Material Design for 3D Multifunctional Hydrogel Structure Preparation

Hydrogels are recognized as one of the most promising materials for e-skin devices because of their unique applicable functionalities such as flexibility, stretchability, biocompatibility, and conductivity. Beyond the excellent sensing functionalities, the e-skin devices further need to secure a target-oriented 3D structure to be applied onto various body parts having complex 3D shapes. However, most e-skin devices are still fabricated in simple 2D film-type devices, and it is an intriguing issue to fabricate complex 3D e-skin devices resembling target body parts via 3D printing. Here, a material design guideline is provided to prepare multifunctional hydrogels and their target-oriented 3D structures based on extrusion-based 3D printing. The material design parameters to realize target-oriented 3D structures via 3D printing are systematically derived from the correlation between material design of hydrogels and their gelation characteristics, rheological properties, and 3D printing processability for extrusion-based 3D printing. Based on the suggested material design window, ion conductive self-healable hydrogels are designed and successfully applied to extrusion-based 3D printing to realize various 3D shapes.     

The dynamic response and failure of Polycarbonate plate by soft body impact

This article is mainly to experimentally and numerically investigate the dynamic response and failure of Polycarbonate (PC) plate against strike by soft body. The experimental results show that high speed soft body impact leads to a large global displacement for PC sheet, though, the obtained strain data shows deformation of PC material are still small. This evidence allows us to employ a thermo‐viscoelastic constitutive model we proposed in our previous work, where the model parameters are determined based on the uniaxial tension test data of PC materials, to describe the PC plate. Then, the simulation is made in finite element (FE) software LS‐DYNA and computational results get a fair agreement with experiments including displacement, strain, and the crack propagations at high velocity impact. The temperature effect on mechanical behavior of PC sheet under impact is numerically studied as well. It is found that the effect gets more significant with the increase of impact velocity, and the higher temperature of PC sheet would lead to its larger deflection but smaller maximum resistance force and principal stress. POLYM. ENG. SCI., 56:1160–1168, 2016. © 2016 Society of Plastics Engineers     

A large‐scale double‐stage‐screw 3D printer for fused deposition of plastic pellets

Fused deposition molding (FDM) is the most popular technology in the fields of three‐dimensional printing, but it is hard to use a variety of plastic materials due to the limitation of filament form of material. Using plastic pellets as printing materials gives advantages in cost, processing speed, and available materials. In this work, a large‐scale double‐screw FDM three‐dimensional printer based on plastic pellets has been designed. It is capable of printing large plastic products at a low cost and high speed. Using ABS + 10%GF as printing material, this work is first focused on the effects of the pressure and speed of the metering screw on the flowrate of melt. The equation for the relationship of these three parameters was established as well. Based on this equation, the effects of melt flow, printing speed, and layer thickness on the width of fused filament were investigated with experiments. Furthermore, the effects of printing spacing between fused filaments on surface accuracy and bonding strength were also explored. By printing models, it was revealed that the designed printer is able to print products with plastic pellets. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45147.     

Evaluation of dynamic viscosity and rheological properties of ceramic materials during liquid phase sintering by numerical‐experimental procedure

The effective shear and bulk viscosity, as well as dynamic viscosity, describe the rheological properties of the ceramic body during the liquid phase sintering process. The rheological parameters depend on the physical and thermo‐mechanical characteristics of the material such as relative density, temperature, grain size, diffusion coefficient, and activation energy. In this paper, the numerical‐experimental method has been developed to study both viscous and rheological behavior of hard porcelain ceramic body during liquid phase sintering. The other aim is to acquire a complete understanding of the response of an incompressible viscose material during sintering such as stress‐strain relations, sintering, and hydrostatic stress. Densification results confirmed that the bulk viscosity was well‐defined with relative density. The stress analysis proved that the sintering stress is more than the hydrostatic stress during the entire sintering time so, the sintering process occurs completely. Deflection results showed that the shear viscosity was a fair estimation of real ones. Dilatometry, SEM, XRD investigations as well as bulk viscosity simulation results confirmed that the “mullitisation plateau” was presented as a very little extraordinary expansion at the final sintering stage.     

Optimization of 3D printing parameters for high-performance biodegradable materials

Developing 3D printing high-performance biodegradable materials is important to protect the environment and deal with emergencies such as COVID-19. Fused deposition modeling (FDM), one of the 3D printing methods, has many advantages, such as low cost and wide range of materials. However, the weak interlayer adhesion is an important factor restricting the development of FDM. In addition to the influence of material properties, the optimization of 3D printing parameters is also an important means to give full play to the inherent properties of materials. The optimal 3D printing parameters are conducive to the diffusion and entanglement of molecular chains between adjacent layers. PLA/PBAT/PLA-g-GMA (70/30/10 wt%, PLA-g-GMA was a compatibilizer synthesized in our lab) was used as the research object. This work aims to analyze the mechanical properties response of biodegradable polymers products manufactured through FDM. Herein, the effect of 3D printing parameters including layer thickness, nozzle temperature, printing speed and platform temperature have been systematically investigated by orthogonal experimental design. The result showed that the excellent performance of 3D printing specimen was obtained when the layer thickness was 0.15 mm, the printing speed was 50 mm·s⁻¹, the nozzle temperature was 200°C and the platform temperature was 50°C. The SEM images showed that the optimal 3D printing products had the best interlayer adhesion and the lowest porosity. Undergoing optimization of 3D printing processing, the yield strength and elongation at break of specimen increased by 115% and 229%, respectively. In this paper, the interlayer adhesion and mechanical properties of 3D printing products can be significantly improved by simply optimizing the 3D printing parameters without complex material modification. This work provided a new method for improving the interlayer adhesion of FDM and the mechanical properties of FDM products.     

Experimental research of drop‐on‐demand droplet jetting 3D printing with molten polymer

Three‐dimensional (3D) printing technology has become an effective method for parts manufacturing and got a certain application in many fields. Now, drop‐on‐demand droplet jetting 3D printing appears as a new method of manufacturing technology which has a proven research progress for metal, colloid, and liquid resin materials. However, there are hardly any researches of droplet jetting 3D printing with molten polymer. So, considering molten polymer as the jetting material with droplet jetting method is an explorative direction. In order to attain the molten polymer droplets and achieve droplet jetting 3D printing with molten polymer, the 3D printing technology of differential melt (3DPDM) is developed independently. According to 3DPDM, a complete set of drop‐on‐demand droplet jetting 3D printer have been developed. In this work, PP (6820) was chosen as the experimental material. Under the different print parameters such as the rotation speed of screw, nozzle diameter, mechanical impact frequency, heating temperature, the space between nozzle and platform, the form, and deposition of droplets were studied. Furthermore, the optimal print parameters were summarized. By printing models with the optimal print parameters, it turned out that the 3DPDM is able to achieve drop‐on‐demand droplet jetting 3D printing with molten polymer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45933.     

Semi‐Crystalline Polymer Blends for Material Extrusion Additive Manufacturing Printability: A Case Study with Poly(ethylene terephthalate) and Polypropylene

Semi‐crystalline polymers are an important class of materials for engineering applications due to their high modulus and barrier properties. Traditional manufacturing methods process semi‐crystalline polymers via rigid molds and well‐controlled temperature and pressure environments to handle the significant change in specific volume occurring during crystallization; however, material extrusion additive manufacturing does not use these features. This often leads to warpage‐induced build failure in fused filament fabrication (FFF). To enable FFF of semi‐crystalline polymers, this work investigates characteristics of immiscible polymer blends (e.g., disparate crystallization behavior and phase separation) to mitigate warping failure during printing. A series of poly(ethylene terephthalate)/polypropylene/polypropylene–graft–maleic anhydride blends are explored and the effect of thermal and morphological characteristics on printability is analyzed. It is shown that these blends can be extruded into filament and printed into a 3D structure. Extrapolations indicate that phase‐separated blends with increased total crystallization half‐time are beneficial for FFF printing.     

基于FDM的可溶性支撑材料打印及溶解工艺研究

讨论了聚乙烯醇(PVA)作为水溶性载体材料,在熔融沉积成型(FDM)三维打印中用于复杂的或镂空产品的支撑部分的应用.首先介绍了PVA材料在FDM打印挤出的难点,然后使用自主研制的PVA材料作为研究对象,通过设计不同的实验方案,优化PVA作为支撑材料的最佳打印参数等.实验采用双喷头FDM打印设备,以丙烯腈-丁二烯-苯乙烯...     

Residual thermal stresses in injection moldings of thermoplastics: A theoretical and experimental study

Internal stresses in injection molded components, a principal cause of shrinkage and warpage, are predicted using a three‐dimensional numerical simulation of the residual stress development in moldings of polystyrene and high‐density polyethylene. These residual stresses are mainly frozen‐in thermal stresses due to inhomogeneous cooling, when surface layers stiffen sooner than the core region as in free quenching. Additional factors in injection molding are the effects of melt pressure history and mechanical restraints of the mold. Transient temperature and pressure fields from simulation of the injection molding cycle are used for calculating the developing normal stress distributions. Theoretical predictions are compared with measurements performed on injection molded flat plates using the layer removal method on rectangular specimens. The thermal stress development in the thinwalled moldings is analyzed using models that assume linear thermo‐elastic and linear thermo‐viscoelastic compressible behavior of the polymeric materials. Polymer crystallization effects on stresses are examined. Stresses are obtained implicitly using displacement formulations, and the governing equations are solved numerically using a finite element method. Results show that residual stress behavior can be represented reasonably well for both the amorphous and the semicrystalline polymer. Similarities in behavior between theory and experiment indicate that both material models provide satisfactory results, but the best predictions of large stresses developed at the wall surface are obtained with the thermo‐viscoelastic analysis.     

Printed thermochromic displays

Thermochromic displays, which were evaluated in this study, combine printed electronics with the thermochromism phenomenon. Conductive lines printed on the reverse side and thermochromic printing ink printed on the front side of cardboard packaging form a thermochromic display that gives cardboard packaging additional value. Displays were printed on different printing materials, and thermochromic printing ink was deposited in one and two layers. In addition, half of the samples were varnished. The influence of the printing material, the thickness of the thermochromic printing ink layer, the varnish, the high temperature, and light fastness on the display's operability were all evaluated. It was clearly shown that the choice of printing material plays a crucial role in the display's operability. Moreover, high temperature and light fastness also have a significant influence, although the impact is negligible when the display is used at room temperature.     

The impact of cupric ion on thermo‐oxidative degradation of chitosan

The thermal degradation of chitosan and chitosan–cupric ion compounds in air was studied using thermogravimetric and differential thermal analyses in the temperature range 30–600 °C. The impact of cupric ion on the thermo‐oxidative degradation of chitosan was investigated. Fourier transform infrared and X‐ray diffraction analyses were utilized to determine the microstructure of the chitosan–cupric ion compounds. Kinetic parameters such as activation energy, pre‐exponential factor, Gibbs energy, and enthalpy and entropy of activation were determined using the Coats–Redfern equation. The results show that the thermo‐oxidative degradation of chitosan and chitosan–cupric ion compounds is a two‐stage reaction. The impact of cupric ion on the thermo‐oxidative degradation of chitosan is significant, and all thermodynamic parameters indicate that the thermo‐oxidative degradation of chitosan and chitosan–cupric ion compounds is a non‐spontaneous process and proceeds via a mechanism involving nucleation and growth, with an Avrami–Erofeev function (A₄) with the integral form [?ln(1 ? α)]⁴. Copyright © 2010 Society of Chemical Industry     

Cyclopentadiene‐functionalized polyketone as self‐cross‐linking thermo‐reversible thermoset with increased softening temperature

Self‐cross‐linkable thermo‐reversible thermosets were obtained by a two‐steps post‐functionalization of aliphatic alternating polyketones yielding two different cyclopentadiene functionalization degree of 9 and 22% (with the respect of initial 1,4‐dicarbonyl units). Thermo‐reversibility was verified by gelation experiments and differential scanning calorimetry (DSC) scans displayed a broad transition varying from 75–100°C till 160°C that can be related to retro‐Diels Alder de‐bonding of the dicyclopentadienyl moieties. The dynamic mechanical thermal (DMTA) analysis showed the complete thermo‐mechanical recovery of the material up to six thermal cycles with a softening temperature around 210°C, thereby ensuring a suitable application window for high‐temperature resistant thermosets. Independently of the exact mechanism at the molecular level and in addition to previous studies which used the same Diels‐Alder diene‐dienophile system, it must be noticed that all prepared materials retained their mechanical behavior during at least six consecutive thermal cycles, thus indicating the re‐workability of the system. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42924.     

丝网印刷条件对陶瓷发热片抗热震性的影响

本文探讨了各种丝网印刷条件对氧化铝陶瓷发热片热震性能的影响。陶瓷的热震性是表征材料承受温度骤变的一种能力,是材料的综合机械-热性能。陶瓷发热片的抗热震性基本取决于材料本性,但其独特的工艺决定了丝网印刷的诸多条件,包括印刷线路设计、印刷网版膜厚、印刷方向、印刷刮刀行程、印刷压力等,对陶瓷发热片的热震性也有不可轻视的影响。     

Synthesis of trimellitic anhydride microcapsule toner by liquid‐phase separation

A microcapsule toner containing trimellitic anhydride for use as a foam inhibitor in printing applications was synthesized by liquid‐phase separation in organic solvents. It is possible to determine materials appropriate for the microencapsulation of trimellitic anhydride from solubility parameters calculated on the basis of the molecular structures of raw material candidates. Considering solubility parameters of various polymers, the polyethylene/methacrylic acid copolymer was selected for the microcapsule wall material. In addition, two kinds of solvents, toluene [solvent (a)] and isoparaffin [solvent (b)], were employed. It was necessary for the microcapsule materials to meet the following conditions: (1) the wall material must completely dissolve in solvent (a); (2) the core material must disperse well, but not dissolve in solvent (a); and (3) the wall and core materials must not dissolve in solvent (b). By using mixtures of either lecithin and basic barium petronate or lecithin and basic calcium petronate as charge control agents, the trimellitic anhydride microcapsules could be charged either positively and negatively, respectively. The microcapsule toner fabricated in this method was successfully applied in commercial printing machines, where it inhibited foaming effectively enough to satisfy product requirements in the printing industry. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3822–3826, 2003     

Temperature/pH dual responsive microgels of crosslinked poly(N‐vinylcaprolactam‐co‐undecenoic acid) as biocompatible materials for controlled release of doxorubicin

Undecenoic acid functionalized thermo/pH responsive microgels, poly(N‐vinylcaprolactam‐co‐undecenoic acid) [poly(VCL‐co‐UA)], were synthesized by precipitation emulsion copolymerization. The microgels exhibit reversible thermo/pH responsive phase transition behavior, which can be tuned by varying the monomer feed ratio. The lower critical solution temperatures (LCSTs) of the materials are close to body temperature. As a result, when temperatures rise above ca. 37°C, a rapid thermal gelation process occurs, accompanied by a phase transition, resulting in expulsion of encapsulated compound. In vitro experiment evaluated its applicability as a drug carrier for controlled release of an anticancer agent (doxorubicin) and showed that the drug encapsulation efficiency (EE), releasing rate, and kinetics are dependent on the temperature and pH value as expected. Minimal cytotoxicity of the microgels was observed by a cytotoxicity assay using 3T3 fibroblast cells. Our finding suggests that the poly(VCL‐co‐UA) based microgels may be considered a promising candidate for temperature or pH‐controlled delivery of anticancer drugs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41146.     

Solid conveying in vane extruder for polymer processing: Effects on pressure establishment

The pressure establishment in the solid conveying section of a vane extruder was theoretically and experimentally studied in the present article. Based on the structural and conveying characteristics of the vane extruder, a four‐plate model was developed. The effects of the device geometry (eccentricity ε and discharge port β), the polymer properties (different materials), and the operating conditions (temperature and rotating speed) on the pressure were also studied using a visual experimental device. The results showed that the experimental data were highly consistent with the theoretical data, which indicated that the theoretical model was sensible. Considering the optimization design of the device and its processing parameters, the eccentricity ε and the discharge port β of the discharge baffle should be appropriately selected, and the setting temperature of the feeding section should be set to a low value. The rotating speed of the rotor had no significant influence on the pressure establishment. In addition, the thermo‐mechanical history of the vane extruder was shorter than that of the conventional screw extruder. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Structural Evolution of PCL during Melt Extrusion 3D Printing

Screw‐assisted material extrusion technique is developed for tissue engineering applications to produce scaffolds with well‐defined multiscale microstructural features and tailorable mechanical properties. In this study, in situ time‐resolved synchrotron diffraction is employed to probe extrusion‐based 3D printing of polycaprolactone (PCL) filaments. Time‐resolved X‐ray diffraction measurements reveals the progress of overall crystalline structural evolution of PCL during 3D printing. Particularly, in situ experimental observations provide strong evidence for the development of strong directionality of PCL crystals during the extrusion driven process. Results also show the evidence for the realization of anisotropic structural features through the melt extrusion‐based 3D printing, which is a key development toward mimicking the anisotropic properties and hierarchical structures of biological materials in nature, such as human tissues.     

某于三维打印的粒状熔融材料成型试验研究

成型材料是粒状熔融材料三维打印工艺的关键环节,直接影响原型件的成型速度、成型精度及应用。通过对粒状聚乙烯和改性粒状聚乙烯材料进行成型试验研究,为粒状熔融材料三维打印工艺成型材料和工艺参数的选择和优化提供了依据。     

Damage analysis of microwave‐dried materials

The aim of this article is to analyze the drying‐induced stresses and destruction of ceramic‐like materials during their microwave drying. The kinetics of microwave drying at various microwave power levels are determined experimentally and numerically, and the distributions of temperature and moisture content in the tested samples are visualized with infrared camera and presented graphically. The experiments are performed on kaolin‐clay samples, where destruction provoked by microwave drying is visualized on photographs taken with the photo camera and microscope. The thermo‐hydro‐mechanical model of drying elaborated by authors is used to determine the distribution of stress components and to calculate the effective stress required to induce the failure of material. The effective stress is formulated with the use of the energetic criterion, and the material spots prone to damage are predicted numerically. The numerically predicted spots are compared with the experimentally appointed places of material damage and a good adherence of the numerical predictions with experiments is confirmed. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

The fabrication of SiBCN ceramic components from preceramic polymers by digital light processing (DLP) 3D printing technology

We present a novel method to fabricate SiBCN ceramic components with complex shapes from preceramic polymers by using digital light processing (DLP) 3D printing technology in this research work. The photocurable precursor for 3D printing was prepared by blending high ceramic yield polyborosilazane with photosensitive acrylate monomers. The material formulation and printing parameters were optimized to fabricate complicated SiBCN ceramic components with high precision. The printed SiBCN ceramic materials were pyrolyzed at different temperatures, and retained their fine features after pyrolysis. Their microstructures were characterized by FTIR, XRD and TEM respectively. Furthermore, the thermal stability and mechanical properties of the SiBCN ceramic samples were investigated and discussed in detail. The 3D printed SiBCN ceramic material exhibited excellent thermal stability and resistance to high temperature oxidation up to 1500?°C.