METHOD FOR THE PRODUCTION OF NANOCOMPOSITE PLASTIC MATERIALS

Abstract

A method for the preparation of nanocomposite plastic materials includes coating thermoplastic polymer granules with sizes from 0.5 to 5 mm, using a physical vapor deposition (PVD) sputtering technique, with a coating layer from 1 to 100 nm of a material dispersible in a matrix of said thermoplastic polymer to form coated thermoplastic polymer granules, and thereafter plasticizing and injection moulding the coated thermoplastic polymer granules at high pressure into a closed mould.

Claims

1. Method for the preparation of nanocomposite plastic materials comprising: coating thermoplastic polymer granules with sizes from 0.5 to 5 mm are coated, using a physical vapor deposition (PVD) sputtering technique, with a coating layer from 1 to 100 nm of a material dispersible in a matrix of said thermoplastic polymer; and plasticizing and injection moulding the coated thermoplastic polymer granules at high pressure into a closed mould.

2. The method according to claim 1, characterized in that said thermoplastic polymer granules have sizes from 1 to 5 mm.

3. The method according to claim 1, characterized in that the coating layer comprises one or more of Al, Ti, Cr, Cd, Co, Fe, Mg, Sc, Ag, Au, Eu, Hf, Pr, and Cu and their alloys, borides, carbides, fluorides, nitrides, oxides, silicides, selenides, sulfides, tellurides, antimonides, and arsenides.

4. The method according to claim 1, characterized in that said thermoplastic polymer is selected from the group consisting of POM, PAN, ABS, SAN, PA6, PA66, PA12, PC, PET, PBT, PP, PE, LDPE, MDPE, HDPE, LLDPE, UHMWPE, PEI, PS, PEEK, PEKK, PSU, PPS, and PVC.

5. Nanocomposite plastic material produced with the method according to claim 1.

6. An additive for the production of a nanocomposite plastic material consisting of thermoplastic polymer granules with sizes from 0.5 to 5 mm coated with a sputtered layer between 1 and 100 nm thick of a material selected from the group consisting of Al, Ti, Cr, Cd, Co, Fe, Mg, Sc, Ag, Au, Eu, Hf, Pr, and Cu and their alloys, borides, carbides, fluorides, nitrides, oxides, silicides, selenides, sulfides, tellurides, antimonides and arsenides.

7. The additive according to claim 6, characterized in that said granules have sizes ranging between 1 and 5 mm.

8. The additive according to claim 6, characterized in that said granules are adapted to produce a nanocomposite plastic material with antimicrobial and antibacterial properties, the coating layer being made of Ag.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Examples of embodiment are provided purely by way of non-limiting example with the aid of the accompanying figures, wherein:

[0025] FIG. 1 schematically illustrates the transformations of the material in the formation of the nanocomposite during injection moulding; and

[0026] FIGS. 2a and 2b are two microscope images illustrating the dispersion of nanometric particles of Ag in the nanocomposite produced in the example described.

PREFERRED EMBODIMENT OF THE INVENTION

[0027] FIG. 1 denotes as a whole with 1 an injection moulding assembly illustrated schematically. The injection moulding assembly 1 comprises an injection cylinder 2, a plasticizing screw 3 housed inside the injection cylinder 2, a plurality of heaters 4 arranged around the injection cylinder 2, a drive motor 5 of the plasticizing screw 3, a hopper 6 for feeding the thermoplastic polymeric granules 7 into the injection cylinder 2 and a closed mould 8. FIG. 1 shows three enlargements (A-C), which illustrate respectively: [0028] (enlargement A) the coating layer arranged externally to the granules; [0029] (enlargement B) a first phase of fragmentation of the coating layer; [0030] (enlargement C) a last phase of fragmentation of the coating layer with the nano fillers dispersed nano-heterogeneously in the polymer matrix.

EXAMPLE

[0031] By means of PVD RF magnetron sputtering, using an INFICON XTC/3 system for monitoring the film deposited, a 80 nm thick coating layer of 99.9% pure metallic silver was produced.

[0032] The polypropylene pellets (isotactic polypropylene (PP) Moplen HP500n by Lyondellbasell, with melt flow index (MFI) 12 g/10 min and density 0.9 g/cm.sup.3 at 23 C.) with a very flat cylindrical shape of around 4 mm in diameter and 3 mm in height.

[0033] The pressure of the first sputtering chamber was 1.710.sup.5 mbar, at a temperature of 35-40 C. and with a distance of the pellets from the Ag target of 60 mm. The deposition parameters were 180 W DC, for 8 min, with only argon gas (purity of 99.999%) at the controllable pressure of 0.3-4 Pa.

[0034] The coated pellets were used for injection moulding of square samples for antibacterial analysis.

[0035] Moulding data: Fanuc Roboshot S-2000i 50B injection press, plate dimensions (80803 mm.sup.3), mould temperature control (30 C.), temperature of the material in the hopper (30), injection speed (10 mm/s), clamping pressure (950 bar), mould clamping force (50 t), cylinder temperatures (from 190 C. to 210 C.), nozzle temperature (220 C.), cooling time (10 s).

[0036] On the nanocomposites moulded and cut to the dimensions 30303 mm.sup.3 antimicrobial tests were performed according to ISO22196: 2007 Plasticsmeasurement of antibacterial activity on plastics surfaces using bacterial strains Staphylococcus aureus, ATCC 6538, and Escherichia coli, ATCC 8739. After 24 hours from inoculation according to the standard (temperature 351 C. with 90% humidity for 24 h) there was a 99.998% reduction in the presence of bacteria on the surface of the nanocomposite and an improvement of 98.44% in antibacterial properties compared to the surface of the same PP moulded without Ag nano coating.

[0037] FIGS. 2a and 2b show the micrographs of the samples produced as above.

[0038] The Ag nano fillers were dispersed in the polymer with a distance between adjacent metallic nanoparticles of around 100-150 m. Moreover, the Ag metallic nano fillers measured have a thickness in the range between 60 nm and 80 nm and a surface between 55 m.sup.2 and 4040 m.sup.2.

[0039] It was highlighted that the Ag nano fillers were substantially in the shape of flakes with: an average thickness of around 70 nm; a minimum equivalent diameter of around 5.65 m; a maximum equivalent diameter of around 45.1 m.

[0040] Moreover, it was measured that the fraction by weight of Ag in the nanocomposite was 0.18%, while the average distance between particles was around 130 m.

ADVANTAGES

[0041] As is evident from the description above, the method forming the subject matter of the present invention offers the advantage of eliminating the step of producing the nanoparticles and consequently of avoiding their use to form additives. These advantages translate necessarily into increased safety and increased productivity.

[0042] Moreover, with the method forming the subject matter of the present invention it is possible to ensure the involvement of only the polymer material concerned. In fact, in the prior art method, the additives are usually produced with a different polymer material compared to the one used to produce the matrix of the nanocomposite end product. This advantage translates necessarily into improved physical and mechanical properties of the nanocomposite end product, due to the absence of critical mechanical points caused by the proximity of different and often incompatible materials.

[0043] It is also important to stress the cost effectiveness of the method according to the invention. In this regard, it must be considered that to ensure the desired nano-heterogeneity of the nanoparticle substance in the polymer matrix, a processing step (injection moulding) already used in the normal preparation of nanocomposite plastic materials is used.

[0044] Finally, the use of thermoplastic polymer granules coated with a layer that will subsequently be subjected to fragmentation, in addition to ensuring visual confirmation of the presence of the substance that will be dispersed into the polymer matrix, also allows other additives to be used in the same polymer matrix without problems.