Synthesis of Disentangled Ultra-High Molecular Weight Polyethylene: Influence of Reaction Medium on Material Properties

The polymerization of ethylene to Ultra-High Molecular Weight Polyethylene (UHMWPE) in certain reaction conditions allows synthesis of nascent powders with a considerably lower amount of entanglements: the material obtained is of great interest from both academic and industrial viewpoints. From an academic point of view, it is interesting to follow the evolution of the metastable melt state with the progressive entanglements formation. Industrially, it is valuable to have a solvent-free processing route for the production of high modulus, high strength tapes. Since the polymer synthesis is performed in the presence of a solvent, it is interesting to investigate the influence that the reaction medium can have on the catalyst activity, resultant molecular characteristics, and polymer morphology at the macroscopic as wells as microscopic level. In this paper, we present the effect that two typical polymerization solvents, toluene and heptane, and mixtures of them, have on the catalytic performance and on the polymer properties. The observations are that an unexpected increase of catalyst activity, accompanied by a significant improvement in mechanical properties, is found when using a carefully chosen mixture of solvents. A tentative explanation is given on the basis of the presented results

Synthesis of disentangled Ultra-High Molecular Weight Polyethylene: influence of reaction medium on material properties

The polymerization of ethylene to Ultra-High Molecular Weight Polyethylene (UHMWPE) in certain reaction conditions allows synthesis of nascent powders with a considerably lower amount of entanglements: the material obtained is of great interest from both academic and industrial viewpoints. From an academic point of view, it is interesting to follow the evolution of the metastable melt state with the progressive entanglements formation. Industrially, it is valuable to have a solvent-free processing route for the production of high modulus, high strength tapes. Since the polymer synthesis is performed in the presence of a solvent, it is interesting to investigate the influence that the reaction medium can have on the catalyst activity, resultant molecular characteristics and polymer morphology at the macroscopic as wells as microscopic level. In this paper we present the effect that two typical polymerization solvents, toluene and heptane, and mixtures of them, have on the catalytic performance and on the polymer properties. The observations are that an unexpected increase of catalyst activity, accompanied by a significant improvement in mechanical properties, is found when using a carefully chosen mixture of solvents. A tentative explanation is given on the basis of the presented results

Laser-flash in-plane thermal analysis: the case of oriented UHMWPE

Laser-flash thermal analysis has been applied to measure the thermal diffusivity of highly oriented samples of Ultra High Molecular Weight Polyethylene. Due to the anisotropy of the sample, in-plane measurements are required instead of through-plane ones

Design and fabrication of novel vaginal ring pessaries with improved performances

Pelvic organ prolapse (POP) is a severe gynaecological condition affecting around 50% of women over the age of 50 [1]. POP can occur due to weakening of the pelvic floor and vaginal tissue, leading to prolapse of the uterus, bladder or rectum. Pessaries are devices inserted into the vagina for treatment of POP by provision of mechanical support to the prolapsed organ, shown in Figure 1. A variety of pessaries exist, with each being suited to a particular type and stage of prolapse, one of the most common is the ring pessary [2]. Pessaries provide an alternative treatment to vaginal mesh, which has now been banned [3] following its link to multiple deaths [4]

Synthesis and electrospinning of polycaprolactone from an aluminium-based catalyst: influence of the ancillary ligand and initiators on catalytic efficiency and fibre structure

In the present study, we investigate the catalytic performance of a 2,2’-methylenebis(6- tert-butyl-4-methylphenol) (MDBP) - aluminium complex for the ring-opening polymerisation (ROP) of ε-caprolactone in combination with various alcohols as initiators. Three different alcohols are investigated, 1-adamantanemethanol (A), 1H,1H,2H,2H-perfluoro-1-octanol (F) and isopropanol (I). Samplings of polycaprolactone (PCL) at various reaction times show a linear increase of polymer molecular weight with time, with very narrow polydispersity, confirming the living nature of the catalytic system. Scanning electron microscope (SEM) images of electrospun PCL fibre mats produced from 30 wt% dichloromethane/dimethyl sulfoxide solutions show a high level of surface porosity with reasonable homogeneity of fibre diameters. Values of liquid absorption and water contact angle have been measured for the electrospun mats, with the F-capped PCL consistently showing absorption values up to three times higher than those of PCL samples capped with the other two alcohols, and increased hydrophobicity. The nature of the alcohol can influence the surface hydrophobicity and absorption ability of the electrospun fibres, demonstrating the possibility of tailoring material properties through controlled polymerisation

Electrospun nanofibres containing antimicrobial plant extracts

Over the last 10 years great research interest has been directed toward nanofibrous architectures produced by electrospinning bioactive plant extracts. The resulting structures possess antimicrobial, anti-inflammatory, and anti-oxidant activity, which are attractive for biomedical applications and food industry. This review describes the diverse approaches that have been developed to produce electrospun nanofibres that are able to deliver naturally-derived chemical compounds in a controlled way and to prevent their degradation. The efficacy of those composite nanofibres as wound dressings, scaffolds for tissue engineering, and active food packaging systems will be discussed

Process for manufacturing ultra high molecular weight polyethylene catalyst

The present invention pertains to a process for manufacturing an ultra-high molecular weight polyethylene, wherein olefin monomers are contacted with a catalytic system under polymerisation conditions under formation of a polyethylene, wherein the catalytic system comprises an active component on a particulate carrier in a site density in the range of 5* 10 (- 9) to 5*10 (-6) mole of catalytic sites per m2 of carrier surface area, the particulate carrier having an average particle diameter in the range of 1-300 nm, wherein the polyethylene has a weight average molecular weight (Mw) of at least 500 000 gram/mole, and an elastic shear modulus G0 N, determined directly after melting at 160°C of at most 1.4 MP a

Activation of a bis-(phenoxyimine) titanium (IV) catalyst using different aluminoxane co-catalysts

The activation of a bis-phenoxyimine catalyst based on titanium (IV) using different aluminoxanes (MAO, PMAO and MMAO12) has been studied. The effect of a co-catalyst modifier (BHT) used in combination with the MAO has been also tested. In particular, the effect of the activation time between the catalyst and the different aluminoxanes has been taken into consideration. On increasing the activation time between catalyst and the different aluminoxanes and TMA-free MAO, differences in the catalyst activities have been observed. UHMWPEs having a reduced number of entanglements have been synthesized activating the FI catalyst with MAO and TMA-free MAO. The obtained reactor powders can be solid-state processed below the melting temperature in order to obtain high modulus/high tenacity tapes used for body armor and vehicle protection applications

Coupled cluster cavity Born-Oppenheimer approximation for electronic strong coupling

Chemical and photochemical reactivity, as well as supramolecular organization and several other molecular properties, can be modified by strong interactions between light and matter. Theoretical studies of these phenomena require the separation of the Schr\"odinger equation into different degrees of freedom as in the Born-Oppenheimer approximation. In this paper, we analyze the electron-photon Hamiltonian within the cavity Born-Oppenheimer approximation (CBOA), where the electronic problem is solved for fixed nuclear positions and photonic parameters. Specifically, we focus on intermolecular interactions in representative dimer complexes. The CBOA potential energy surfaces are compared with those obtained using a polaritonic approach, where the photonic and electronic degrees of freedom are treated at the same level. This allows us to assess the role of electron-photon correlation and the accuracy of CBOA.Comment: 9 pages, 8 figure

Cancer stem-like cells in uveal melanoma: novel insights and therapeutic implications

Uveal melanoma (UM) is the most common primary ocular tumor in the adult population. Even though these primary tumors are successfully treated in 90% of cases, almost 50% of patients ultimately develop metastasis, mainly in the liver, via hematological dissemination, with a median survival spanning from 6 to 12 months after diagnosis. In this context, chemotherapy regimens and molecular targeted therapies have demonstrated poor response rates and failed to improve survival. Among the multiple reasons for therapy failure, the presence of cancer stem-like cells (CSCs) represents the main cause of resistance to anticancer therapies. In the last few years, the existence of CSCs in UM has been demonstrated both in preclinical and clinical studies, and new molecular pathways and mechanisms have been described for this subpopulation of UM cells. Here, we will discuss the state of the art of CSC biology and their potential exploitation as therapeutic target in UM