Abstract:
A method for coloring fibers or fibrous materials where the fibrous material is initially chemically pretreated in order to achieve natural/white color for the fibrous materials. Next the pretreated fibrous material, a polymer base, and the colorant concentrate(s) are combined under suitable conditions to form a biocomposite mixture. The chemical pretreatment of the fibrous material prevents damage from being done to the fibrous material, such that the fibrous material retains its strength enhancing properties when combined with the polymer to form the biocomposite mixture. Additionally, the chemical pretreatment enables the fibrous material to chemically and mechanically bond with the colorant when combined into the biocomposite mixture.

Description:
FIELD OF THE INVENTION 
     The subject matter disclosed herein relates generally to biocomposite materials and, in particular, to a method and system to provide desired colors to biocomposite materials. 
     BACKGROUND OF THE INVENTION 
     Fibrous materials such as straw from flax, sisal, hemp, jute and coir, banana, among others, are used or combined with various polymers in the formation of biocomposite, or bio-fiber composite materials. Biocomposite materials utilizing these fibrous materials or fibers mixed with selected polymers provide enhanced desirable properties, such as increased strength, to the biocomposite material compared with polymer-only materials. 
     However, when the biocomposite material is formed, it is often desired to color the biocomposite material due to the particular use or product into which the biocomposite material is formed. Colorants are used in these biocomposite materials in order to increase the brand identity and aesthetic appeal of the products made from these materials. To accomplish this various colorants are utilized. These colorants are intermixed with the biocomposite material and provide the biocomposite material with the desired color for the end use of the biocomposite material. In one example of the use of colorants with biocomposite materials, these materials are colored by pre-coloring the fibrous material with liquid colorant before combining the fibrous material with the polymer base to form the biocomposite material. For example, the fibrous material and colorant are placed within a suitable container and boiled in order to bond the colorant to the fibrous material. 
     However, a significant problem with coloring bio-fiber composite materials is that the fibrous material, e.g., the cellulose material, interacts with the colorant differently than the polymer component of the biocomposite material resulting in an inconsistent finish/coloration over the entirety of the product formed with the biocomposite material and colorant. 
     Further, traditional methods for introducing the colorant into the biocomposite material, such as boiling, can damage the fibrous material, which can significantly degrade the strength of the fibrous material. This can result in the fibrous material acting within the biocomposite material as a filler material instead of a strength-enhancer. 
     As a result, it is desirable to develop an improved method for adding or introducing a colorant into a biocomposite formed with a fibrous material and polymer base in that provide a uniform color finish over the entire biocomposite material product, while not detrimentally affecting the strength/reinforcement properties of the fibrous material in the biocomposite. 
     SUMMARY OF THE INVENTION 
     According to one aspect of an exemplary embodiment of the invention, a method is provided to add a colorant to a biocomposite material that provides a uniform color across the entirety of the biocomposite material. In the method, the fibers or fibrous materials are initially chemically pretreated in order to achieve natural/white color for the fibrous materials. Next the pretreated fibrous material, a polymer base, and the colorant concentrate(s) are combined under suitable conditions to form a biocomposite mixture. This biocomposite mixture is then compounded to thoroughly mix the components. The colored biocomposite mixture is subsequently formed into pellets, which can be utilized in various thermoplastic processing technologies, such as extrusion, injection molding, compression molding, rotational molding, among other suitable processes, to create a thermoformed biocomposite product. The chemical pretreatment of the fibrous material prevents damage from being done to the fibrous material, such that the fibrous material retains its strength enhancing properties when combined with the polymer to form the biocomposite mixture. Additionally, the chemical pretreatment enables the fibrous material to chemically and mechanically bond with the colorant when combined into the biocomposite mixture. 
     According to another aspect of an exemplary embodiment of the invention, the method requires only a single step in order to bond the colorant to the fibrous material, making the method less labor intensive than prior art processes. 
     These and other objects, advantages, and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawing furnished herewith illustrates an exemplary embodiment of the present invention in which the above advantages and features are clearly disclosed as well as others which will be readily understood from the following description of the illustrated embodiment. 
       In the drawing: 
       The FIGURE is a schematic illustration of an exemplary embodiment of a biocomposite material coloring method performed according to the present disclosure; 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference now to the drawing FIGURE in which like reference numerals designate like parts throughout the disclosure, an exemplary embodiment of a method  10  for coloring biocomposite materials formed of combinations of various types of fibrous materials and polymers is illustrated. 
     In the illustrated embodiment, the method  10  includes an initial step  12  of pretreating the fibrous material  11  for use in the biocomposite. The fibrous material  11  can be selected from any suitable fibrous material used in the formation of biocomposites, and in an exemplary embodiment is a cellulosic based fibrous material such as oilseed flax, fiber flax, industrial hemp, coir, jute, banana, and sisal, among others. 
     In the pretreatment step  12 , the fibrous material which decorticated through the combing process where molecules of the cellulose fibers are not stressed, e.g., such as by those systems and methods disclosed in co-pending and co-owned U.S. Non-Provisional patent application Ser. No. 13/648,738, filed on Oct. 12, 2012, the entirety of which is expressly incorporated by reference herein in its entirety. For example, in the pretreatment step  12  the cellulose fibers are not separated from the other components of the fibrous material  11  by hammer mills, where the cellulose fiber molecules are stressed and compressed mechanically, and it is difficult to remove all of the lignin without damaging the cellulose fiber quality. In doing so, the fibrous material  11  is placed within a suitable enclosure and then chemically modified by alkaline treatment, e.g., in a solution of sodium hydroxide at a concentration 1-10% w/w, for a residence time of 1-24 hours, as necessary, followed by hydrogen peroxide treatment, e.g., in a solution including hydrogen peroxide at a concentration of 4-10% w/w hydrogen peroxide and sodium silicate at a concentration of 0.5-5% w/w, for a residence time of 1-10 hours, as necessary, to remove the color causing group from the cellulose fibers or by using sodium hydrosulfite which eliminates the color causing group from the fibers. This treatment helps to increase the aspect ratio of fiber, increase the interlocking capacity of fiber, while consequently reducing the weight and diameter of the fibers. 
     After this initial component of the pretreatment step  12 , the cellulose fibers are cleaned with distilled water to remove all chemicals and modified in a suitable treatment step  12 A to provide better mechanical and molecular bonding of the biocomposite material with colorant/pigment. In general, the addition of a colorant/pigment to a biocomposite material reduces the strength of the biocomposite. This modifying treatment step  12 A protects the mechanical properties of the composite. One example of a step  12 A of this type is by modifying the cellulose fibers with a triethoxyvinylsilane solution having triethoxyvinylsilane present in a concentration of 1-6% w/w, with the remainder being a mixture of water and alcohol in a ratio of between (40-60):(60-40)% w/w, for a residence time of between 1-6 hours, as necessary. After the triethoxyvinylsilane treatment the cellulose fibers are again cleaned with distilled water to remove all chemicals and optionally or subsequently dehumidified in step  13 , such as by utilizing the device and method disclosed in co-owned and co-pending U.S. Non-Provisional patent application Ser. No. 14/640,500, filed on Mar. 6, 2015, the entirety of which is expressly incorporated by reference herein, to remove all moisture from the fiber without destroying the fiber quality to ultimately produce a cellulose fiber is bright and whitish in color. 
     Once the fibrous material  11  is pretreated in this manner to achieve the desired natural or white color for the fibrous material  11  and output from step  12 , in step  14  the pretreated fibrous material  11  is compounded with the selected and suitable polymer(s)  17  and the colorant  15  in a suitable compounding device to form the colored biocomposite material, for example by using those steps disclosed in co-owned and co-pending U.S. Non-Provisional patent application Ser. No. 14/087,326, filed on Nov. 22, 2013, the entirety of which is expressly incorporated by reference herein. 
     In the biocomposite formation/compounding step  14 , an amount of the desired colorant  15  is added to the device holding the fibrous material  11  and the polymer  17 , such that the process for forming the colored biocomposite material  16  can be achieved in a single step, without having to color the fibrous material in a separate and independent step. With regard to the colorant  15 , any suitable type of natural, synthetic, and food/medical/industrial grade colorant can be used in this process. Further, the colorant can be in liquid or powder form without affecting the quality or coloration of the biocomposite material  18  and any end product  20  formed in a suitable thermoforming process  22  from the material  18 . The end product  20  can be formed from pellets (not shown) of the biocomposite material  18  output form the compounding step  16  and input into the selected thermoforming process  22 . For example, if white biocomposite material is required, then the process of the biocomposite formulation includes the addition of one or more of zinc oxide/titanium dioxide in an amount of 0.5-5% w/w to the biocomposite material is employed to get a white biocomposite. In addition, these chemicals enhance the bonding between cellulose fiber and the selected polymer and enhance the strength of the biocomposite, while also rendering the biocomposite non-porous and improving the moisture and UV resistance of the biocomposite. Similarly any other suitably colored pigments as are known in the art can be added to the biocomposite material, for example in amounts of 0.5-3% w/w, to achieve the required biocomposite color. 
     In the mixing and/or compounding step  16 , as the fibrous material has natural/white color when introduced, no color manipulation is required. In other words, a colorant having the desired color for the biocomposite material/end product can be used directly in this step, instead of mixing colorants with different colors to account for the grey/brown color of the fibrous material utilized in prior art coloring processes. In the compounding step  16 , the fibrous material completely blends in with the polymer base once colored with the colorant. Further, there is no leaching of colorant out of the biocomposite material once formed due to the mechanical and chemical bonding that occurs between the colorant and fibrous material as a result of the chemical pretreatment of the fibrous material, allowing the biocomposite material  18  to be used to from products  20  for use in the agricultural, automotive, construction and packaging industries, among others. 
     In addition, because the illustrated exemplary embodiment of the method of the invention does not involve processes that can damage or otherwise detrimentally affect the physical properties of the fibrous material, such as the prior art step of boiling of the fibrous material to color the fibrous material, the reinforcement properties of cellulose material are maintained. Further, any swelling of the fibrous material is minimized during coloring process of the illustrated exemplary embodiment of the invention, and the fibrous material is not placed under any thermal stress in the process, as opposed to traditional coloring processes that require heat, i.e., boiling, for the colorant and fibrous material to bond, which consequently reduces the strength of the fibrous material. 
     It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention.