Shrinkage behaviour of semi-crystalline polymers in laser sintering: PEKK and PA12

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordShrinkage is extensively mentioned in the literature as one of the main causes for dimensional instability or poor performance in Laser Sintering (LS). This study proposes and examines a methodology to describe shrinkage in cooling from a material perspective. Thermal behaviour and crystallisation effects were measured to determine the influence of powder structure and density on overall LS shrinkage. PEKK and PA12 powders were used to assess such behaviour in LS. The shrinkage parameter associated with powder bulk properties has the greatest impact in PEKK, contributing to 57% of the total shrinkage observed in cooling for this material as supported by the low values of bulk density, irregular morphology and internal porosity observed for these particles. For PA12, crystallisation is responsible for 60% of the overall shrinkage observed. In LS, PEKK shows an overall shrinkage approximately 30% lower than PA12, which makes it a promising material for maintaining final part dimensions.Arkema Innovations Chemistr

Methods for evaluating particle coalescence and their implications in laser sintering

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordAn experimental study on the melt and coalescence of different Poly(aryl ether ketones) (PAEK) powders was carried out. The study consisted of evaluating individual particles and neck growth using a hot stage platform. Three different methods of assessing particles dimensions were evaluated, and the coalescence was compared for the grades on three different substrates: glass, glass coated silicone and amorphous PEKK films, the last substrate with the intent to relate with the laser sintering process. It was found that all individual particles shrink prior to melting, achieving up to 30% reduction in perimeter at temperatures just above melting. This shrinkage is followed by an increase in size, mostly driven by viscous flow. Shrinkage is expected to affect neck growth by delaying coalescence, as particles are pulled away whilst neck increases. This is a plausible explanation for why neck growth occurs at a lower rate than predicted by most coalescence models. The use of different substrates does not seem to affect particle coalescence or change in dimension. Viscosity and particle size influence overall particle behaviour and melt, whilst morphology and porosity do not have a great impact in particles coalescence.The authors would like to acknowledge the financial support of Arkema Innovations Chemistry for this study

The influence of structure geometry and material on seismic metamaterial performance

Diverting, and controlling, elastic vibrations impacting upon infrastructure is a major challenge for seismic hazard mitigation, and for the reduction of machine noise and vehicle vibration in the urban environment. Seismic metamaterials (SMs), with their inherent ability to manipulate wave propagation, provide a key route for overcoming the technological hurdles involved in this challenge. Engineering the structure of the SM serves as a basis to tune and enhance its functionality, and inspired by split rings, swiss-rolls, notch-shaped and labyrinthine designs of elementary cells in electromagnetic and mechanical metamaterials, we investigate altering the structure geometries of SMs with the aim of creating large bandgaps \textcolor{black}{in a subwavelength regime}. We show that square stiff inclusions, perform better in comparison to circular ones, whilst keeping the same filling fraction. En route to enhancing the bandgap, we have also studied the performance of SMs with different constituent materials; we find that steel columns, as inclusions, show large bandgaps, however, the columns are too large for steel to be a feasible material in practical or financial terms. Non-reinforced concrete would be preferable for industry level scaling up of the technology because, concrete is cost-effective, easy to cast directly at the construction site and easy to provide arbitrary geometry of the structure. As a part of this study, we show that concrete columns can also be designed to exhibit bandgaps if we cast them within a soft soil coating surrounding the protected area for various civil structures like a bridge, building, oil pipelines etc

Repetibilidade dos pesos e ganho de peso do nascimento a desmama de bezerros da raça Nelore.

Repetibilidade do ganho de peso ao nascimento e a desmama

Benign anal lesions, inflammatory bowel disease and risk for high-risk human papillomavirus-positive and -negative anal carcinoma.

A central role in anal carcinogenesis of high-risk types of human papillomaviruses (hrHPV) was recently established, but the possible role of benign anal lesions has not been addressed in hrHPV-positive and -negative anal cancers. As part of a population-based case-control study in Denmark and Sweden, we interviewed 417 case patients (93 men and 324 women) diagnosed during the period 1991-94 with invasive or in situ anal cancer, 534 patients with adenocarcinoma of the rectum and 554 population controls. Anal cancer specimens (n = 388) were tested for HPV by the polymerase chain reaction. Excluding the 5 years immediately before diagnosis, men, but not women, with anal cancer reported a history of haemorrhoids [multivariate odds ratio (OR) 1.8; 95% confidence interval (CI) 1.04-3.2] and unspecific anal irritation (OR 4.5; CI 2.3-8.7) significantly more often than controls. Women with anal cancer did not report a history of benign anal lesions other than anal abscess to any greater extent than controls, but they had used anal suppositories more often (OR 1.5; CI 1.1-2.0). Patients with hrHPV in anal cancer tissue (84%) and those without (16%) reported similar histories of most benign anal lesions, but anal fissure or fistula was more common among hrHPV-positive cases. Ulcerative colitis and Crohn's disease, reported by <1% of study participants, were not associated with anal cancer risk. The higher proportion of hrHPV-positive anal cancers among case patients with anal fissure or fistula suggests that such mucosal lesions may provide direct viral access to basal epithelial layers. Since risk associations with benign anal lesions in men may be confounded by unreported sexual behaviour, and since risk associations in women were generally negative, it seems unlikely that benign anal lesions act as promoters in hrHPV-associated anal carcinogenesis. Moreover, benign anal lesions appear not to be linked to an alternative, hrHPV-unassociated causal pathway to anal cancer. Ulcerative colitis and Crohn's disease were not supported as causal factors for anal cancer

Macromolecular modifications of poly(etherketoneketone) (PEKK) copolymer at the melting state

Macromolecular modifications of poly(etherketoneketone) (PEKK) copolymer prepared from diphenyl ether (DPE), terephthalic acid (T) and isophthalic acid (I) with a T/I ratio of 60/40 have been investigated above its melting temperature by gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and rheological measurements to assess the evolution of PEKK matrix during composite consolidation step. We mainly focused in this study on anaerobic conditions, i.e. degradation under nitrogen or in lack of oxygen. During exposure, thermal degradation leads to an increase of weight average molar mass Mw and viscosity which is typical to crosslinking/branching mechanism as already observed for PEEK in the literature. However, thanks to GPC measurements, it appears that a chain scission mechanism occurs in the same time related to a constant number average molar mass Mn. Crosslinking kinetics are identified at several temperatures between 320 and 400 °C with rheological measurements from a kinetic scheme governing the crosslinking mechanism. At last, the influence of the crosslinking process on PEKK crystallization is investigated. The final crystallinity and crystallization kinetics decrease with crosslinking due to branching of macromolecular chains

A route to improving elongation of high-temperature laser sintered PEKK

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordData availability: The dataset generated during the current study is not publicly available due to confidentiality reasons but can be made available on reasonable request with the approval of all authors.Laser sintering (LS) is one of the most popular additive manufacturing (AM) techniques as it produces parts of complex geometry with high dimensional accuracy and good mechanical strength. However, the nature of the LS process often leads to brittle behavior characterized by a low elongation at break if compared to conventional polymer processing techniques, e.g., injection molding (IM). For poly(ether ketone ketone) (PEKK), such elongation is currently below 3%. This study determines and then optimizes the relationship between cooling time and crystallization of PEKK during LS and the resulting elongation at break. The elongation at break of PEKK was successfully improved by using shorter cooling times. The combination of the slow crystallization kinetics of PEKK and a short cooling time of 1 h increased elongation at break to 14%; this is a striking result never achieved for PAEKs in LS before. A calibration curve was developed that can be used to correlate PEKK structure and mechanical properties to cooling conditions according to the application. This methodology can also be applied to select and optimize the mechanical properties of other LS polymers sharing similar kinetics of crystallization and processing temperatures. This work suggests a great potential for a wide range of “post-processing” heat treatments to be used in AM to tailor the ultimate mechanical properties.Arkema Innovations Chemistr

On the shape of a small sessile drop and the measurement of contact angle.

Free liquid surfaces in equilibrium are described by the Laplace capillary equation with suitable boundary conditions generally given in terms of the contact angle. By a fortuitous formulation in the axisymmetric case, the second order ordinary differential equation can be reduced to a pair of coupled first order equations. For the case of a small liquid drop, the present formulation allows perturbation solutions to second order to be derived in closed form. Furthermore the solutions obtained can be used to calculate contact angles, if the height and maximum width of the drop is known, the method being equally simple whether the contact angle is less than or greater than 90 ͦ

Identification of genomic regions determining the phenological development leading to floral transition in wheat (Triticum aestivum L.)

Autumn-seeded winter cereals acquire tolerance to freezing temperatures and become vernalized by exposure to low temperature (LT). The level of accumulated LT tolerance depends on the cold acclimation rate and factors controlling timing of floral transition at the shoot apical meristem. In this study, genomic loci controlling the floral transition time were mapped in a winter wheat (T. aestivum L.) doubled haploid (DH) mapping population segregating for LT tolerance and rate of phenological development. The final leaf number (FLN), days to FLN, and days to anthesis were determined for 142 DH lines grown with and without vernalization in controlled environments. Analysis of trait data by composite interval mapping (CIM) identified 11 genomic regions that carried quantitative trait loci (QTLs) for the developmental traits studied. CIM analysis showed that the time for floral transition in both vernalized and non-vernalized plants was controlled by common QTL regions on chromosomes 1B, 2A, 2B, 6A and 7A. A QTL identified on chromosome 4A influenced floral transition time only in vernalized plants. Alleles of the LT-tolerant parent, Norstar, delayed floral transition at all QTLs except at the 2A locus. Some of the QTL alleles delaying floral transition also increased the length of vegetative growth and delayed flowering time. The genes underlying the QTLs identified in this study encode factors involved in regional adaptation of cold hardy winter wheat