Poly(lactic acid) phase transitions in the presence of nano calcium carbonate: Opposing effect of nanofiller on static and dynamic measurements

Abstract

The effect of stearic acid-coated nano calcium carbonate (NCC) on transitions and chain mobility of poly(lactic acid) (PLA) was investigated. Dispersion state of NCC in polymeric matrix was explored using scanning electron microscopy and surface tension component measurements. Trends of PLA transitional phenomena were investigated using the results of dynamical mechanical analysis (DMA) and differential scanning calorimetry (DSC) in the nanocomposite systems based on PLA and NCC. In addition, two types of crystal structures and decreasing the glass transition temperature were distinguished using temperature-modulated DSC (TMDSC). Higher melting points of polymer crystals were found in TMDSC experiments due to low and dynamic heating rate compared to the conventional DSC. Dynamics of polymer chains, affected by NCC, were quantified using cooperativity length, ξ α, and the number of relaxing structural units, Nα, in the glass transition region. NCC particles hindered the cooperative motion of polymer chains at glass transitions and crystallization in TMDSC measurements, whereas the DMA results indicated that NCC particles may act as lubricant and simplified chain mobility.

Investigation of microstructure, electrical behavior, and EMI shielding effectiveness of silicone rubber/carbon black/nanographite hybrid composites

“…The incorporation of both fillers in SR drastically decreased the damping characteristics of crosslinked SR as a result of reduced dynamics of SR chain segments. Also, the onset of damping behavior of all GN‐ and CB‐based composites has shifted to higher temperatures compared with the unfilled SR, indicating polymer–filler interactions and enlargement of relaxation times of SR segments . Two peaks of damping appeared in the tan(δ) plot reported by Tsagaropoulos and Eisenberg in un‐crosslinked filled polymers .…”

“…However, the extent of restriction of segmental motilities significantly governed by filler type and GN:CB ratio. The E ′′ plots of CB contained samples compared to SR/GN revealed the considerable effect of CB on the segmental motions of SR and viscoelastic properties of samples .…”

Segmental relaxation and partial crystallization of chain‐extended Poly(l‐lactic acid) reinforced with carboxylated carbon nanotube

“…It was found that the molecular weight of the polymer, the presence of crystalline regions, and that of nanoparticles dispersed in the polymer matrix, are all factors that influence the size of CRR . This is because the characteristic CRR size of amorphous polymers is in the range of a few nm, which is also the typical range of polymer–filler interaction.…”

Nanocomposites based on chain extended poly(l-lactic acid)/carboxylated carbon nanotubes: Crystallization kinetics and lamellar morphology

“…Variation of the time-dependent degree of crystallinity, X t , determined from equations (6) and (7) allows a typical Avrami analysis to be performed according to equations (2) to (4). Figure 8(a) compares the crystallization exotherms, the evolutions of X t and X T and the Avrami plots for several PLLA and nanocomposite samples at the lower cooling rate (i.e., 2.5 C/min), while values of main crystallization parameters at the four cooling rates are summarized in Table 2.…”

“…[1][2][3] PLLA can be found either in both completely amorphous or semi-crystalline forms, depending on its chemical structure (i.e., the enantiomeric content) and the processing conditions. [4][5][6][7] In addition, physicochemical characteristics of PLLA deserve deeper studies according to a more fundamental/basic point of view. It is well known that PLLA slowly crystallizes from the melt state, which allows preparing materials with tuned degrees of crystallinity and different lamellar morphologies by changing the thermal history.…”