Patent Application
20090007818
The present invention relates to composite materials comprising wood and thermoplastics, in which lignocellulosic material, such as wood in the form of particles, for example as wood flour, wood fibers or wood chips, mixed with a thermoplastic forms a composite material. Furthermore, the present invention relates to a process for producing a composite material comprising lignocellulosic material and a thermoplastic.
U.S. Pat. No. 4,717,742 describes wood-reinforced thermoplastic composite materials of the generic type comprising wood pulp and polyethylene or isotactic polypropylene, the plastic containing in each case maleic anhydride. For improving the adhesion between lignocellulosic fibers on the one hand and plastic on the other hand, the lignocellulosic fibers are treated with γ-aminopropyltriethoxysilane in a solvent, the solvent is allowed to evaporate off and drying is effected at 105° C. The maleic anhydride serves as a coupling agent between the silanized cellulose fibers and the plastic.
Compared with the known composite materials comprising a thermoplastic and lignocellulosic fibers, it is the object of the present invention to provide a composite material of the generic type having improved properties.
In particular, it is the object of the present invention to provide a composite material comprising a thermoplastic and lignocellulosic material, which composite material has improved mechanical properties, for example a higher notched impact strength, an improved modulus of elasticity and a higher tensile strength and, preferably, lower water absorption.
It is a further object to provide a process for producing the composite material, which can be carried out substantially without an organic solvent.
The invention achieves the abovementioned objects by derivatizing lignocellulosic fibers by treatment with silanes which firstly produce an adhesion-promoting effect between lignocellulosic fibers and thermoplastic and secondly render the lignocellulosic fibers water-repellent.
In the preferred process, an oligomeric condensate of different silanes, referred to below as organopolysiloxane, which serves as an adhesion promoter and as a water repellent, are brought into contact with the lignocellulosic fibers in aqueous solution so that substantially no organic solvents are used.
Furthermore, it is preferable if, after the treatment with the silane mixture, the lignocellulosic fibers are dried and are subjected to heating at about 80-120° C., preferably about 100-105° C. This drying and heating can be carried out in one stage or a plurality of stages, for example as predrying at 40° C. and curing at 120° C.
The content of lignocellulosic fibers in composite materials according to the invention is, for example, from 10 to 90% by weight, it being possible to use wood flour, wood turnings and/or wood chips from hardwoods or softwoods and mixtures thereof as lignocellulosic fibers. In particular, polyolefins, polyethylene, polypropylene, preferably isotactic polypropylene, block copolymers and copolymers of polyethylene units and polypropylene units, PVC, polystyrene, acrylonitrile-butadiene-styrene (ABS) or melamine resin are suitable as plastic, which is preferably thermoplastic. Particularly preferably, the plastic is not derivatized or provided with functional groups, for example not provided with carboxyl groups.
According to the invention, lignocellulosic fibers are reacted by a treatment with organopolysiloxanes or copolymers thereof in a water-based mixture. As a result, the adhesion promotion between lignocellulosic fibers and thermoplastic in the composite material is improved. Consequently, both the physicomechanical properties of the composite material are improved and the absorption of liquid and gaseous water is reduced.
The organopolysiloxanes to be used according to the invention are obtainable by mixing water-soluble aminoalkylalkoxysilanes which have the general formula I
R—Si(R1)y(OR1*)3−y (I)
with water-insoluble alkyltrialkoxysilanes which have the general formula II
R2—Si(OR1**)3 (II)
optionally additionally in combination with water-insoluble dialkyldialkoxysilanes of the general formula III
AA′-Si(OR1***)2 (III).
Here, R is an aminofunctional group, aliphatic, branched or straight-chain or aromatic with 2 to 8 carbon atoms, which contains primary, secondary, tertiary, preferably quaternary aliphatic or aromatic amino groups or may have the general formula IV:
[Z(f+g+h)](f+g+h)-[NH2+f(CH2)b(NHg+1)c(CH2)d(NHh+1)e(CH2)i](f+g+h)+ (IV)
in which 0≦b≦3; 0≦d≦3; 0≦i≦3; 0≦f≦1; 0≦g≦1; 0≦h≦1; 0≦c≦1; 0≦e≦1 and b+d+i≠0 and also c=0 for b=0, also e=0 for d=0, also e=0 for i=0 and also c=0 for d=i=0. Here, Z is a monovalent inorganic or organic acid radical. R1, R1*, R1** and R1***, independently of one another, are a methyl or ethyl radical, R2 is a linear, cyclic or branched alkyl radical having 1 to 8 carbon atoms, A is a straight-chain or branched alkyl radical having 1 to 3 carbon atoms and A′ is a straight-chain or branched alkyl radical having 1 to 3 carbon atoms and 0≦y≦1. Preferably, the molar ratio of compounds of the formula I to the sum of those of the formulae II and III is from 0 to 2.
In a preferred embodiment, the water-soluble aminoalkylalkoxysilane is 3-aminopropyltriethoxysilane and the water-insoluble alkyltrialkoxysilane is isobutyltrialkoxysilane.
The organopolysiloxane, which consists of water-soluble aminoalkylalkoxysilane and at least one water-insoluble alkyltrialkoxysilane, optionally at least one further water-insoluble dialkyldialkoxysilane, is preferably prepared with acid catalysis. Acid catalysis preferably means that the pH has a value from 1 to 8, more preferably from 3 to 5. The organopolysiloxane can therefore be defined as a condensate of at least one water-soluble aminoalkylalkoxysilane and at least one water-insoluble alkyltrialkoxysilane, optionally at least one further water-insoluble dialkyldialkoxysilane. The organopolysiloxane can therefore also be described as a condensate of the at least one water-soluble aminoalkylalkoxysilane hydrolyzed with acid or base catalysis and of the at least one water-insoluble alkyltrialkoxysilane. The number of silane units in the organopolysiloxane, which as a rule is present in distribution or in a mixture, preferably comprises an average distribution of from 5 to 20, preferably from 10 to 18, particularly preferably 15, siloxane units. In this way, a preferred degree of oligomerization of the organopolysiloxane can be described. The preparation of a preferred organopolysiloxane is described in EP 0 716 128 or EP 0 716 127.
In a particularly preferred embodiment, the organopolysiloxane used is water-based and substantially free of alcohols, it being possible to prepare the organopolysiloxane by mixing the water-soluble aminoalkoxysilane with the water-insoluble dialkylalkoxysilane in water, adjusting the pH to a value of from 1 to 8, preferably from 3 to 5, and removing alcohol, preferably by vacuum distillation prepared. For the acid catalysis or for adjusting the pH, inorganic or organic acids may be used, preferably formic acid or acetic acid. A preferred, water-based organopolysiloxane composition is disclosed in EP 0 716 128 A2 and is available under the name Dynasylan® from Degussa AG, Germany.
It is preferable if the treatment of the lignocellulosic fibers takes place over a relatively long period, for example over two hours, with agitation. It is preferable if the silanization of the lignocellulosic fibers is carried out at from about 40 to 70° C., preferably 40° C., which leads to an increase in the amount of organopolysiloxane introduced into the lignocellulosic material. Furthermore, it is preferable if an aqueous formulation of the organopolysiloxanes according to the invention has a pH of from 3 to 4 during the treatment, for example established by formic acid, and is completely hydrolyzed by relatively long mixing of the aqueous solution for use.
Alternatively, an organopolysiloxane-containing composition, preferably based on water, can be prepared by mixing water-soluble aminoalkylalkoxysilanes of the general formula I
R—Si(R1)y(OR1*)3−y (I)
in the molar ratio >0 to not more than 2 with water-insoluble aminoalkoxysilanes of the general formula II
R2—Si(OR1**)3 (II)
R being an aminofunctional organic group of the general formula V
[Z(f+c+f*)](f+c+f*)-[AdNH−(2+f−d)[(CH2)aNA1eH−(1−e+f*)]c(CH2)b−](f+c+f)*+ (V)
in which 0≦a≦6; 0≦b≦1; 0≦c≦1; 0≦d≦2; 0≦e≦1; 0≦f≦1; 0≦f*≦1, A and A1 are a benzyl or vinylbenzyl radical, N is nitrogen and Z is a monovalent inorganic or organic acid radical, for example selected from the group consisting of Cl−, NO3−, HCOO−, CH3COO, R1, R1** and R**,
R1, R1* and R1** being a methyl or ethyl radical and
R2 being a linear, cyclic or branched alkyl radical having 1 to 6 carbon atoms or a ureidoalkyl group of the general formula VI
NH2—CO—NH—(CH2)b— (VI)
and 0≦y≦1,
subsequently adding water to the mixture,
adjusting the pH to a value of from 1 to 8, and
removing the alcohol present and/or formed in the reaction.
The invention will now be described with reference to the figures, in which
As an example of lignocellulosic fibers, spruce wood turnings were suspended and stirred with various silanes in water, for control only in water. Before addition of the spruce wood turnings, the organopolysiloxanes were prepared to a concentration of 3% by weight in water, adjusted to pH 4 by addition of acetic acid and stirred for 30 minutes in order to ensure complete hydrolysis. It was observed that the initially formed emulsion became a clear solution. 40 g of turnings (10.2% moisture) were added to the solution and shaken for 2 hours in a horizontal shaker and then filtered off.
For the organopolysiloxanes, methyltriethoxysilane (Dynasylan® MTES), 3-glycidyloxypropyltrimethoxysilane (Dynasylan® GLYMO), propyltriethoxysilane (Dynasylan® PTEO), vinyltrimethoxysilane (Dynasylan® VTMO) and 3-aminopropyltriethoxysilane (Dynasylan® AMEO) were used. The organopolysiloxanes having the designation Dynasylan® are available from Degussa AG, Marl, Germany.
Aliquots were dried at 25° C., 60° C. and 103° C., respectively for 72 hours. Thereafter, the turnings were conditioned at 20° C. and 25% relative humidity to constant weight and were weighed. The dry weight or the moisture content of each sample was determined by drying at 103° C. and weighing.
The results of the weight increase of spruce wood turnings are shown in
The weight loss of the control turnings, which were treated only in water without organopolysiloxane, was 1.0% (103° C.).
In
Spruce wood turnings treated according to Example 1 were suspended in water and left to stand for 48 hours. This so-called float test is shown in
Spruce wood turnings silanized with organopolysiloxane comprising Dynasylan® VTMO or Dynasylan® AMEO and control turnings treated with water were processed with isotactic polypropylene to give composite materials. A proportion of turnings of 60% by weight with 40% by weight of polypropylene was used.
The composite material comprising silanized spruce wood turnings and polypropylene was produced by preparing a mechanical mixture of the silanized spruce wood turnings with granulated polypropylene (random polypropylene copolymer (randomly distributed copolymer), melt flow index according to ISO 1133 (MFI)=1.8±0.4 g/10 min at 230° C./2.16 kg) in a roll mill and then pressing said mixture. For this purpose, homogeneous mill hides were produced on the roll mill from the mixture of granulated polypropylene and silanized spruce wood turnings at 180° C. and a circumferential speed of 25 rpm over 5 to 10 min, which mill hides were then heated in the press (e.g. platen press “Schwabendan”, type Polystat 400A), initially without pressure for 20 min to about 180° C. and then pressed for 30 s at 10 bar. The cooling to room temperature was effected for 20 min in the press while maintaining the pressure.
The mechanical properties were then determined with reference to the standards ISO 180 (notched impact strength), ISO 527-2 (tensile strength) and ISO 1183-1 (density) and are shown in Table 1 below.
The results in Table 1 show that the notched impact strength of the composite materials was increased compared with the control material comprising untreated spruce wood turnings, while the modulus of elasticity was lower. The tensile strength remained virtually unchanged for the spruce wood turnings treated with organopolysiloxane comprising Dynasylan® VTMO, whereas it has increased substantially for the composite material of the spruce wood turnings treated with organopolysiloxane comprising Dynasylan® AMEO. The density of the composite materials according to the invention was increased, which, like the increased notched impact strength and the identical or increased tensile strength, indicates a tighter bond between lignocellulosic fibers and plastic.
For determining the storage in water, the composite materials were stored in water for 14 days with reference to EN ISO 62, the weight increase being determined after 1, 3, 7 and 14 days. The percentage weight increases are shown in Table 2 below.
On the basis of the smaller weight increase in the case of the composite materials according to the invention for the spruce wood turnings treated with organopolysiloxane comprising Dynasylan® VTMO or Dynasylan® AMEO in combination with polypropylene, by way of example, the values of Table 2 show a substantially smaller incorporation of water compared with the composite material comprising water-treated or untreated spruce wood turnings (control).
Spruce wood turnings were incubated according to Example 1 with an aqueous formulation of organopolysiloxane comprising 3-aminopropyltriethoxysilane and isobutyltriethoxysilane, commercially available under the designation Dynasylan® HS 2909 (Degussa AG, Germany), in concentrations of 3, 4, 5 and 7.5% by weight for 12 hours with shaking. The turnings were then separated off by sieving and were dried at 103° C. for 72 hours.
The spruce wood turnings treated with Dynasylan® HS 2909 were processed with isotactic polypropylene in a ratio of 60% by weight to 40% by weight by mixing with granules and subsequent extrusion to give a composite material according to the invention. The mechanical properties are shown in Table 3 below as a function of the concentration of organopolysiloxane (Dynasylan® HS 2909) used.
The values in Table 3 show that at least the notched impact strength and the tensile strength of the composite material were improved by the treatment of the lignocellulosic fibers with an organopolysiloxane according to the invention compared with the control which contained spruce wood turnings treated only with water.
The incorporation of water was determined according to Example 2; the values are summarized in Table 4 below.
The measured values of Table 4 show that the incorporation of water is substantially reduced by the treatment with an organopolysiloxane according to the invention, the treatment with only a 3% by weight solution being sufficient to reduce the weight increase after 14 days to a value of less than 4%, which corresponds approximately to the water increase by isotactic polypropylene without spruce wood turnings. A higher content of organopolysiloxanes according to the invention, for example obtainable by treatment of the spruce wood turnings with higher concentrations of the aqueous organopolysiloxanes according to the invention, leads to further reduced values for the incorporation of water into the composite material.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102006 013090.1 | Mar 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP07/52620 | 3/20/2007 | WO | 00 | 9/4/2008 |
