Abstract
The preparation method of a polymer composite and the filler loading are amongst the factors that influence the properties of the final composites. This article studies the effect of these factors on the thermal stability and thermal degradation kinetics of poly(methyl methacrylate) (PMMA)/mesoporous silica (MCM-41) composites filled with small amounts of MCM-41. The PMMA/MCM-41 composites were prepared through in situ polymerisation and melt mixing methods, with MCM-41 loadings of 0.1, 0.3, and 0.5 wt.%. The presence of MCM-41 increased the thermal stability of PMMA/MCM-41 composites prepared by melt mixing, but in the case of the in situ polymerised samples, the MCM-41 accelerated the degradation of the polymer. As a result, the activation energy was low and less energy was required to initiate and propagate the degradation process of these composites. The small-angle X-ray scattering (SAXS) measurements showed that the preparation method of the composites had no influence on the pore size of MCM-41, but the PMMAs used in the two methods both had shorter chains than the MCM-41 pore size. This allowed the polymer chains to be trapped inside the pores of the filler and be immobilised, as was observed from nuclear magnetic resonance (NMR) spectroscopy. The immobilisation of the polymer chains was more significant in the in situ polymerised samples.
Highlights
Organic–inorganic hybrid materials, especially polymer matrices with inorganic nanoscale building blocks, have drawn extensive attention of researchers, mostly because they combine superior mechanical and thermal properties of inorganic phases with the flexibility and processability of organic polymers [1, 2]
This paper reports on these factors, where the structures of the composites were investigated through small-angle X-ray scattering (SAXS). 13C cross-polarisation magic-angle spinning nuclear magnetic resonance (13C {1H} CP-MAS NMR) spectroscopy measurements were carried out to investigate the interaction between the poly(methyl methacrylate) (PMMA) and the MCM-41, and thermogravimetric analysis (TGA) was used to study the thermal stability and thermal degradation kinetics of the composites
The TGA curves of PMMA and the PMMA/MCM-41 composites illustrated in Fig. 1 show the three degradation steps described above, indicating that the in situ polymerisation followed a free radical route in our case
Summary
Organic–inorganic hybrid materials, especially polymer matrices with inorganic nanoscale building blocks, have drawn extensive attention of researchers, mostly because they combine superior mechanical and thermal properties of inorganic phases with the flexibility and processability of organic polymers [1, 2]. Mesoporous molecular sieves have been widely used in other applications, their use as polymer additives has attracted less attention. Nano-mesoporous silica has been used as an additive with the goal of enhancing the mechanical and thermal properties of polymers. A polymer can be introduced inside the mesopores by melt compounding or through in situ polymerisation of organic monomers, depending on the mesoporous size, the molecular weight, the structure of the polymer, and the physical or chemical interactions. It has been reported that the polymer in the nano-sized pores, extending along the channels to the openings, can enhance the miscibility through entanglement and inter-diffusion between the matrix and the particulate, but can strongly supress the aggregation of the fillers [9,10,11,12]
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