WO2020118038A1

WO2020118038A1 - Coupling agent modified polyolefins to maximize sintering and part performance in 3d printing, methods thereof, and articles formed therefrom

Info

Publication number: WO2020118038A1
Application number: PCT/US2019/064656
Authority: WO
Inventors: Alessandro Bernardi; Alexandre Di Pintor DA LUZ; Ana Paula DE AZEREDO
Original assignee: Braskem America, Inc.
Priority date: 2018-12-05
Filing date: 2019-12-05
Publication date: 2020-06-11

Abstract

Methods of manufacturing an article that include depositing a polyolefin composition at a target surface, wherein the polyolefin composition includes a polyolefin and a coupling agent; and melting and sintering the polyolefin composition with radiation from a radiation source at an intensity to produce the article, wherein the intensity initiates a reaction between the polyolefin and the coupling agent. Articles may include a sintered polyolefin composition, wherein the sintered polyolefin composition is prepared from the reaction of a polyolefin with a coupling agent in the presence of a radiation source.

Description

COUPLING AGENT MODIFIED POLYOLEFINS TO MAXIMIZE SINTERING AND PART PERFORMANCE IN 3D PRINTING, METHODS THEREOF, AND

ARTICLES FORMED THEREFROM

BACKGROUND

[0001] Rapid prototyping or rapid manufacturing processes are manufacturing processes which aim to convert available three-dimensional CAD data directly and rapidly into workpieces, as far as possible without manual intervention or use of molds. In rapid prototyping, construction of the part or assembly is usually done in an additive, layer-by-layer fashion. Those techniques that involve fabricating parts or assemblies in an additive or layer-by-layer fashion are termed “additive manufacturing” (AM), as opposed to traditional manufacturing methods which are mostly reductive in nature. Additive manufacturing is commonly referred to by the general public as“3D printing” and“3DP.”

[0002] There are currently several basic AM technologies: powder bed fusion, material extrusion, material jetting, binder jetting, material jetting, vat photopolymerization, sheet lamination, and directed energy deposition. Of particular interest to the present disclosure, powder bed fusion techniques include, among others, selective heat sintering (SHS), selective laser melting (SLM), selective laser sintering (SLS), selective absorbing sintering (SAS), high speed sintering (HSS), and selective inhibition sintering (SIS). The aim in all these methods is the production of printed articles having the same density as the polymeric material from which the powder has been produced, without the presence of cavities and/or inclusions.

[0003] Preserving density of the polymer material in the final produced article is a function of coalescence of the partly or fully molten powder particles, which is aided by polymers having particular viscosity profiles in the melt stage. However, simply reducing the viscosity of the polymer material to improve particle coalescence often results in compromise in other polymer properties such as melt strength and compromised mechanical properties in the final printed article. SUMMARY

[0004] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0005] In one aspect, embodiments disclosed herein relate to methods of manufacturing an article that include depositing a polyolefin composition at a target surface, wherein the polyolefin composition includes a polyolefin and a coupling agent; and melting and sintering the polyolefin composition with radiation from a radiation source at an intensity to produce the article, wherein the intensity initiates a reaction between the polyolefin and the coupling agent.

[0006] In another aspect, embodiments of the present disclosure relate to articles that include a sintered polyolefin composition, wherein the sintered polyolefin composition is prepared from the reaction of a polyolefin with a coupling agent in the presence of a radiation source.

[0007] .Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

[0008] FIG. 1 is a graphical representation showing complex viscosity as a function of angular frequency for polymer samples in accordance with embodiments of the present disclosure.

[0009] FIG. 2 is a graphical representation showing melt strength as a function of draw rate for polymer samples in accordance with embodiments of the present disclosure.

[0010] FIG. 3 is a graphical representation of the results of size exclusion chromatography (SEC) showing the weight fraction as a function of the log of the molecular weight for polymer samples in accordance with embodiments of the present disclosure. DETAILED DESCRIPTION

[0011] In one aspect, embodiments disclosed herein relate to polyolefin compositions containing coupling agents for powder based fusion additive manufacturing techniques. Methods in accordance with the present disclosure may include depositing a polyolefin composition containing a coupling agent that activates during subsequent melting and sintering steps, increasing the number of intra- and inter-strand crosslinks in the polyolefin component. The increase in crosslinking of the polyolefin results in a printed article having modified mechanical properties, such as stiffness and modulus, over the unreacted polyolefin.

[0012] Additive manufacturing techniques in accordance with the present disclosure include powder based fusion techniques such as selective laser sintering and high speed sintering using tailored compositions containing polyolefins mixed with coupling agents that activate at selected operating temperatures.“Sintering” as used herein refers to the coalescence of the particles in a printed powder. In this system, the build-up of material strength is associated with sintering.

[0013] Selective laser sintering (SLS) is an additive manufacturing technique in which an articulating platform carries a layer of dispersed polymer powder, which is warmed to just below its melting point. The layer is then heated with a radiation source, often a laser, which traces the initial layer of a printed article. When contacted with the radiation source, the powder particles partially melt, coalesce, and re-solidify as the powder cools. The surface is lowered by the height of the layer and another layer of powder is applied to the previous layer. Then the process is repeated until the article is complete. The completed object is removed from, or broken out of, the powder that has accumulated on the surface. Each powder layer supports subsequently printed layers, which allows overhanging structures to be created. Additionally, the variety of materials that can be sintered allows the designer considerable latitude in the design of objects fabricated by selective laser sintering.

[0014] However, the properties, surface finish, and porosity of the completed object depend to a large extent on the size of the powder granules, which are often on the order of 50 microns. Another important factor is the degree of sintering and melt between the particles in each deposited layer. While some polymer materials may be advantageous in terms of mechanical strength, other properties such as viscosity, resistance to melt and coalescence, and chain diffusion may limit the applicability of many polymers in sintering applications where poorly consolidated particles create voids or weak regions in the final product.

[0015] In high speed sintering (HSS), manufacturing occurs by depositing a fine layer of polymeric powder, after which inkjet printheads deposit an infrared (IR) absorbing fluid (or toner powder) directly onto the powder surface where sintering is desired. The entire build area is then irradiated with an IR radiation source such as an infrared lamp, causing the printed fluid to absorb this energy and then melt and sinter the underlying powder. This process is then repeated layer by layer until the build is complete.

[0016] While SLS and HSS are detailed as examples, it is also envisioned that the polyolefin compositions and coupling agents may be adapted for use in other powder bed fusion techniques such as selective heat sintering (SHS), selective laser melting (SLM), selective absorbing sintering (SAS), and selective inhibition sintering (SIS). In some embodiments, polyolefin compositions and coupling agents may be adapted for use in other additive manufacturing techniques, including filament-based methods such as fused deposition modeling (FDM) or fused filament fabrication (FFF).

[0017] In general, higher molecular weight (MW) polyolefins are often preferred for product manufacture in many manufacturing techniques because of their enhanced mechanical properties and durability when compared to low MW polyolefins. However, in sintering processes, higher MW polyolefins exhibit correspondingly higher viscosity under melt conditions, which impacts the sintering performance in powder based fusion methods due to the poor polymer chain diffusion and poor coalescence of the polymer particles. As a result, printed articles prepared from high MW polyolefins often exhibit less mechanical resistance compared to injection molded articles of the same material. On the other hand, low MW polymers exhibit good coalescence and sintering properties when deposited during powder based fusion processes, but create parts of low mechanical performance and with higher occurrence of shrinkage in the final geometry.

[0018] While a number of factors are involved, the lack of sintering among particles of high MW polyolefin leads to articles having lower mechanical resistance, because the lack of chain diffusion between particles creates weak inter-particle and inter layer adhesions. Methods in accordance with the present disclosure increase chain diffusion among particles by depositing a polyolefin composition containing a polyolefin having acceptable viscosity and coalescence performance and a coupling agent. Upon activation of the coupling agent during the melt and/or sintering phase of a powder based fusion process, the polyolefin component of the composition is converted to higher MW polymer structures in situ through the introduction of crosslinking and branching to the polyolefin by the coupling agent.

[0019] In one or more embodiments, methods may use a polyolefin composition containing a polyolefin and a coupling agent that is activated during the melting and/or sintering process when the temperature of the composition rises above the activation temperature of the selected coupling agent. Activated coupling agents contain functional groups that react with the polyolefin, generating crosslinking/bridges between the constituent polymer chains, creating branched structures that exhibit enhanced mechanical performance and reduced shrinkage.

[0020] Methods in accordance with the present disclosure enable the use of polyolefins exhibiting acceptable sintering performance, but otherwise unacceptable mechanical properties or shrinkage, by combining the polyolefin with a coupling agent that improves the mechanical properties of the final article upon crosslinking of the polyolefin in a subsequent activation step. While the approach may be applied to expand the utility of low molecular weight polymers, the approach may also be extended to improve mechanical resistance in relatively high MW polyolefins as well. For example, methods in accordance with the present disclosure may also employ ultrahigh molecular weight polyethylene that is combined with a coupling agent dispersed throughout the composition or at the surface of the composition particles may function to increase mechanical resistance by acting as a“glue” that forms adhesion points between the particles during a combined melt/sintering step.

[0021] Polyolefin compositions in accordance with the present disclosure may be formulated as a powder composition, where a coupling agent may be dispersed within the powder or on the surface of the constituent powder particles. Powder compositions in accordance with the present disclosure may have a high porosity, which allows the absorption of the coupling agent in liquid or solid form. In one or more embodiments, polyolefin powders may be obtained from the polymerization reactor in some embodiments prior to combination with a coupling agent. In some embodiments, a polyolefin may be combined with a coupling agent at a temperature below the activating temperature of the coupling agent, and pulverizing the obtained polyolefin composition using any suitable technique known in the field. In yet other embodiments, the coupling agent may be dispersed in solid or liquid form during the manufacturing process.

[0022] Powder bed fusion methods in accordance with the present disclosure may include the general steps of melting a powder prepared from a polyolefin composition containing a coupling agent at a temperature below the activation temperature for the coupling agent, followed by sintering at a temperature at or above the activation temperature to initiate crosslinking of the polyolefin. The activation temperature is dependent on the selected coupling agent or agents. For example, in embodiments in which the coupling agent is 4,4'-oxydi- benzenesulfonylazide (DPO-BSA), a powdered polyolefin composition may be melted at a temperature below 190°C to avoid the reaction of coupling agent. Operating a temperature below the activation temperature ensures a portion of the polyolefin composition maintains the properties of the initial polymer, including the associated performance characteristics of increased coalescence and sintering performance.

[0023] Following (or concurrent with) deposition, sintering is initiated by irradiation with a suitable radiation source, which raises the temperature of targeted regions above the activation temperature of the coupling agent. The activated coupling agent then initiates crosslinking within the polyolefin and creates adhesion sites among neighboring polymer particles. Continuing with the DPO-BSA example, sintering the temperature above 190°C initiates radical formation and reaction within and among the polyolefin composition particles. While melting and sintering are discussed as distinct steps, it is also envisioned that melting and sintering may occur in a single step in some embodiments. For example, melting and sintering may be combined into a single step in which the material is deposited above the activation temperature of the coupling agent. Following activation of the coupling agent and sintering, the printing stage is lowered and the process is repeated with the addition of another polyolefin composition powder layer. In embodiments directed to HSS methods, IR absorbers may be applied prior to irradiation to enhance the absorption of radiation in the targeted printing areas, followed by irradiation with an IR lamp or laser to initiate melting and sintering.

[0024] In one or more embodiments, multiple radiation sources of varying intensity may be used for melting and sintering processes. For powder bed fusion methods, a first radiation source may be used at an intensity that begins the melt and coalescence of the polymer particles, but does not activate (or minimally activates) the coupling agent. A second radiation source is then used at a second intensity (higher than the intensity of the first radiation source, for example) that activates the coupling agent and imitates crosslinking and branching reactions in the polyolefin. In some embodiments, a single radiation source of variable intensity may be used for the melting and sintering steps. In still other embodiments, a single radiation source having a single intensity may be used where the method entails a combined melt and sintering step.

[0025] In one or more embodiments, printed articles may undergo additional processing in post-treatment to fully convert any reactive species such as free radicals or unreacted coupling agent. In some embodiments, a post-treatment stage may be employed at the completion of the printed article, or after the printing of each layer. Post-treatment may include treatment with additional chemical curing agents such as organosilanes. In addition, post-treatment may include the use of physical methods that heat or pulse print articles for a period of time adequate to convert any remaining reactive species and enhance chain diffusion among printed particles and layers. Physical post-treatments may include secondary lasers, ceramic heaters, quartz heater, or ultrasonic apparatuses.

[0026] The size of the printed polymer particles may also be modified to tune the density of formed articles. For example, in SLS, polymer powders with good flow and appropriate particle size distribution may result in good powder spreading performance and particle packing. Polymer viscosity is also another important factor, as a polymer with good melt flow characteristics often results in good particle coalescence and layer to layer adhesion, which affects that final mechanical strength of the printed part. [0027] Coupling rates of the polyolefin by the coupling agent are impacted by several factors including temperature and reactivity of the functional groups present on the coupling agent. In one or more embodiments, coupling rates may be tuned by adjusting temperature (and radiation intensity) at which deposition and sintering occur during additive manufacturing. For example, DPO-BSA exhibits a general trend of increasing crosslinking activity with increasing temperature, where the molecular weight and degree of branching of a modified polyolefin is greater at 230° C, as compared to 210° C, and as compared to 190° C. However, the increase in the kinetic rate of coupling is also offset by enhanced degradation rates at elevated temperatures. For example, the rate of degradation is higher at 270°C, than 250° C or 230° C, and above 270° C the reaction rates favor degradation over coupling.

[0028] Polyolefins

[0029] Polyolefins may include homopolymers, random copolymers, block copolymers, and multiphasic polymer compositions such as impact copolymers. In some embodiments, polyolefin compositions may include a polymer matrix phase that surrounds other components such as an internal phase polymer and/or other additives. Polyolefins in accordance with the present disclosure may include a combination of one or more polymers or copolymers that may be blended pre- or post-polymerization in a reactor.

[0030] Polyolefin compositions in accordance with the present disclosure may be prepared from polymers and copolymers of C2 to C8 olefins such as ethylene, propylene, butene, pentene, hexene, heptene, octene, and the like. In some embodiments, examples of suitable polyolefins include polyethylene, low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), ultrahigh molecular weight (UHMWPE), and polypropylene (PP). In some embodiments, polyolefins may be obtained from renewable resources and/or may be post-consumer recycled polyolefin.

[0031] Polyolefins in accordance with the present disclosure may be modified by one or more coupling agents during melting or sintering during a powder bed fusion process in which coupling agents graft onto the polyolefin backbone and creating intra- and inter-strand crosslinks within the polyolefin matrix. In one or more embodiments, polyolefin compositions may be grafted with coupling agents or curing agents prior to use in an additive manufacturing technique that activate during melt and/or sintering steps. In some embodiments, stoichiometry or multiple orthogonal functional groups may be used to control the level of crosslinking between the coupling agent and the polyolefin to maintain favorable viscosity profiles. For example, a polyolefin may be copolymerized or grafted with a bifunctional coupling agent or curing agent having a first alkene functional group that covalently bonds to the polyolefin backbone, while a second functional group such as a silane group is activated in a subsequent powder based fusion process when exposed to moisture or elevated temperatures.

[0032] In one or more embodiments, polyolefins may include a polypropylene polymer have a percent by weight (wt%) of a C2 to C8 polyolefin comonomer that ranges from a lower limit selected from 0.5, 1, or 5 wt%, to an upper limit selected from 2.5, 5, or 10 wt%, where any lower limit may be combined with any upper limit.

[0033] Polyolefins in accordance with the present disclosure may be formulated as a polymer powder having an average particle diameter in a range having a lower limit selected from 1 pm, 2 pm, 5 pm, and 10 pm, to an upper limit selected from 50 pm, 100 pm, 500 pm, and 1000 pm, where any lower limit may be paired with any upper limit.

[0034] In one or more embodiments, the strength of the adhesions created during melting and sintering may be modified by tuning the porosity of a polymer powder, which governs the concentration of the coupling agent available at the powder particle surface.

[0035] Polyolefins in accordance with the present disclosure may be formulated as a polymer powder having a porosity in a range having a lower limit selected from 0.1 cm³/g, 0.2 cm³/g, and 0.5 cm³/g, to an upper limit selected from 0.5 cm³/g, 0.20 cm³/g, and 0.30 cm³/g, where any lower limit may be paired with any upper limit.

[0036] Internal Rubber Phase

[0037] In one or more embodiments, polyolefin compositions in accordance with the present disclosure include multiphasic polymer compositions having an internal rubber phase dispersed in a polyolefin matrix phase. In some embodiments, polymer compositions may include polymer compositions classified as impact copolymers (ICP).

[0038] In one or more embodiments, rubbers suitable for use as an internal rubber phase include homopolymers and copolymers having one or more monomers. In some embodiments, rubbers may include including graft copolymers such as maleated ethylene-propylene copolymers, and terpolymers of ethylene and propylene with nonconjugated dienes such as 5-ethylidene-2-norbornene, 1,8 octadiene, 1,4 hexadiene cyclopentadiene, and the like. Other polymers may include low density polyethylene, ethylene propylene rubber, poly(ethylene-methyl acrylate), poly(ethylene-acrylate), ethylene propylene diene rubber (EPDM), vinyl silicone rubber (VMQ), fluorosilicone (FVMQ), nitrile rubber (NBR), acrylonitrile-butadiene- styrene (ABS), styrene butadiene rubber (SBR), styrene-ethylene rubber, styrene- butadiene-styrene block copolymers (SBS and SEBS), polybutadiene rubber (BR), styrene-isoprene-styrene block copolymers (SIS), partially hydrogenated acrylonitrile butadiene (HNBR), natural rubber (NR), synthetic polyisoprene rubber (IR), neoprene rubber (CR), polychloropropene, bromobutyl rubber, chlorobutyl rubber, polyurethane, elastomer polyolefins as ethylene-octene copolymer, and combinations thereof.

[0039] In some embodiments, the internal rubber phase may be an ethylene -propylene rubber (EPR), which may include EPRs having one or more comonomers in addition to ethylene and propylene. Other comonomers may include, for example, a-olefins such as 1 -butene, 1-pentene, 1 -hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1- undecene, 1-dodecene, and the like.

[0040] In one or more embodiments, polyolefin compositions may include a multiphasic polymer having a polyolefin matrix phase and internal rubber phase present at a percent by weight (wt%) of the composition that ranges from a lower limit selected from any of 2, 3, 5, and 10 wt%, to an upper limit selected from any of 50, 60, 70, and 75 wt%, where any lower limit may be paired with any upper limit.

[0041] In one or more embodiments, polyolefin compositions may include a multiphasic polymer having an internal rubber phase prepared from ethylene and a C3 to C8 polyolefin comonomer, where the ethylene is present at a percent by weight (wt%) of the internal rubber phase that ranges from a lower limit selected from any of 5, 10, 15, and 20 wt%, to an upper limit selected from any of 50, 60, 70, and 75 wt%, where any lower limit may be paired with any upper limit.

[0042] Coupling Agent

[0043] In one or more embodiments, polyolefin compositions may include one or more coupling agents that react with the polyolefin component to form one or more covalent intra- and inter- strand bonds between polymer chains. Coupling agents in accordance with the present disclosure include chemical compounds that contain at least two reactive groups that are capable of forming bonds with the backbone or sidechains of the constituent polymers in the branched polymer composition.

[0044] In one or more embodiments, coupling agents may include sulfonyl azides, polysulfonyl azides, phosphazene azides, diazo alkanes, formyl azides, azides, dienes, geminally-substituted methylene groups, polymeric coupling agents, metallocarbenes, peroxides, aminosilanes, silanes, acrylates, methacrylates, and alpha-beta unsaturated acids, and the like.

[0045] Polysulfonyl azides in accordance with the present disclosure may have the general formula of X— R— X wherein each X is SO2N3 and R is a carbon chain that may be saturated or unsaturated, cyclic or acyclic, aromatic or non- aroma tic, may contain one or more heteroatoms including oxygen, nitrogen, sulfur, or silicon, and one or more additional azide functionalities. Suitable coupling agents may include an R that is aryl, alkyl, aryl alkaryl, arylalkyl silane, siloxane or heterocyclic, groups and other groups which are inert and separate the sulfonyl azide groups as described. In some embodiments, R may include at least one aryl group between the sulfonyl groups, most preferably at least two aryl groups (such as when R is 4,4' diphenylether or 4,4 '-biphenyl).

[0046] Polysulfonyl azides may include 4,4’-oxydibenzenesulfonyl azide, naphthylene his(sulfonyl azides), 1,5-pentane bis(sulfonyl azide), 1,8-octane bis(sulfonyl azide), 1,10-decane bis(sulfonyl azide), 1 ,10-oetadecane bisisulfonyi azide), 1 -octyl-2, 4,6-benzene trisisulfonyi azide), 4,4'- bis(benzenesulfonyl azide), 1 ,6-bis(4'-sulfonazidophenyl)hexane, 2,7-naphthalene bis(sulfonyl azide), and mixed sulfonyl azides of chlorinated aliphatic hydrocarbons containing an average of from 1 to 8 chlorine atoms and from about 2 to 5 sulfonyl azide groups per molecule, and mixtures thereof in some embodiments, coupling agent may include bissulfonyl azide, polysulfonyl azides such as oxy-bis(4- sulfbnylazidobenzene), 2,7-naphthalene bis(sulfonyl azido), 4,4'-bis(sulfonyl azido)biphenyl, 4,4'-oxybis(benzenesulfony] azide) and bis(4-sulfony] azidophenyljmethane, and mixtures thereof.

[0047] Polymeric coupling agents in accordance with the present disclosure may include polyolefins having reactive groups on the terminal ends and/or the backbone of the polyolefin chain. The polyolefin backbone may be linear or branched with two or more terminal ends, and reactive groups on the polymeric coupling agent may be the same or mixed. In one or more embodiments, polymeric coupling agents may have the general structure of R(X)_nR’, where R and R’ are independently selected from reactive groups that may include peroxide, alkyl borane, halogen, thiol, amine, amide, aldehyde, alcohol, carboxylic acid, ester, isocyanate, silane, phosphorous- containing group, dithioester, dithiocarbamate, dithiocarbonate, trithiocarbonate, alkoxyamine, aryl sulfonyl halide, aryl sulfonyl azide, phosphoryl azides, vinyl, alkyl vinyl, vinylidene, aryl vinyl, diene, alkyl azide, or derivatives thereof; (X) is a polyolefin having n number of olefin units, where the polyolefin may be linear or branched, saturated or unsaturated, and may contain one or more heteroatoms such as fluorine, chlorine, bromine, iodine, oxygen, sulfur, selenium, nitrogen, phosphorous, silicon, and boron; and n may be an integer in the range of 2 to 1000.

[0048] Any polyolefin may be used to prepare the modified polyolefin of the polymeric coupling agent. Polyolefins include polymers and copolymers prepared from linear or branched olefins having 2 to 20 carbon atoms. The polyolefin for preparing the polymeric coupling agent may be a homopolymer synthesized from a single olefin, or a copolymer synthesized from two or more olefins. For example, the polyolefin for preparing the polymeric coupling agent may be polyethylene; polypropylene; and copolymers of ethylene and propylene.

[0049] In one or more embodiments, coupling agents may include peroxides that generate free radicals that interact with polyolefins to create one or more crosslinks or branches in the polyolefin. Peroxides in accordance with the present disclosure may include benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, tert-butyl cumyl peroxide, tert-butyl 3,5,5-trimethylhexanoate peroxide, tert-butyl peroxybenzoate, 2-ethylhexyl carbonate tert-butyl peroxide, 2,5-dimethyl-2,5-di (tert-butylperoxide) hexane, l,l-di(tert-butylperoxide)-3,3,5- trimethylcyclohexane,2,5-dimethyl-2,5-di(tertbutylperoxide), hexyne-3,3,3,5,7,7- pentamethyl-l,2,4-trioxepane, butyl 4,4-di (tert-butylperoxide) valerate, di (2,4- dichlorobenzoyl) peroxide, di(4-methylbenzoyl) peroxide, peroxide di(tert- butylperoxyisopropyl) benzene, 2, 5-di(cumylperoxy)-2, 5-dimethyl hexane, 2,5- di(cumylperoxy)-2, 5-dimethyl hexyne-3,4-methyl-4-(t-butylperoxy)-2-pentanol, 4- methyl-4-(t-amylperoxy)-2-pentanol,4-methyl-4-(cumylperoxy)-2-pentanol, 4- methyl-4-(t-butylperoxy)-2-pentanone, 4-methyl-4-(t-amylperoxy)-2-pentanone, 4- methyl-4-(cumylperoxy)-2-pentanone, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-amylperoxy)hexane, 2,5-dimethyl-2,5-di(t- butylperoxy)hexyne-3, 2,5-dimethyl-2,5-di(t-amylperoxy)hexyne-3, 2,5-dimethyl-2- t-butylperoxy-5-hydroperoxyhexane, 2,5-dimethyl-2-cumylperoxy-5-hydroperoxy hexane, 2,5-dimethyl-2-t-amylperoxy-5-hydroperoxyhexane, m/p-alpha, alpha-di[(t- butylperoxy)isopropyl]benzene, l,3,5-tris(t-butylperoxyisopropyl)benzene, 1,3,5- tris(t-amylperoxyisopropyl )benzene, l,3,5-tris(cumylperoxyisopropyl)benzene, di [1, 3 -dimethyl- 3 - (t-butylperoxy)butyl] carbonate , di [ 1 , 3 -dimethyl- 3 - (t- amylperoxy )butyl]carbonate, di[l,3-dimethyl-3-(cumylperoxy)butyl Jcarbonate, di-t-amyl peroxide, t-amyl cumyl peroxide, t-butyl-isopropenylcumyl peroxide, 2,4,6- tri(butylperoxy)-s-triazine, l,3,5-tri[l-(t-butylperoxy)-l-methylethyl]benzene, 1,3,5- tri-| (t-butylperoxy)-isopropyl |benzene, 1,3 -dimethyl- 3 -(t-butylperoxy)butanol, 1,3- dimethyl-3-(t-amylperoxy)butanol, di(2-phenoxyethyl)peroxydicarbonate, di(4-t- butylcyclohexyl)peroxydicarbonate, dimyristyl peroxydicarbonate, dibenzyl peroxydicarbonate, di(isobomyl)peroxydicarbonate, 3-cumylperoxy-l,3- dimethylbutyl methacrylate, 3-t-butylperoxy-l,3-dimethylbutyl methacrylate, 3-t- amylperoxy- 1 ,3-dimethylbutyl methacrylate, tri(l,3-dimethyl-3-t-butylperoxy butyloxy)vinyl silane, l,3-dimethyl-3-(t-butylperoxy)butyl N-[l-{3-(l- methylethenyl)-phenyl)l-methylethyl]carbamate, l,3-dimethyl-3-(t- amylperoxy)butyl N- [ 1 - { 3 ( 1 -methylethenyl)-phenyl } - 1 -methylethyl |carbamate, 1,3- dimethyl-3 -(cumylperoxy))butyl N- [ 1 - { 3 -( 1 -methylethenyl)-phenyl } - 1 - methylethyl |carbamate, 1 , l-di(t-butylperoxy)-3 ,3 ,5-trimethylcyclohexane, 1 , 1 -di(t- butylperoxy)cyclohexane, n-butyl 4,4-di(t-amylperoxy)valerate, ethyl 3,3-di(t- butylperoxy)butyrate, 2,2-di(t-amylperoxy)propane, 3,6,6,9,9-pentamethyl-3- ethoxycabonylmethyl- 1 ,2,4,5-tetraoxacyclononane, n-butyl -4, 4-bis(t- butylperoxy)valerate, ethyl-3, 3-di(t-amylperoxy)butyrate, benzoyl peroxide, OO-t- butyl-O-hydrogen-monoperoxy-succinate, OO-t-amyl-O-hydrogen-monoperoxy- succinate, 3,6,9, triethyl-3, 6, 9-trimethyl-l, 4, 7-triperoxynonane (or methyl ethyl ketone peroxide cyclic trimer), methyl ethyl ketone peroxide cyclic dimer, 3,3,6,6,9,9-hexamethyl-l,2,4,5-tetraoxacyclononane, 2,5-dimethyl-2,5- di(benzoylperoxy)hexane, t-butyl perbenzoate, t-butylperoxy acetate, t-butylperoxy- 2-ethyl hexanoate, t-amyl perbenzoate, t-amyl peroxy acetate, t-butyl peroxy isobutyrate, 3-hydroxy- 1,1-dimethyl t-butyl peroxy-2-ethyl hexanoate, OO-t-amyl- O-hydrogen-monoperoxy succinate, OO-t-butyl-O-hydrogen-monoperoxy succinate, di-t-butyl diperoxyphthalate, t-butylperoxy (3,3,5-trimethylhexanoate), l,4-bis(t- butylperoxycarbo )cyclohexane, t-butylperoxy-3,5,5-trimethylhexanoate, t-butyl- peroxy-(cis-3-carboxy)propionate, allyl 3-methyl-3-t-butylperoxy butyrate, OO-t- butyl-O-isopropylmonoperoxy carbonate, 00-t-butyl-0-(2-ethyl hexyl)monoperoxy carbonate, 1,1, 1 -tris [2-(t-butylperoxy-carbonyloxy)ethoxymethyl]propane, 1,1,1- tris[2-(t-amylperoxy-carbonyloxy)ethoxymethyl]propane, l,l,l-trls[2-

(cumylperoxy-cabonyloxy)ethoxymethyl]propane, OO-t-amyl-O- isopropylmonoperoxy carbonate, di(4-methylbenzoyl)peroxide, di(3- methylbenzoyl)peroxide, di(2-methylbenzoyl)peroxide, didecanoyl peroxide, dilauroyl peroxide, 2,4-dibromo-benzoyl peroxide, succinic acid peroxide, dibenzoyl peroxide, di(2,4-dichloro-benzoyl)peroxide, dicetylperoxide dicarbonate, and combinations thereof. Peroxides may also include azo-peroxide initiators that include mixtures of peroxide with azodinitrile compounds such as 2,2'-azobis(2- methyl-pentanenitrile), 2,2'-azobis(2-methyl-butanenitrile), 2,2'-azobis(2-ethyl- pentanenitrile), 2-[(l-cyano-l-methylpropyl)azo]-2-methyl-pentanenitrile, 2-[(l- cy ano- 1 -ethylpropyl)azo] -2-methyl-butanenitrile, 2- [( 1 -cyano- 1 -methylpropyl)azo] - 2-ethyl, and the like.

[0050] In one or more embodiments, activating agents may be included at a percent by weight (wt%) of the polymer composition that ranges from a lower limit selected from any of 0.0001, 0.001, 0.1, and 1 wt%, to an upper limit selected from any of 2.5, 3, 5 and 10 wt%, where any lower limit may be paired with any upper limit.

[0051] Curing Agents

[0052] Polymer compositions in accordance with the present disclosure may undergo a post-treatment with one or more curing agents following activation and deposition during a material extrusion process. Curing agents in accordance with the present disclosure may include organosilane containing functional groups that may react with the polymer composition including vinyl groups, epoxys, acryloxys, methacryloxys, amino groups, ureides, mercapto groups, isocyanates, isocyanurate, and the like. In one or more embodiments, may include unsaturated organosilanes such as vinyl triethoxysilane, vinyl-tris-(beta-methoxyethoxy)silane, methacryloylpropyltrimethoxysilane, gamma-amino-propyl triethoxysilane, 3- thiocyanatopropyl-triethoxy silane, gamma-mercaptopropyltrimethoxysilane, and the like.

[0053] In one or more embodiments, unsaturated organosilanes may be grafted to the polyolefin component. When the grafted polyolefin is exposed to ambient humidity or aqueous fluids in a curing step, hydrolysis of the grafted silane groups produces reactive silanes that condense and produce siloxane crosslinks in the cured polymer.

[0054] Additives

[0055] Polymeric compositions in accordance with the present disclosure may include additives that modify various physical and chemical properties when added to the polymeric composition during blending that include one or more polymer additives such as flow lubricants, antistatic agents, clarifying agents, nucleating agents, beta- nucleating agents, slippage agents, antioxidants, antacids, light stabilizers such as HALS, IR absorbers, silica, titanium dioxide, silicon dioxide, organic dyes, organic pigments, inorganic dyes, and inorganic pigments.

[0056] Physical properties

[0057] In one or more embodiments, polyolefin compositions prior to reaction with a coupling agent may have an initial melt flow index (MFI) at 190 °C and 2.16 kg as determined according to ASTM D1238 in a range having a lower limit selected from any of 1 g/lOmin, 5 g/lOmin, 10 g/lOmin, and 15 g/10min, to an upper limit selected from any of 50 g/lOmin, 100 g/lOmin, 500 g/lOmin, and 600 g/10min, where any lower limit may be paired with any upper limit. In some embodiments, the polyolefin may be a polyethylene having an initial MFI in the range of 1 to 50 g/10min. For polymer compositions containing polyproplylene, the polymer may have an initial MFI at 230°C and 2.16 kg in the range of 5 to 500 g/lOmin. [0058] In one or more embodiments, polyolefin compositions prepared from a reaction with a coupling agent may have an final melt flow index (MFI) at 190 °C and 2.16 kg as determined according to ASTM D1238 in a range having a lower limit selected from any of 0.1 g/lOmin, 0.2 g/10min, 0.5 g/lOmin, and 1 g/lOmin, to an upper limit selected from any of 5 g/lOmin, 10 g/10min, 50 g/lOmin, and 60 g/10min, where any lower limit may be paired with any upper limit. In some embodiments, the polyolefin may be a polypropylene having a final MFI in the range of 0.5 to 50 g/10min. In some embodiments, the polyolefin may be a polyethylene having a final MFI in the range of 0.2 to 10 g/lOmin.

[0059] In one or more embodiments, the initial intrinsic viscosity of polyolefins in accordance the present disclosure prior to reaction with a coupling agent may be in a range having a lower limit selected from 3 dL/g, 5 dL/g, and 10 dL/g, to an upper limit selected from 15 dL/g, 20 dL/g, 40 dL/g, and 50 dL/g, where any lower limit may be paired with any upper limit.

[0060] In one or more embodiments, polyolefin compositions may exhibit a final density following a reaction with a coupling agent determined according to ASTM D792 in a range having a lower limit selected from any of 0.9 g/cm³, 0.91 g/cm³, and 0.92 g/cm³, to an upper limit selected from any of 0.95 g/cm³, 0.97 g/cm³, and 0.98 g/cm³, where any lower limit may be paired with any upper limit.

[0061] Preparation of the Polyolefin Composition

[0062] In one or more embodiments, coupling agents may be dispersed in a suitable solvent and applied to polyolefin powders in accordance with the present disclosure. Solubilization of coupling agents may be achieved by any suitable method, including combination with the solvent and shaking at room temperature. In order to prepare the polyolefin composition, the polymer powder is then added to the solution to coat the powder particles, and the solvent is removed by evaporation at a temperature lower than the activation temperature of the coupling agent. For example, an acetone solution of DPO-BSA may be combined with a polyolefin powder and then heated to 50°C. After the evaporation of the solvent, the coupling agent will be impregnated in the surface and in the porous of the powder. In some embodiments, polyolefin powder and coupling agents may be combined by admixing the components in solid phase without solvent addition.

[0063] Applications

[0064] In one or more embodiments, articles in accordance with the present disclosure may be formed using an additive manufacturing system that prints, builds, or otherwise produces 3D parts and/or support structures. The additive manufacturing system may be a stand-alone unit, a sub-unit of a larger system or production line, and/or may include other non-additive manufacturing features, such as subtractive- manufacturing features, pick-and-place features, two-dimensional printing features, and the like.

[0065] Articles that may be formed, include, for example, packaging, rigid and flexible containers, household appliances, molded articles such as caps, bottles, cups, pouches, labels, pipes, tanks, drums, water tanks, medical devices, shelving units, and the like. Specifically, any article conventionally made from the polymer compositions of the present disclosure (using conventional manufacturing techniques) may instead be manufactured from additive manufacturing.

[0066] The use of polyolefin compositions in accordance with the present disclosure may provide greater flexibility in the products produced by the additive manufacturing methods. Specifically, for example, the articles produced by additive manufacturing may have a lower flexural modulus and excellent fatigue resistance as compared to PLA or ABS.

[0067] Radiation Sources

[0068] Methods in accordance with the present disclosure may incorporate one or more radiation sources to generate ionizing radiation at intensities that induce heating in polyolefin compositions. In some embodiments, radiation sources may have variable intensity that may span from intensity suitable to initiate melting of a polyolefin composition to intensity suitable to heat the polyolefin composition to or above the activation temperature of the coupling agent.

[0069] Radiation sources may include sources used in commercial additive manufacturing applications and include lamps and lasers that operate in across spectra such as infrared (IR), ultraviolet (UV), gamma, and xray, electron beams, and the like. In one or more embodiments, radiation sources may be focused on a polyolefin composition during melting and/or sintering, and the radiation source may be stationary or mobile.

[0070] IR absorbers

[0071] In one or more embodiments, methods may also include the step of applying an IR absorber to a deposited polyolefin composition prior to irradiation with a radiation source. The absorber may also be in the form of particles such as black toner. Absorbers may be applied uniformly or selectively, in different amounts. For example, the absorber may be applied as a mixture of absorbers with different absorption maxima, or different absorbers may be applied independently, in an alternating manner, or in a predetermined sequence. In one or more embodiments, IR absorbers may be oil-based absorbers containing carbon particles such as oil- based soot particle ink.

[0072] Examples

[0073] In the following examples, a linear polypropylene is combined with a bissulfonyl azide 4,4'-oxydibenzenesulfonylazide at 190°C to produce a crosslinked and branched polypropylene composition and assayed for various physical properties. With particular respect to FIG. 1, the effect of long chain branching on the viscosity at 200°C for a linear polypropylene and a branched polypropylene generated by the reaction of a polymer with a coupling agent is shown in a graph of complex viscosity as a function of angular frequency. It is noted that the viscosity of the branched polypropylene is higher relative to the linear polymer, particularly at lower angular velocities.

[0074] With particular respect to FIG. 2, the melt strength at 190°C was compared as a function of draw rate for a linear polypropylene and the corresponding polymer reacted with bissulfonyl azide, which highlights the increase in melt strength with increasing branching. Size exclusion chromatography (SEC) was also performed on samples of the linear and branched polymer to study the effect of coupling on the molecular weight of the polymers. With particular respect to FIG. 3, a graph of the weight fraction of the polymer samples as a function of the log of the molecular weight (log M) is shown for a linear and branched polypropylene. The broadening of the distribution of the branched polypropylene confirms the formation of high molecular weight polymer formations, which contribute to the observed increase in mechanical properties.

[0075] Although the preceding description is described herein with reference to particular means, materials and embodiments, it is not intended to be limited to the particulars disclosed herein; rather, it extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. In the claims, means -plus -function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. § 112(f) for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.

Claims

CLAIMS What is claimed:

1. A method of manufacturing an article, comprising:

depositing a polyolefin composition at a target surface, wherein the polyolefin composition comprises a polyolefin and a coupling agent; and melting and sintering the polyolefin composition with radiation from a radiation source at an intensity to produce the article, wherein the intensity initiates a reaction between the polyolefin and the coupling agent.

2. The method of claim 1, wherein the melting and sintering comprises:

melting the polyolefin composition with radiation from a first radiation source at a first intensity; and

sintering the polyolefin composition with radiation from a second radiation source at a second intensity to produce the article, wherein the second intensity initiates a reaction between the polyolefin and the coupling agent.

3. The method of claim 2, wherein melting the polyolefin composition is performed at a temperature below the activation temperature of the coupling agent.

4. The method of claim 2, wherein sintering the polyolefin composition occurs at a temperature above the activation temperature of the coupling agent.

5. The method of claim 2, wherein melting the polyolefin composition is performed at a temperature below 190°C.

6. The method of claim 2, wherein sintering the polyolefin composition occurs at a temperature above 190°C.

7. The method of any of the above claims, further comprising post-treating the sintered polyolefin composition with one or more post-treatments selected from a third laser, ceramic heater, quartz heater, and ultrasonic treatment.

8. The method of any of the above claims, wherein the polyolefin composition is a powder.

9. The method of any of the above claims, wherein the polyolefin composition is prepared by combining a polyolefin powder with a solution of coupling agent in a solvent; and evaporating the solvent to obtain the polyolefin composition

10. The method of claim 9, wherein the solvent is acetone.

11. The method of any of the above claims 1 to 8, wherein the polyolefin composition is prepared by combining a polyolefin powder with coupling agent powder to obtain the polyolefin composition.

12. The method of any of the above claims 8 to 11, wherein the polyolefin powder is a powder obtained from a polymerization reactor.

13. The method of any of the above claims, wherein the coupling agent is selected from sulfonyl azides, polysulfonyl azides, phosphazene azides, diazo alkanes, formyl azides, azides, dienes, geminally-substituted methylene groups, polymeric coupling agents, metallocarbenes, peroxides, aminosilanes, silanes, acrylates, methacrylates, and alpha-beta unsaturated acids.

14. The method of any of the above claims, wherein the coupling agent is a bissulfonyl azide.

15. The method of any of the above claims, wherein the polyolefin composition comprises one or more additives selected from a group consisting of flow lubricants, antistatic agents, clarifying agents, nucleating agents, beta-nucleating agents, slippage agents, antioxidants, antacids, IR absorbers, silica, titanium dioxide, silicon dioxide, organic dyes, organic pigments, inorganic dyes, and inorganic pigments.

16. The method of any of the above claims, further comprising: repeating the depositing, melting, and sintering to build a three-dimensional article.

17. The method of any of the above claims, wherein the polyolefin composition further comprises an IR absorber, and wherein at least one of the first radiation source or the second radiation source is an IR source.

18. The method of any of the above claims, wherein the polyolefin composition comprises polymer powder having particles with an average diameter of 5 pm to 1,000 pm.

19. An article prepared by the method of any of claims 1 to 18.

20. An article comprising:

a sintered polyolefin composition, wherein the sintered polyolefin composition is prepared from the reaction of a polyolefin with a coupling agent in the presence of a radiation source.

21. The article of claim 20, wherein the polyolefin composition is prepared combining a polyolefin powder with a solution of coupling agent; and drying the resulting mixture to obtain the polyolefin composition.

22. The article of claim 21, wherein the solution of coupling agent further comprises a solvent.

23. The article of any of claims 20-22, wherein the polyolefin composition is coupled with a bissulfonylazide.

24. The article of any of claims 20-23, wherein the polyolefin composition is melted at a temperature below 190°C prior to sintering to produce the sintered polyolefin composition.

25. The article of any of the claims 20-24, wherein sintered polyolefin composition is sintered at a temperature above 190°C.

26. The article of any of claims 20-25, wherein the ionizing radiation is provided by an IR lamp.

27. The article of any of claims 20-26, wherein the coupling agent is one or more selected from a group consisting of azides, sulfonazides, peroxides, acrylates, silanes, dienes, and alpha-beta unsaturated acids.

28. The article of any of claims 20-27, wherein the sintered polyolefin composition is post-treated after sintering with one or more post-treatments selected from a third radiation source, ceramic heater, quartz heater, and ultrasonic treatment.

29. The article of any of claims 20-28, wherein the polyolefin is one or more selected from a group consisting of polyethylene, low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), ultrahigh molecular weight (UHMWPE), and polypropylene (PP).

30. The article of any of claims 20-28, wherein the polyolefin polymer comprises a polymer or copolymer prepared from C2 to C8 olefins.

31. The article of any of claims 20-28, wherein the polyolefin is a multiphasic polymer comprising a matrix polymer selected from a polymer or copolymer prepared from C2 to C8 olefins, and an internal rubber phase.