Thais H.S. Costa

Polypropylene-wood fiber composites : Effect of treatment and mixing conditions on mechanical properties

Polypropylene/wood fiber composites were prepared at three different temperatures: 170°C, 180°C, and 190°C. The surface of wood fibers was modified through the use of silane coupling agents and/or coating with polypropylene or maleated polypropylene. The fiber coating was performed by propylene polymerization in the presence of wood fibers or by immersion in an o-dichlorobenzene polypropylene (or maleated polypropylene) solution. Tensile and three-point bending tests were performed in order to evaluate the adhesion between matrix and wood fibers. Evidence shows that 180°C is the best mixing temperature, while the use of vinyl-tris (2-methoxy ethoxy) silane with or without maleated polypropylene coating is the best surface treatment.

Statistical experimental design and modeling of polypropylene-wood fiber composites

Abstract The influence of the amount of maleated polypropylene coating of vinyl-tris (2-methoxy ethoxy) silane treated wood-fibers (2 or 10 wt%), type of matrix (polypropylene or maleated polypropylene) and composition (10, 20 or 30 wt%) on the tensile and flexural performance of polypropylene–wood fiber composites was studied. The effect of these variables on tensile strength, Youngs modulus, elongation at yield and flexural strength was determined through a 22·31 factorial design. The analysis of variance of the experimental and predicted data shows that the constructed models provide a fair approximation of actual experimental measurements. Finally, experimental details regarding the preparation of optimum composites as predicted by empirical models are discussed.

Sawdust reinforced polypropylene composites: a study of fracture behavior

Sawdust (20wt%) reinforced polypropylene composites were prepared with 22.4 wt% maleated polypropylene coated fibers. Tensile tests were performed at 400, 5 and 0.1 mm/min for composites and matrix. Scanning electron microscopy of these fracture surfaces together with the shape of the stress strain curves characterized ductile, brittle and ductile-to-brittle transition fracture modes. Processing conditions as well as the development of interfacial fiber/matrix adhesion are also discussed.

Thermal behaviour of modified wood fibers

Wood-fibers were modified by silanes treatments and/or by coating with polypropylene or polystyrene. Enhancement in thermal stability of wood fibers treated with γ-aminopropyl triethoxy silane and in fibers coated with polypropylene or polystyrene are discussed. Thermoanalytical data (TGA, TMA and DSC) of the samples may aid to predict the behaviour of these modified fibers in composites of polypropylene or polystyrene matrices.

Controlled degradation of polypropylene in solution by organic peroxides

Abstract Commercial polypropylene (PP) samples were submitted to degradation reaction in o-dichlorobenzene solution by organic peroxides. Four different peroxides (DHBP, DTBP, DCUP and DIPP) were tested at different concentrations. The degradation process was evaluated by determining the melt flow index (MFI) and molecular weight distribution of the degraded PP samples. The peroxide which caused a greater increase in MFI values was DIPP and the least effective one was DTBP. The elastic modulus of none of the samples changed with peroxide treatment although the molecular weight distribution narrowed considerably. The M w / M n ration of untreated PP changed from 8·6 to 3·5 with 0·30% wt DIPP treatment.

Characterization of Ziegler-Natta catalysts based on TiCl3 synthesized by different methods*

SummaryCatalysts based on TiCl3, modified by ethers, were prepared by different methods. Using di-n-butyl ether (DBE) as an internal base, complexes were formed in one-step reaction, either with TiCl4 and diethylaluminum chloride (DEAC) in iso-octane solution (System A) or with triethylaluminum (TEA) in toluene solution (System B). Diisoamyl ether (DIAE) and tetrahydrofuran (THF) were used as internal bases for the β-TiCl3 treatment during a three-step synthesis (System C). DIAE was also complexed with DEAC in a one-step synthesis in toluene solution (System D) or in iso-octane solution (System E). While the use of DIAE in the three-step synthesis has mainly led to the formation of γ-TiCl3 (System C), the use of DIAE in the one-step synthesis led to a highly active and stereospecific β-TiCl3 (Systems D and E). The type of solvent employed in systems A and B had a strong influence on the properties of the catalyst. Possible causes for the formation of different crystalline structures of TiCl3 are discussed by comparing the different routes of the TiCl3 synthesis.

Influence of the method of synthesis on the properties of TiCl3

Abstract The role of ethers in the synthesis of a highly active and stereospecific catalyst for propylene polymerization has been investigated. Diisoamyl ether (DIAE) and tetrahydrofuran (THF) were employed as electron-donors in the β-TiCl 3 treatment during the three-step synthesis. Dibutyl ether (DBE) was used as a first internal base complexed with TiCl 4 and Et 2 ClAl (DEAC) in iso-octane solution in the one-step synthesis. While the use of DIAE and THF in the three-step synthesis has mainly led to the formation of λ-TiCl 3 , the use of DBE in the one-step synthesis has led to the formation of a highly active and stereospecific δ-TiCl 3 . The effects of ethyl benzoate, tributyl phosphate and diisobutyl phthalate as second internal bases on the crystalline modification, activity and stereospecificity of TiCl 3 have also been studied. Possible causes for the formation of different TiCl 3 crystalline structures are discussed through comparison of both routes of TiCl 3 synthesis.

Síntese de catalisadores Ziegler-Natta: algumas rotas e suas dificuldades

The Ziegler-Natta catalyst and the polymerization thereof are systems which require careful handling and special treatment of chemicals. In spite of the use of inert atmosphere and dry chemicals, some Ziegler-Natta systems may present low activities or even may deactivate because of unsuitable handling. Some features of the TiCl3 synthesis and its characterization when related to the presence of impurities are described. Evidences of poor handling of chemicals and/or laboratory devices while in synthesis of the catalyst are emphasized. The problems arising from butadiene polymerization and some relevant details in propylene polymerization are also presented with teaching objectives.