Flexural response of polypropylene/E-glass fibre reinforced unidirectional composites

This paper presents a study of the flexural response of continuous E-glass fibre reinforced polypropylene composites. Experiments were designed to investigate monotonic and cyclic flexural response using three point bending test for laminates with different angle-ply and cross-ply arrangements. Results show that the monotonic and cyclic flexural response of the composites are influenced by the plastic deformation of the matrix. The study observed that increasing numbers of cyclic loads led to significant energy dissipation, stiffness reduction and micro-damage accumulation within the composite and especially at the matrix-fibre interface. Significant energy dissipation and damage were observed to dominate the first load-unload cycle. With subsequent cycles, the magnitude of energy dissipation and global damage reduces to a threshold value which is cycle independent. This study has also developed a phenomenological model to predict the dependence of energy dissipation with number of cycles. The experimental data generated here will be useful in the development of holistic macroscale constitutive models and finite element studies of the chosen test composite

Cyclic pressure on compression-moulded bioresorbable phosphate glass fibre reinforced composites

The use of thermoplastic composites based on poly(lactic) acid and phosphate glass fibres over metallic alloys for clinical restorative treatment is highly beneficial due to their biocompatibility and biodegradability. However, difficulties in achieving a thorough melt impregnation at high fibre contents while limiting polymer degradation is one of the main issues encountered during their manufacture. This paper reports for the first time on the effects of pressure cycling on the mechanical properties of compression moulded polylactic acid-phosphate glass fibre composites. The strength of the composites consolidated under pressure cycling were at least 30% higher than those in which conventional static pressure was used. The marked disparity was attributed to the influence of pressure cycling on the fibre preform permeability, the melt viscosity and the capillary pressure, leading to improved fibre wet-out with respect to static pressure. Implementation of a cyclic pressure appeared to promote the occurrence of transcrystallinity in the polymer matrix as suggested by DSC traces. The fibre content influenced PLA thermal degradation since the matrix molecular weight decreased as the fibre content increased on account of the moisture adsorbed by the glass surface. However, this extent of degradation did not impair the matrix mechanical performance in the composites

High-temperature creep resistant ternary blends based on polyethylene and polypropylene for thermoplastic power cable insulation

The impact of a small amount of polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) on the thermomechanical and electrical properties of blends comprising low-density polyethylene (LDPE) and isotactic polypropylene (PP) is investigated. SEBS is found to assemble at the PP:LDPE interface as well as within isolated PP domains. The addition of 10\ua0wt% SEBS significantly increases the storage modulus between the melting temperatures of the two polyolefins, 110 and 160\ub0C, and results in improved resistance to creep during both tensile deformation as well as compression. Furthermore, the ternary blends display a very low direct-current (DC) conductivity as low as 3.4 7 10 \ua0S m at 70\ub0C and 30 kV mm , which is considerably lower than values measured for neat LDPE. The here presented type of ternary blend shows potential as an insulation material for high-voltage direct current power cables

Performance of the 2023 Duke-ISCVID diagnostic criteria for infective endocarditis in relation to the modified Duke criteria and to clinical management- reanalysis of retrospective bacteremia cohorts

BackgroundRevised diagnostic criteria for infective endocarditis (IE), the 2023 Duke-ISCVID criteria, were recently presented and need validation. Here, we compare the 2000 modified Duke criteria for IE with Duke-ISCVID among patients with bacteremia and relate the diagnostic classification to IE-treatment.MethodsWe reanalyzed patient cohorts with Stapylococcus aureus, Staphylococcus lugdunensis, non-beta-hemolytic streptococci, Streptococcus-like bacteria, Streptococcus dysgalactiae, Enterococcus faecalis and HACEK bacteremia. Episodes were classified as definite, possible or rejected IE with the modified Duke and Duke-ISCVID criteria. Reclassification included the microbiology criteria, PET-CT and cardiac implanted elect-ronical devices. To calculate sensitivity, patients treated as IE were considered as having IE.ResultsIn 4050 episodes of bacteremia, the modified Duke criteria criteria assigned 307episodes (7.6%) as definite IE, 1190 episodes (29%) as possible IE and 2553 episodes (63%) as rejected IE. Using the Duke-ISCVID criteria, 13 episodes (0.3%) were reclassified from possible to definite IE and 475 episodes (12%) were reclassified from rejected to possible IE. With the modified Duke criteria, 79 episodes that were treated as IE were classified as possible IE and eleven of these episodes were reclassified to definite IE with Duke-ISCVID. Applying the decision to treat for IE as reference standard, the sensitivity of the Duke-ISCVID criteria was 80%. None of the 475 episodes reclassified to possible IE were treated as IE.ConclusionsThe Duke-ISCVID criteria reclassified a small proportion of episodes to definite IE at the expense of more episodes of possible IE. Future criteria should minimize the possible group while keeping or improving sensitivity

Rate dependencies and energy absorption characteristics of nanoreinforced, biofiber, and microcellular polymer composites

The effects of loading rate on bio‐, nano‐, and microcellular composite systems have been studied. Fiber–resin systems have been manufactured and dynamically tested at various speeds to assess their strain‐rate dependencies (rate hardening) and energy‐dissipation characteristics compared to conventional materials. The following composite systems have been fabricated and studied: polypropylene/sisal fiber biocomposite, hemp/vinyl ester biocomposite, thermoplastic olefin/nanoclay composite, microcellular polypropylene/sisal fiber biocomposite, and microcellular thermoplastic olefin/nanoclay composite. It has been determined that the biocomposite systems studied possess unique energy dissipation characteristics and muted rate dependence, while the nanocomposite system did not. In addition, microcellular foaming of these materials further enhanced the effects. Though the exact mechanisms at play are not fully understood at this point, it has been found that in addition to the microcellular voids, the anatomical vasculature of the natural fibers may play a role in energy dissipation processes in these hybrid materials. POLYM. COMPOS., 2011. © 2011 Society of Plastics EngineersPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87107/1/21169_ftp.pd

Highly insulating thermoplastic nanocomposites based on a polyolefin ternary blend for high-voltage direct current power cables

Octyl-silane-coated Al2O3 nanoparticles are found to be a promising conductivity-reducing additive for thermoplastic ternary blends comprising low-density polyethylene (LDPE), isotactic polypropylene and a styrenic copolymer. The ternary blend nanocomposites were prepared by compounding the blend components together with an LDPE-based masterbatch that contained the nanoparticles. The nanoparticles did not affect the superior stiffness of the ternary blends, compared to neat LDPE, between the melting temperatures of the two polyolefins. As a result, ternary blend nanocomposites comprising 38 wt% polypropylene displayed a storage modulus of more than 10 MPa up to at least 150 degrees C, independent of the chosen processing conditions. Moreover, the ternary blend nanocomposites featured a low direct-current electrical conductivity of about 3 x 10(-15) S m(-1) at 70 degrees C and an electric field of 30 kV mm(-1), which could only be achieved through the presence of both polypropylene and Al2O3 nanoparticles. This synergistic conductivity-reducing effect may facilitate the design of more resistive thermoplastic insulation materials for high-voltage direct current (HVDC) power cables

Highly insulating thermoplastic blends comprising a styrenic copolymer for direct-current power cable insulation

The impact of the composition of blends comprising low-density polyethylene (LDPE), isotactic polypropylene (PP) and a styrenic copolymer additive on the thermomechanical properties as well as the direct-current (DC) electrical and thermal conductivity is investigated. The presence of 5 weight percent (wt%) of the styrenic copolymer strongly reduces the amount of PP that is needed to enhance the storage modulus above the melting temperature of LDPE from 40 to 24 wt%. At the same time, the copolymer improves the consistency of the thermomechanical properties of the resulting ternary blends. While both the DC electrical and thermal conductivity strongly decrease with PP content, the addition of the styrenic copolymer appears to have little influence on either property. Evidently, PP in combination with small amounts of a styrenic copolymer not only allows to reinforce LDPE at elevated temperatures but also functions as an electrical conductivity-reducing additive, which makes such thermoplastic ternary formulations possible candidates for the insulation of high-voltage power cables

Nanocomposites and polyethylene blends: two potentially synergistic strategies for HVDC insulation materials with ultra-low electrical conductivity

Among the various requirements that high voltage direct current (HVDC) insulation materials need to satisfy, sufficiently low electrical conductivity is one of the most important. The leading commercial HVDC insulation material is currently an exceptionally clean cross-linked low-density polyethylene (XLPE). Previous studies have reported that the DC-conductivity of low-density polyethylene (LDPE) can be markedly reduced either by including a fraction of high-density polyethylene (HDPE) or by adding a small amount of a well dispersed, semiconducting nanofiller such as Al2O3 coated with a silane. This study demonstrates that by combining these two strategies a synergistic effect can be achieved, resulting in an insulation material with an ultra-low electrical conductivity. The addition of both HDPE and C8–Al2O3 nanoparticles to LDPE resulted in ultra-insulating nanocomposites with a conductivity around 500 times lower than of the neat LDPE at an electric field of 32 kV/mm and 60–90 \ub0C. The new nanocomposite is thus a promising material regarding the electrical conductivity and it can be further optimized since the polyethylene blend and the nanoparticles can be improved independently