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Based on the three-phase model of semi-crystalline polymers, we determined all phase fractions of the NiAl-LDH/PLLA nanocomposites in dependence on the concentration of the nanofiller. Moreover, the rigid amorphous fraction (RAF) was separated into the RAFcrystal and the RAFfiller unbiasedly. A detailed comparison to the related nanocomposite system MgAl-LDH/PLLA was made considering that Mg and Ni have different atomic weights. As a first result is was found that NiAl-LDH/PLLA displays a higher crystallization rate compared to MgAl-LDH/PLLA, which is related to the different morphologies of the two nanocomposite systems. For both systems RAFcrystal increases with increasing concentration of the nanofiller. This means in the case of the nanocomposite not each crystal produces the same amount of RAF, as often assumed. Also, RAFfiller increases with the concentration for both systems but in a different way. This is discussed considering again the different morphologies of both nanocomposites.
Nanocomposites based on poly(L-lactide) (PLA) and organically modified Ni/Al layered double hydroxides (NiAl/LDHs) are prepared by melt blending and investigated by a combination of size exclusion chromatography, differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), wide-angle X-ray scattering, and broadband dielectric spectroscopy. A detailed comparison to the behavior of the corresponding MgAl/LDH–PLA nanocomposites is made. SAXS investigations show that the morphology of the NiAl/LDH–PLA nanocomposites is more intercalated compared to the MgAl/LDH based PLA nanocomposite, which is more exfoliated. The DSC investigation gives a different dependence of the degree of crystallization on the concentration of LDH for NiAl/LDH–PLA than for MgAl/LDH–PLA nanocomposite system. These differences are discussed taking the differences of the morphologies of both systems into account. Broadband dielectric spectroscopy reveals information about the molecular dynamics where essential differences are observed for all relaxation processes taking place in both systems which were related to the different morphologies.
Semicrystalline polymers have to be described by a three phase model consisting of a mobile amorphous (MAF), a crystalline (CF), and a rigid amorphous fraction (RAF). For nanocomposites based on a semicrystalline polymer the RAF is due to both the crystallites (RAFcrystal) and the filler (RAFfiller). Polymer nanocomposite based on poly(L-lactide) and MgAl layered double hydroxide nanofiller were prepared.
Due to the low crystallization rate of PLA ist crystallization can be suppressed by a high enough cooling rate, and the RAF is due only to the nanofiller. The MAF, CF, and RAF were estimated by Temperature Modulated DSC. For the first time CF, MAF, RAFcrystal, and RAFfiller could be estimated. It was found, that RAFfiller increases linearly with the concentration of the nanofiller for this system. Furthermore, RAFcrystal is only slightly influenced by the presence of the nanofiller.
Two kinds of synthesized NiAl (NiAl-LDH) and MgAl (MgAl-LDH) layered double hydroxides were melt blended with commercial polylactide to prepare different polymer based nanocomposites. The MgAl-LDH based nanocomposites and NiAl-LDH based nanocomposites have a diferent but mixed intercalated / exfoliated structure. Based on the different structures, the crystallization behaviors of polymer based nanocomposites were investigated by differential scanning calorimetry (DSC) and temperature modulated differential scanning calorimetry (TMDSC) specificly where the heating and cooling rates were varied in a extrmely wied range. In a first step, the cooling rate where crystallization can be completely surpressed is estimated. In a second step, based on a specified temperature program the crystalline fraction (CF), the rigid amorphous fraction (RAF) and the mobile amorphous fraction (MAF) were calculated from the the enthalpy and specific heat capacity in dependence on the concentration of the nanofiller. The rigid amorphous fraction was considered as resulting from the the crystallites and the nanofiller. For the first time both fractions were calculated quantitatively without any additional assumption.