阅读说明：本技术 用于3d打印的改进的长丝 (Improved filaments for 3D printing ) 是由 D·J·加德纳 L·王 J·E·桑德斯 于 2018-11-15 设计创作，主要内容包括：本文提供了用于包括聚丙烯的材料的改进的3D打印材料、方法和系统。在一些实施方式中,本公开提供了一种用于改进的3D打印的复合材料,其包括聚合物基体和多种纤维。例如,所述聚合物基体可以具有如下组合物,所述组合物包括聚丙烯(PP)和聚乙烯(PE)(例如,高密度聚乙烯(HDPE)、低密度聚乙烯(LDPE)、线性低密度聚乙烯(LLDPE))的聚合物共混物、抗冲改性聚丙烯共聚物和/或具有多种纤维的聚丙烯无规共聚物。在一些实施方式中,所述多种纤维包括纤维素纳米纤维(例如天然纤维素纳米纤维,例如纤维素纳米原纤维)。在一些实施方式中,通过熔融配混聚合物基体(例如,PP共聚物和/或PP/PE粒料)和多种纤维并挤出混合物,从而由所述复合材料来制备长丝。(Provided herein are improved 3D printed materials, methods, and systems for materials including polypropylene. In some embodiments, the present disclosure provides a composite for improved 3D printing comprising a polymer matrix and a plurality of fibers. For example, the polymer matrix may have a composition comprising a polymer blend of polypropylene (PP) and Polyethylene (PE) (e.g., High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE), Linear Low Density Polyethylene (LLDPE)), an impact modified polypropylene copolymer, and/or a polypropylene random copolymer having a plurality of fibers. In some embodiments, the plurality of fibers comprises cellulose nanofibers (e.g., natural cellulose nanofibers, such as cellulose nanofibrils). In some embodiments, filaments are prepared from the composite by melt compounding a polymer matrix (e.g., PP copolymer and/or PP/PE pellets) and a plurality of fibers and extruding the mixture.)

1. A composite material (e.g. a composite thermoplastic material, e.g. for additive manufacturing, e.g. fusion layer modelling) comprises a polymer matrix.

2. The composite material of claim 1, wherein the polymer matrix has a composition comprising one or more components selected from the group consisting of: (i) a polymer blend comprising polypropylene (PP) and Polyethylene (PE) (e.g., High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE), Linear Low Density Polyethylene (LLDPE)), (ii) a modified (e.g., impact modified) polypropylene copolymer and/or (iii) a polypropylene random copolymer.

3. The composite material of any one of the preceding claims, wherein the polymer matrix has a Melt Flow Index (MFI) in the range of about 5 to 30g/10 minutes.

4. The composite material of any one of the preceding claims, further comprising a plurality of fibers (e.g., natural cellulose nanofibers).

5. The composite material of claim 4, wherein the plurality of fibers comprises a plurality of natural cellulose nanofibers (e.g., cellulose nanofibrils) (e.g., natural cellulose nanofibers, wherein the average diameter of the nanofibers is less than about 1000 nm).

6. The composite material of claim 4 or 5, wherein the weight percentage of the plurality of fibers is in the range of 3% to 30% (based on the total weight of the composite material).

7. A pellet comprising the composite material of any one of the preceding claims.

8. A filament comprising the composite material of any one of the preceding claims.

9. A method of 3D printing, the method comprising 3D printing with the filament of claim 7.

10. The method of claim 9, wherein the temperature of the substrate (e.g., the plate on which the printing is performed) is at least 35 ℃ (e.g., maintained at a relatively high temperature to reduce crystallization and shrinkage of the composite).

11. A system for 3D printing of the method of claim 9 or 10.

12. A system for making the filament of claim 8.

Background

Additive manufacturing or 3D printing is an important manufacturing tool in many industries for manufacturing automotive parts, aerospace parts, packaging materials, building parts, medical parts, and the like. Fused Filament Fabrication (FFF) is one type of additive manufacturing used to print thermoplastic parts. During FFF, three-dimensional parts can be printed from thermoplastic filaments. In this process, thermoplastic filaments are fed through a heated extruder head, which melts the thermoplastic. Thereafter, as the extruder head moves in an appropriate pattern (e.g., under computer control), the molten thermoplastic is printed on the surface to form a layer of the printed part. The printing is done in a layer-by-layer manner such that one layer is printed and allowed to cool (e.g., to solidify the printed thermoplastic). After the printed thermoplastic layer cools, subsequent layers are printed until the desired part is obtained.

FFF is a popular 3D printing technique due to its low cost and relatively simple operation. However, not all thermoplastic polymers are compatible with FFF. In particular, the thermoplastic polypropylene (PP) commonly used in many applications is not readily compatible with FFF because the PP layer tends to shrink after printing. This shrinkage of the printed PP results in dimensional instability of the printed PP part such that subsequent layers cannot be reliably printed after previously printed layers shrink and become bent.

Summary of The Invention

Presented herein are materials, methods, and systems for improved 3D printing of materials including polypropylene. In some embodiments, the present disclosure provides a composite material comprising a polymer matrix and a plurality of fibers for improved 3D printing. For example, the polymer matrix may have a composition comprising a polymer blend of polypropylene (PP) and Polyethylene (PE) (e.g., High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE), Linear Low Density Polyethylene (LLDPE)), an impact modified polypropylene copolymer, and/or a polypropylene random copolymer having a plurality of fibers. In some embodiments, the plurality of fibers comprises cellulose nanofibers (e.g., natural cellulose nanofibers, such as cellulose nanofibrils). In some embodiments, filaments are prepared from the composite by melt compounding a polymer matrix (e.g., PP copolymer and/or PP/PE pellets) and a plurality of fibers and extruding the mixture. In some embodiments, the formulation of these composites provides improved 3D printing (e.g., FFF or melt layer modeling, also referred to as "FLM"). For example, the composite may have a slower crystallization rate than PP. For example, a printed layer of composite material may undergo less shrinkage during crystallization than a PP layer. For example, the composite material may have greater dimensional stability and result in improved reproducibility of printed parts compared to PP alone. In some embodiments, the plurality of fibers enhances the mechanical properties of the printed product. In some embodiments, the composite filaments are printed on a plate at an elevated temperature to slow the crystallization rate and improve the quality of the 3D printed product.

In one aspect, the present disclosure relates to a composite material (e.g., a composite thermoplastic material, e.g., for additive manufacturing, e.g., melt layer modeling) including a polymer matrix.

In some embodiments, the polymer matrix has a composition comprising one or more components selected from the group consisting of: (i) a polymer blend comprising polypropylene (PP) and polyethylene (e.g., High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE), Linear Low Density Polyethylene (LLDPE)), (ii) a modified (e.g., impact modified) polypropylene copolymer and/or (iii) a polypropylene random copolymer.

In some embodiments, the polymer matrix has a Melt Flow Index (MFI) in the range of about 5 to 30g/10 minutes.

In some embodiments, the composite further comprises a plurality of fibers (e.g., natural cellulose nanofibers).

In some embodiments, the plurality of fibers comprises a plurality of natural cellulose nanofibers (e.g., cellulose nanofibrils) (e.g., natural cellulose nanofibers wherein the average diameter of the nanofibers is less than about 1000 nm).

In some embodiments, the weight percentage of the plurality of fibers is in the range of 3% to 30% (based on the total weight of the composite).

In one aspect, the present disclosure relates to a pellet comprising the composite material described herein.

In one aspect, the present disclosure relates to a filament comprising a composite material described herein.

In one aspect, the present disclosure relates to a 3D printing method comprising 3D printing with a filament as described herein.

In some embodiments, the temperature of the substrate (e.g., the plate on which the 3D printing is performed) is at least 35 ℃ (e.g., maintained at a relatively high temperature to reduce crystallization and shrinkage of the composite).

In one aspect, the present disclosure relates to a system for 3D printing according to the methods described herein.

In one aspect, the present disclosure is directed to a system for making a filament as described herein.

Brief Description of Drawings

The foregoing and other objects, aspects, features, and advantages of the disclosure will become more apparent and better understood by reference to the following description when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 shows a plot of ln [ -ln (1-Xt) ] versus ln (t) for an iPP/CNF 10% composite material during crystallization at different cooling rates in accordance with one exemplary embodiment in accordance with the Jeziorrny model.

FIG. 2 shows a plot of ln [ -ln (1-Xt) ] versus ln (λ) for an iPP/CNF 10% composite based on the Ozawa method, according to an exemplary embodiment.

Fig. 3 shows a graph of ln (λ) versus ln (t) at different Xt values for the iPP/CNF 10% composite, based on the liu method, according to an exemplary embodiment.

FIG. 4 shows a plot of ln (λ/Tp2) versus 1/Tp for calculating a value of Δ E based on the Cinciger method, according to an example embodiment.

FIG. 5 shows Polarized Light Micrographs (PLMs) of iPP and iPP/CNF composites. Circles depict the maltese cross pattern of iPP spherulites. The lower left and lower right plots show the effect of MAPP on the lateral crystallization.

The features and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements.

Detailed Description

It is contemplated that the materials, methods, and processes of the present invention encompass variations and adaptations developed using information from the embodiments described herein. The materials, methods, and processes described herein may be adapted and/or modified as contemplated by the present specification.

Throughout the specification, where articles of manufacture, devices, systems and architectures are described as having, including, or comprising specific components, or where processes and methods are described as having, including, or comprising specific steps, it is contemplated that there may additionally be articles of manufacture, devices, systems and architectures according to the present invention consisting essentially of, or consisting of, the recited components, and there may be processes and methods according to the present invention consisting essentially of, or consisting of, the recited process steps.

It should be understood that the order of steps or order of performing certain operations is immaterial so long as the operability of the invention is maintained. Also, two or more steps or operations may be performed simultaneously.

Any publication mentioned herein, for example in the background section, is not an admission that the publication is prior art to any claims presented herein. The background section is provided for clarity and is not meant to be a description of the prior art of any claim.

Headings are provided for the convenience of the reader, and the presence and/or arrangement of headings is not intended to limit the scope of the subject matter described herein.

The present disclosure encompasses the following recognition: the polymer matrix (e.g., a composition having (i) a polymer blend comprising PP and PE (e.g., HDPE, LDPE and/or LLDPE), (ii) a modified PP copolymer, and/or (iii) a PP random copolymer) may have a lower crystallization rate than PP, thereby improving 3D printing. The present disclosure further encompasses the recognition that a composite material comprising a polymer matrix and a plurality of fibers in an appropriate concentration (e.g., weight percent) may have improved 3D printing performance. For example, a composite comprising PP and 10 weight percent of a plurality of fibers (e.g., spray-dried cellulose nano-fibrils) may have a reduced crystallization rate as compared to PP alone.

During 3D printing (e.g., FFF), non-isothermal crystallization may occur under different conditions. Crystallization can occur at high cooling rates (greater than 20 ℃/minute), which occurs primarily when the printing nozzle is close to the printed polymer. This form of crystallization may produce only a very small portion of the crystallized product. Crystallization ofMay occur at a relatively low cooling rate (in the range of about 5 to 10 c/min). The crystallization rate may be based on the so-called crystallization half-time (t)_1/2) To perform the evaluation. For example, isotactic polypropylene (iPP) may crystallize faster than poly (L-lactide) (PLLA). T of iPP_1/2About 2.93 minutes (molecular weight (Mn) at 120 ℃ based on numbers of 4.18 × 10⁴g/mol) of PLLA_1/2About 21.5 minutes (Mn of 4.5 × 10 at 120 ℃ C.)⁴g/mol). Thus, PLLA is more commonly used in 3D printing (e.g., FFF) using conventional methods because it crystallizes more slowly than iPP under the same processing conditions.

At temperatures below the crystallization temperature (Tc) of the polymer, the shrinkage of the polymer can be controlled by thermal expansion of the amorphous portion of the polymer. It is known that PP crystallizes more shrinkage above Tc when cooled from the molten state than when crystallized below Tc. Thus, PP shrinkage is primarily a result of the crystallization process.

According to various embodiments, provided materials/compositions may exhibit a variety of Melt Flow Indices (MFI). For example, in some embodiments, a material/composition is provided that has an MFI of 50g/10 minutes or less (e.g., 40g/10 minutes, 35g/10 minutes, 30g/10 minutes, 25g/10 minutes, 20g/10 minutes, 15g/10 minutes, 10g/10 minutes, 5g/10 minutes or less). Without wishing to be bound by a particular theory, it is expected that the use of a relatively low MFI material will result in excellent mechanical properties of the final product.

Preparation method

In some embodiments, the composite material may be prepared using a "rapid masterbatch production process. For example, the polymer matrix and the plurality of fibers may be dried in an oven, such as at a temperature greater than 90 ℃ for at least one hour (e.g., at 105 ℃ for 2 hours). For example, the polymer matrix may have a composition comprising one or more components selected from the group consisting of: (i) a polymer blend comprising polypropylene (PP) and Polyethylene (PE) (e.g., High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE), Linear Low Density Polyethylene (LLDPE)), (ii) a modified (e.g., impact modified) polypropylene copolymer, and/or (iii) a polypropylene random copolymer. For example, as a non-limiting example, the polymer matrix may have a PP/PE composition of 70/30, 75/25, 80/20, 85/15, or 90/10. In some embodiments, the plurality of fibers may be or include a plurality of natural cellulose nanofibers (e.g., cellulose nanofibrils). For example, the fibers can have an average diameter of less than about 1000nm (e.g., less than 900nm, 800nm, 700nm, 600nm, 500nm, 400nm, 300nm, 200nm, or 100 nm).

Subsequently, the dried components can be compounded, for example, by manually mixing the polymer and the plurality of fibers. In some embodiments, the fiber content may be at least 7.5 weight percent (based on the total weight of the composite). In some embodiments, the fiber content may be at least 10 weight percent (based on the total weight of the composite). In some embodiments, the fiber content may be at least 15 wt% (based on the total weight of the composite). In some embodiments, the fiber content may be at least 20 wt% (based on the total weight of the composite). In some embodiments, the fiber content may be at least 25 wt% (based on the total weight of the composite). In some embodiments, the fiber content may be at least 30 wt% (based on the total weight of the composite material, e.g., 35 wt%, 40 wt%, 45 wt%, 50 wt%, or more). In some embodiments, the fiber content can be in the range of 3% to at least 30% (e.g., in the range of 3 to 25%, 3 to 30%, 3 to 15%, 3 to 10%, 5 to 30%, 5 to 25%, 5 and 20%, 5 and 15%, 5 and 10%, etc.).

The heating section of the extruder may be operated at, for example, 200 ℃. In some embodiments, the extruder temperature can be between 175 ℃ and 250 ℃ (e.g., between 185 ℃ and 250 ℃, between 195 ℃ and 250 ℃, between 200 ℃ and 250 ℃, between 175 ℃ and 240 ℃, between 175 ℃ and 230 ℃, between 175 ℃ and 220 ℃, between 175 ℃ and 210 ℃, between 175 ℃ and 200 ℃). In some embodiments, the extruder temperature can be at least 175 ℃ (e.g., 180 ℃, 185 ℃, 190 ℃, 195 ℃, 200 ℃, 205 ℃, 210 ℃ or higher). In some embodiments, the extruder temperature can be up to 250 ℃ (e.g., 240 ℃, 230 ℃, 220 ℃, 210 ℃, 200 ℃, 190 ℃, or lower). The extrusion speed may be set, for example, to about 250 revolutions per minute (rpm). To obtain "masterbatch" pellets, the extrudate may be continuously collected, cooled, and milled, for example, using a pelletizer. In some embodiments, the resulting "masterbatch" pellets and polymers, polymer blends, and/or copolymers may be dried, for example, in an oven. These dried components can then be mixed and compounded to produce pellets having a desired amount of a plurality of fibers (e.g., 1 wt%, 3 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, etc.). The pellets may be dried, for example, in an oven, prior to transferring the pellets to an injection molding machine (e.g., model #50 "Minijector"). In some embodiments, the injection molding machine may operate at 200 ℃ at an injection pressure of about 17 MPa. It is to be understood that in certain embodiments, other injection pressures may be used, for example, at least 10MPa at 200 ℃ (e.g., at least 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20MPa at 200 ℃). In some embodiments, the injection pressure can be at most 30MPa at 200 ℃ (e.g., at most 25, 20, 19, 18, 17, 16, 15, or 10MPa at 200 ℃).

In some embodiments, for composites comprising PP copolymers, the pellets can be fed directly into a twin screw extruder to prepare filaments for printing. In some embodiments, for composites comprising a PP/PE blend, PP and PE pellets may be mixed together. For example, the mixed pellets may be fed into a twin screw extruder equipped with a circular die. The filaments may then be drawn to a diameter, cooled, and collected on a spool for printing, for example. In some embodiments, a plurality of fibers may be added to the polymer matrix in dry form. Subsequently, the mixture may be, for example, shear mixed and fed into an extruder to produce composite filaments that are useful for 3D printing.

In some embodiments, the composite material includes a polymer matrix having a low MFI (e.g., in the range of 5 to 40g/10 minutes, such as 5 to 30g/10 minutes, 5 to 20g/10 minutes, 5 to 10g/10 minutes, 10 to 40g/10 minutes, 20 to 40g/10 minutes, 30 to 40g/10 minutes, 10 to 30g/10 minutes, 5 to 20g/10 minutes). This MFI range may improve the mechanical properties of parts printed using the composite material. In some embodiments, the composite does not require inorganic fillers and thus can be low cost, lightweight, and environmentally friendly. In some embodiments, a plurality of fibers may provide improved stiffness to the printed product.

Printing using composite materials

In some embodiments, the filaments of the composite material may be printed without additional finishing. In some embodiments, the plate may be maintained at a higher temperature during printing to reduce crystallization and shrinkage of the composite material.

While PP and PE (e.g., HDPE, LDPE, and/or LLDPE) are ubiquitous in many products and industries, these semi-crystalline polyolefins are rarely used in additive manufacturing. Those skilled in the art will appreciate that other semi-crystalline polyolefins may also be used in the methods and compositions described herein. The ability to use these materials for additive manufacturing will reduce the cost of the technology and make it useful for creating a wider range of products.

Experimental examples

Example 1: preparation of exemplary composite samples

In an exemplary embodiment, an iPP homopolymer (H19G-01) was obtained from Ineos Olefins&Polymer USA (League City, Tex.). The density of the iPP homopolymer (H19G-01) was 0.91g/cm³The melt flow index was 19g/10 min (230 ℃/2.16kg), the tensile strength (yield) was 37.2MPa, the flexural modulus was 1.78GPa, and the notched Izod impact strength was 2.8kJ/m². MAPP pellets (Polybond3200) with a maleic anhydride content of about 1.0 wt.% were obtained from Chemtura Corporation (Lawrence ville, GA). The density of the MAPP pellets (Polybond3200) was 0.91g/cm³The MFI was 115g/10 min (190 ℃/2.16 kg). A suspension (about 3 wt%) of Cellulose Nanofibrils (CNF) was obtained from the process development center of maine university. By using a semi-industrial scale spray dryer (GEA-Niro,germany) a 1.2 wt% CNF suspension was spray dried to obtain CNF powder. Drying was carried out at an inlet temperature of 250 deg.C, a disc rotation speed of 30,000rpm and a pump feed rate of 0.4L/min.

Table 1 shows examples of composites comprising isotactic polypropylene (iPP), maleic anhydride polypropylene (MAPP), Cellulose Nanofibrils (CNF) and/or Maleic Anhydride (MA).

Table 1 formulation of iPP/CNF composite.