5,503 research outputs found
UHMWPE/SBA-15 nanocomposites synthesized by in situ polymerization
Different nanocomposites have been attained by in situ polymerization based on ultra-high molecular
weight polyethylene (UHMWPE) and mesoporous SBA-15, this silica being used for immobilization of the
FI catalyst bis [N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] titanium (IV) dichloride and as
filler as well. Two distinct approaches have been selected for supporting the FI catalyst on the SBA-15
prior polymerization. A study on polymerization activity of this catalyst has been performed under
homogenous conditions and upon heterogenization. A study of the effect of presence of mesoporous
particles and of the immobilization method is also carried out. Moreover, the thermal characterization,
phase transitions and mechanical response of some pristine UHMWPEs and UHMWPE/SBA-15 materials
have been carried out. Relationships with variations on molar mass, impregnation method of catalyst and
final SBA-15 content have been established
MCM-41 as Nanofiller in Polyethylene Hybrid Materials
Mesoporous MCM-41 exhibits a stable framework structure, well-defined nanopores and a large surface area. When combined with metallocene polymerisation catalyst, these mesoporous materials, provide a unique route
for preparing polyolefin-based nanocomposites by in situ polymerisation
New HDPE/MCM41 nanocomposites with improved mechanical performance: synthesis and characterizatio
Ordered mesoporous silicas with a channel structure of well-defined geometries and
dimensions at nanometer scale are excellent candidates to host intercalation reactions.
In recent years, our research group has shown that mesoporous silicas of the M41S class
combined with metallocene complexes give rise to excellent supported catalysts for ethylene
polymerisation. Due to the support characteristics, the reaction is allowed to occur in the
channels and in this way hybrid organic-inorganic materials can be prepared within a large
range of nanofiller concentration. These HDPE/MCM-41 nanocomposites exhibit an
improved mechanical performance and an easier degradability due to the additional role of
MCM-41 as a promoter for PE degradation
The anticancer effect related to disturbances in redox balance on Caco-2 cells caused by an alkynyl gold(I) complex
The alkynyl gold(I) derivative Au(C=CPh)(PTA)] (PTA = 1, 3, 5-triaza-7-phosphaadamantane) induces apoptosis in colorectal carcinoma tumour cells (Caco-2) without affecting to normal enterocytes. Au(C=CPh)(PTA)] is a slight lipophilic drug, stable in PBS (Phosphate Buffered Saline) and able to bind BSA (Bovin Serum Albumin) by hydrophobic interactions. Once inside the cell, Au(C=CPh)(PTA)] targets seleno proteins such as Thioredoxin Reductase 1, increasing ROS (Reactive Oxygen Species) levels, reducing cell viability and proliferation and inducing mitochondrial apoptotic pathway, pro-apoptotic and anti-apoptotic protein imbalance, loss of mitochondrial membrane potential, cytochrome c release and activation of caspases 9 and 3. Moreover, unlike other metal-based drugs such as cisplatin, Au(C=CPh)(PTA)] does not target nucleic acid, reducing the risk of side mutation in the DNA. In consequence, our results predict a promising future for Au(C=CPh)(PTA)] as a chemotherapeutic agent for colorectal carcinoma
A novel approach for preparation of nanocomposites with an excellent rigidity/deformability balance based on reinforced HDPE with halloysite
An innovative approach, designated as supported activator (SA), allows preparation of high density polyethylene
(HDPE)-based highly performant hybrid materials. This procedure makes use of a nano-sized supported methylaluminoxane (MAO)-activator, based on halloysite natural nanotubes (HNT), combined with an in situ supporting concept. The new protocol when compared with a more conventional approach gives rise to higher
polymerization activities as well as ultimate materials with better morphological features, greater crystallinity,
thicker crystals, and highly increased stiffness. Moreover, a remarkable synergy between rigidity and toughness
is attained. The Young’s modulus of a film obtained from the nanocomposite with the highest HNT content
increases more than 70 % relatively to a pristine HDPE film, while retaining the limit stretching ability of pristine
HDPE (more than 800%). A beneficial impact of using a high aspect ratio support such as HNT in the mechanical
properties is also observed, when compared to similar HDPE hybrid materials derived from dendrimer-like silica
(DS) nanospheres. Interestingly, polymerization activity, polymer features and derived properties found in the
ultimate materials are less impacted by support/filler nature than by preparation method. This fact highlights the
crucial role of the synthetic methodology used and corroborates the high potential of the SA route for the
preparation of high-performance polyethylene-based nanocomposites with an excellent balance between stiffness
and deformability.info:eu-repo/semantics/publishedVersio
UHMWPE/HDPE in-reactor blends, prepared by in situ polymerization: synthetic aspects and characterization
This work covers the synthesis and characterization of in-reactor Ultra-High Molecular Weight Polyethylene/
High Density Polyethylene, UHMWPE/HDPE, blends by in situ polymerization in a single reactor, through dual catalyst
immobilization. These blends are synthesized combining two different catalysts (one for each targeted molar mass) co-immobilized
in mesoporous Santa Barbara Amorphous, SBA-15, particles. First, the ethylene polymerization behavior is investigated,
under different polymerization conditions. Then, studies on the thermal, mechanical and rheological characteristics
of the produced in-reactor blends are presented and their performance is compared and discussed in a comprehensive way.
Moreover, the effect of different filler contents on the properties exhibited by the resulting materials is investigated.
Results have shown that these in-reactor UHMWPE/HDPE blends exhibit a complex thermal, mechanical and rheological
behavior, which depends mainly on the proportion between the two polymer components and on the amount of SBA-15.info:eu-repo/semantics/publishedVersio
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