Characterization of the auto‐curing behavior of rapid prototyping materials for three‐dimensional printing using dielectric analysis

Three‐dimensional printing technology applies the high efficiency of the ink jet printer technology to manufacture functional prototypes. To optimize the printing process of PMMA powder containing an initiator and a liquid binder consisting of polymerizable monomers with activator molecules, the knowledge of the curing kinetics is required. Therefore, a methodology was developed to apply dielectric analysis measuring changes of the ion and dipole mobility in terms of a quantity called ion viscosity. Connecting time‐dependent changes of ion viscosity and reaction heat determined by DSC leads to detailed insight into the curing process. The results show that the styrene concentration of the binder determines the curing kinetics—reduces thermal stresses and provides time for stress relaxation. The curing process differs significantly with respect not only to composition of the binder, but also to its aging state. The proposed approach can be implemented directly to a printer to detect dielectric changes of the materials during the manufacturing process. POLYM. ENG. SCI., 55:1485–1493, 2015. © 2015 Society of Plastics Engineers     

Superposed flow properties of ceramic powder‐filled polymer melts

Complicated shape products from ceramic composite materials are nowadays intensively processed via flow molding technologies. Rheological properties of these materials are essential for the clarification of the deformation behavior through channels under various conditions. In this article, ceramic powder (zirconia) was mixed (10–50 vol%) with polypropylene, paraffin, and stearic acid in an elastic extruder. Parallel superposed steady and oscillatory shear flows were measured on a cone‐plate rheometer. Flow properties at high shear rates were evaluated on a capillary rheometer. The effects of powder content, shear rate/angular frequency, and temperature were clarified. The studied filled systems showed highly non‐Newtonian behavior and apparent yield stress; their viscoelastic properties were influenced remarkably under the superposed shear flow at low shear rate and angular frequency, and they showed significantly different behavior from unfilled and fiber‐filled systems. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Pressure-affected flow properties of powder injection moulding compounds

The effect of pressure and temperature on the flow properties of the materials intended for Powder Injection Moulding (PIM) technology was studied using a single-piston capillary rheometer modified by additional backpressure chamber. The influence of pressure and temperature on shear viscosity has been quantified through pressure and temperature sensitivity coefficients derived from Carreau-Yasuda model. The temperature sensitivity of the 50 vol.% compound based on cemented carbide powder is lower than that of pure polymeric binder, and it varies only slightly with pressure. In contrast, the pressure sensitivity of compounds was found to be higher than that of pure polyolefin binder, and it is decreasing function of temperature. In addition, it is shown that temperature sensitivity of binder, which is considerably enhanced by pressure (in contrast to the PIM demands), cannot be determined as being equal to the properties of particular binder components.     

An evaluation of the pressure‐dependent melt viscosity of polyphenylsulfone

A method for the determination of pressure‐affected viscosity from capillary rheometry and pressure–volume–temperature (PVT) data was tested on polyphenylsulfone melt. Shear viscosity data evaluated at selected temperatures (345–375°C) were interlinked to the PVT data at pressures ranging from 1 to 200 MPa. According to the recently proposed correlation approach, a pressure‐dependent shear viscosity is derived from the relationship (verified on several commodity polymers) between temperature‐dependent viscosity and a free volume parameter computed using the Simha–Somcynsky equation of state. Finally, the predicted pressure‐viscosity coefficient was compared with the value obtained experimentally on a modified single piston rheometer. POLYM. ENG. SCI., 54:711–715, 2014. © 2013 Society of Plastics Engineers     

The effect of powder characteristics on pressure sensitivity of powder injection moulding compounds

Pressure effect on the rheological behaviour of powder-polymer compounds intended for powder injection moulding was determined. A single-piston capillary rheometer modified by addition of a second chamber with a restricting needle valve generating backpressure increasing the pressure in the melted material during the flow through the die was employed to determine pressure sensitivity coefficients. The results obtained for three compounds varying in the characteristics of powders used confirmed that compounds at the loading level close to the maximum packing are more sensitive to pressure than polymer binder. It is shown that pressure sensitivity coefficients of these materials are strongly dependent on powder characteristics — particle size and particle size distribution. The highest coefficient (32.9 GPa⁻¹) was found for compound containing broad particle size distributed powder having a perceptible portion of small particles.     

Synthesis of New Tricyclic 1,2-Thiazine Derivatives with Anti-Inflammatory Activity

New, tricyclic compounds containing a sulfonyl moiety in their structure, as potential safer COX inhibitors, were designed and synthesized. New derivatives have three conjugated rings and a sulfonyl group. A third ring, i.e., an oxazine, oxazepine or oxazocin, has been added to the 1,2-benzothiazine skeleton. Their anti-COX-1/COX-2 and cytotoxic effects in vitro on NHDF cells, together with the ability to interact with model membranes and the influence on reactive oxygen species and nitric oxide, were studied. Additionally, a molecular docking study was performed to understand the binding interaction of the compounds with the active site of cyclooxygenases. For the abovementioned biological evaluation of new tricyclic 1,2-benzothiazine derivatives, the following techniques and procedures were employed: the differential scanning calorimetry, the COX colorimetric inhibitor screening assay, the MTT, DCF-DA and Griess assays. All of the compounds studied demonstrated preferential inhibition of COX-2 compared to COX-1. Moreover, all the examined tricyclic 1,2-thiazine derivatives interacted with the phospholipid model membranes. Finally, they neither have cytotoxic potency, nor demonstrate significant influence on the level of reactive oxygen species or nitric oxide. Overall, the tricyclic 1,2-thiazine derivatives are good starting points for future pharmacological tests as a group of new anti-inflammatory agents.     

Electrical properties of composites of hard metal carbides in a polymer matrix

The electrical conductivity of composites containing hard metal carbide powder in a nonconducting polymer matrix has been studied. In composites with low and medium filler contents, the expansion of the nonconducting matrix with increasing temperature caused interruption of conducting paths and a rapid drop in conductivity (switching effect). In contrast, at high filler loadings (Φ_P > 50 vol%), a continuous and slight decrease in conductivity with temperaute inducates a specific composite structure with a dense particle arrangement and a great number of conducting contants, which change only little during heating.