Description

The invention relates to a composite pole composed of a bamboo cane as core and a continu ous fiber reinforced polymer layer. The invention further relates to a process for producing the composite pole.

Composite poles can be used in many applications, for example as lamp pole, power pole, tele communication pole, fencing post, design element, concrete reinforcement or in scaffolding. Usually such poles are made from concrete, wood, a metal like steel or a composite material. A disadvantage of poles made from concrete, wood or a metal is that they are very heavy and special equipment is needed for handling and for their installation. Further, particularly in terrain with difficult access, it is necessary to carry the poles. Further, it is disadvantageous that wood may be attacked by pests or animals, metals may corrode and concrete may break. Further, particularly in use of concrete poles as power poles or telecommunication poles, due to the weight of the pole, in case of heavy winds or snow the concrete pole may get beyond its break ing point. As such utility poles are usually connected to each other by wires its falling weight can increase the loads on the neighboring poles, pulling the wires on the poles causing them to break and starting a cascade-type of chain reaction which may bring down numerous poles and impact a wide community as power supply and telecommunication is interrupted.

Further, it is known to use composite poles made of continuous fiber reinforced polymers.

These composite poles usually are produced by winding processes as described for example in WO2018/036790.

For replacing at least a part of the synthetic material of endless fiber reinforced polymers, it is known for example from CN 205315879 to use bamboo fibers as reinforcing fibers. In WO-A 2017/177708 bamboo rafts are wound around the composite pole for additional reinforcement.

Particularly for additional reinforcement to achieve the mechanical requirements a power pole requires, in CN 109025458 a composite pole is described which comprises a bamboo cane as core, a first wrapping layer composed of a polyvinyl chlorine resin, a first winding layer com posed of a glass fiber roving impregnated with a polyester resin, a second winding layer com posed of an alkali-free glass fiber axial fabric or multi-directional fabric, a second wrapping layer composed of a woven fabric which is coated with a reinforced glue layer and an outer sheath layer composed of a low-smoke halogen-free flame-retardant polyolefin. This composite pole has the disadvantage of a complex structure with many different polymers and is using different production technologies for both thermoplastic and thermoset resins which results in relatively high investment costs. It is an object of the present invention to provide a composite pole which fulfils the mechanical properties required for the respective use and has a less complex structure than the power pole of the art.

This object is achieved by a composite pole composed of a bamboo cane as core and a contin uous fiber reinforced polymer layer, wherein the continuous fiber reinforced polymer layer is made of polymer-saturated continuous fibers which are directly wound around the bamboo cane.

By winding the polymer-saturated continuous fibers directly onto the bamboo cane, a less com plex structure can be achieved. Particularly by such a design, it is possible to use less different polymers, for example only one type of polymers and also only one type of fibers.

To achieve satisfactory mechanical properties of the composite pole, it is preferred to arrange fibers in the continuous fiber reinforced layer such that the continuous fiber reinforced polymer layer comprises a first layer in which the continuous fibers are wound perpendicular to a central axis around the bamboo cane and a second layer in which the continuous fibers are wound around the bamboo cane in an angle between 10° and 80° with respect to the central axis. Preferably, the continuous fibers of the second layer are wound around the bamboo cane in an angle in the range from 30° to 60° with respect to the central axis.

By the first layer and second layer in which the continuous fibers are wound in different angles around the bamboo cane with respect to the central axis, namely perpendicular to the central axis in the first layer and an angle between 10° and 80° in the second layer, essentially isotropic properties in tensile strength, compression strength and flexural strength can be achieved based on the angles in which the continuous fibers are wound around the bamboo cane.

Depending on the intended use of the composite pole, it is also possible that the continuous fiber reinforced polymer layer is composed of only one layer, either the first layer in which the continuous fibers are wound perpendicular to the central axis around the bamboo cane or the second layer in which the continuous fibers are wound around the bamboo cane in an angle between 10° and 80° with respect to the central axis. However, it is particularly preferred that the continuous fiber reinforced polymer layer comprises at least one first layer and at least one second layer.

For achieving essentially isotropic properties, it is further preferred, if in the second layer contin uous fibers are wound around the bamboo cane in such a way that fibers lying above another enclose an angle between 20° and 160°, preferably between 40 and 140° and particularly be tween 60 and 120°. To wind the continuous fibers around the bamboo cane in such a way that they enclose an angle between 20° and 160° it is for example possible to move a feeder for the continuous fiber along the bamboo cane from one end of the bamboo cane to the other end of the bamboo cane parallel to the axis of the bamboo cane while the bamboo cane rotates to achieve fibers being wound around the bamboo cane in a first angle and to move the feeder back from the second end to the first end of the bamboo cane to wind the fibers in a second angle which is aligned in the opposite direction to the angle of the movement of the feeder from the first end to the second end. The angle of the continuous fiber with respect to the central axis of the bamboo cane thereby depends on the rotational velocity of the bamboo cane and the velocity of the feeder. The slower the bamboo cane rotates and the faster the feeder moves, the larger is the angle of the continuous fiber with respect to the central axis of the bamboo cane.

By repeating the movement of the feeder from the first end to the second end of the bamboo cane and back from the second end to the first end, usually a woven pattern of the continuous fiber is formed.

Further it is preferred if the continuous fiber reinforced polymer layer comprises at least two first layers and at least one second layer or at least one first layer and at least two second layers, the numbers of layers differing in not more than one, wherein first and second layers are ar ranged alternately. By such an arrangement comprising at least two first and one second layer or alternatively at least one first and two second layers, it is possible to adjust the mechanical properties of the composite pole particularly in regard to stiffness, stability and/or flexibility. The mechanical properties thereby are adjusted by number, fiber pattern and thickness of each of the first and second layers.

To achieve the mechanical properties required for the target applications the choice of suitable bamboo material is important. The term bamboo is understood as subfamily Bambusoideae, in particular the tribes Arundinarieae and Olyreae both characterized by a wooden stem. Preferred genera comprise Dendrocalamus and Bambusa. For loadbearing applications preferred species of bamboo comprise the genus Dendrocalamus.

A bamboo cane usually is characterized by the following parameters:

A: Length of the bamboo cane

B _n : Diameter of the bamboo cane (measured at node positions)

C _n : Diameter of the bamboo cane (measured in the middle between two nodes)

Bi: Diameter of the bamboo cane at the bottom section (measured at node positions)

B _m : Diameter of the bamboo cane at the top section (measured at node positions)

D: Bi-B _m : Tapering of bamboo cane E _n : B _n -C _n : Node effect F _n : Internodal distance G _n : Thickness culm wall

H _n : ratio of wall thickness to diameter G _n : C _n (measured in the middle between two nodes)

I: Sagging of bamboo cane when it is fixed in a winding machine (measured in the middle of the bamboo cane

J _n : Thickness of septa

K _n : specific density

L _n : water content

M _n : content of lignin wherein the index n refers to the section (n = 1 denotes the bottom section)

In general the length A of suitable bamboo tubes can be 2 m to 35 m, a preferred length is 5 to 20 m and particularly 7 to 15 m. The diameter B of the bamboo tube is selected depending on the target application. There are diameters B _n which are measured at the individual node posi tions and diameters C _n measured in the middle between two nodes. In general, naturally grown bamboo with any diameter can be used in the inventive process. If the composite pole shall be used for example as a lamp pole, a power pole or a telecommunication pole, it is preferred to use a bamboo cane having a diameter B _n in the range between 100 and 300 mm. On the other hand, if the composite pole shall be used for example as a fencing post or in scaffolding, it is preferred that the bamboo cane has a diameter B _n in the range from 30 to 100 mm. For using as a design element, the bamboo cane may have any diameter naturally grown bamboo may have depending on the intended use of the design element.

A further characteristic feature of bamboo is the degree of tapering which is defined as the dif ference in diameters between the bottom and the top section of the pole. Any tapering naturally grown bamboo may have can be used in the invention.

Another bamboo feature are the nodes, especially the average difference in diameter between the nodes and the neighboring culm and the distance between nodes. All values found in natu rally grown bamboo are suitable to be used in the inventive process.

An important parameter is the thickness of the culm wall G _n which decreases to the tip of the cone. A thicker wall and a longer growth period will result in higher bamboo strength and thus require adding less polymer reinforced layers. In particular the wall thickness in the lower sec tions of the bamboo cane is important, more specifically the ratio H _n of wall thickness to diame ter. If the pole is intended to be used as a fencing post or as map pole or in other applications which bear a rather small load a smaller culm wall thickness G _n in the upper sections is useful to reduce weight, here a culm wall thickness at the top of the bamboo cane of 0,05 to 0,5 cm is sufficient. For power poles, telecommunication poles or scaffolds the top culm wall thickness is preferred between 0.2 and 2 cm.

The tapering of the bamboo cane D is a feature to optimize the pole weight. Preferred is a ta pering based on the length of the bamboo cane of less than 1 .5 cm/m. For power poles, tele communication poles or scaffolds the tapering preferably is less than 1 cm/m, particularly less than 0,5 cm/m.

Another important feature is the sagging I of a bamboo cane measured in the center after the bamboo cane has been fixed at both ends. Bamboo canes with a small sagging are preferred, particularly a sagging based on the length of the bamboo cane of less than 4 cm/m, preferably of less than 2.5 cm/m and particularly of less than 1 .5 cm/m. The specific density K _n of bamboo can vary depending from the position (bottom, middle, top), from the bamboo species and the age of the individual specimen. In general a density K _n of the bamboo cane of greater than 40 kg/m ³ is considered suitable. For products intended to carry high loads the bamboo has a preferred density K _n of at least 60 kg/m ³ and more preferred at least 100 kg/m ³ . The density thereby denotes the mass per volume of the bamboo cane includ ing culm wall and the cavities (lacuna) enclosed by the culm wall.

Bamboo canes reach the desired maximum stress, strength and modulus after 3 years of growth. In addition to the structural parameters A to J there are also parameters relating to chemical composition of certain parts of the bamboo, for example the content of lignin M _n or particularly the moisture content of the bamboo. It is preferred that the bamboo is stored at a defined temperature and moisture prior to production. The water content L _n of a bamboo cane is determined by a first weighing of the bamboo as received or after a certain treatment. The same bamboo cane is then placed in a drying oven for several hours at 110°C. The second weight is measured immediately after leaving the oven. The water content is then calculated as difference of the first and the second weighing results.

Optionally a treatment with hot steam is possible to reduce the sagging effect of bamboo by bringing it into a straight geometry. The hot steam treatment will also help to protect the product from biological attacks by microorganisms, fungi or pest like insects, particularly termites. If polyurethane is selected as the resin, a low moisture content of less than 20 wt-% and more preferred of less than 10 wt-% of the bamboo cane is preferred to avoid unintended foaming reactions at the interface bamboo - polyurethane.

As there is a certain variation in naturally grown bamboo with respect to the parameters A to M characterizing the bamboo, in one embodiment of the invention a part of the parameters or all parameters A to J are determined using a visual inspection tool for the respective bamboo cane before use. Depending on the result of the measurement, a predetermined winding program is selected accordingly. By using a small number of predetermined winding programs it is possible to overcome the variations in geometry of different bamboo canes and to achieve the required mechanical properties of the final bamboo composite.

The polymer used in the continuous fiber reinforced polymer layer can be a thermoplastic poly mer or a thermoset. Preferably, the polymer used in the continuous fiber reinforced polymer layer is a thermoset. Using a thermoset as polymer used in the continuous fiber reinforced pol ymer layer has the additional advantage that in general polymer precursors which usually are liquid at ambient temperature are used for producing the continuous fiber reinforced polymer layer and therefore no hot polymer melt is applied onto the bamboo cane but the continuous fibers saturated with the polymer precursors. Heating of the polymer precursor and the bamboo cane only is necessary if activation energy is needed for starting the chemical reaction of the polymer precursors forming the polymer. Even if activation energy must be applied, the temper ature usually is lower than the temperature of a melt of a thermoplastic polymer. If a thermoplastic polymer is used, the polymer may comprise a polystyrene (PS), polyvinylchlo ride (PVC), polybutylene terephthalate (PBT), polymethylmethacrylate (PMMA), acrylonitrile butylene styrene copolymers (ABS), a polyamide (PA), polycarbonate (PC), polyethylene ter ephthalate (PET), ethylene-vinyl acetate copolymer (EVA), poly lactic acid (PLA), polypropylene (PP), or polyethylene (PE) or a mixture thereof. Preferably, the polymer comprises a polyamide (PA), polycarbonate (PC), polyethylene terephthalate (PET), ethylene-vinyl acetate copolymer (EVA), poly lactic acid (PLA), polyhydroxybutyrate (PHB), polypropylene (PP), or polyethylene (PE) or a mixture thereof.

Suitable thermosets for example are polyurethane (PUR), epoxy resin (EP), vinyl ester resin (VE), unsaturated polyester resin (UP), phenolic resin (PF) or a mixture or hybrid blend thereof. Preferably, polyurethane or unsaturated polyester resins are used.

Independently, of whether a thermoplastic polymer is used or a thermoset, the polymer may comprise additives. Additives which can be added to the polymer can be any additives known to a skilled person. Typical additives for example are surface-active substances, fillers, flame re tardants, nucleating agents, dispersing agents, antioxidants, lubricants and catalysts, dyes and pigments, stabilizers, e.g. with respect to hydrolysis, light, heat or discoloration, reinforcing agents, and plasticizers.

The fibers in the continuous fiber reinforced polymer layer can be any continuous fibers usually used for fiber reinforced polymers. Preferably, the fibers are selected from glass fibers, mineral fibers, carbon fibers, aramid fibers, poly(p-phenylene-2,6-benzobisoxazol fibers, natural fibers, metal fibers and mixtures thereof. Particularly preferably, the fibers are glass fibers or natural fibers like flax, hemp, bamboo or sisal.

To further adapt the properties of the composite pole to the intended use, it is preferred that an additional layer is applied on the continuous fiber reinforced polymer layer. The additional layer differs from the continuous fiber reinforced polymer layer for example in at least one of:

- the additional layer comprises continuous fibers and is saturated with a second polymer which differs from the polymer in the continuous fiber reinforced polymer layer;

- the additional layer comprises a non-woven or felt being saturated with a polymer

- the additional layer comprises fibers which differ in material or structure from the fibers used in the continuous fiber reinforced polymer layer.

By the different polymer, the different fibers and/or the non-woven or felt it is possible to further modify the properties of the composite pole depending on the different feature(s) compared to the continuous fiber reinforced polymer layer. The polymer for the additional layer also may be a thermoplastic polymer or a thermoset. The polymer for the additional layer either may be a pol ymer which is of the same type but different monomer units, the same polymer but comprising different additives for achieving different properties or a completely different polymer. Prefera bly, for producing the additional layer, winding of the continuous fiber used in the continuous fiber reinforced polymer layer is continued and a different polymer is used or for achieving a smooth surface the additional layer is made of a non-woven saturated with a polymer.

To adapt the surface properties, it is further possible to apply a topcoat as final layer on top of the continuous fiber reinforced polymer layer or on top of the additional layer. By the topcoat it is for example possible to achieve a smooth surface or to provide a colored surface.

As the topcoat generally is not used to further modify the mechanical properties of the compo site pole, the topcoat also may contain additives which might weaken the mechanical stability of the polymer but improve other properties of the composite pole. Besides pigments, dyes or col orants for providing a colored surface the topcoat alternatively or additionally may contain one or more of flame retardants, anti-slip agents or UV-stabilizers.

It is particularly preferred to provide a topcoat in case the polymer of the continuous fiber rein forced polymer layer cannot contain the respective additives for properties the composite pole should have, for example a UV-stabilizer or a flame retardant. Further, it is preferred to provide a topcoat in case the composite pole should have a smooth surface.

Particularly preferably, the composite pole consists of the bamboo cane and the continuous fiber reinforced polymer layer, consists of the bamboo cane, the continuous fiber reinforced pol ymer layer and the topcoat or the additional layer, or consists of the bamboo cane, the continu ous fiber layer, the additional layer and the topcoat. By only one to three layers on the bamboo cane a composite pole is achieved which is much less heavy than a composite pole as known from the state of the art and which can be produced by a less complex process having less pro cess steps.

Preferably, the composite pole can be produced by a process comprising:

(a) fixing a bamboo cane as a mandrel in a winding machine;

(b) winding continuous fibers on the bamboo cane, the continuous fibers being saturated with a polymer precursor or a molten thermoplastic polymer or winding continuous fibers on the bamboo cane and saturate the fibers after winding with a polymer precursor or a thermoplastic polymer;

(c) curing the polymer precursor forming a polymer or solidifying the molten thermoplastic polymer and/or consolidating the polymer to form a continuous fiber reinforced polymer layer;

(d) optionally applying an additional layer on the continuous fiber reinforced polymer layer by winding continuous fibers which are saturated with a second polymer precursor or a sec ond molten thermoplastic polymer which differs from the polymer precursor or molten thermoplastic polymer used in step (b) or by winding a non-woven or felt which is saturat- ed with a polymer precursor or a molten thermoplastic polymer on the continuous fiber re inforced polymer layer, wherein step (d) can be carried out before or after step (c);

(e) optionally applying a topcoat on the continuous fiber reinforced polymer layer or on the additional layer.

The winding machine used for producing the composite pole can be any winding machine known to a skilled person and which allows for fixing a bamboo cane as mandrel. The winding machine for example can be established in such a way that the continuous fibers to be wound around the bamboo cane are guided through a feed eye which is movable parallel to the axis of the axis of the bamboo cane used as mandrel and the bamboo cane rotates for winding the continuous fibers around the bamboo cane. Additionally it is also possible that the feed eye for feeding the continuous fiber moves around the bamboo cane. In this case the bamboo cane either can be fixed in the winding machine and not rotate or the bamboo cane may rotate oppo site to the direction in which the feed eye moves around the bamboo cane for winding the con tinuous fiber around the bamboo cane.

In this context the feature that the feed eye is movable parallel to the axis of the bamboo cane does not only include a movement of the feed eye parallel to the fixed bamboo cane but also a movement of the bamboo cane parallel to its axis. In this case the feed eye may be fixed.

However, particularly preferably, the feed eye moves parallel to the axis of the bamboo cane and the bamboo cane fixed in the winding machine rotates around its axis for winding the con tinuous fibers.

For producing the continuous fiber reinforced polymer layer, the continuous fibers which are wound around the bamboo cane are saturated with a polymer precursor or a molten thermo plastic polymer. If the polymer is a thermoplastic polymer, it is possible to either saturate the fibers with polymer precursors which form the polymer or with a melt of the used thermoplastic polymer. Using the polymer precursors may have the advantage that the precursors form the polymer at a temperature which is below the melting temperature of the thermoplastic polymer formed by the polymer precursor. Due to the lower temperature there is less thermal stress on the bamboo cane.

If the polymer for the continuous fiber reinforced polymer layer is a thermoset, the continuous fibers preferably are saturated with precursors forming the thermoset before being wound around the bamboo cane.

Besides winding impregnated continuous fibers around the bamboo cane, independently of us ing a thermoplastic polymer or a thermoset as polymer for the continuous fiber reinforced poly mer layer, it is also possible to firstly apply continuous fibers which are not saturated with poly mer precursor or molten thermoplastic polymer on the bamboo cane and to impregnate the fi- bers with the polymer precursor or thermoplastic polymer after winding them around the bam boo cane.

However, it is preferred to wind impregnated fibers around the bamboo cane. Impregnating of the fibers thereby can be carried out in any way known to a skilled person, for example by guid ing the fibers through a bath containing the molten thermoplastic polymer or the polymer pre cursor. The fibers thereby can be impregnated in situ by saturating the fibers and wind them immediately after impregnation around the bamboo cane. Another possibility is the use of fibers which are pre-impregnated with resin (prepregs) instead of the dry fibers which are impregnated in situ in a bath. In this case after the winding is completed, the prepreg is consolidated to form a laminate using any method known to a skilled person.

Polymer precursors according to the present invention can be for example monomers or oligo mers which form the polymer by chemical reaction. For saturation of the continuous fibers, the polymer precursors must be liquid at application temperature. After application of the saturated continuous fibers or after impregnating the continuous fibers being wound around the bamboo cane, the polymer precursor is cured to form the polymer. The conditions for curing the polymer precursor thereby depend on the used polymer precursor. Thus it is for example possible that the polymer forms at ambient temperature. In this case, curing can be carried out at ambient temperature. If activation energy must be applied or curing only starts at a temperature above ambient temperature, it is necessary to apply heat which can be carried out according to any method known to a skilled person, for example by circulating hot air around the bamboo cane with the impregnated continuous fibers wound around or by passing the bamboo cane with the impregnated fibers thereon through a heating coil or an oven.

If a molten thermoplastic is used, the bamboo cane with the continuous fibers being saturated with the molten thermoplastic polymer is cooled to solidify the thermoplastic polymer forming the continuous fiber reinforced polymer layer.

Independently of using polymer precursors or a molten thermoplastic polymer for impregnating the continuous fibers, either the polymer precursor or the molten thermoplastic polymer may comprise additives for adapting the properties of the polymer. Additives used in the process can be any additives known to a skilled person and as described above in connection with the con tinuous fiber reinforced polymer layer.

To achieve a desired pattern of the continuous fibers, for example a woven pattern or parallel fibers, it is preferred that the continuous fibers are guided through a feed eye which is movable parallel to the axis of the bamboo cane and the angle in which the continuous fiber is wound on the bamboo cane is adjusted by rotational speed of the bamboo cane and speed parallel to the axis of the bamboo of the feed eye or if a feed eye is used which rotates around the bamboo cane, by the rotational speed of the feed eye and the speed of the feed eye parallel to the axis of the bamboo cane. If continuous fibers being saturated with a polymer precursor or a molten thermoplastic polymer are wound around the bamboo cane, generally the fibers are guided through the feed eye after saturation with the polymer precursor or the molten polymer.

After producing the continuous fiber reinforced polymer layer, the additional layer can be ap plied on the continuous fiber reinforced polymer layer. If the additional layer also comprises con tinuous fibers, the application of the additional layer preferably corresponds to the application of the continuous fiber reinforced polymer layer. If the additional layer comprises a non-woven or a felt, it is possible to wind the non-woven or the felt around the continuous fiber reinforced poly mer layer and subsequently impregnate the non-woven or the felt with a polymer or to wind a polymer-impregnated non-woven or a felt around the continuous fiber reinforced polymer layer.

If the additional layer comprises a different polymer or different fibers compared to the polymer or fibers used in the continuous fiber reinforced polymer layer, the polymer or the material of the fibers preferably is selected from the same polymer and fiber materials as also can be used for the continuous fiber reinforced polymer layer. If a non-woven or a felt is used in the additional layer, the non-woven preferably is made of artificial fibers like glass or natural fibers like wool, flax, sisal, bamboo or hemp.

To achieve a desired surface condition or desired function of the surface of the composite pole, a topcoat can be applied on the additional layer or on the continuous fiber reinforced polymer layer. The topcoat for example can be applied by spraying, painting, brushing, varnishing, cast ing or pouring.

If it is intended to provide the composite pole with a patterned surface it is possible to apply the topcoat by an impressing process, for example by calendering using patterned rolls.

Depending on the used materials in the continuous fiber reinforced polymer layer, and - if pre sent - in the additional layer and the topcoat and the dimensions of the produced composite pole, the composite pole may be used in many different applications, for example as lamp pole, power pole, telecommunication pole, fencing post, design element, concrete reinforcement or in scaffolding.

In one preferred embodiment the complete pole is made essentially from renewable materials from natural sources. Preferably, at least 90% by weight of the pole are made from renewable materials, and particularly 100% by weight. Renewable materials in this context mean raw ma terials from agricultural or forestry sources which are used in the non-food sector. Such materi als include products originating from animals, plants, from maritime sources or biological waste streams.

For collecting or transmitting information for example regarding the service life of an inventive composite pole, it is possible to integrate at least one electronic device, for example at least one of a sensor, a data storage or an amplifier, optionally in combination with a power supply, in the composite pole. Data to be collected and/or transmitted by such an electronic device for exam- pie include the location of the pole, temperature, moisture and loads, wherein besides the tem perature and the moisture of the material of the composite pole, particularly of the bamboo cane, also the ambient conditions can be measured. If an electronic device is integrated in the composite pole, it is particularly preferred to attach the electronic device during the winding pro cess, particularly below the outermost fiber-reinforced layer or during application of the top coat.

It is possible to connect functional elements, for example a crossbar like a crossbar to connect power lines or telecommunication cables, ladder spokes, or supports for electrical devices like transformers, control boxes, with the bamboo pole by using standard bonding technology pro cedures known to persons skilled in the art such as nailing, screwing, drilling or by using an ad hesive. In none of these cases, the bamboo pole is significantly damaged.

The advantage of the invention is the use of a lightweight porous and anisotropic natural mate rial bamboo and to reinforce it with impregnated continuous fibers. The inventive bamboo com posite has a lower weight than corresponding materials such as wood, steel, concrete or fiber- reinforced polymers. To reach material failure higher loads are required than for neat bamboo. The failure mechanism is more ductile as the bamboo composite can still carry significant loads even after the start of failure.

Illustrative embodiments of the invention are shown in the figures and explained in more detail in the following description.

In the figures:

Figure 1 shows a cross sectional view of an inventive composite pole;

Figure 2 shows a partial section of an inventive composite pole;

Figure 3 shows exemplary a process for producing a composite pole;

Figures 4a and 4b show parameters for characterizing a bamboo cane;

Figure 5 shows a result of a bending test of a neat bamboo cane and a bamboo laminate containing one layer of PU reinforced continuous glass fiber at an angle of 90° and one layer of the same material at +/-45° orientation.

Figure 1 shows a cross sectional view of an inventive composite pole.

A composite pole 1 comprises a bamboo cane 3. The size of the used bamboo cane 3 depends on the intended use of the composite pole 1. If the composite pole 1 shall be used for example as a lamp pole, a power pole or a telecommunication pole, it is preferred to use a bamboo cane 3 having a diameter in the range between 100 and 300 mm. On the other hand, if the composite pole shall be used for example as a fencing post or in scaffolding, it is preferred that the bam boo cane 3 has a diameter in the range from 30 to 100 mm. For using as a design element, the bamboo cane 3 may have any diameter naturally grown bamboo may have depending on the intended use of the design element. On the bamboo cane 3, a continuous fiber reinforced polymer layer 5 is applied. The continuous fiber reinforced polymer layer 5 thereby preferably is composed of at least one first layer 7 in which the continuous fibers are wound perpendicular to a central axis of the bamboo cane 3 and at least one second layer 9 in which the continuous fibers are wound around the bamboo cane in an angle between 10° and 80° with respect to the central axis.

As final layer in figure 1 , on the second layer 9 of the continuous fiber reinforced polymer layer 5 an additional layer 11 is applied. The additional layer 11 also may be a fiber reinforced polymer layer which differs from the fiber reinforced polymer layer 5 in the polymer used for impregnat ing the fibers and/or in the material of the fibers. Alternatively, the additional layer 11 may com prise a non-woven or a felt as reinforcing material instead of the continuous fibers. In this case the polymer used in the additional layer may be the same as used in the continuous fiber rein forced polymer layer or a different one. Which polymer is used in the additional layer depends on the intended use of the composite pole and thus in the properties the composite pole must have.

Figure 2 shows a further embodiment of an inventive composite pole in a partial section.

The composite pole 1 of figure 2 differs from the composite pole 1 of figure 1 in the number of first layers 7 and second layers 9. Here, on the bamboo cane 3 a first first layer 13 is applied in which the continuous fibers 23 are wound perpendicular to the central axis 15 of the bamboo cane 3. The first first layer 13 is followed by a first second layer 17 in which the continuous fi bers 23 are wound around the bamboo cane in an angle with respect to the central axis, in the embodiment shown here, in an angle of 45°. The continuous fibers 23 of the first second layer 17 thereby form a woven pattern and the continuous fibers 23 in the second layer which lay one above the other enclose an angle of 90°.

On the first second layer 17 a second first layer 19 is applied. The second first layer 19 thereby corresponds to the first first layer 13 with the continuous fibers 23 being wound perpendicular to the central axis 15 around the bamboo cane 3.

As a final layer, the continuous fiber reinforced polymer layer 5 comprises a second second layer 21 in which the continuous fibers 23 form the same pattern as in the first second layer 17. However, besides the same pattern of the continuous fibers 23 in the second layers 9, it is also possible that the pattern in the second layers 9 differs. Further, it is also possible that the con tinuous fiber reinforced polymer layer 5 only consists of a first layer 7 or a second layer 9. Fur ther, the first and second layers 7, 9 of the continuous fiber reinforced polymer layer 5 may only differ in the angle in which the continuous fibers 23 are wound around the bamboo cane 3, the angle in each layer being in the range between 10° and 80°. Thereby, preferably the angle which is enclosed by continuous fibers lying above another is in the range between 20° and 160° Finally, on top of the continuous fiber reinforced polymer layer 5 a topcoat 25 is applied. By the topcoat for example the composite pole is established with a desired color or additional proper ties are applied, for example by using a topcoat containing UV-stabilizers or a flame retardant. Additionally, by applying the top coat 25, a smooth surface of the composite pole 1 can be ob tained.

Figure 3 shows exemplary a process for producing a composite pole.

For producing the composite pole 1 , a bamboo cane 3 is fixed in a rotatable holding device 27 of a winding machine 29. From a fiber stock 31 continuous fibers are withdrawn and passed into a bath 33 which contains a liquid polymer precursor or a molten thermoplastic polymer. In the bath 33, the continuous fibers 23 are impregnated with the liquid polymer precursor or the mol ten thermoplastic polymer. The thus impregnated continuous fibers 35 then are passed through a feed eye 37 to the bamboo cane 3.

To achieve the continuous fiber reinforced polymer layer, the bamboo cane 3 is rotated around its central axis by rotation of the rotatable holding device 27. Due to the rotation of the bamboo cane 3, the impregnated continuous fibers 35 are wound around the bamboo cane 3.

For placing the impregnated continuous fibers 35 in a desired pattern around the bamboo cane 3, the feed eye 37 is movable parallel to the central axis of the bamboo cane 3. Depending on the speed of the feed eye 37, the impregnated continuous fibers 35 are placed in a certain an gle with respect to the central axis of the bamboo cane 3. To produce the first layer in which the continuous fibers are wound perpendicular to the central axis of the bamboo cane 3, the feed eye 37 has to move with such a speed that the distance the feed eye 37 moves during one rota tion of the bamboo cane 3 corresponds to the sum of the diameters of the number of continuous fibers passed through the feed eye. For obtaining an angle which is in the range from 10° to 80° with respect to the central axis of the bamboo cane 3, the feed eye has to move with such a speed that the desired angle is achieved. For an angle of 45°, the distance the feed eye 37 moves during one rotation of the bamboo cane corresponds to twice the diameter of the bam boo cane 3.

Besides passing 4 continuous fibers through the feed eye 37 as shown in figure 3, it is possible to pass any other number of continuous fibers through the feed eye 37. The number of continu ous fibers depends on the geometry of the feed eye and the desired thickness and geometry of the continuous fiber reinforced polymer layer. The number of the continuous fibers thereby cor responds to known processes for producing composite poles of continuous fiber reinforced pol ymers in which a mandrel is used which is removed after producing the composite pole.

Further, the bath being used for impregnating the fibers also can be any bath known to a skilled person and which is used in common winding processes for producing composite poles.

Figures 4a and 4b show parameters for characterizing a bamboo cane. A bamboo cane 3 which can be used in the inventive process generally comprises a plurality of segments 47 which are separated by nodes 41 . At the nodes 41 generally the segments are closed by septa 49. A bamboo cane 3 which can be used in the inventive process usually has a length A in the range from 2 m to 35 m and a diameter B in the range from 30 to 300 mm. The bamboo cane 3 thereby is characterized by diameters B _n which are measured at the individual node positions and diameters C _n measured in the middle between two nodes .

Another bamboo feature are the nodes 41 , especially the average difference E _n in diameter be tween the nodes 41 and the neighboring culm 43 and the distance between nodes F _n .

An important parameter is the thickness of the culm wall G _n which will decrease to the tip of the bamboo cane 3. In particular the wall thickness in the lower sections of the bamboo cane 3 is important, more specifically the ratio H _n of wall thickness to diameter.

Another important feature is the sagging I of a bamboo cane measured in the center after the bamboo cane has been fixed at both ends 45. The sagging is shown in figure 4b. Bamboo canes with a small sagging are preferred.

The specific gravity L _n of bamboo can vary depending from the position (bottom, middle, top), from the bamboo species and the age of the individual specimen. In general a density L _n of the bamboo cane 3 of greater than 40 kg/m ³ is considered suitable. For products intended to carry high loads bamboo is used having a preferred density L _n of at least 60 kg/m ³ and more preferred at least 100 kg/m ³ . The weight of a suitable bamboo cane is between 70 g/m and 10 kg/m, pre ferred between 100 g/m and 7.5 kg/m.

Figure 5 shows results of a bending test of a neat bamboo cane (length A = 120 cm, diameter Bi = 4,1 cm, B _m = 4,0 cm, wall thickness Gi = 0,5 cm, G _m = 0,5 cm) and a bamboo laminate (length A = 120 cm, diameter Bi = 4,1 cm, B _m = 4,0 cm, wall thickness Gi = 0,5 cm, G _m = 0,5 cm) containing one layer of PU reinforced continuous glass fiber at an angle of 90° with respect to the central axis of the bamboo cane and one layer of the same material at +/-45° orientation with respect to the central axis of the bamboo cane. In the diagram in figure 5, the elongation in percent is plotted on the abscissa 55 and the force in Newton on the ordinate 57. Curve 51 in figure 5 is a load-strain curve of the neat bamboo cane and curve 53 the load-strain curve of the bamboo laminate. The reinforcement leads to an increase of the maximum force by a factor of about 2.5.

The bamboo composite may break or may delaminate without break. In any case it can still car ry a higher load at high elongation of more than 40% than the neat bamboo cane before break. Due to the reinforcement the bamboo cane composite has a much lower deflection upon bend ing than the neat bamboo.