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Polymer infiltrated ceramics are hybrid materials that combine the strength of ceramics and the flexibility of polymers. The aim of this study was to compare the fracture load capacity of monolithic CAD/CAM crowns with different occlusal thicknesses, made from polymer infiltrated ceramic network. Fifteen full contour CAD/CAM crowns made of Vita Enamic with occlusal thicknesses of 0.5 mm, 1.0 mm and 1.5 mm were fabricated with a wet milling machine. Restorations were cemented on human molars with adhesive cement. Samples were loaded along the long axis until fracture, with a single static compressive force. A scanning electron microscope (SEM) was used to examine the fracture surface of specimens after the fracture. The results of this study reveals that the fracture load of the samples increased progressively with the occlusal thickness. The highest fracture value was recorded for1.5 mm occlusal thickness of the crown. No statistically significant difference was reported between the three experimental groups. It can be concluded that hybrid monolithic CAD-CAM crowns showed sufficient fracture strength to be used for single restorations in the posterior area, even with a reduced occlusal thickness.

The paper is part of a series in which the influence of the manufacturing defects on the functional behavior in biodegradation medium of some items obtained, both by 3D printing and by classical procedure (pressing), from an originaly renwable matrials based on polylatic acid will be presented. The first results regarding the correlation of the defects appeared at manufacturing into plates with the biodegradation behavior in an Aspergillus Niger(A.niger) medium, studied by SEM microscopy, are presented. These results demonstrated that the development of the A. Niger microorganism is related manly to the defects appeared at the melt processing of renewable polymeric material into finished product. A notable role in controlling the appearance of the manufacturing defects belongs both to the melt rheological properties which are responsible for the continuous or discontinuous flow and to the technical performance of the used equipement, 3D printer or classic hydraulic press. If the polymeric material melt has too high viscosity than the continuous flow is not possible and so the overlapped melt fronts are created which generate the voids formation, sometimes joined by small nano and/or micrometric channels. The rheological properties of the melts depend both on the material formulation and the seleted melt processing conditions.

The widespread use of thermoplastic polymeric materials in various industrial fields has shown considerable interest in understanding the frictional and wear behavior. Among these polymers, polytetrafluoroethylene, also called PTFE, is a high-performance plastic that offers high chemical and thermal resistance and low friction. Additives such as fiberglass, carbon and graphite fillers are added to PTFE to significantly increase thermal conductivity, stiffness and self-lubricating properties. The materials subjected to the experimental analysis were pure PTFE, PTFE + 15% fiberglass, PTFE + carbon-graphite which slipped, under conditions of dry friction, on a sample of non-alloy steel construction SR EN 10025 from 1994. The tests were performed on a pin-on-disc tribometer. The effect of loading and sliding speed on the tribological properties of the polymer / steel combination under dry slip conditions was investigated and the specific wear rate for the experimental conditions was evaluated. The tests were performed at loads of the pin of Fn1=1N, Fn2=3N, Fn3=5N and Fn4=10N and sliding speeds of 1=1m/s, 2=3m/s. The results obtained indicated that the coefficient of friction decreases with increasing load. The wear rate for the analyzed materials was between 10-13...10-15 m2/N, the fiberglass reinforced PTFE material having the lowest wear rate. The present paper, through a comparative analysis of the friction and wear behavior, highlights the effects that the ingredients introduced in the basic material have, under the action of the exploitation factors (loading, sliding speed).

Due to its chemical and mechanical properties, polyurea gains more and more interest in military applications. In this study, polyurea and carbon nanotubes were processed as coating polymer composites for ballistic plates and/or packages, in order to increase their protection potential, meanwhile maintaining an appropriate weight and an economic accessibility. In this respect, the composite material was layered on various commercially-available materials and various thicknesses and further, the performances of the products obtained were tested in order to assess their behavior against traumas produced by shockwave, blunt, shooting and fragment.

This work is aimed at synthesizing an organic compound N, N`-bis(benzoyl) 1,3-cyclohexane-dicarboxylic acid dihydrazide (CABH) to focus on its effect on the non-isothermal crystallization of poly(L-lactide) (PLLA), meanwhile the melting behavior, thermal decomposition process and optical property of PLLA/CABH samples in different CABH concentrations were also investigated. It was found that CABH acted as efficient heterogeneous nucleating agent for inducing PLLA’s crystallization through comparative analysis of melt-crystallization process of the virgin PLLA with PLLA/CABH samples, and a high amount of CABH played a much more significant role in promoting PLLA’s crystallization. Additionally, the melt-crystallization processes also showed that both the cooling rate and the final melting temperature affected the crystallization behavior of PLLA, an increase of cooling rate could weaken the crystallization ability of PLLA/CABH samples, and the final melting temperature of 180°C made PLLA/CABH exhibit the best crystallization ability. For the cold-crystallization process, the cold-crystallization peak became flatter and shifted toward the lower temperature with increasing of CABH concentration, but an increase of heating rate could prevent the cold-crystallization peak from moving to low temperature because of the thermal inertia. The melting behaviors of PLLA/CABH depended on the previous crystallization and heating rate in heating, and the difference in melting behavior of PLLA/CABH samples effectively reflected the nucleation role of CABH, as well as the double melting peaks behavior of PLLA/CABH was thought to due to the melting-recrystallization. The introduction of CABH led to a drop in light transmittance, moreover, this negative effect were more obvious with an increase of CABH loading. In contrast, the fluidity of PLLA was significantly enhanced due to the existence of CABH.

There is always time and energy optimization and reduction of faults the aim of research and in this context our article presents a study of a practical case of the deformation of a plastic part placed in a refrigerator for food storage, and that the use increases in number of these types of metals, are found in several sectors, and because of their industrial performance, a minimum residence time of the part in the mold is sought in order to reduce the cycle time of the process at the same time that the injection process is quite complex and requires a certain number of recurring questions to succeed. In the desired model. These are linked to residual stresses and deformations, pressure, mold temperature, filling threshold, shape of the part, but also to other mechanical and optical properties. Several investigations have been carried out and according to the authors the causes of these failures vary according to the manufacturing technique used. In this article, we try to find the origin of a deformation detected on a part at the end of the mold. Our work consists first of all in presenting, according to different studies, the thermomechanical properties of the material injected at different stages of the injection process. In a second step, compare the theoretical and analytical results. At the end of our study, we propose an optimization of the parameters necessary for the success of the molding and of the geometry of the assembly (mold and part).

An additive is a substance, which when incorporated into polymer materials might lead at improvements on the electrical, thermal or mechanical properties of finished products in dependence of their applications, such as automotive, electronics, packaging and consumer goods. This study is based on the idea of using inorganic agents to change the basic properties of an epoxy resin. The well-known plasticizer 1-methyl-2-pyrrolidinone (NMP) was used to solve the inorganic agents and the mixture of obtained solutions was added, in certain amounts, into the epoxy resin prior the hardener of the epoxy system. The idea is to test the hypothesis of forming of ceramic nanostructures into the polymer structure based on local chemical interaction between solved inorganic compounds in certain conditions. The present paper concerns with the effect of changes on the mechanical properties of the epoxy resin.

The aim of this work was to find the influence of the addition of low amount of hydrophilic and hydrophobic TiO2 nanoparticles on compressive strength, microhardness and rheological properties of flowable dental composite material. Specimens were prepared by adding 0.05; 0.2 and 1 wt. % of hydrophilic and hydrophobic 20 nm TiO2 nanoparticles. These specimens were compared to non-modified control specimens in compressive strength and microhardness. Furthermore, their rheological properties were determined. The optimal nanoparticle loading was 0.2 % hydrophobic TiO2, resulting in significantly higher compressive strength and microhardness than those of the control specimen group. Mechanical properties of flowable composites reinforced with hydrophilic and hydrophobic TiO2 at higher loadings are lower than those of control specimens, which is the result of nanoparticle agglomeration. TiO2 nanoparticles addition resulted in the decrease in viscosity in all specimens except for the specimewn with 1% hydrophilic TiO2 nanoparticles. In accordance to the obtained results, hydrophobic nanoparticle addition results in a more resistant and durable material, combined with an increased flowability compared to a non-modified composite.

Although polymethylmethacrylate (PMMA) is widely used as a denture base material, its disadvantages include low strength and low thermal conductivity. The effects on thermal conductivity, flexural strength, thermal diffusivity, and elastic modulus of adding Al2O3 and SiC powders in different volumes to PMMA were investigated. A total of 60 specimens were prepared in 10 groups (five groups for the thermal conductivity test and five groups for the flexural strength test (n:6). The specimens were immersed in water for 30 days before the testing. Thermal conductivity values were measured by the transient hot bridge (THB) method, and flexural strengths were measured by the 3-point bend test. A significant difference was found in thermal conductivity, flexural strength, thermal diffusivity and elastic modulus values between independent groups (P < 0.001) using the Kruskal-Wallis test. The Kruskal Wallis 1-way ANOVA was used for the post hoc tests after Kruskal Wallis (á=.05). The thermal conductivity of PMMA increased significantly with the addition of 15% SiC and 15% Al2O3. The flexural strength values decreased significantly with the addition of 10% SiC and 15% Al2O3. The thermal diffusivity values increased significantly with the addition of 10% and 15% SiC. The Young modulus of PMMA decreased when 10% SiC, 10% Al2O3 and 15% Al2O3 were added. Environmental scanning electron microscope (ESEM) showed that ceramic powders were dissipated in PMMA. The addition of 15% SiC powders to PMMA increased thermal conductivity without significantly reducing flexural strength. This study helped determine the optimum volumes for the use of SiC and Al2O3 powders. Knowledge of the importance of this variable will help in more effective modification of denture base resin with SiC and Al2O3 powders to improve heat transfer without adversely affecting strength.

Renewability, recyclability and biodegradable contents are similar to glass fibers in natural fiber reinforced polymer composites (NFRP) which have definite mechanical properties. The interface of polymer matrix and natural fibers results the composites to achieve superior properties of products. Researchers have extended their product designs and production techniques by using renewable materials such as jute fiber, cotton fiber, silk fiber, etc. which are enormous and used in the manufacture of durable industrial goods of high-end quality. This paper reviews the current developments and the brief findings needed in literature, concentrating on the mechanical properties and applications of NFRP.