Electrical and Electro-Thermal Characteristics of (Carbon Black-Graphite)/LLDPE Composites with PTC Effect.

Electrical properties and electro-thermal behavior were studied in composites with carbon black (CB) or hybrid filler (CB and graphite) and a matrix of linear low-density polyethylene (LLDPE). LLDPE, a (co)polymer with low crystallinity but with high structural regularity, was less studied for Positive Temperature Coefficient (PTC) applications, but it would be of interest due to its higher flexibility as compared to HDPE. Structural characterization by scanning electron microscopy (SEM) confirmed a segregated structure resulted from preparation by solid state powder mixing followed by hot molding. Direct current (DC) conductivity measurements resulted in a percolation threshold of around 8% (w) for CB/LLDPE composites. Increased filler concentrations resulted in increased alternating current (AC) conductivity, electrical permittivity and loss factor. Resistivity-temperature curves indicate the dependence of the temperature at which the maximum of resistivity is reached (Tmax(R)) on the filler concentration, as well as a differentiation in the Tmax(R) from the crystalline transition temperatures determined by DSC. These results suggest that crystallinity is not the only determining factor of the PTC mechanism in this case. This behavior is different from similar high-crystallinity composites, and suggests a specific interaction between the conductive filler and the polymeric matrix. A strong dependence of the PTC effect on filler concentration and an optimal concentration range between 14 and 19% were also found. Graphite has a beneficial effect not only on conductivity, but also on PTC behavior. Temperature vs. time experiments, revealed good temperature self-regulation properties and current and voltage limitation, and irrespective of the applied voltage and composite type, the equilibrium superficial temperature did not exceed 80 °C, while the equilibrium current traversing the sample dropped from 22 mA at 35 V to 5 mA at 150 V, proving the limitation capacities of these materials. The concentration effects revealed in this work could open new perspectives for the compositional control of both the self-limiting and interrupting properties for various low-temperature applications.

Construction Products between Testing Laboratory and Market Surveillance: Case study of Cementitious Ceramic Tile Adhesives.

This article presents the results of the interlaboratory comparison (ILC) study of the following four characteristics of ceramic tile adhesives (CTAs): initial tensile adhesion strength, tensile adhesion strength after heat ageing, tensile adhesion strength after immersion in water, and tensile adhesion strength after freeze-thaw cycles. The results showed that the objective of the ILC was achieved-the z-score analysis carried out following ISO 13528 allowed for classifying all results obtained by 23 laboratories out of 27 as satisfactory. The results of the remaining four laboratories were rated worse. Despite the achieved goal, the ILC notes high heterogeneity of the results in terms of failure patterns, as well as significant differences between the lowest and the highest values of tensile adhesion strength for various measurement conditions. The results of the ILC were discussed in terms of the possibility of including them in the risk analysis conducted by the manufacturer. The results of the ILC are also valuable information for market surveillance authorities, who, in the authors' opinion, should be more cautious about results on samples taken from the market. The ILC results for CTAs are also a valuable recommendation for a possible revision of EN 12004.

Thresholds of Basal- and Calcium-Stimulated Calcitonin for Diagnosis of Thyroid Malignancy.

Since medullary thyroid carcinoma is an aggressive cancer, it is important to have an early detection based on stimulated calcitonin (CT), especially when basal-CT is slightly elevated. The objective of this work was to set specific thresholds for basal-CT- and calcium-stimulated calcitonin for prediction of thyroid malignancy in female population. The study included 2 groups: group A-women with elevated basal-CT (>9.82 pg/ml) and group B-women with normal basal-CT (control group). After calcium stimulation test precise protocol, histopathological reports of those that required surgery were correlated with both basal and stimulated calcitonin. The best basal and stimulated calcitonin cut-offs for distinguishing female patients with medullary thyroid carcinoma or C-Cell-hyperplasia from other pathologies or normal cases were: 12.9 pg/ml, respectively 285.25 pg/ml. For basal-CT above 30 pg/ml, malignancy was diagnosed in 9/9 patients (100%): 9 MTC. For stimulated calcitonin above 300 pg/ml, malignancy was diagnosed in 17/21 patients (80.95%): 12 MTC and 5 papillary thyroid carcinomas. The smallest nodule that proved to be medullary thyroid carcinoma had only 0.56/0.34/0.44 cm on ultrasound, with no other sonographic suspicious criteria. In conclusion, we have identified in Romanian female population basal and stimulated calcitonin thresholds to discriminate medullary thyroid carcinoma or C-Cell-hyperplasia from other cases. We recommend thyroid surgery in all women with stimulated calcitonin above 285 pg/ml. Further studies on larger groups are necessary to establish and confirm male and female cut-offs for early diagnosis of medullary thyroid carcinoma, and interestingly, maybe for macro-papillary thyroid carcinomas alike. The calcium administration has minimum side-effects, but continuous cardiac monitoring is required.

Interlaboratory Comparison as a Source of Information for the Product Evaluation Process. Case Study of Ceramic Tiles Adhesives.

In this study, the results obtained by 19 laboratories participating in 2 editions of the interlaboratory comparison (ILC) determining 2 properties of ceramic tiles adhesives (CTAs), i.e., initial tensile adhesion strength and tensile adhesion strength after water immersion following EN 12004, were analyzed. The results show that participating laboratories maintain a constant quality of their work. The use of z-score analysis, under ISO 13528, allows for classifying 89.5% to 100% of laboratories as satisfactory, depending on the measurement's kind and edition. The remaining laboratories are classified as questionable. The investigation of the predominant mode of failure of the CTA's samples tested in the two editions shows significant differences. From the perspective of laboratories, the goal of the ILC has been achieved. From the standpoint of a manufacturer who evaluates a product's properties when placing it on the market, the results indicate the necessity of a particular treatment of the product evaluation process because the variability of the obtained results is significant. It increases the possibility of the product failing to meet the assessment criteria verified by the construction market supervision authorities. The manufacturer must consider all possible variations in the risk analysis, including the ILC results, to improve the assessment process of CTAs.

Polyethylene Nanocomposites for Power Cable Insulations.

This review represents a comprehensive study of nanocomposites for power cables insulations based on thermoplastic polymers such as polyethylene congeners like LDPE, HDPE and XLPE, which is complemented by original results. Particular focus lies on the structure-property relationships of nanocomposites and the materials' design with the corresponding electrical properties. The critical factors, which contribute to the degradation or improvement of the electrical performance of such cable insulations, are discussed in detail; in particular, properties such as electrical conductivity, relative permittivity, dielectric losses, partial discharges, space charge, electrical and water tree resistance behavior and electric breakdown of such nanocomposites based on thermoplastic polymers are described and referred to the composites' structures. This review is motivated by the fact that the development of polymer nanocomposites for power cables insulation is based on understanding more closely the aging mechanisms and the behavior of nanocomposites under operating stresses.