A MOLDEABLE PAD BASED ON A COMBINATION OF NATURAL FIBERS AND THERMOPLASTIC POLYMER
TECHNICAL FIELD AND APPLICABILITY
INDUSTRIAL OF THE INVENTION The present invention relates in general to a moldable material, suitable for use in current technologies for molding fiber-reinforced composites. The invention further relates to moldable pads based on a combination of natural fibers and a thermoplastic polymer material. More particularly, the invention relates to molding tablets, each comprising a core of natural fibers that has been coated with a liner of thermoplastic material. The resulting pellets allow the retention of the length of the fibers at a high level during the molding process and impart a high level of mechanical performance. BACKGROUND OF THE INVENTION Compounds or plastics reinforced with fibers as are known, are well known with materials that are light in weight, generally non-metallic and extremely strong. Accordingly, these materials are used in a variety of applications where impact resistance, high capacity is desired
of load bearing and resilience without the disadvantage of using materials such as metals, which may be very heavy or which may be susceptible to atmospheric degradation such as corrosion. Many methods are available for the manufacture of fiber reinforced composites. Typically, producing these compounds includes first shaping or shaping a convenient molding medium comprising fiber reinforcing stretches and a polymeric molding material in the desired shape, then curing the formed material in this manner causing it to set or harden into an article Reinforced of resistant or hardened fibers. While numerous processes have been developed using different types of molding media and curing molding processes, all in general require combining a fiber reinforcement with a polymeric molding material, to form a moldable mixture, such that reinforcement of fibers can improve the strength properties of the resulting product. Furthermore, all composite manufacturing processes generally share the goal of maximizing dispersion of fiber reinforcement through the polymer, thereby ensuring that when the molded compound is formed, it does not include areas with lower amounts of fiber dispersion. , what can cause
that the compound experiences performance failures such as trapping or cracking. While it is desired that the fiber reinforcement be evenly dispersed throughout the composite matrix, it has been found that this goal is often difficult to achieve. Accordingly, the process of combining the fiber reinforcement with the molding polymer typically requires mixing to formulate these ingredients, and this in turn causes shearing or breaking of the fiber reinforcement into shorter lengths. The length of cut fibers in some aspects reduces the physical strength of the composite, since there is less crosslinking of the fiber reinforcement stretches in the composite matrix, and therefore the load carrying capacity and impact resistance is reduced. It is therefore convenient that molding materials for producing compounds contain reinforcements of fibers of maximum length, and it is also convenient that these molding materials facilitate the retention of the fiber length during the molding process. A means for increasing the fiber reinforcement dispersion in the composite matrix is to apply a thin layer of sizing to the fiber reinforcing surfaces. Typically, the sizing contains ingredients that chemically modify the reinforcing surfaces of
fibers both to aid in their dispersion and to promote bonding and adhesion between the fiber reinforcements and the molding polymer. In this regard, a more stable combination of fiber reinforcement and molding polymer is achieved. Additionally, sizing provides some protection to fiber reinforcement, making it less susceptible to breakage in shorter lengths. Considerable effort has been made in the development of sizing agents that are effective in aiding dispersibility and reducing breakage of fiber reinforcements. In addition to the need to develop molding and sizing materials that promote fiber length retention during molding, there is also a need for fiber reinforced composites that include cost-effective and environmentally friendly alternatives for reinforcements of conventional fibers such as glass fibers. Fiberglass, while lighter and less susceptible to corrosion than metal reinforcements, carries some inherent processing difficulties. For example, during the mechanical processing of glass fibers, loose fibers or fragments of fibers also known as lint can be trapped or entrained in the air. These loose fibers or fragments may disperse
finely in the processing environment or can be collected on equipment surfaces. Additionally, even when glass fiber is lighter than metal reinforcements, it adds more weight to the composite product than alternate reinforcements such as polymer fibers or natural fibers. Accordingly, these alternate reinforcements, in particular natural fibers, are extremely desirable options for use as fiber reinforcers in composite manufacture. However, attempts to use natural fibers in the manufacture of compounds have encountered some difficulties. While conventional molding processes, such as extrusion molding or compression molding have successfully employed glass reinforcements and even polymers in the manufacture of fiber reinforced composites, the pre-casting conditions that are routinely required, such as mixing and formulation at high temperatures, have imposed significant demands on the materials used. In particular, natural fibers in general have been excluded for use in compound molding processes, because they do not adequately support high temperature processing conditions and have been extremely susceptible to rupture.
Additionally, it has been observed that extrusion, formulation and subsequent molding degrade the length and chemical composition of natural fibers, while compression molding results in an undesirable felt or mat type product, which can not be handled by molding processes. high performance and high speed. In view of the deficiencies of the art, an object of the present invention is to provide a moldable material for use in a compound molding process, which has the advantages of incorporating environmentally and economically desirable natural fibers, such as fiber reinforcement, while that this moldable material is generated in a form that allows it to be processed easily without losing significant fiber length during a subsequent molding process. This process must be capable of producing suitable moldable materials to form natural fiber composites, without causing any loss of physical properties or processability of these fibers due to prolonged exposure to high heat. This process should also be capable of high-speed performance to ensure rapid and efficient manufacture of the product that contains natural moldable fibers. There is also a need for a moldable material reinforced with fibers
natural that has better fiber dispersion qualities, which will then help in improving its performance. Additionally, there is a need for a moldable material reinforced with natural fibers that has low environmental impact, since the fiber component is of natural origin and therefore is easily biodegradable and recyclable, is formed by a process that requires less energy and eliminates the problem of accumulation of glass fluff in the processing equipment. Furthermore, there is a need for a moldable product reinforced with natural fibers, which is prepared in such a way that unpleasant odors that are normally caused by degrading natural fibers during processing to form the mouldable material have been minimized and eliminated. These needs are met by the products and processes of the present invention. SUMMARY OF THE INVENTION It has now been discovered that suitable materials for use in the manufacture of fiber-reinforced composites can be prepared using a natural fiber reinforcement. In one aspect therefore, the invention is a mouldable material comprising a core of natural fibers that form a strand of natural fibers that has been wrapped in a thermoplastic material. The material
moldable can optionally be cut into pellets or pellets for use in compound molding. In another aspect, the invention comprises a multifilament fiber reinforcing product comprising a reinforcing strand of natural fibers and a coating of a sizing composition disposed on the surfaces of the fibers in the strand. The sizing composition can be aqueous or non-aqueous, in any variation comprising a selected coating ingredient of thermoplastic polymers, thermoset polymers and hydrocarbon oils and waxes and further comprises one or more ingredients selected from coupling agents, lubricants and other conventional additives. The strand of natural fibers with sizing can be lined in a thermoplastic material to form a mouldable material according to the invention. The invention further comprises a process for producing a material containing moldable natural fibers comprising: (a) providing a strand of multifilament natural fibers; and (b) covering the strand of natural fibers in a thermoplastic material.
The invention further comprises a process for producing a fiber reinforced composite article, comprising: (a) providing a moldable material comprising a strand of natural fibers lined in a thermoplastic material; (b) heating to melt the thermoplastic material; (c) working the material to make strands of the strand and disperse the filaments thereof from the thermoplastic material; (d) molding the mouldable material to form an article; and (e) cooling the article to form a fiber reinforced composite article. The concept of the invention also extends to fiber reinforced articles formed in accordance with this process. The present invention, which has low environmental impact and is totally recyclable, overcomes the limitations in the previous processes or by minimizing the exposure of the fibers to excessively high temperatures, thereby virtually eliminating chemical degradation and any associated odors. In addition, limitations caused by poor
dispersion of natural fibers in a composite molding matrix, has been overcome. On the other hand, an improved dispersion of the fibers and a performance of part of the increased compound have been obtained through the application of a sizing composition on the surfaces of the natural fibers. The present invention also overcomes limitations that have previously prevented or restricted the use of natural fibers as reinforcements in composite molding, in particular the mechanical degradation of the fiber structure during conversion of the natural fiber material into moldable reinforcement materials. In contrast, the present invention provides pellets or nodes containing long, undamaged fibers, which can be molded to form high quality compounds. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a process for manufacturing moldable wafers comprising a strand material based on natural fibers and a thermoplastic lining material according to the invention. Figure 2 is a three-dimensional representation of a tablet formed in accordance with the invention. Figure 3 is a cross section of a tablet formed according to the invention.
DETAILED DESCRIPTION AND PREFERRED MODALITIES OF THE INVENTION The present invention uses natural fibers as the basis for forming a strand of natural fibers, which subsequently act as a substrate in which a thermoplastic material is placed to form a moldable material. Accordingly, in one embodiment, the mouldable material of the present invention comprises a multi-filament natural fiber strand in combination with a thermoplastic material such that the thermoplastic material is formed as a liner around the strand of natural fibers. The natural fiber strand may optionally comprise a size comprising the filaments in the strand and improving the compatibility of the filament surfaces with the thermoplastic material of the sheath. The resulting lined strand can be used continuously, or as segments cut into a molding compound to form fiber reinforced composites. The term "natural fiber" as used in conjunction with the present invention, refers to fibers of cellulosic plants extracted from any part of a plant, including the trunk, seeds, leaves, roots or phloem or coarse fibers. Any natural fibers that meet the requirements of the process
The process described herein can be used in the present invention. Suitable natural fibers may include but are not limited to jute, bamboo, ramin, cotton, bagasse, hemp, bonnet, linen, kenaf, sisal, flax fiber, henequen, or any combination thereof. In addition, the term "substrate" is used in reference to the strand of natural fibers in its ability to function as the base element of the present invention, on which the sizing composition and / or thermoplastic material may be placed. Any arrangement of a plurality of filaments of natural fibers collected that form a strand of multiple filaments can be used as a substrate in the present invention. The filaments can be placed linearly as a connection in parallel alignment, or they can be formed as a twisted strand constituted by one or more layers. Preferably, the filaments of natural fibers are in the form of a twisted strand of a layer. However, since different types of natural fibers have different shapes or configurations and varying densities, there may be a wide range in the number of fibers required to form a convenient strand. Accordingly, the characteristics of the natural fiber strand can best be described and measured in terms of
parameters such as twisting factor and weight per unit length, due to the wide array of dimensional characteristics of natural fibers. The twisting factor is a measure of the average amount of helical twisting imparted to the strand over its length. Twisting is an important aspect of the present invention because it allows the formation of a continuous strand that retains sufficient structural integrity to serve as a substrate for the coating processes used to apply the sizing composition and / or the thermoplastic material to the strand according to the invention. Natural fibers are discontinuous or short fibers, as they naturally exist in relatively short stretches, typically in the range of approximately 5.08 cm (2") to approximately 1.83 meters (6 ft.) A continuous coating process, for example the lining process The strand of natural fibers with a thermoplastic material requires a continuous strand, therefore, in order to properly utilize this process, the natural fibers must be entangled together to form a strand that has a minimum amount of structural integrity. , in addition to increasing the strength of the fiber strand, the amount of twisting can also decrease the
dispersibility of natural fibers in the subsequent molding process. Consequently, when the twisting is increased, a more severe processing of the fiber strand may be required, either by means of increased temperature or increased shear forces which are applied to the fiber strand to achieve adequate dispersion. Increasing any one or one of these processing conditions typically results in fiber degradation. Accordingly, since the fewer bursts there are per 2.54 cm (1") correlates with an increased dispersion ease of the fibers, generally a range of about one twist per 2.54 cm (1") to about one twist per 10.16. cm (4") of strand length, it has been found to provide optimum dispersion, while retaining sufficient tensile strength to survive sizing and strand-lined processes.The basis weight of the natural fiber strand should also be sufficient to facilitate the use in a continuous coating process, preferably, the weight of the natural fiber strand should be in the range from approximately 1.093 grams per meter (1 gram per yard) in length to approximately 4.372 grams per meter (4 grams) x yard) in length.
example, sisal twine that has a weight of approximately 3,279 grams x meter (3 grams x yard) can be used as the strand of natural fibers. The strand of natural fibers which serves as the lining substrate with a thermoplastic material according to the invention, can optionally be dressed with a suitable sizing composition before the thermoplastic material is applied. This sizing composition may comprise a coating ingredient that provides a uniform layer or film on the surfaces of the filaments in the strand. This coating ingredient may be selected from thermoplastic polymer, thermoset polymers and hydrocarbon oils or waxes. The proportion of each type of coating ingredient in the size composition will vary depending on which one is used. The proportion of the coating ingredient will also depend on whether the size is an aqueous or non-aqueous formulation. In one embodiment of the invention, the coating ingredient may be a thermoplastic polymer. Any suitable thermoplastic polymer can be employed. The thermoplastic polymer can be added in emulsified form to an aqueous sizing composition, or it can be used without prior
emulsification in a non-aqueous sizing composition. Examples of these polymers include maleic polypropylenes, hydrocarbons, waxes, wax emulsions and polyurethanes. Preferably, the thermoplastic polymer that functions as the coating ingredient is a maleated polypropylene that is not in emulsified form. An example of this polymer is "E-43", commercially available from Eastman Chemicals Inc., which has a molecular weight of approximately 9100 atomic mass units, and softens at approximately 153 ° C (307 ° F). Typically, when the coating ingredient is a thermoplastic polymer, it can be employed in an aqueous sizing composition at a concentration that provides a proportion of the weight of sizing with sizing from about 0.1% by weight to about 10% by weight based on the total weight of the strand of natural fibers with sizing; or in a non-aqueous sizing composition, to provide a ratio of from about 0.1 wt% to about 25 wt%, based on the total weight of the strand of natural fibers with sizing. The coating ingredient can also be conveniently selected from the group consisting of thermoset polymers. Examples of these thermoset polymers include unsaturated polyesters, resins
epoxy and polyurethane. The thermoset polymer when a coating ingredient is employed, can be used in an aqueous sizing composition at a concentration that provides a proportion of the weight of strand with sizing from about .1% by weight to about 10% by weight, based on the total weight of the strand of natural fibers with sizing; or in a non-aqueous sizing composition to provide a final proportion from about .1% by weight to about 25% by weight, based on the total weight of the natural fiber strand with sizing. In an alternate embodiment, the coating ingredient may be selected from the group consisting of hydrocarbons, which include for example liquid hydrocarbon oils and waxes which may already be in amorphous or fluid solid form at room temperature. The hydrocarbon oil is preferably a mineral oil such as "WHITEREX 425", which is commercially available from Mobil Chemicals. An example of a suitable hydrocarbon wax is "SHELL AX 100", which is commercially available from Shell Chemical Co. The hydrocarbon coating ingredient may be employed in an aqueous sizing composition to provide a proportion of the weight of strand with sizing from about .1% by weight to about 10% by weight.
weight, based on the total weight in the strand of natural fibers with sizing; or in a non-aqueous sizing composition to provide from about .1% by weight to about 25% by weight, based on the total weight of the natural fiber strand with sizing. Preferably, the coating ingredient employed in the aqueous or non-aqueous sizing compositions of the present invention is a hydrocarbon oil or wax having a molecular weight in the range of about 250 atomic mass units (UMA) to about 4000 UMA. . The amount of this hydrocarbon coating ingredient that is incorporated in the aqueous sizing composition, before it is applied to the strand of natural fibers can vary from about 5% by weight to about 10% by weight, based on the weight total of the aqueous sizing composition. Preferably, the amount that is added to the aqueous base size is from about 1% by weight to about 3% by weight based on the total weight of the aqueous sizing composition. In non-aqueous sizing compositions according to the invention, the amount of hydrocarbon coating ingredient may be in the range from about 0.5 wt% to about 25 wt%, and preferably is about 10%
by weight up to about 15% by weight, based on the total weight of the non-aqueous sizing composition. The sizing composition may also include a convenient coupling agent. Coupling agents promote bonding between the strand of natural fibers and the sizing composition, thereby allowing better adhesion of the sizing composition to the surfaces of the strand. Examples of these coupling agents include organosilanes, titanates, zirconates, aluminates, zircoaluminates and chromium methacrylates. Certain organosilane coupling agents, which can be polymerized during use in the presence of natural fibers, exhibit some adhesive properties by promoting the wetting of natural fiber surfaces, which in turn causes the molecules on the fiber surfaces to interact and adhere together. As a result, an adhesive effect is observed with the use of these organosilanes. In this regard, these organosilane coupling agents demonstrate thermosetting properties resembling the thermosetting coating ingredients which may also be included in the sizing compositions of the invention. A suitable organosilane acting as a coupling agent in the aqueous or non-aqueous sizing compositions of the invention is gamma-amino propyltriethoxy
silane, which is an aminosilane that is commercially available under the trademark "A-1100" of C.K. Witco Inc. The coupling agent is used in an effective amount to provide the coupling effect necessary to adhere the sizing composition to the natural fiber strand surfaces. Additionally, one or more conventional additives selected from processing aids, lubricants, viscosity modifiers, surfactants, odor inhibitors, fragrances, fungicides, biocides and polymeric compatibilizers may also be included. A person skilled in the art can determine the selection and quantity of each of these additives in proportion to the desired effect on the sizing composition. The sizing composition if used, therefore, can be applied to form a multi-fiber reinforcing product, consisting of a strand of natural fiber reinforcements that has been impregnated or coated with the sizing composition. The sizing composition can be applied by any conventional means, including dip-extraction baths, rollers, cushions, or sprinklers. The sizing composition can be applied using an inline applicator in a continuous process or can be applied separately
out of line. Preferably, the sizing is applied at a temperature ranging from about 10 ° C (50 ° F) to about 200 ° C (392 ° F) depending on the type of natural fiber used. However, the application temperature in general should not exceed 200 ° C (392 ° F) for a prolonged period as this will cause degradation of the cellulose fibers. The sizing can be applied, for example to a plurality of individual filaments, which after treatment with the sizing composition can be collected and twisted into a strand, or alternatively the sizing composition can be applied to a previously formed strand. In the latter process, the sizing composition should be of a viscosity that allows flow to the sizing composition to impregnate or penetrate through the filaments in the strand of natural fibers, in order to coat substantially all surfaces of the individual filaments in the thread. For both aqueous and non-aqueous sizing compositions, the viscosity may be in the range of about 1 cP (.001 Pa »s) to about 200 cPs (.2 Pa« s). Preferred aqueous sizing compositions may be in a viscosity range of about 1 cP (.001 Pa »s) to about 20 cPs (02 Pa * s) to about 60 ° C (140 ° F), depending on the amount
of mixing solids, and more preferably are of a viscosity from about 1 cP (001 Pa »s) to about 10 cPs (.01 Pa» s) at 60 ° C (140 ° F). When the sizes are non-aqueous, the viscosity may be in the range of about 20 cPs (.02 Pa »s) to about 200 cPs (.2 Pa« s) at 60 ° C (140 ° F), and is preferably from approximately 20 cPs (.02 Pa 's) to approximately 60 cPs (06 Pa' s) at 60 ° C (140 ° F). These preferred viscosities typically promote sufficient penetration and coating of the filaments in the strand of natural fibers by the sizing composition. As described above, one embodiment of the present invention is a moldable material comprising a strand of a continuous natural fiber reinforcement comprising a plurality of natural fibers, which are substantially coated in a coating of thermoplastic material. The thermoplastic material is preferably one suitable for use with a casting matrix resin in the formation of fiber reinforced composites. The thermoplastic material typically has a molecular weight of at least about 7,000 units of atomic mass, up to a molecular weight of several hundred thousand units of atomic mass, and can be selected from the group included, but is not
limited to polyolefins, polyamides, thermoplastic polyesters, vinyl polymers, polymer modified asphalts and mixtures thereof. Examples of these thermoplastic materials include polypropylene, polyethylene, polypropylene modified asphalts, recycled polypropylene, polyvinyl chloride, polyethylene terephthalate, polybutylene terephthalate, polypropylene copolymers, polyamides, and mixtures thereof. The amount and type of thermoplastic material can be such that the mouldable material formed in combination therewith can be molded in a conventional molding process, without further addition of any other molding resin, to form a fiber reinforced composite article. Optionally, the mouldable material can also be combined with a conventionally known molding resin, additional during the molding process. These additional molding resins include polyolefins, polyamides or any other thermoplastic polymers suitable for molding purposes, as will be apparent to a person skilled in the art. The process for producing the molding materials of the invention comprises providing a strand of multifilament natural fibers and coating the strand with a liner of the thermoplastic material. Before lining
With the thermoplastic material, the strand of natural fibers can optionally be prepared with a composition as previously described. Figure 1 is illustrative of one embodiment of a process for manufacturing a moldable material, using a non-aqueous sizing in accordance with the present invention. According to Figure 1, one or more ends of the strand of natural fibers 1 are unwound from nozzles 2 and pass over one or more rollers 3, after which the strand ends of natural fibers 1 are immersed in and extracted from. an immersion bath 4. The immersion bath 4 contains a sizing composition with sufficient viscosity to allow impregnation or penetration through the filaments at the strand ends of natural fibers 1. For example, the sizing composition may comprise an ingredient of coating such as a hydrocarbon oil as well as one or more other conventional additives as described herein. After leaving immersion bath 4, the strand ends 1 can optionally be removed or directed onto one or more roller bars 5 to provide tensioning and picking of the ends to form a consolidated end, comprising multiple strands, around which a layer of thermoplastic material is
Apply to form a liner. In an alternate mode, where an aqueous sizing is used, the consolidated end can be passed through one or more furnaces
(not shown) before the coating of the thermoplastic material is applied. A particularly preferred method for applying a thermoplastic material around a continuous fiber material to form a liner is described in U.S. Pat. No. 5,972,503. According to this method, the strand of natural fibers can be extracted or otherwise passed through a convenient coating device. The coating device conveniently includes a means for providing a source of molten thermoplastic material for coating the strand, such as an extruder. The coated strand can then be passed through a die, which regulates the amount and thickness of the layer of molten thermoplastic material on the surface of the strand, and smoothes the molten thermoplastic material to form a lining that circumscribes the strand. A plurality of lined strands can be formed by extracting or otherwise passing a quantity of coated strands through a corresponding number of matrices, with each matrix having an orifice sized to form a coating in a thermoplastic lining of the thickness
wanted. Preferably, the coating device is a wire coating applicator (which is a device or group of devices capable of coating or lining one or more strands with a thermoplastic material to form a liner with relatively uniform thickness in each strand. , the wire coating applicator also includes a matrix that forms the liner at the desired uniform thickness and / or cross section.The strand is fed or passed through the coating device, using a convenient mechanism such as an extractor or puller, which the strand is removed from or forming part of the wire-coating applicator The wire-coated strand can subsequently be wound on a reel or its equivalent or otherwise passed through. of a shredder to be segmented into pellets A shredder can be adapted to also function as an extract or o assist the extractor in extracting the strand through the wire coating applicator. The velocity of the strand of natural fibers through the wire coating matrix can vary between 508-1,524 meters per second (100 to 300 feet per minute). This fast performance speed
allows exposure of the strand of natural fibers to the thermoplastic material while being at a relatively high temperature, however, it minimizes the exposure time, so that the temperature of the natural fiber strand itself does not rise to the point where fiber degradation will occur. As a result, the strand of natural fibers has a better thermal history and is more capable of forming a moldable material that provides excellent reinforcement for composite manufacture. This technique is represented in Figure 1, wherein a consolidated end formed by collecting the ends of strand of individually sized natural fibers 1, is passed through a wire coating applicator 6 as the coating device. The wire coating applicator 6 is equipped with a shaped die 7 which may be of round configuration or any other desired configuration depending on the desired cross-sectional profile of the wire-coated strand after it leaves the die 7. The applicator 6 is supplied with a molten thermoplastic material which is derived from melting a molten thermoplastic source material such as pellets in a headbox 8. The thermoplastic material
The melt is then fed to an extruder 9. From the extruder 9, a stream of molten thermoplastic material is forced through a nozzle opening (not shown) over the consolidated end as it passes through the wire coating applicator 6. As the consolidated end is passed through the matrix 7, the thermoplastic material is caused to flow around the consolidated end thereof, thus forming a strand lined with thermoplastic 10, where the filaments of natural fibers are formed into bundles in assembly to form a core surrounded by an outer layer of the thermoplastic material. The thermoplastic lined strand 10 leaves the wire coating applicator 6 and is directed through a water bath 11 at room temperature, which serves as a cooling medium. Any suitable alternate cooling means can be employed, for example air drying, cooling units or water sprinklers. The cooled thermoplastic lined strand 10 can be wound and stored for subsequent molding in continuous form or can be cut into pellets and packaged for subsequent use in molded applications. Cutting the continuous strand into discrete chips can be done through online or offline processes.
In this aspect, the apparatus may include means such as a shredder to segment the continuous strand into a plurality of discrete pads. In one embodiment represented by Figure 1, the thermoplastic-lined end 10 can be tensioned on one or more rollers 12, then directed through a slitter 13 which segments the strand 10 in approximately equal lengths of the desired size. Preferably, the thermoplastic-lined strand 10 is cut into pads 14 from about .635 cm (.25") to about 5.08 cm (about 2") in length. Optionally, the thermoplastic-lined end 10 can be removed through the wire-coating applicator by an extractor (not shown) located downstream of the wire-coating applicator and before the cutting means. Alternatively, the cutting means themselves can be adapted to perform the function of the extractor or to assist the extractor in extracting the strand of natural fibers squeezed through the wire-coating applicator. The resulting pellets 14 preferably range in length from about .635 cm (.25") to about 5.08 cm (about 2") with the most preferred length being about 1.27 cm (.5") to about 2.54 cm (1"). Nevertheless,
The lengths of the pads can be adjusted to longer lengths or shorter lengths as required for appropriate applications. Accordingly, the pad sizes can be selected to provide the appropriate fiber length retention, as well as providing a close dimensional relationship for automated processing and handling equipment. As illustrated in Figure 1, the pellets 14 can be collected in a hopper 15 and stored for future processing or packing, or can be packaged directly by integrating an in-line packing device in the forming operation (not shown). The pellets formed according to the invention are typically cylindrical in shape, although the shape can be modified by changing the configuration of the matrix through which the wire-coated strand is passed after the liner of thermoplastic material is applied. Figure 2 shows a pellet 14 having an approximately cylindrical shape, comprising a circular liner 16 of thermoplastic material forming an enclosure or container around a core 17 constituted by a plurality of filaments of natural fibers derived from one or more ends of wick . A cross section of this type of pills
formed by the invention, as illustrated in Figure 3, indicates that the core 17 of the natural fiber filament is substantially surrounded by the liner 16, such that the liner 16 provides a layer of thermoplastic material that is substantially consistent in thickness around the core. The tablets may contain varying proportions, by weight, of the thermoplastic lining material. In a preferred embodiment, the thermoplastic liner material can provide all of the molding resin used to form the composite matrix during molding of the molding materials to form a composite article, such as the formulation with an additional molding resin before it is unnecessary molding. Accordingly, the thickness of the thermoplastic liner can be varied to increase or decrease the proportion of the thermoplastic material in a mouldable material. The present invention furthermore relates to the manufacture of fiber reinforced composite articles from the molding materials of the invention, using a molding process selected from injection molding, compression molding, extrusion-compression molding, extrusion molding. injection, compression-injection molding or any combination thereof. A preferred process to produce a
fiber reinforced composite article, comprises molding tablets of the invention in a molding process comprising heating and / or extrusion, to make the thermoformable moldable material and dispersing the natural fiber segments of the tablets through the thermoplastic material. The mixture of molten thermoplastic material and fiber is then introduced into a convenient mold by a conventionally known process, such as injection or extrusion, or else it can be formed or shaped in an article and cooled. During the cooling process, the mixture of molten thermoplastic material and segments of natural fibers hardens into a hard and resilient compound. EXAMPLES Example 1. Non-aqueous sizing method. Sisal Bramante Comercial (Bambra untreated Ambraco 16000 twine) weighing approximately 3.50 grams per meter (3.2 grams per yard) and approximately one twist per 2.54 cm (inch) was used. The number of sisal fibers in the twine was approximately 120. Three non-aqueous sizing samples, samples A-C, were prepared: A. 1000 grams of mineral oil (WHITEREX 425). B. 750 grams of mineral oil and 250 grams of PP PP malleable wax (EPOLENE E-43) were combined
and heated to about 150 ° C (302 ° F) with stirring. C. 675 grams of mineral oil, 225 grams of maleated wax and 100 grams of stearic acid, were combined and heated to approximately
175 ° C (347 ° F) with agitation. . A ball of sisal twine was unwound from the interior and submerged using a dip bath in each of the sizing and then rewound in a winding machine. Sizing A was applied at room temperature, but sizing B and sizing C were heated in the sizing bath and applied at high temperature (100 ° C ± 20 ° C) (212 ° F ± 68 ° F) to the sisal. The sizing quantity collected by sisal was in the range of approximately 15 to 20% by weight, based on the total weight of the sizing strand (unless otherwise noted, all proportions in the examples described herein) they are designated as percentage by weight, based on the total weight of the strand with sizing). The small winding packages of sisal twine with sizing are then ready to be coated with wire as the next stage. The natural fibers with sizing were passed through an extrusion matrix with crosshead (wire-lined) with an exit hole with
3 mm diameter connected to a 5.08 cm (2") Killion extruder, all reference point temperatures in the extruder were 225 ° C (437 ° F) .The extruder was used to feed molten polypropylene Huntsman P4C6Z-059 ( MFI = 35) which has been previously dry blended with 2% Polybond 3200 polymeric coupling agent around the fibers as they pass through the matrix.After leaving the matrix, the coated strand immediately passes into a water bath 2 meters long that is maintained at 10 ° C (50 ° F) and on a Killion 4-24 double-band shooter In this example, the shooter's speed was adjusted to .508 meters per second
(100 feet per minute) and the exit of the extruder was adjusted to obtain a strand with a weight of 10.93 grams per meter (10 grams per yard) which was calculated to give a fiber content (dry) of 30% by weight. In this example, the strand was fed directly from the extractor into a Conair Jetro 2047 punch that cut the strand into pads of 12 mm length suitable for feeding in an injection molding machine. The pellets from each of samples A, B and C were pre-dried overnight at 88 ° C (190 ° F) and then injection molded to form discs using a Van Dorn 300-RS-25 molding machine. . Mold benchmark temperatures were
150 ° C-171 ° C (302 ° F-340 ° F), spindle speed D was 60 rpm (6.28 radians per second) and counter pressure of 551.58 kPa (80 psi). The die cavity had a thickness of 3 mm and a diameter of 177 mm. The die temperature was adjusted to 88 ° C (190 ° F). The molded discs were evaluated by visual examination. It was observed that all the molded discs emitted minimal odors due to the low molding temperatures. Additionally, the sisal fibers maintained their natural light brown color, indicating that no more than a minimum level of degradation occurred during processing. Disk A (molding of the pellets of sample A) clearly showed a collection of undispersed fiber bundles distributed in the PP matrix; based on a visual estimate only about 10% of the fibers were dispersed in the matrix. Disk B showed a high level of dispersion. It was estimated that only less than about 10% of the fiber bundles were not dispersed in the matrix. Disk C showed substantially complete fiber dispersion, no beams were visible. Example 2. Aqueous sizing method. An aqueous sizing consisting of 21.5 grams of gamma-aminopropyltriethoxy silane and 100 grams of mallowed PP emulsion (CHEMCOR
43N40) were added to demineralized water such that the final sizing amount was 8823 grams. The mixing solids were calculated as 0.6% by weight. An amount of 1135 grams of sisal twine (same type as Example 1) was unwound in a plastic bucket with a capacity of 18.93 liters (5 gallons). It was left loose in the bucket. The aqueous sizing was emptied on the sisal twine and left to impregnate for 10 minutes. The upper end of the sisal was found and the twine was transferred by hand and the excess sizing was squeezed as the twine was transferred. The weight of the sisal with sizing after sizing was 2853 grams, which indicated that the sisal collected approximately 150% of its weight in the sizing composition. Other experiments have shown that the amount of water collected by sisal when immersed in water is approximately 150% of the weight of the sisal. The cuvette was placed in a forced air oven at 105 ° C (221 ° F) and the water was removed after approximately 30 hours of drying time. The amount of dry sizing composition in the dry sisal was about 0.9% by weight. The sisal was then coated with wire as described in Example 1. It is considered that the invention of the applicants includes many other modalities that are not specifically described here, accordingly, this
The description will not be read as limited to the foregoing examples or preferred embodiments.