Abstract
In this paper we used high- and low-resolution solid state Nuclear Magnetic Resonance (NMR) techniques to investigate a series of polyisoprene samples filled with silica generated in situ from tetraethoxysilane by sol-gel process. In particular, 1H spin-lattice and spin-spin relaxation times allowed us to get insights into the dynamic properties of both the polymer bulk and the bound rubber, and to obtain a comparative estimate of the amount of bound rubber in samples prepared with different compositions and sol-gel reaction times. In all samples, three fractions with different mobility could be distinguished by 1H T2 and ascribed to loosely bound rubber, polymer bulk, and free chain ends. The amount of bound rubber was found to be dependent on sample preparation, and it resulted maximum in the sample showing the best dispersion of silica domains in the rubber matrix. The interpretation of the loosely bound rubber in terms of “glassy” behaviour was discussed, also on the basis of 1H T1 and T1ρ data.
Highlights
The use of inorganic fillers is a well consolidated practice for conferring and/or improving the most various technologically relevant properties, such as mechanical, optical, thermal, etc., to polymeric materials [1]
In a previous work by some of us we investigated the interrelation between preparation conditions, structure, and mechanical reinforcement in a series of vulcanized composites of isoprene rubber (IR)
We focused on the characterization of the polymeric fraction in this wide set of composite samples by exploiting 13 C and 1 H solid state Nuclear Magnetic Resonance (NMR) techniques
Summary
The use of inorganic fillers is a well consolidated practice for conferring and/or improving the most various technologically relevant properties, such as mechanical, optical, thermal, etc., to polymeric materials [1]. In spite of the scientific progress achieved and of an extensive practical use, it is still quite difficult to precisely define the composition-process-performance relation in filler-polymer, and in particular in silica-rubber composites. It is commonly accepted that a crucial role is played by the complex balance between filler-filler and filler-polymer interfacial interactions, and, in particular, that a good dispersion of the filler in the organic matrix is a necessary condition for a well-performing composite [5]. Preparation methods are usually designed and tuned for optimizing the dispersion of the filler in the rubber. There are three main approaches to the preparation of silica-rubber composites: (1) direct mixing of preformed silica and rubber in the melt state under strong shearing forces; (2) in situ
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