NON-CORRODING FIBER-REINFORCED POLYMER COMPOSITIONS

Abstract

The invention relates to an injection-molding composition comprising at least one polyolefin, at least one delignified wood pulp fiber, at least one maleic anhydride-grafted polyolefin and at least one metal oxide chosen from oxides of alkaline earth metals or of zinc.

Claims

1. An injection-molding composition comprising at least one polyolefin, at least one delignified wood pulp fiber, at least one maleic anhydride-grafted polyolefin and at least one metal oxide chosen from oxides of alkaline earth metals or of zinc.

2. The injection-molding composition according to claim 1, wherein the at least one polyolefin is present in an amount of from 10 weight percent to 85 weight percent, the weight percent being based on the total weight of the injection-molding composition.

3. The injection-molding composition according to claim 1, wherein the delignified wood pulp fiber is present in an amount of from 10 weight percent to 85 weight percent, the weight percent being based on the total weight of the injection-molding composition.

4. The injection-molding composition according to claim 1, wherein the delignified wood pulp fiber is sulfite pulp.

5. The injection-molding composition according to claim 1, wherein the at least one maleic anhydride-grafted polyolefin, is present in an amount of from 2 weight percent to 15 weight percent, the weight percent being based on the total weight of the delignified wood pulp fiber.

6. The injection-molding composition to claim 1, wherein the at least one metal oxide is present in an amount of from 0.5 weight percent to 5 weight percent, the weight percent being based on the total weight of the injection-molding composition.

7. The injection-molding composition according to claim 1, having a moisture content of more than 0.5 wt % when measured by Karl Fischer titration.

8. The injection-molding composition according to claim 1, wherein the at least one metal oxide is present in an amount of from 1 weight percent to 3 weight percent, the weight percent being based on the total weight of the injection-molding composition.

9. The injection-molding composition according to claim 1, wherein the at least one metal oxide is chosen from calcium oxide, barium oxide, zinc oxide or magnesium oxide.

10. The injection-molding composition according to claim 1, wherein the at least one polyolefin is a polyethylene or polypropylene.

11. The injection-molding composition according to claim 1, wherein the at least one polyolefin is an impact polypropylene copolymer.

12. (canceled)

13. A process for the production of a molded object by injection-molding, comprising the steps of: a. forming a precursor agglomerate of at least one thermoplastic polymer, at least one delignified wood pulp fiber, at least one maleic anhydride-grafted polyolefin and at least one metal oxide chosen from oxides of alkali metals or of alkaline earth metals, b. processing the precursor agglomerate into a melt and optionally to increase the dispersion of the delignified wood pulp fiber, c. introducing, the molten composition into a mold made of steel, and allowing the melt of the composition to cool and solidify in the mold made of steel, wherein the steel from which the steel mold is made comprises less than 11% of chrome.

14. The injection-molding composition according to claim 1, wherein the at least one metal oxide is calcium oxide.

15. The process for the production of a molded object by injection-molding according to claim 13, wherein the molten composition is introduced into the mold made of steel by injecting it into the mold made of steel.

16. The injection-molding composition according to claim 1, wherein the at least one maleic anhydride-grafted polyolefin is maleic anhydride-grafted polypropylene or maleic anhydride-grafted polyethylene, and is present in an amount of from 2 weight percent to 15 weight percent, the weight percent being based on the total weight of the delignified wood pulp fiber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings,

[0043] FIG. 1 shows a photograph of the unused and uncorroded mould before sample testing.

[0044] FIG. 2 shows a photograph of the mould after moulding of 80 parts, when using composition RC1 (neat PP, bleached sulphite hardwood pulp, coupling agent) having a moisture content below 0.5 wt %. No rust formation can be observed.

[0045] FIG. 3 shows a photograph of the mould after moulding of 20 parts, when using composition RC2 (neat PP, bleached sulphite hardwood pulp, coupling agent) having a moisture content of above 0.5 wt %. Slight rust formation can be observed.

[0046] FIG. 4 shows a photograph of the mould after moulding of 30 parts, when using composition RC3 (neat PP, bleached sulphite hardwood pulp, coupling agent) having a moisture content of above 1.5 wt %. Significant rust formation can be observed.

[0047] FIG. 5 shows a photograph of the mould after moulding of 30 parts, when using composition RC4 (neat PP, bleached sulphite hardwood pulp, coupling agent), which further includes hydrotalcite as acid scavenger, having a moisture content of above 0.5 wt %. Significant rust formation can be observed.

[0048] FIG. 6 shows a photograph of the mould after moulding of 80 parts, when using composition IC1 (neat PP, bleached sulphite hardwood pulp, coupling agent), which further includes CaO, having a moisture content of above 0.5 wt %. No rust formation can be observed.

[0049] FIG. 7 shows a photograph of the mould after moulding of 20 and 80 parts, when using composition RC5 (neat PP, Kraft-based dissolving hardwood pulp, coupling agent), having a moisture content of above 0.5 wt %. Slight rust formation can be observed.

[0050] FIG. 8 shows a photograph of the mould after moulding of 80 parts, when using composition IC2 (neat PP, Kraft-based dissolving hard wood pulp, coupling agent), which further includes CaO, having a moisture content of above 0.5 wt %. No rust formation can be observed.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0051] It is an object of the present invention to provide a molding composition comprising at least one thermoplastic polymer, at least one delignified wood pulp fiber, at least one maleic anhydride-grafted polyolefin and at least one metal oxide chosen from oxides of alkali metals or of alkaline earth metals or of zinc.

[0052] In a preferred embodiment, the molding composition comprises at least one polypropylene, at least one bleached sulfite pulp fiber, at least one maleic anhydride-grafted polypropylene and at least calcium oxide.

[0053] In a preferred embodiment, the molding composition comprises at least one polypropylene, at least one bleached Kraft pulp fiber, at least one maleic anhydride-grafted polypropylene and at least calcium oxide.

[0054] The molding composition may be obtained by any available method in which the components are combined. For example, the molding composition may be formed by combining a pre-blend of the least one thermoplastic polymer, the at least one delignified wood pulp fiber and the at least one maleic anhydride-grafted polyolefin with the at least one metal oxide in a melt blender or an extruder. The pre-blend may itself be obtained by blending the at least one thermoplastic polymer, the at least one delignified wood pulp fiber and the at least one maleic anhydride-grafted polyolefin in a K-Mixer or a thermokinetic mixer such as a Gelimat mixer or a vertical high-speed mixer, single or twin screw extruder or kneader such as to form a preferably particulate pre-blend.

[0055] Alternatively, the molding composition may be formed by combining the at least one thermoplastic polymer, the at least one delignified wood pulp fiber and the at least one maleic anhydride-grafted polyolefin with the at least one metal oxide in a K-Mixer or a vertical high-speed mixer, which are equipped with a hot stage and a cool stage (so-called hot-cold mixers). In this case, the at least one metal oxide is added to the other components preferably in the form of masterbatch, i.e. as a highly concentrated dispersion of metal oxide particles in polyolefin matrix. As an example a masterbatch may comprise of from 50 to 90 weight percent, preferably of from 65 to 85 weight percent of metal oxide dispersed in a thermoplastic polyolefin. In general, the resulting agglomerates can be used for injection molding as-is, or may be subsequently compacted in a compactor to yield granulates of said agglomerate or extruded or further compounded in a single or twin screw extruder to yield pellets. Additional compounding or extrusion of the aggregates may increase the homogeneity of the molding composition by more thoroughly mixing the individual components before pelletizing.

EXAMPLES

[0056] Materials and Methods

[0057] Polypropylene P1 corresponds to polypropylene, obtainable from Braskem, Brazil under the trade designation Inspire 382, comprising maleic anhydride-grafted polypropylene as coupling agent, obtainable from BYK, Netherlands under the trade designation Priex 20097A.

[0058] Polypropylene P2 corresponds to polypropylene, obtainable from Sabic, Netherlands under the trade designation PP 579S, comprising maleic anhydride-grafted polypropylene as coupling agent, obtainable from BYK, Netherlands under the trade designation Priex 20097A.

[0059] Delignified wood pulp F1 used was bleached sulphite hardwood pulp.

[0060] Delignified wood pulp F2 used was Kraft-based dissolving hardwood pulp.

[0061] Calcium oxide used was a masterbatch of LDPE/CaO (30 wt %/70 wt %), introduced at 3 wt % during extrusion.

[0062] Hydrotalcite used was masterbatch designated QT00 12.708 from Qolortech (NL) introduced at 2 wt % during injection molding.

[0063] Compounds were prepared by extrusion to obtain compositions with about 40 wt % of delignified wood pulp and either 60 wt % of polypropylene (“neat” polypropylene+maleic anhydride-grafted polypropylene as a coupling agent) or 57 wt % polypropylene (“neat” polypropylene+maleic anhydride-grafted polypropylene as a coupling agent) and an additive such as for example 3 wt % CaO Masterbatch (i.e. 2.1 wt % CaO and 0.9 wt % LDPE) in case of IC1 and IC2. The exact compositions are provided in the below Table.

[0064] Samples were injection molded using constant standard injection moulding procedure in a circular mould equipped with a disk insert made from stainless steel 12/2312 (1.9% Cr) from Meusburger. The remainder of the mould, bushings and backplate are made from the same stainless steel.

[0065] The moisture uptake of the compositions was determined at the time the composition was injection-molded prior to introduction into the injection-molding device. Moisture uptake varied depending on storage conditions such as duration, relative humidity and temperature.

[0066] Compositions

TABLE-US-00001 Composition Moisture P1 P2 F1 F2 Hydrotalcite CaO uptake Samples (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) Reference 60 40 0.3 compound 1 (RC1) Reference 60 — 40 — — — 0.7 compound 2 (RC2) Reference 60 — 40 — — — 1.7 compound 3 (RC3) Reference 58.8 —   39.2 — 2 — n.d. compound (above 4 (RC4) 0.5) Reference — 60 — 40 — — 1.1 compound 5 (RC5) Inventive 57, and — 40 — — 2.1 2.3 compound 0.9 1 (IC1) LDPE Inventive — 57, and — 40 — 2.1 1.1 compound 0.9 2 (IC2) LDPE

[0067] Results

[0068] The surface state of the mould was inspected every 10 injected parts and photographs were made to record the occurrence of rust as brown deposits or corrosion pitting. The photographs are shown in FIGS. 1 to 8.

[0069] As can be seen from the Figures, when corrosion occurs, it is mainly seen at the inner and outer periphery of the mould, and especially also on the back plate.

[0070] From FIG. 2, it is apparent that the compositions of polypropylene and delignified wood pulp (RC1), when dried to a moisture content of 0.3 wt %, i.e. less than 0.5 wt %, do not lead to rust formation even after 80 parts are injection molded. In FIG. 3, for a composition that is essentially the same as RC1 except for the fact that the moisture content is 0.7 wt % i.e. above 0.5 wt % (RC2), already light corrosion is observed after 20 parts are injection molded. Much stronger corrosion is observed in FIG. 4 for compound RC3, which is the same as RC2 except for the fact that the moisture content is 1.7 wt % i.e. even more above 0.5 wt %, corroborating the concept that water contents above 0.5 wt % enable corrosion caused when injection moulding compounds comprising polyolefins and delignified wood pulp.

[0071] As is apparent from FIG. 5, the introduction of a standard acid scavenger (hydrotalcite) in RC4 (moisture content >0.5 wt %) does lead to a reduction of the rust formation.

[0072] Shifting from a bleached sulphite wood pulp fibre to a Kraft-based dissolving wood pulp (RC5) that contains essentially no residual lignin and much lower amount of hemicellulose significantly reduces the amount of mould corrosion, as seen in FIG. 7, without however eliminating it completely. Only the introduction of a basic metal oxide like calcium oxide in IC1 (bleached sulphite pulp) or IC2 (Kraft-based dissolving wood pulp) allows to completely suppress mould corrosion even at moisture contents in excess of 0.5 wt% (FIG. 6 and FIG. 8, respectively), as evaluated after the injection of 80 parts.

LIST OF REFERENCE SIGNS

[0073] none