fluidity is characterized by an index called MFR (for "Melt Flow Rate") which corresponds to the flow rate in the molten state. This index is expressed in g / 10 min at a given temperature and under given mechanical stress (weight of 2.16 kg). For polypropylene (PP) this temperature will typically be 230 ° C. Under these conditions, virgin Borealis® PP BH345MO resin has a MFR of 45 g / 10mn. With light ashes having a particular geometry and resulting from the combustion of de-inking sludge as a filler, the thermoplastic composite material thus formed will have a higher MFR under the same conditions of experimentation. This is due on the one hand to an increased density because the ashes are heavier than the plastic, therefore to equal volume a mass of larger material will be passed, and on the other hand, to the plasticizing properties of the ashes that contribute to a plasticization melted medium. This latter effect can also be observed with glass microbeads as a filler.

The present invention also relates to a filler for thermoplastic composite material, consisting of light ash from the combustion of production waste of the paper industry, in particular de-inking sludge.

In a particular embodiment, the filler is present in a proportion of 1% to 99% by weight in the thermoplastic composite material, preferably from 10% to 50% by weight and ideally from 30% to 40% by weight.

Thermoplastic composite materials according to the invention are intended for the manufacture of plastic materials or plastic objects by all techniques known to those skilled in the art and in particular the injection-molding, or possibly 1 extrusion.

These new thermoplastic composites with increased melt flow make it possible to produce workpieces with increased productivity. Moreover, these new materials also make it possible to produce parts having very thin thicknesses and also to make injection-molding transformable thermoplastic resins in a natural state, constituted in particular by recycled polymers.

The thin plastic parts are made in molds whose walls interact with the thermoplastic material filling it. The flow therein of molten thermoplastic material generates shear stresses which, when the walls are very close together, as in the particular case of the molds for the production of fine parts, can become sufficiently large to damage the polymer resin by degrading the length of the macromolecular chains. To limit the consequences of this phenomenon, it is obvious for those skilled in the art to find the most fluid thermoplastic materials possible or to significantly lower the injection speeds and increase the temperature of the mold. The implementation of these last two actions induces a considerable increase in the cycle time, thus limiting the technical and economic attractiveness of this option.

Recycled polymers, also called regenerated polymers, are generally not very fluid because of the mixing of different grades of a polymer of the same kind. Polypropylene, for example, has a melt index (MFI) ranging from 0.1 to more than 50. A recycled polypropylene generally has a low fluidity, of the order of 4 to 10. The addition of light ash from of the combustion of production waste of the paper industry and in particular de-inking sludge according to the invention, makes it possible to increase the fluidity of regenerated polymers and thus to give them operating capacities comparable to those of the virgin matrixes. more efficient.

When combined with matrices dedicated to injection molding, light ash from the combustion of production waste from the paper industry, and in particular de-inking sludge, makes it possible to obtain a highly fluid thermoplastic composite material which allows the production of larger pieces; and that by force of constant closing of press. Indeed, the increased fluidity allows filling of the mold in a shorter time than the time required for cooling the material. In addition, the presence of light ash according to the invention gives the thermoplastic composite material a greater rigidity. As a result, the large parts made of this material have a greater geometric stability. The presence of light ash of regular and spherical shape resulting from the combustion of production waste from the paper industry and in particular deinking sludge dispersed in the thermoplastic matrix thus makes it possible to ensure a better dimensional stability of the parts produced.

Moreover, the thermoplastic material according to the invention makes it possible to increase the productivity during the production of parts made of thermoplastic material. Indeed, there is a significant productivity gain during the implementation of the injection-molding technique in particular. The cycle time required for molding a piece of a given weight is decreased. In addition, the number of parts injected to obtain a thousand pieces without defects and the time required to obtain said thousand pieces are both significantly reduced. The defects observed are generally related to a problem of complete filling of the mold. The thermoplastic material according to the invention has improved rheological properties, therefore it presents less problem of filling the complete mold. An example of such productivity measures is illustrated by Example 3 and the values in Table 2.

Finally, the presence of light ash from the combustion of production waste in the paper industry and in particular of de-inking sludge considerably limits the mold release. This means that during the molding of plastic parts such as plates, the thermoplastic composite material will retract while cooling, which will cause a shift between the dimensions of the mold and the dimensions of the object thus molded, this physical phenomenon is called phenomenon withdrawal. With a thermoplastic composite material according to the invention, shrinkage decreases significantly. Therefore, it is possible to use all types of molds and not just molds for thermoplastic materials. This property is particularly interesting in the case of the use of polyolefins which naturally have a significant shrinkage. An example of such withdrawal measures is illustrated by Example 1 and the values in Table 1. The present invention also relates to a process for obtaining light ash of regular and spherical shape from the combustion of production waste of the paper industry for the manufacture of a thermoplastic material having improved rheological properties. The method for obtaining light ash comprises the following steps:

- select a mixture of fuels from the paper industry containing de-inking sludge,

- burn this mixture at a minimum temperature of 850 ° C for 2 seconds,

harvest the light ashes using a filter or sieve.

The fuel mixture according to the present invention typically contains de-inking sludge in a majority amount, and additional fuels in the form of other sludges from sewage plants and bark and end-of-life wood which are ground. Any other type of additional fuel is usable in the context of the present process. The fuel mixture according to the invention contains from 60% to 100% of de-inking sludge and from 0% to 40% of other fuels from the paper industry.

Harvesting light ash is no problem for those skilled in the art who will implement appropriate procedures such as the introduction of filters or sieves.

The present invention also describes a process for recycling waste from the paper industry. Indeed, as mentioned above, the invention makes it possible to transform the ultimate waste of the paper industry into a secondary raw material. This secondary raw material is likely to serve as a load in the manufacture of thermoplastic composite materials.

Waste recycling is a major industrial issue from an ecological, economic and technical point of view. In the industrial field, the paper industry is considered to be an industry producing large quantities of waste in the form of sludge, including de-inking sludge, bark and debris. Of wood. While bark and wood debris are frequently used as fuel both on-site and in other industries, sludge is not exploited to a large extent. These sludges are then stored or possibly burned if their nature allows. None of these solutions is technically satisfactory. Indeed, these solutions leave waste in another form and / or they consume energy. The possibility of transforming sludge production waste, especially de-inking sludge, into a raw material, therefore solves a thorny problem for the paper industry, which will thus be able to develop new types of exploitation.

For this purpose, the present invention describes a process for recycling sludge from the paper industry, comprising the following steps:

to transform sludge from the pulp and paper industry into light ash by combustion;

harvesting said light ashes with a filter or a sieve;

- Incorporate the light ash thus obtained in a thermoplastic composite material.

The transformation into light ash can be carried out by the method described above, namely by combustion of said sludge at a minimum temperature of 850 ° C for 2 seconds. Any other process for obtaining chemically inert ash is also acceptable. Thus, in a preferred embodiment, the present invention relates to a process for recycling sludge from the paper industry, comprising the following steps: converting the sludge from the paper industry into light ash of regular and spherical shape by combustion in the paper industry. a minimum temperature of 850 ° C for 2 seconds, collect said ash with a filter or sieve, and then incorporate the light ash thus obtained in a thermoplastic composite material.

The incorporation of light ash of regular and spherical shape thus obtained into a thermoplastic composite material is made by a simple mixture or any other technique known to those skilled in the art for the manufacture of such a thermoplastic composite material.

This process allows sludge recycling on the site of production and subsequent exploitation of the light ash thus formed. Sludge therefore no longer has to be stored which represents a major advantage both ecologically and economically.

The properties of the thermoplastic composite material according to the invention will be described in more detail in the following examples. These examples are in no way limiting.

Example 1

Obtaining a thermoplastic composite material

The light ash resulting from the combustion of de-inking sludge is incorporated in a proportion of 30% by weight to a thermoplastic resin based on polypropylene (Boréalis® BH345MO). The mixture is produced using a corotative twin-screw extruder of the Clextral® BC21 type (length 900 nm, sheath diameter 25 mm, spacing 21 mm). A standard screw profile for the assembly of mineral fillers with propylene is selected. The temperature is increased to 200 ° C at the extruder head.

This integration of light ash in a polypropylene-based resin results in a gray coloring of the thermoplastic matrix. Thermoplastic rods are formed through a suitable grid. These rods are then cooled in air and converted into granules of 2 to 3 mm in diameter.

Injection molding

After drying, the granules obtained are tested by injection molding. The injection molding machine has a maximum closing force of 275 T (Ferromatik Milacron® K-Tec 275). A double cavity test mold is installed to perform rectangular plates. Each rectangular plate footprint has a dimension of 200 x 150 x 4 mm.

Results

The melt flowability of the thermoplastic matrix according to the invention (30% light ash, 70% PP BH345MO) was compared with that of the virgin polypropylene resin (PP BH345MO). It follows from the observation of a decrease in the cycle time required for producing a piece of thermoplastic material according to the invention, under constant operating conditions, that the fluidity in the molten state is increased.

Assessment of withdrawal

The shrinkage during cooling was also evaluated and the results are detailed in Table 1 below.

Table 1: Properties of the thermoplastic matrix according to the invention

It has been observed that if we consider the plate obtained with the thermoplastic material according to the invention, a length of 198 mm and a width of 149 mm are observed from a mold which is 200 mm long and 150 mm wide. . For the plate made with PP virgin resin BH345MO, a length of 194 mm and a width of 146 mm are observed from the same mold.

The shrinkage observed during the cooling of the parts produced is approximately 3% in the case of PP virgin resin BH345MO whereas it is only 1% in the case of the thermoplastic composite material according to the invention. Furthermore, the stiffness of the sheets obtained with the thermoplastic composite material according to the invention is increased compared to that of the plates made with the virgin resin. This reflects an increase in modulus of elasticity.

Example 2

Traction module

The determination of a tensile modulus is based on the analysis of uniaxial tensile characterization results according to ISO 527.

The tensile modulus of the polypropylene used in Example 1 (Borealis® BH435MO) is 1600 MPa.

The tensile modulus of the thermoplastic composite material according to the invention, consisting of a base resin of BH435MO type and charged to 30% by weight of light ash from the combustion of de-inking sludge, is around 3000 to 4500. MPa.

Example 3: Influence of increased fluidity

The present example illustrates the influence of increasing the fluidity of the composite material according to the invention on productivity. Indeed, the increased rheological properties of the composite material according to the invention are capable of increasing the productivity of parts made of thermoplastic material.

The impact of the rheological properties of each thermoplastic material on productivity is measured by performing two sets of one thousand pieces by injection molding. The cycle time required for molding a piece of 500 g is calculated. (polypropylene base), we count the number of parts injected to obtain 1000 pieces without defects and the time necessary to obtain these 1000 parts without defects. The cycle time required for molding a 500 g piece. is given in seconds and the time required to obtain 1000 pieces without defects is given in hours.

Results

Table 2: Properties of the thermoplastic matrix according to the invention

It is found that the cycle time required for the production of a piece of 500 g. injection-molding is inferior in the case of the use of a composite material according to the invention. Indeed, this cycle time goes from 60 sec for a polypropylene thermoplastic material type BH345MO to 46 sec for a thermoplastic material according to the invention.

Moreover, the number of parts injected to obtain 1000 pieces without defects and the time required to obtain these 1000 parts without defects are considerably reduced. The molding defects of the parts are generally due to poor filling of the mold. This poor filling can be caused by a problem of fluidity of the thermoplastic material in the molten state. The thermoplastic material according to the invention having improved rheological properties, this step of filling the mold no longer presents at all or in any case much less problems.

Indeed, the addition of light ash to the polypropylene matrix facilitates the filling of the mold due to increased fluidity. It follows from this greater ease of filling that the number of defective parts by default of complete filling of the mold is considerably reduced from 5.2% to 1.2% on the one hand, and that the time required for molding a unit piece is also reduced from 60s to 46s, a gain of 23%, on the other hand. In addition to the material savings achieved by the limitation of production rejects, the time required to obtain 1000 fault-free parts (integration of the improvement of the cycle time and the limitation of rebuses) increases from 17.5 hours. using virgin polypropylene at 13 hours using the same polypropylene loaded with 30% ash according to the invention, a productivity gain of nearly 26%.

Example 4

I. Composition of analyzed samples

The samples were made from polypropylene homopolymer DOMOLEN 1101s and light ash according to the invention. A granulometric analysis of the light ash is carried out using a MALVERN Mastersizer S granulometer. The results of the particle size analysis are presented in FIG. 1.

The composition of the ashes was verified by X-ray diffraction.

The incorporation of the ashes is carried out by means of a Clextral BC 21 co-rotating twin-screw extruder. The temperature profile increases from 170 ° C to 220 ° C to facilitate the mixing of the materials and is then brought back to 205 ° C. level of the die by means of which a rod is obtained then cooled and finally granulated. The rotational speed of the screws of the extruder is 155 rpm.

Charges of 10%, 20%, 30% and 40% have been achieved. The charge rates were verified by measuring the ash content of the composites after calcination.

II. Mechanical properties of the samples

The composites obtained were compared and characterized with respect to a DOMOLEN 1101S virgin matrix.

The characteristic magnitudes of the tensile, bending and impact resistance behaviors were obtained by respecting the operating protocols of the respective standards NF EN ISO 527-1 "Plastics - Determination of tensile properties - Part 1: General principles" and NF EN ISO 527-2 "Plastics - Determination of tensile properties - Part 2: Test conditions for molding and extrusion plastics", NF EN ISO 178 "Plastics - Determination of bending properties" and NF EN ISO 179-1 "Plastics - Determination of Charpy impact strength - Part 1: Non-instrumented impact test".

A. Modules in traction

Tensile characterization results are shown in Tables 3 to 8.

Table 3: Characterization in traction of virgin polypropylene Domolen 1101S

This is our witness that does not contain light ash. The traction module is on average 1440 MPa. The maximum stress is on average 34.1 MPa and the maximum elongation is 7.9% on average.

Table 4: Characterization in traction of the composite integrating 10% of light ash

These composite materials according to the invention contain 10% light ash. The average tensile modulus is 1700 MPa. The Maximum stress is on average 32.1 MPa and the maximum elongation is 5.4% on average.

Table 5: Characterization in traction of the composite integrating 20% of light ash

These composite materials according to the invention contain 20% light ash. The average traction module is 2013 MPa. The maximum stress is on average 29.4 MPa and the maximum elongation is 4.0% on average.

Table 6: Characterization in traction of the composite integrating 30% of light ash

These composite materials according to the invention contain 30% light ash. The average tensile modulus is 2350 MPa. The maximum stress is on average 25.7 MPa and the maximum elongation is 3.0% on average.

Table 7: Characterization in traction of the composite integrating 40% of light ash

These composite materials according to the invention contain 40% light ash. The average tensile modulus is 2667 MPa. The maximum stress is on average 24.0 MPa and the maximum elongation is 2.2% on average.

These five tables describe the characteristics of each sample relative to a blank light ash blank as to its tensile, bending and impact resistance behavior. It is noted in particular that the tensile modulus of the thermoplastic composite materials according to the invention increases with the light ash content incorporated. This is illustrated in FIG. 2 which shows the evolution of the modulus in traction as a function of the light ash content.

B. Flexural modules

The same samples as in Ά) above were tested for flexural modulus. The results are presented in the tables below.

Table 8: Characterization in flexion of virgin polypropylene Domolen 1101S

For the blank light ash blank, the flexural modulus averages 974 MPa.

Table 9: Characterization in bending of the composite integrating 10% of light ash

A composite material according to the invention containing 10% light ash has a flexural modulus of 1162 MPa on average.

Table 10: Characterization in bending of the composite integrating 20% of light ash

A composite material according to the invention containing 20% light ash has a flexural modulus of 1429 MPa on average.

Table 11: Characterization in bending of the composite integrating 30% of light ash

A composite material according to the invention containing 30% light ash has a flexural modulus of 1721 MPa on average.

Table 12: Characterization in flexion of the composite integrating 40% of light ash

A composite material according to the invention containing 40% light ash has a flexural modulus of 2086 MPa on average.

Conclusion: the flexural modulus changes as a function of the proportion of light ash incorporated in the composite material according to the invention. This is illustrated in FIG. 3 which shows the evolution of flexural modulus as a function of light ash content.

C. Shock resistance

The "Charpy" test is performed on the composite materials containing 10% and 30% light ash according to the invention. The DOMOLEN 1101S control has a Charpy impact strength of 110 kJ / m ² . Table 13: Charpy impact resistance of the composite incorporating 10% light ash

The impact strength of a composite material according to the invention containing 10% of light ash is on average 18.0 kJ / m ² .

Table 14: Charpy impact resistance of the composite incorporating 30% light ash

The impact strength of a composite material according to the invention containing 30% of light ash is on average 8.7 kJ / m ² .

There is therefore a decrease in the impact resistance compared to the blank control of light ash but also according to the light ash content.

Conclusion: The characteristics measured in flexion and in tension show that the addition of ash in the polymer resin increases its rigidity. This increase in stiffness is also reflected in a significant decrease in impact resistance.

III. Rheological properties

The melt flow rate of thermoplastics in bulk (MFR) was measured according to standard NF EN ISO 1133: "Determination of the melt thermoplastic (MFR) and volume (MVR) hot melt index: Method A ".

The evolution of the melt index as a function of the ash loading rate is shown in Table 15 and FIG. 4. The test temperature is 230 ° C and the imposed load of 2.16 kg.

Table 15: melt index as a function of light ash content

The addition of ash in the polymer matrix leads to a decrease in the melt index which reflects an increase in the viscosity of the medium. This result is antagonistic with the observations made during the extrusion and injection molding tests of the composite materials according to the invention described above. In these tests, the fluidity of the composite materials was visibly increased by the presence of light ash. Characterization of the viscosity by determination of the melt flow index (MFR) does not subject (or very little) shear stress to the supercooled material, we proceeded to rheological analyzes by means of a rotational rheometer of ARES type (Advanced Rheological Expansion System, Rheometric Scientific). The rotational rheometer is a mechanical spectrometer capable of subjecting a sample to dynamic (sinusoidal) or stationary (linear) deformation. Depending on the geometry used, the mechanical properties of the material can be determined by measuring the torque resulting from the imposed shear rate.

Table 16 and Figure 5 show the evolution of the complex dynamic viscosity (Eta *) as a function of the rate of charge of the temperature and the angular frequency of shear (1, 10 and 100 rad / s). Table 16

The measurements carried out show that by the addition of energy in thermal form (temperature increase) and mechanical (shear stresses) the light ash used acts as a shear-thinning agent and explains the observations made during the implementation tests.

The small particle size of the ashes as well as their spherical morphology (see photo SEM in Fig. 6) induced by a heat treatment at very high temperature allow them to be placed between the polymer chains and thus to act on them. as the balls of a ball bearing when the polymer matrix is in the supercooled state and subjected to shear stresses.

Conclusion:

The addition of light ash from the combustion of de-inking sludge improves the stiffness of polypropylenes, both in traction and flexion. The increase in these properties will however be limited by a decrease in the impact resistance. A charge rate of the order of 30% will generally be an optimal rate.

In addition to this mechanical reinforcing effect, a shear-thinning effect is observed during the implementation of the composites (by injection molding or extrusion in particular) and confirmed by dynamic rheological analyzes.

Claims

1. Thermoplastic composite material characterized in that it contains a thermoplastic base resin and light ash of regular and spherical shape, said ash being derived from the combustion of production waste of the paper industry.

2. Thermoplastic composite material according to claim 1, characterized in that it contains a thermoplastic base resin and light ash of regular and spherical shape, said ashes being derived from the combustion of de-inking sludge.

Thermoplastic composite material according to either of Claims 1 and 2, characterized in that the light ash is obtained by a process comprising the following steps:

- select a mixture of fuels containing de-inking sludge from the paper industry,

- burn this mixture at a minimum temperature of 850 ° C for 2 seconds,

harvest the light ashes using a filter or sieve.

4. thermoplastic composite material according to any one of claims 1 to 3, characterized in that it is obtained by mixing a thermoplastic base resin and light ash from the combustion of waste production of the paper industry .

5. thermoplastic composite material according to any one of claims 1 to 4, characterized in that its mass contains 1% to 99% by weight of light ash of regular and spherical shape from the combustion of waste production of the paper industry, preferably from 10% to 50% and ideally from 30% to 40%.

6. thermoplastic composite material according to any one of claims 1 to 5, characterized in that the base resin is selected from polyolefins, polyamides (PA), ethylenic polyterephthalates (PET) and butylenic (PBT), polycarbonates (PC), phenylene polyoxides (PPO), polyoxymethylenes (POM), polyamide-imide (PAI), polyetherimide (PEI), polyether sulphone (PES) and polyetheretherketone (PEEK).

7. thermoplastic composite material according to any one of claims 1 to 6, characterized in that the base resin is a polyolefin.

8. Thermoplastic composite material according to claim 7, characterized in that the base resin is polypropylene

(PP).

9. thermoplastic composite material according to any one of claims 1 to 6, characterized in that the base resin is a polyamide (PA).

10. Process for recycling sludge from the paper industry, comprising the following steps:

harvesting said light ashes with a filter or a sieve; incorporating the light ashes thus obtained into a thermoplastic composite material according to claim 1.