The subject of the invention involves the method of manufacturing a cellulosic modifier based on MDF and HDF waste for thermoplastics and thermoplastic composites modified with the resultant modifier.

Modification of physicochemical properties of thermoplastic polymers with cellulose filler- modifiers is well known in the literature and most often relates to wood in the form of finely divided particles or fibers.

Wood used as a polymer filler has several disadvantages, such as flammability and hydrophilicity. The hydrophilicity of wood as a filler affects the instability of the dimensions of the composites which were obtained with the use of wood, and over time contributes to the change in their colour ("turning greenish"), especially composites exposed to external conditions. Moreover, the hydrophilicity of polymer- wood composites causes their tendency to mold.

The main disadvantage of wood in structural applications is the anisotropy of the mechanical properties of the resultant composite products which manifests in varied tensile strengths along and across the fibers. This phenomenon adversely affects the performance of polymer-wood composites. Anisotropy of mechanical properties largely depends on the size of wood particles used in the production of polymer-wood composites. The smallest anisotropy is observed when wood flour is used as a filler. By using flour from MDF or HDF waste, both post- consumer waste and post-production waste from the furniture industry, additionally it is possible to prevent excessive water absorption.

Urea or melamine binders are used in the manufacture of MDF and FfDF. It is difficult to get rid of the post-production waste coming from MDF, HDF or old furniture which were produced by use of urea or melamine, and not to contaminate the environment, however it is advisable for ecological reasons.

The use of fibers or fine particles from MDF or HDF waste to produce polymer composites is described in patent document PL / EP 1498241. The disclosed process for manufacture of the composite includes mixing wood fibers derived from MDF or HDF products, without prior modification thereof, with the polymer, and then extruding the resultant mixture to bind the polymer with the waste particles so that the particles are at least partially encapsulated by the polymer. Polypropylene, polyethylene, PVC, polystyrene, ethyl-vinyl acetate, ABS and/or polyolefin used as the polymer produce positive results. A positive embodiment of the invention involves the use of at least one additive which constitutes maleic anhydride, polyurethane, unsaturated polyester, epoxy resin, phenol, sodium carbonate, poly (methyl methacrylate), polypropylene or polyethylene filled with melamine anhydride, wax and/or pure wood fibers. According to the specification, a defined amount of the polymer, including a specified amount of the additive (if used), is introduced into a twin screw extruder, then they are mixed together, and subsequently a specific amount of particles derived from MDF or HDF molded products comprising a cured binder, is added, and as a result a polymer-wood composite product is produced.

Patent application WO2014197954 describes the method of manufacture of a composite material which involves mixing PVC resin with additives, cooling, mixing the obtained masterbatch with MDF (or MDP) waste, and then injection molding of the resultant mixture. The method of obtaining the composite panels presented patent application US2004/0202857 comprises milling of MDF fibers comprising a cured binder to a suitable size. The resultant flour is dried and mixed with the polymer (polyethylene, polypropylene or PVC). In order to improve flexural modulus, a mineral filler is added which may be talc, calcium carbonate or aluminium hydroxide. Lubricants are added to improve the melt flow index.

Another wood-derived material is lignocellulose. In the process of patent application WO03000475, the lignocellulosic material is hydrolysed, then the modified material is dried, then mixed with the binder and the composite is obtained by compression.

Composites of patent application WO00/21743 contain fibers of cellulosic pulp dispersed in a polymer matrix, preferably a thermoplastic polymer having a melting point above 180°C. According to the invention, fibers of cellulosic pulp should demonstrate purity greater than 80% by weight with respect to alpha-cellulose. The invention also includes a method of composite manufacture and application.

Surprisingly, it has been found that by adequate modification of the network of wood fibers with hardened binder, at elevated temperature and under shear forces, active forms are obtained in result of a free radical reaction - macrostoids capable of further interacting with the polymer matrix.

The method of manufacturing a cellulosic modifier for thermoplastics according to the invention consists in that the particles containing the hardened binder fibers derived from MDF or HDF boards or mixtures thereof, in any weight ratio, are mixed with a solution of the modifying compound, capable of forming in free radical reactions, with wood-hardened binder particles derived from MDF or HDF or their mixtures of active macroradans, and left at room temperature, then subjected to further dispersing at elevated temperatures to give a homogeneous mixture.

Preferably, the hardened binder wood fibers derived from MDF or HDF or mixtures thereof are used as flour.

Preferably, flour is used in the form of grains of size 30 to 90 mesh, more preferably 50 to 80 mesh.

Preferably, the hardened binder wood fibers derived from MDF or HDF boards or mixtures thereof are mixed in equilibrium with a solution of the modifying compound.

Preferably, an aqueous solution of the modifying compound is used.

Preferably, an aqueous solution of the 20-30% modifying compound is used.

Preferably, the mixture is allowed to stand at room temperature for 24 hours.

Preferably, the mixture is dispersed at elevated temperature for 10 minutes.

Preferably, the hardened binder wood fibers derived from MDF or HDF boards or mixtures thereof are dispersed at elevated temperatures with aqueous citric acid as the modifying compound.

The mixture is preferably dispersed at 170-190°C.

The mixture is preferably dispersed using a paddle mixer.

The modifiers obtained according to the invention were submitted to the FTIR (Fourier transform infrared spectroscopy) and the EPR (Electronic Paramagnetic Resonance) analysis. In the spectrum of unmodified MDF or HDF waste, among others, a band at a wavelength of 1641 cm-1 is observed, which is the absorption band of the carbonyl group (C=0) present in the urea moiety. This band is characteristic for the first amid band of secondary amide. Changes occur within this band changes if the MDF and HDF wastes undergo chemical modification. In the IR spectrum of modified MDF and HDF waste, the shift of the said band to lower frequencies (from 1641 to 1626 cm-1) is observed, which confirms the changes made within the amide group.

During the processing process, in order to prove the inductive ability of polymer radicals produced in the system due to a specific chemical modifier structure, the EPR test was performed using a spin trap - DPPH (l,l-diphenyl-2-picrylhydrazyl). The blank sample in the form of unmodified MDF and HDF waste exhibits a higher EPR signal intensity than the modified sample, indicating the presence of fewer free radicals that have been captured by DPPH. Therefore, the conducted EPR tests indicate that the citric acid used in the modifier preparation process, under the influence of temperature, reacts with the MDF and HDF waste particles. Such form of the obtained modifier is advantageous to produce further interaction with the polymer matrix, which in consequence results in its enhancement effect.

The invention also involves thermoplastic polymer composites with modified mechanical properties.

Modified thermoplastic composites containing thermoplastic polymer, modifier, optionally assistants, according to the invention, per 100 weight units of thermoplastic polymer, contain 10- 70 weight units of cellulosic modifier prepared by the method described above.

Modified thermoplastic composites per 100 weight units of thermoplastic polymer, contain 15-60 weight units of cellulosic modifier.

Preferably, the thermoplastic polymer is polyolefin.

Preferably, the thermoplastic polymer is polypropylene, low density polyethylene or polyvinyl chloride.

Modified thermoplastic composites are obtained by mixing (by any method) of the produced cellulosic modifier with a thermoplastic polymer. The processing of the prepared mixtures is carried out by a known method applied in the processing of polyolefins, and the extrusion is preferably carried out in a co-rotating twin screw extruder (for example using polypropylene, low density polyethylene) or counter rotation twin screw extruder (for example with polyvinyl chloride), in the temperature range from 160 to 210°C (i.e. at the processing temperature of the composite matrix polymer).

Thermoplastic polymer composites with a modifier obtained according to the invention are characterised by significantly better mechanical properties, including stiffness and impact strength compared to composites obtained from unmodified MDF and HDF waste wood fibers. For example, in the case of composites on polypropylene and low density polyethylene matrix, a noticeable increase in Young's modulus value was observed while the relative elongation at break was decreased. On the other hand, in the case of the composites on polyvinyl chloride matrix, a noticeable increase in impact, tensile and flexural strengths, and bending modulus as well as Young modulus were recorded.

Thermoplastic composites according to the invention may be useful for obtaining decorative elements, panels, interior and exterior furniture components or structural components in the automotive industry.

The invention is presented in the following examples: Example 1

100 g of MDF and HDF waste (mixture) with a particle size of 50-80 mesh were mixed with 100 g of 25% aqueous citric acid solution (colourless crystal body with Mcz = 192 g/mol and d = 1.65 g/cm) and allowed to stand for 24h at room temperature. The resultant mixture was subjected to shear forces at 180°C using a Brabender type mixer equipped with paddle stirrers (sigma type). Modification process was performed for 10 min. at a rotation speed of 70 rpm. The product was then unloaded and allowed to cool. Cellulosic modifier (CELMOD) was obtained.

Example 2

100 weight units of low density polyethylene (PE-LD) (Malen E FG X 23-D022, MFI = 1.95 g/1 Ornin, TmVicat = 90°C) in the form of granules was mixed with 15 weight units of produced cellulosic modifier and processed at 160-180°C using a co-rotating twin screw extruder. The speed of rotation of the screw was 40 rpm. Composite 1 was obtained.

Example 3

100 weight units of low density polyethylene (PE-LD) (Malen E FGNX 23-D022, MFI = 1.95 g/lOmin, TmVicat = 90°C) in the form of granules was mixed with 60 weight units of produced cellulosic modifier and processed at 160-180°C using a co-rotating twin screw extruder. The speed of rotation of the screw was 40 rpm. Composite 2 was obtained.

Example 4

100 weight units of polyethylene (PE-LD) (Moplen HP456J, in the form of granules was mixed with 15 weight units of produced cellulosic modifier and processed at 190-210°C using a co-rotating twin screw extruder. The speed of rotation of the screw was 40 rpm. Composite 3 was obtained.

Example 5

100 weight units of polyethylene (PE-LD) (Moplen HP456J, in the form of granules was mixed with 60 weight units of produced cellulosic modifier and processed at 190-210°C using a co-rotating twin screw extruder. The speed of rotation of the screw was 40 rpm. Composite 4 was obtained.

Example 6

100 weight units of a ready PVC mixture consisting of 100 weight units of PVC (type S-67 HBD, number K = 67, viscosity = 110 ml/g, relative bulk density = 0.585g/ml), 7 weight units of impact strength modifier (ADD-CPE 6035 chlorinated polyethylene, supplier: ADD- Chemie), 4 weight units of thermal stabiliser (ADD-55 calcium-zinc stabiliser, supplier ADD- Chemie), 1.2 weight units of Polyethylene wax (ADD-Lub 700 PE WAX type, supplier: ADD- Chemie), 1.2 weight units of plasticiser (PA type: ADD-PA 125, supplier: ADD-Chemie) was mixed with 15 weight units of produced cellulosic modifier and processed at 175-183°C using a counter-rotating twin screw extruder. The speed of rotation of the screw was 35 rpm. Composite 5 was obtained. Example 7

100 weight units of a ready PVC mixture consisting of 100 weight units of PVC (type S-67 HBD, number K = 67, viscosity = 110 ml/g, relative bulk density = 0.585g ml), 7 weight units of impact strength modifier (ADD-CPE 6035 chlorinated polyethylene, supplier: ADD-Chemie), 4 weight units of thermal stabiliser (ADD-55 calcium-zinc stabiliser, supplier ADD-Chemie), 1.2 weight units of Polyethylene wax (ADD-Lub 700 PE WAX type, supplier: ADD-Chemie), 1.2 weight units of plasticiser (PA type: ADD-PA 125, supplier: ADD-Chemie) was mixed with 60 weight units of produced cellulosic modifier and processed at 175-183°C using a counter-rotating twin screw extruder. The speed of rotation of the screw was 35 rpm. Composite 6 was obtained.

The following tables summarize the mechanical properties of thermoplastic composites obtained using the cellulosic modifier according to the invention (CELMOD).

Table 1. Mechanical properties of composite on PE-LD matrix.

type/amount Tensile Relative Young Flexural Deflection Flexural [weight unit] strength elongation at Module strength [mm] modulus break [MPa] [MPa] of

[MPa] [%] elasticity

[MPa]

0-PVC unmodified 7.5 1 1443 29 2 2320

MDF HDF IIS

5 CELMOD/15 11 1.5 1655 47 3 2821

6 CELMOD/60 8.8 1 1777 36 2 3020

Table 4. Impact strength of composite on PVC matrix.