Browsing by Author "Cramail, Henri"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
- Extraordinary mechanical performance in disentangled UHMWPE films processed by compression moldingPublication . Ferreira, Ana E.; Ribeiro, M. Rosário; Cramail, Henri; Lourenço, João P.; Lorenzo, Vicente; Pérez, Ernesto; Cerrada, Maria L.An approach to obtain disentangled ultra-high molecular weight polyethylene (UHMWPE) films is proposed using a common compression molding. For that, disentangled UHMWPE nascent powders from reactor are processed at temperatures lower than the main melting peak and at high pressure. Then, disentangled UHMWPE films obtained from homogeneous polymerization powders and from those that incorporate SBA-15 mesoporous silica can be easily achieved by this simple methodology. These disentangled UHMWPE based materials show very high crystallinity and, consequently, outstanding elastic modulus and hardness, both further increasing by presence of mesoporous SBA-15 in the hybrids.
- Hafnocene catalyst for polyethylene and its nanocomposites with SBA-15 by in situ polymerization: immobilization approaches, catalytic behavior and properties evaluationPublication . Ferreira, Ana E.; Cerrada, María L.; Pérez, Ernesto; Lorenzo, Vicente; Cramail, Henri; Lourenço, J. P.; Quijada, Raul; Ribeiro, M. RosárioA hafnocene catalyst combined with methylaluminoxane (MAO) has been used as catalytic complex for the preparation of a set of polyethylene homopolymers by in situ polymerization under homogenous conditions and of different nanocomposites with mesoporous SBA- 15 particles, the latter playing the dual role of catalyst support and nanofiller. Distinct immobilization approaches have been explored for obtainment of these nanocomposites. Moreover, catalytic features, thermal stability, melting and crystallization transitions and mechanical behavior have been evaluated for those materials.
- Nanostructured silica materials in olefin polymerisation: from catalytic behaviour to polymer characteristicsPublication . Campos, João M.; Lourenço, J. P.; Cramail, Henri; Ribeiro, M. R.This paper reviews progress in organometallic -olefin polymerisation catalysts supported on zeolites or mesoporous silicas, discussing the role of these nanostructured materials in establishing new catalytic behaviours and polymer properties. Zeolites and other nanostructured materials show unique structural and surface features that have been used with advantage in the immobilisation of a large variety of catalysts, including -olefin polymerisation catalysts such as metallocene complexes. The characteristics of these materials, such as the ordered porous system, the large surface area and a tuneable acidity have a great impact on the immobilisation of the catalyst, with implication on the formation and nature of active species and polymerisation activity. Methods of preparation, diffusion limitations and confinement effects are rationalised and their role on the catalytic system and final polymer properties is discussed. This review is mainly focused on metallocene catalysts but examples of post-metallocene catalysts and olefin polymerisation behaviour of nonorganometallic complexes, covering Ziegler-Natta Ti/V catalysts and Phillips Cr catalysts, as well as metal-modified mesoporous carriers are described and discussed. Additionally, the effects of the nanostructured supports on the morphologies and physical properties of the polyolefins are also covered, and an account is made on how mesoporous materials can be used in the preparation of novel polyolefin nanoblends and nanocomposites.
- UHMWPE/SBA-15 nanocomposites synthesized by in situ polymerizationPublication . Ferreira, Ana E.; Cerrada, M. L.; Pérez, Ernesto; Lorenzo, Vicente; Cramail, Henri; Lourenço, J. P.; Ribeiro, M. RosárioDifferent 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.