ES2363076A1 - COMPOSITE MATERIAL. - Google Patents

Abstract

The present invention describes a composite material formed by a plastic polymer and biomass nanoparticles that act as reinforcement. These biomass nanoparticles are alloyed with said plastic polymer, which allows a percentage by weight of said biomass nanoparticles higher than those achieved in the technique. The invention also includes the procedure for obtaining said composite by a solid cryo-milling process, which it avoids the molten state of the polymer and with it the problems of agglomeration of the particles during the mixing. The subsequent shaping of the material is carried out using conventional plastic transformation processes.

Description

Composite material.

Technical sector

The present invention relates to a material polymer matrix composite with a high percentage of biomass nanoparticles The result is a thermoplastic material. strongly reinforced with application in construction, in automotive industry generally for interior parts and in Furniture manufacturing.

Prior art

A composite material is one that combines two or more materials to form a new product in which you can distinguish said original materials. In general, it is called matrix to the base and majority material that you want to transform with the addition of charges or reinforcements, which are minority, that modify and improve its mechanical, thermal, electrical properties, wear, etc.

A type of composite materials or composites they are those of polymeric matrix, either thermoplastic or thermosetting, to which are added reinforcements of different types that can be continuous (woven or nonwoven) or discontinuous, of sizes and variable morphologies. Reinforcements are usually less malleable and provide the composite with greater strength compared to the matrix. The matrix acts as a load transfer through the Different fibers and layers of reinforced material. The best established in the industry for a long time are the fiberglass and carbon fiber composites. Plus recently polymeric fibers have also been incorporated Synthetics such as aramid (kevlar), polyester fibers, etc. The manufacturing processes of these materials are classified based on type of polymer used. For thermostable composites, whose monomers are normally in a liquid state before polymerize and harden, open mold techniques are used in that woven or discontinuous fibers are impregnated with resin well by spray or manually with roller, or closed mold techniques such as resin transfusion (RTM, Resin Transfer Molding) or Infusion techniques by vacuum bag. In the case of thermoplastic composites, first of all, the mixing the polymer with the reinforcement by methods that involve a good dispersion and homogenization, being the most used the twin screw extrusion. The composite polymer blend with reinforcements is then molded by methods known in the technique for thermoplastics, such as injection, blow-molding, extrusion, etc.

They have recently joined the market composites that use biomass reinforcements. He main interest of these materials is that, providing similar properties than traditional composites are more Cheap and environmentally more respectful. Natural fibers such as hemp, linen, cotton, sisal, bamboo, wood or jute are becoming an alternative to conventional fibers of glass, carbon or aramid in use as reinforcement of materials thermoplastics The rapid market growth of this type of Compounds are justified by the advantages they provide; for example, a lower cost of charge particles than others traditional like fiberglass, lower density and reduction significant weight, good soundproofing properties and thermal insulation and environmental aspects since the Natural materials used represent a renewable source and They are biodegradable.

The nature of polymer matrices more used to obtain composite materials with fibers natural are thermoplastics such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), etc., shaped mainly by compression molding and, minority, injection molding.

The manufacturing processes used for Composite materials with reinforcements of natural origin are, in principle, the same as for reinforcements not coming from biomass In the case of thermoplastic composites, and especially when it comes to small reinforcements, it is very difficult to obtain a good dispersion in the molten polymer, since particle agglomerations occur. This is because fundamentally to the hydrophobic character of the polymer and hydrophilic of reinforcement, with a tendency to capture moisture. They exist in the technique several processes for the production of composites in general:

Low energy grinding for polymer size reduction using cryogenic temperatures

The use of cryogenic temperatures in the crushing or grinding of polymers is common since, at temperatures below its glass transition temperature (Tg) the amorphous phase is in a crystalline or vitreous state, that is, they are fragile. Cryogenic grinding is used to develop ultra-thin plastic, especially for those that melt or soften at low temperatures, using mostly liquid nitrogen. (Xing, L et al . "Research on cryogenic grinding of plastics with air turbine refrigeration system", 2008, Proceedings of the Institution of Mechanical Engineers, part E: Journal of process mechanical engineering, vol. 222, iss. 2, pp. 93-101). This technique offers a decrease in particle size and a homogeneous distribution, as well as morphologies that allow the development of new manufacturing processes that reduce the generation of bubbles and porosity in the final products. The main feature of using cryogenic temperature is the elimination of heat generation, so it is a useful way to study the properties of polymers in the production of new materials and their modification, as well as for the recycling of plastics and elastomers ( Sadadinovi \ acute {c}, J .; Ili \ check {c} kovi \ acute {c}, Z. "Polyurethane recycling. Journal of chemists and chemical engineers", 2002, vol. 51, iss. 10, pp. 431 -436).

High energy grinding for size reduction or alloy polymeric

High energy grinding, mechanical alloy or reactive grinding, is commonly used in powder metallurgical technology for the mechanical alloy of powders and to obtain composite materials in which within the same particle there are at least two different types of structures. Inert atmospheres are used for this mechanical alloy process that prevent the reaction of new species and control the process temperature. This technique has been incorporated very recently for the modification of the properties of the polymers by decreasing their particle size, or for obtaining polymer alloys. Recently, cryogenic mechanical milling has been studied in several homopolymers, such as high density polyethylene, isotactic polypropylene, polyvinylidene fluoride, syndiotactic polystyrene, in a liquid nitrogen bath (Stranz M. et al . "Stress induced formation of stable & metastable phases in semi-crystalline polymers during cryogenic mechanical milling ", 2005, Journal of metastable and nanocrystalilne materials series, vol. 24-25, pp. 463-466; Stranz M., Koster, U." Cryogenic mechanical milling of syndiotactic polystyrene (sPS) ", 2005, Journal of metastable and nanocrystalilne materials series, vol. 20-21, pp. 281-286). The resulting pulverized polymers show transformations in the crystalline phases that influence their thermal properties. On the other hand, this technique has been incorporated into the research lines for the polymer alloy (or blends), so that thanks to the impacts produced between particles at cryogenic temperatures that prevent the material from melting, the mechanical alloy is produced between the different polymers This process has demonstrated the feasibility to produce polymer alloys that are normally incompatible (Smith, AP et al . "Temperature-induced morphological evolution in polymer blends produced by cryogenic mechanical alloying", 2000, Macromolecular materials and engineering, vol. 274, iss .1, pp. 1-12).

         \ vskip1.000000 \ baselineskip
      

High energy cryololienda for polymer composites reinforced with metallic or ceramic particles

High energy mechanical grinding is an alternative method for the preparation of nanocomposite materials. A high degree of dispersion of nanoparticles in a polymer matrix is achieved thanks to the transfer of energy between the very hard grinding spheres and the mixture of alloyed materials. It is worth mentioning the appearance of the first works that employ this high energy grinding technique for the manufacture of nanocomposites, with polymers such as ABS, PAÑI or PET with Fe nanoparticles, SiO2 or Al2O3. These works show the good results regarding the good dispersion and homogenization of the mixtures, avoiding the agglomeration of small particles (Zhu, Y. et al . "Electromagnetic nanocomposites prepared by cryomilling of polyaniline and Fe nanoparticles", 2008, Journal of polymer science, part B: polymer physics, vol. 46, iss. 15, pp. 1571-1576).

With regard to this process, the peculiarity of The present invention of polymer cryololienda lies in the particular behavior of thermoplastic materials with the temperature. So that they maintain their crystalline state and the Mechanical alloy must be below its Tg. During the cryololienda cycle, ramps must be applied heating-cooling depending on the stage of the process so that the polymer alloy is produced first with the fibers and secondly the subsequent alloy between already reinforced polymer particles, and give rise to particles of larger size that can be processed. Therefore the manufacture of product object of the invention requires a controlled evolution of grinding energy and temperature to cover successive mixing and loading stages of the matrix polymer, unlike the conventional grinding mixing processes that are more continuous

         \ vskip1.000000 \ baselineskip
      

Manufacture of polymer matrix composite materials reinforced with fibers of natural origin (biomass)

Bio-composites are those composites that use materials from biomass. Currently, the production of bio-composites is carried out by processes where the polymer is in a liquid state, in the case of thermosetting polymers, or in a molten or softened state for thermoplastic polymers. In the case of thermoplastic polymers, the previous mixing process is carried out with mixing equipment such as twin-screw extruders that exert the appropriate shear stress. However, there is a very important problem when using fibers, which is the poor adhesion between the natural fiber and the polymer matrix due to its low interaction. Therefore, the fiber surface must be modified to reduce its polarity and improve interface compatibility. Some of the modification methods used are alkaline treatments, or the addition of coupling agents with maleic anhydride copolymer and silanes (P. Threepopnatkul et al . "Effect of surface treatment on performance of pineapple leaf fiber-polycarbonate composites", 2009, Composites: Part B -In Press-; S. Alix et al . "Biocomposite materials from flax plants: Preparation and properties", 2008, Composites: Part A, vol. 39, pp. 1793-1801). This previous preparation complicates the process of manufacturing the processes.

The manufacture of nano-composites in which the reinforcement is nano-fiber of natural origin are based on composites of "nano-whiskers". Nanometric reinforcements (<100 nm) derived from cellulosic materials are currently obtained by various methods, including physical treatments by shear or high pressure, biological treatments by enzymatic hydrolysis, and chemical treatments by acid hydrolysis. The latter is the most used to eliminate amorphous regions and obtain crystalline cellulose, or whiskers. Conventional processes to reinforce a polymer matrix with nano-whiskers via molten polymer leads to many problems due to the tendency of these particles to agglomerate and not achieve a good dispersion. This process reaches a maximum reinforcement load of 10% by weight, which limits the improvements produced by nanoparticles in the composite material (Yun Chen et al , "Bionanocomposites based on pea starch and cellulose nanowhiskers hydrolyzed from pea hull fiber: Effect of hydrolysis time ", 2009, Carbohydrate Polymers 76, pp. 607-615). The process of the invention, however, by eliminating chemical treatments of adaptation of organic nanofibers and achieving it by their alloy with the polymer, results in a percentage of up to 20%, which greatly increases their properties with respect to the technique.

International application WO2009058426 is considered to be the closest document in the art. It describes the manufacture of a bio-composite by cryogenic grinding process, although it describes said cryolomienda simply as a method to condition the plastic by spraying it and not as a method of mixing or alloy. It is simply a process of incorporation of biological material that is previously processed by cryogenic crushing. The subsequent mixing is carried out in a molten state and not by mechanical alloy, so that the same technical limitations described in terms of maximum load admitted in the polymer matrix and dispersion thereof are obtained. In this case, these limitations are not a major problem because the functionality that biomass brings to the polymer is chemical for adsorption and odor control. The ability to add a cryogenic grind to improve the ability to combine the biological material by mechanical activation is mentioned, but not as an immediate process, but later and by batch, so that this activation is not used in all its
capacity.

Instead of a previous preparation followed by a subsequent mixture, the process object of the present invention combines both stages into a single one that includes activation and alloy, followed by agglomeration, mixing and dispersion, all mechanically and by the appropriate evolution of temperature and Cryomolienda process energy. The result is a proportion surprisingly increased fiber in the final composite.

The problem posed by the technique is therefore the need to find a nano-composite material with physicochemical properties suitable for industry, cheaper than the current ones. The solution provided by the Present invention is a nano-composite material with biomass nanoparticles in proportion greater than 10% by weight thanks to the method of manufacturing the cryololienda.

The present invention is a novelty in the Preparation of cellulose nanoparticles by high grinding energy, a faster and more efficient method than current, facilitated by the availability of ball mills horizontal rotor with ceramic chamber, control technologies energy invest for grinding energy control, and the combination of cooled jacket with liquid nitrogen bed for temperature control. The process of the invention avoids the process of mixing in the molten state when performing said mixing in solid state, so the agglomeration and dispersion difficulty They represent a problem solved.

         \ vskip1.000000 \ baselineskip
      

Description of the invention

The present invention relates to a new polymer matrix composite material with nano-reinforcements of fibrous nature from biomass It is a composite material that comprises at least one polymer thermoplastic that acts as a matrix and nanoparticles in alloy with said polymer, said biomass nanoparticles in a percentage greater than 10% by weight with respect to the total weight. One realization it is preferred that the percentage of the biomass particles be greater than 12%, more preferably greater than 15% by weight, and more preferably even more than 20% by weight.

A preferred embodiment is that the matrix polymer of said thermoplastic polymer is a polyolefin, preferably polyethylene and / or polypropylene, and more preferably high density polyethylene.

Another preferred embodiment is that the matrix polymeric be a thermoplastic biopolymer that can present biodegradable characteristics, preferably a biopolymer from vegetable starches, and more preferably a Poly-L-Lactide (PLLA).

Another embodiment is that the nanoparticles that come from biomass are natural fibers, and preferably selected from the group consisting of hemp fibers, flax fibers, sisal fibers and fibers from
algae.

The process for obtaining the composite material is also the subject of the present invention, so that another embodiment is a process for obtaining a composite material comprising the liquid nitrogen cryololdering of biomass particles in the form of fibers and plastic polymer in cryogenic state. . Thus, the alloy of all the particles constituting said composite material is obtained. This procedure avoids the molten state of the polymer and thereby the problems of particle agglomeration during the first mixing. The subsequent shaping of the resulting material will be carried out through the conventional processes of transformation of
plastics

The process of the invention may include the previous activation of said biomass particles and the micronization of said polymer. In this application, means "activation of the fibers" to that process that get the fibers to reach submicron sizes and be in situation of interacting physically and chemically with the polymeric matrix and can be alloyed with the polymer by having a specific surface area sufficient, very high, and numerous free radicals.

Another embodiment of the invention is that said procedure comprises the subsequent stage of decreasing the energy of said cryololienda to obtain the agglomeration of said alloy. Said energy decrease can be carried out. decreasing the cryogenic contribution to the cryololienda process, it is say opening at rising temperature. In this application, means "rising temperature" to an increase of temperatures from -80ºC to 20ºC in a period of time between 40 and 60 min.

Finally, the procedure also includes the final dispersion of nanofibers in the polymer matrix by grinding at room temperature and moderate energy. In this application "moderate energy" means kinetic energy enough that it allows a mechanical aggregation in plastic state of the matrix polymer, which requires less energy than necessary for the mechanical alloy in cryogenic state, which in turn understood as "high energy".

By offering an overview, the process complete includes first the preconditioning of the fibers and the plastic matrix according to conventional procedures. He fiber preconditioning can include washing in Basic and filtered solution. The conditioning of the matrix plastic can comprise spraying the polymer in a state of supply. The mixture of preconditioned fibers and polymer are a then subjected to the process of the invention, which comprises Multi-stage high energy cryogenic grinding.

In a first stage, the grinding is done at increased energy levels in a bed of liquid nitrogen, in that micronization processes of the particles are forced polymeric and activation of natural fibers. The mixture of polymer and fibers with the liquid nitrogen bed results in a sludry or cryogenic slurry within which reactions will occur later. Then the grinding is kept very high energy resulting in the mechanical alloy of the particles polymeric with natural fibers, a cycle that must undergo temperatures below the Tg of the polymer so that it find in crystalline state. The next cycle is performed at temperature higher than Tg but lower than the temperature of fusion of the polymer so that it is in a plastic state, so that collisions between polymer particles lead to the growth of particles The resulting particles must be agglomerated or palletized for later forming into final product, agglomeration that can be performed by fusion-extrusion-crushing, or by compression molding. The resulting pellets or lentils can be used for extrusion, injection or any other route usual thermoplastic processing.

The resulting polymer obtains advantages from emerging properties of nanoparticles in concentrations high, especially prolonged durability, resistance to wear and abrasion, as well as increased mechanical strength without loss of elasticity

In the process of the present invention it is A rigorous temperature control is essential during grinding carried out in the different stages.

With the intention of showing this invention in an illustrative way although in no way limiting, They provide the following examples.

         \ vskip1.000000 \ baselineskip
      

         \ global \ parskip0.950000 \ baselineskip
      

Examples Example 1 In which the polymer matrix is polypropylene and the reinforcement of linen nano-fibers, reaching a percentage of 20% charge

The cut flax fibers were introduced in a mill (Fritsh Pulverisette) until fine particles are achieved. These were then treated with a 4% NaOH solution at 80 ° C for 2 h with stirring to remove all constituents present in fibers that are not valid. Then the fibers were filtered and washed with distilled water until removed completely alkali. The treated flax fibers were introduced in the high energy mill (Simoloyer model, ZOZ house) subjecting them to criomolienda with steel balls of diameter 3 mm To decrease its size. This process was carried out for 4 grinding hours On the other hand, polypropylene in pellets is introduced into the mill (Fritsh Pulverisette) in cryogenic state to decrease its size until pulverized. Both compounds, treated linen nano-fibers and polypropylene in powder, were introduced into the high energy mill in a weight ratio similar to the desired alloy. For the material PP compound reinforced with 20% nano-fibers of linen, 20% of the total weight of the material was introduced in nano-fibers 500 g of material were prepared reinforced by introducing 400 g of PP powder and 100 g of nano-fibers together with 5 kg of 3 steel balls mm The cryogenic alloy process was started, proceeding in first to the liquid nitrogen charge in the chamber, after the which starts the mill. In the first stage of micronization and activation a rotation of 1500 rpm was maintained for 1 h. The second stage of polymer + fiber mechanical alloy was performed at a speed of 1800 rpm for a time of 3 h. In the third stage the spin was maintained at 600 rpm in which the energy is moderate and finally, a final stage of 300 rpm was performed for 30 min. The unloading of the alloyed material was done automatically at 400 rpm for 20 min, in which the balls remained in the camera. The yield of the process was 90%. The material obtained in powder form it was then processed for manufacturing of 3 mm size pellets to be injected. One time pelletized was injected to mold a valve seat, such as final piece The mechanical properties of this valve seat they were represented in a tensile test that showed a maximum tension of 152 MPa, and an improvement to wear in tests of 30% tribology with respect to the unreinformed polymer, so the material was apt to prolong the life of the piece and, Therefore, reduce your maintenance requirements. The resistance obtained is three times greater than that of the polymer without load, and represents a substantial improvement over reinforcements with nanoparticles below 10% by state dispersion cast (see figure 3).

         \ vskip1.000000 \ baselineskip
      

Example 2 In which the polymer matrix is a Polycaprolactone (PCL), of High biocompatibility and reinforcement consists of nanocellulose 15% commercial

30 grams of nanocellulose and 200 grams were loaded grams of PCL in delivery status, together with 3 kg of balls 3 mm diameter steel grinding in a horizontal mill high energy (ZOZ Simoloyer). Then 750 ml of liquid nitrogen to the grinding chamber and the mixture was subjected to a multi-stage grinding cycle. The first stage consisted of grinding at 1500 rpm for 1 h in a bed of liquid nitrogen. The second stage consisted of grinding at 1000 rpm for 4 h at a temperature of -30ºC. Finally, grinding was maintained at 500 rpm for 3 more hours, allowing a temperature rise of 1ºC / min until reaching room temperature forming a mud. Finally The grinding chamber was discharged in the usual manner. The material resulting from grinding is used to then extrude a 0.5 mm high biocompatibility and high strength sheet, Especially suitable for surgical instruments.

         \ vskip1.000000 \ baselineskip
      

Brief description of the figures

Figure 1.- Product production process polymer-fiber alloy.

one.

Grinding balls

2.

Polymer.

3.

Fibers.

Four.

Rotor.

5.

Refrigerated shirt

6.

Mixing chamber

7.

Polymer.

8.

Nanofibers

9.

Grinding medium

10.

Cryogenic sludge, formed by liquid nitrogen with suspended particles.

eleven.

Liquid nitrogen bed.

12.

Nanostructured Polymer

13.

Alloy polymer + fiber product.

         \ vskip1.000000 \ baselineskip
      

Figure 2.- Temporary Evolution of the Energy of grinding (E) and temperature (T) throughout the entire duration of the cryogenic grinding process for polymer production final nanostructured At first the load is produced with liquid nitrogen and sudden cooling of the load, subjected to grinding under high mechanical energy, to then progress in successive stages of different duration, each with greater temperature and lower energy to produce different effects mechanics

one.

Load of polymer matrix and fibers natural

2.

Micronization and activation.

3.

Mechanical alloy polymer + fiber.

Four.

Nanostructured polymer (structure mobile).

5.

Nanostructured (dispersed) polymer.

         \ global \ parskip1.000000 \ baselineskip
      

Figure 3.- Resistance of a polymer with charges of nanoparticles of plant origin by cryololienda, in function of the proportion of added load.

Figure 4.- General scheme of the process of production.

Claims (11)

1. Composite material comprising at least one thermoplastic polymer that acts as a matrix and nanoparticles of alloy biomass with said polymer, said nanoparticles of biomass in a percentage greater than 10% by weight with respect to weight total. 2. Composite material according to claim 1, wherein said polymer matrix is a polyolefin. 3. Composite material according to claim 2, wherein said polyolefin is polyethylene and / or polypropylene. 4. Composite material according to claim 3, wherein said polyethylene is high density polyethylene. 5. Composite material according to any of the claims 1 to 4, wherein said polymeric matrix is a thermoplastic biopolymer. 6. Composite material according to claim 5, wherein said biopolymer is a PLLA. 7. Composite material according to any of the previous claims, wherein said biomass particles They are natural fibers. 8. Composite material according to claim 7, wherein said natural fibers are selected from the group comprised of hemp fibers, flax fibers, sisal fibers and fibers from algae. 9. Procedure for obtaining a material composite, which comprises cryololienda in liquid nitrogen of biomass particles in the form of fibers and plastic polymer in cryogenic state, to obtain the alloy of said material composite 10. Method according to claim 9, which it comprises the previous activation of said biomass particles and the micronization of said polymer. 11. Method according to claim 9, which it comprises the later stage of decreasing the energy of said cryololienda to obtain the agglomeration of said alloy.