Search results for "polymers"

Advanced ultra-high molecular weight polyethylene/antioxidant-functionalized carbon nanotubes nanocomposites with improved thermo-oxidative resistance

2015

Multiwalled carbon nanotubes (CNTs) functionalized with hindered phenol moieties are dispersed in ultra-high molecular weight polyethylene (UHMWPE), and the stabilizing action of the antioxidant (AO) functionalized CNTs (AO-f-CNTs) is studied through a combination of rheological and spectroscopic (FT-IR) analyses. The effectiveness of two alternative compounding methods, namely hot compaction (HC) and melt mixing (MM), is compared. The combination of high temperature and mechanical stress experienced during MM brings about noticeable degradation phenomena of the matrix already in the course of the compounding step. Differently, the milder conditions of the HC process preserve the stability …

Formulation, Characterization and Optimization of the Processing Conditions of Blends of Recycled Polyethylene and Ground Tyre Rubbers: Mechanical an…

2005

Abstract Recycling represents a valid alternative to the disposal of post-consumer plastics in common landfills if it is possible to obtain new materials with good final properties compatible with practical application and, above all, by using cheap methods. In this work the possibility to produce secondary materials by blending recycled polyethylene (RPE) coming from greenhouses and post-consumer ground tyre rubber (GTR) has been studied. In particular, the preparation of these blends has been carried out in a common industrial twin screw extruder. RPE pellets and GTR powder were fed to the extruder without any other additive. Temperature, processing speed, mixing procedure and composition…

Reductive Decationizable Block Copolymers for Stimuli-Responsive mRNA Delivery

2016

Messenger ribonucleic acids (mRNAs) are considered as promising alternatives for transient gene therapy, but to overcome their poor pharmacokinetic properties, smart carriers are required for cellular uptake and stimuli-responsive release. In this work, a synthetic concept toward reductive decationizable cationic block copolymers for mRNA complexation is introduced. By combination of RAFT block copolymerization with postpolymerization modification, cationic block copolymers are generated with disulfide-linked primary amines. They allow effective polyplex formation with negatively charged mRNA and subsequent release under reductive conditions of the cytoplasm. In first in vitro experiments w…

A contribution to the kinetics of the polymerization of styrene with CF3SO3H as catalyst

1978

The time dependence of the cationic polymerization of styrene in CH2Cl2 with CF3SO3H as catalyst can be formally described as being first-order with respect to monomer concentration [M]0. The reaction rate shows a third-order dependence in catalyst concentration [C]0. A high polymer and a low polymer polystyrene fraction are found at [M]0>0.2 mole · l−. The reaction rate of the high polymer fraction is proportional to [C] 0 3 , that of the low polymer fraction probably proportional to [C] 0 2 . The polymerization active species may thus be triple ions in the first and ion pairs in the second case.

Optimization of Cell Growth on Bacterial Cellulose by Adsorption of Collagen and Poly-L-Lysine

2015

Poly-L-lysine and collagen were separately added to bacterial cellulose (BC) nanofibers. The ionic surface charge had been previously modified in order to promote the adsorption of poly-L-lysine and collagen. Cell adhesion of Chinese hamster ovary (CHO) cells on BC surfaces was confirmed by removing unattached cells from the BC substrates. Cell viability was calculated and it was determined that both poly-L-lysine-BC and collagen-BC substrates are viable for cell growth. The results showed that the cell viability in poly-L-lysine modified BC substrate is similar to the one observed in polystyrene tissue culture plates.

Influence of small amounts of polyvinylchloride on the recycling of polyethyleneterephthalate

1999

Abstract Polyethylene terephthalate (PET), and polyvinyl chloride (PVC), are commonly encountered in plastics stream coming from separate collections of plastic bottles. The presence of PVC in the recycled PET is very dangerous because of the chain scission provoked by the hydrogen chloride evolved from the macromolecules during degradation of PVC. Recycled PET must be free of PVC; contents of PVC as little as 100 ppm can induce degradation and discoloration of the polyester. PET, in its turn, is degraded when the processing is carried out in the presence of water. In previous work, however, the degradation of PET was eliminated and rather an increase of the molecular weight has been measur…

Influence of sodium bicarbonate treatment on the aging resistance of natural fiber reinforced polymer composites under marine environment

2019

Abstract Aim of the current study is to investigate how an innovative and eco-friendly chemical treatment based on sodium bicarbonate solution (10 wt%) can improve the aging resistance in marine environment of epoxy based composites, reinforced with flax and jute fibers. To this scope, treated and untreated fiber reinforced composites were manufactured through vacuum infusion technique. The resulting composites were then exposed to salt-fog spray conditions up to 60 days, according to ASTM B117 standard. The assessment of their durability was made by means of tensile, flexural quasi-static tests and Charpy impact tests. Furthermore, the water uptake evolution of each composite was monitored…

The effect of prepolymerization of a titanium catalyst on its deactivation in propylene polymerization

1997

Propylene polymerization rate was investigated in the presence of anunsupported titanium catalyst (TiCl3) that had been modified with a Lewis base (di-n-butyl ether) and activated (precat), or not activated (cat), by being used in a suspension prepolymerization (70°C, 0.6 MPa) of an identical monomer. The initial polymerization rate was higher with the precat than with the cat catalyst. Prepolymerization was also found to enhance the kinetic stability of catalyst's active sites, presumably by reason of the prepolymerization-induced modification of catalyst's morphology. Deactivation rate constants were evaluated for the active sites of either catalyst examined.

Dynamic Model Metallo‐Supramolecular Dual‐Network Hydrogels with Independently Tunable Network Crosslinks

2020

Studies of alumina as a support of titanium catalyst for low-pressure ethylene polymerization

1986

The effect of alumina treatment with aqueous solutions of hydrochloric acid and ammonium fluoride as well as temperature of its calcination on the activity of Al-Ti/Al2O3 supported organometallic catalyst for ethylene polymerization has been studied. The dependence between the spe­cific surface area of the support and both the kind and concentration of the modifying agent, concentration of OH-groups on Its surface and concentration of active centres with various activities is discussed with reference to the activity of the supported Al-Ti/Al2O3 catalyst. It was demonstrated that there is no simple relationship between the concentration of OH-groups on the support and the activity of the Ti-…