Patent Publication Number: US-2023151201-A1

Title: Biodegradable material for additive manufacture

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of additive manufacture wherein a three dimensional object is generated through layerwise build-up of material corresponding to consecutive cross sections of the object to be built. In particular, the invention relates to a biodegradable material for such additive manufacture. 
     BACKGROUND OF THE DISCLOSURE 
     Additive manufacturing offers the potential for production of customized parts as well as certain business advantages such as just in time production - thus maximizing performance of a part for a customer or application while at the same time enabling a business to run with limited or no inventory. 
     However, in the field of polymer additive manufacturing, the same challenges continue to exist with respect to end of life disposal of plastic parts as they do with all traditional plastics. At this time there are no known commercially available environmentally friendly, i.e., biodegradable, materials, such as polymers, available for additive manufacture (AM). AM of the type in point here is very often referred to as 3D printing. The present disclosure is discussed in the context of polymeric powders in particular used in powder bed fusion AM processes, but the invention is considered to be broader in scope, and applicable to other AM processes. 
     SUMMARY OF THE INVENTION 
     The present invention in one form is an AM material made from polymers and designed to be biodegradeable in a landfill or oceanic environment. The material may be made of bio-based polymers made from caster beans, cellulose, corn, starch, sugarcane, etc., such as nylon 11, bio-based polyethylene, polylactic acid, polyhydroxyalkanote, polyvinyl acetate, etc., to which is added microorganism, such as a bacteria, an enzyme or other additive to facilitate/accelerate the decomposition of the polymer in an environment where the object made through AM has been disposed, e.g., discarded after useful life. This would typically be the decompositiom or compostability of the biodegradeable treated polymer in a landfill environment. The microorganism or other additives that facilitate/accelerate the decomposition of polymers can also be added to petroleum-based, non bio-based polymers. 
     The same process can also be applied to non-bio based polymers such as those manufactured from petroleum bases (e.g., nylon-12), for example by mixing an additive like Ecopure from Bio-Tec Environmental, LLC (www.goecopure.com) into a petroleum based polymer. The Ecopure additives are organic compounds that attract microbes when the waste polymer product is placed in a microbe rich environment such as a landfill. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a chart compiling testing data of the degradation process according to at least one of the presently disclosed embodiments. 
         FIG.  2    illustrates a graph showing biodegradation over time according to at least one of the presently disclosed embodiments. 
         FIG.  3    illustrates another graph showing biodegradation over time according to at least one of the presently disclosed embodiments. 
     
    
    
     DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     In some forms of the inventive materials and method of making the materials, applicable additives considered would be: 
     Enzymes 
     Polymerisation for several technical polymers (e.g. polycondensation products like PA, PC, PET) is an equilibrium driven reaction: monomer(s) ⇌ polymer + side product e.g.: laurinlactam ⇌ polyamide 12 + water 
     Here, changing the composition of the system, e.g. by removing/consuming one of the components, the equilibrium is shifted. Different degrading enzymatic additives would consume the depolymerisation products (monomers, oligomers), thereby the equilibrium is directed towards forming these degradation products. 
     Examples known in literature, but not heretofore applied to AM, are:
     Nylonase (PA6 degradation)   Manganese peroxidase (lignin degradation) ➔ no thermal stability data available e.g. Negoro, Seiji (2009): Biodegradation of Nylon and other Synthetic Polyamides. In: Alexander Steinbüchel (Hg.): Biopolymers. Biology, chemistry, biotechnology, applications. Weinheim: Wiley-VCH.   

     Crystallization Inhibitors 
     Minerallic or organic additives that reduces the crystallinity in parts, thus attack on the polymer by surrounding conditions (moisture, pH, solvent, acids) could be used. Such are disclosed for instance in e.g. Montmorillonite for PLLA (Shuai, C.; Li, Y.; Feng, P.; Yang, W.; Zhao, Z.; Liu, W. Montmorillonite reduces crystallinity of poly-l-lactic acid scaffolds to accelerate degradation. Polymers for Advanced Technologies 2019, 30, 2425-2435.) But again, not heretofore applied to AM manufacture. 
     Salts 
     Water sensitive/water soluble salts that induce a change in pH-value to support degradation (depolymerisation) and thus act as catalysts, could be applied in another form of the invention. For instance, 
     Acetate salts ( e.g. potassium∼ (degradation »200° C.), sodium∼ (degradation &gt;300° C.), calcium∼ (degradation &gt;160° C.)   Formate salts (e.g. sodium formate: degradation 261° C.)   Hygroscopic salts, forming mild basic conditions ➔ might support depolymerisation   Sodium carbonate, aqueous (at increased temperature).   

     Specific Exemplary Embodiments 
     Any of the above additives could be incorporated into the AM polymer in the form of compounding or dry mixing into an existing powder. In the case of compounding, the raw material polymer and the additive would be melt mixed together and then extruded into a pellet or other shape (fiber, etc). The resulting shape would then be size reduced into a powder usable in powder bed fusion additive manufacturing such as would be useful for selective laser sintering (SLS), a process commercialized by EOS GmbH. Similarly, said polymer mixture could be extruded into other forms useful in other additive manufacturing processes, such as a filament for used in FDM, a process popularly commercialized by Stratasys Inc. 
     Certain additives can also be incorporated directly into powder. In this case, known SLS powders such as EOS PA 2200 (nylon-12 petroleum based powder) or EOS PA 1101 (nylon-11 castor bean based powder) would be mixed in a blender with the additive, also present in powder form. EOS PA 2200 and EOS PA 1101 are both products of EOS GmbH. 
     There are multiple choices of additives available for to enhance or introduce biodegradability in polymers available on the market. Three such examples are provided by Bio-Tec in their Ecopure line. These examples are:
     Ecopure EVA Powder EP-06P-EVA. This is a powder in the sub 600 micron range which would have to be further size reduced for the SLS powders typical in the additive market today to be dry blended as an additive. EP-06P-EVA is typically used in concentrations around 1% by weight in and is most effective for producing bio- degradability in polypropylene, nylons, and thermoplastic elastomers. EP-06P-EVA powder further classified to remove particles in excess of 200 microns and added in a 1% by weight mixture to EOS PA 2200, EOS PA 1101 and a specialty polypropylene manufactured by Braskem and powderised by Advanced Laser Materials, LLC of Temple, TX (“PP 05”) are specific mixtures embodied.   Ecopure EP-04C-NY. A pelletized material suitable for either powderising and dry mixing or melt mixing. This material features a high melting point of 220° C. which is advantageous for mixing with certain SLS polymers and processing in the SLS process. For example, when mixed with EOS PA 2200 which has a melting point in powder form of 184° C., the EP-04C-NY offers the advantage of not melting at the processing temperature of the SLS machine (e.g. 180° C. in an EOS P396 sintering system when running EOS PA 2200). However, it would melt under the temperature of the laser when the PA 2200 is melted to form a part. EP-04C-NY can be used further in concentrations around 0.5% by weight.   Ecopure EP-01B-EVA. A similar additive to EP-04C-NY but offering the particular advantage of having higher melt flow (measured at 10-28 g/10 minutes at 190° C. under a 2.16 kg weight tested according to ASTM D1238). This higher melt flow has the advantage of more efficient mixing in the molten state, especially if added as a dry mix in a powder form to another SLS polymer.   And see also U.S. Pat. Pub. 2013/337530, the disclosure of which is incorporated herein by reference.   

     Testing has been done with regard to certain materials. The ASTM D 5511-18 testing procedure was followed. The results of the testing have been positive in terms of biodegradability. Set forth below are the powder properties that have been tested, and the resulting tensile properties.
     1) The PCG-LV an Arkema grade of nylon 11 in pellet form. Generically, a low viscosity nylon 11 pellet. The PC refers to the part cake, which is the powder bed material that the part is removed from surrounding the object after the melting/solidification process.   2) PCG-LV, which had no additive, functioning as the control. PCG-LV 0.5% MB-67, PCG-LV with 0.5% of the EcoTech/EcoPure MB-67 additive PCG-LV 1% BS-201j, PCG-LV with 1% of the BioSphere BS-201j additive   3) ASTM D638, type 1 bar, 6”x½”x⅛”   

     
       
         
           
               
               
               
               
               
               
             
               
                 Power Properties 
               
               
                 Sample 
                 eos(*C) 
                 Melt Temp(*C) 
                 PSD(µm) 
                 ADT(/cc) 
                 MFR(g/10min) 
               
             
            
               
                 PCG-LV 
                 16 
                 189.44 
                 79.7 
                 0.37 
                 75.5 
               
               
                 PCG-LV PC 
                 16 
                 189.50 
                 76.6 
                 0.38 
                 53.4 
               
               
                 PCG-LV 0.5% MB-67 
                 16 
                 189.46 
                 74.8 
                 0.37 
                 76.7 
               
               
                 PCG-LV 0.5% MB-67 PC 
                 17 
                 189.86 
                 67.2 
                 0.033 
                 49.7 
               
               
                 PCG-LV 0.5% MB-67 PC Oxidized 
                 19 
                 189.98 
                 67.9 
                 0.031 
                 37.7 
               
               
                 PCG-LV 1% BS-201j 
                 17 
                 189.64 
                 80.1 
                 0.39 
                 77.4 
               
               
                 PCG-LV 1% BS-201j PC 
                 20 
                 188.29 
                 66.2 
                 0.37 
                 47.5 
               
               
                 EOS - Extrapolated Onset - Distance between onset of melting and onset of recrystallization on DSC Curve 
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                 Tensile Properties 
               
               
                 Sample 
                 Part Density (g/cc) 
                 Tensile Strength (MPa) 
                 Tensile Modulus (MPa) 
                 % Elongation 
               
             
            
               
                 PCG-LV 
                 1.03 
                 48 
                 1673 
                 23 
               
               
                 PCG-LV 0.5% MB-67 
                 1.03 
                 50 
                 1586 
                 27 
               
            
           
         
       
     
     From the test data, it appears that increasing from a 1% concentration to a 2% of the additive concentration increases the degradation rate by 60%. The end result is that the entire product will completely return to nature. The majority of the mass will be released of methane gas and the balance will be biomass and water. The expectation is that the degradation, once begun, will be complete in a span of just a handful of years, versus tens or hundreds of years. 
       FIG.  1    is a chart compiling testing data of the degradation process, here at approximately 83 days.  FIG.  2    charts the biodegradation during this testing period.  FIG.  3    charts the data over the same timeframe. 
     Inculum refers to the representative bacterium, such as would be found in a common landfill, as inoculum. Negative is a nylon sample (polyethylene) with no additive. Positive is cellulosic material. Percent in  FIG.  2    is the amount of degradation over time.  FIG.  3    Percent in this table compares the percentages as set forth in the chart of  FIG.  1   , to the Negative material; essentially, a more granular (more detailed) representation of the curves of  FIG.  2   , with the POS curve removed. 
     Thus, while the invention has been described herein as to certain embodiments, objectives, advantages and the like, those of skill will recognize changes, modifications, further properties and alternatives which will still fall within the scope and spirit of the invention.