Melt processing of poly(L‐lactic acid) in the presence of organomodified anionic or cationic clays

Abstract

Poly(L-lactic acid) (PLA) films are in use for various types of food packaging; however, a wider range of applications would be possible if the barrier properties of these films could be improved. To make such improvements, combinations of PLA with two nanofillers, laurate-intercalated Mg-Al layered double hydroxide (LDH-C 12 ) and a cationic organomodified montmorillonite (MMT) clay (CloisiteV R 30B), were investigated. The dispersion of these fillers in PLA by melt processing was explored using two methods, either by mixing the nanofillers with PLA granulate immediately before extrusion or by preparation and subsequent dilution of PLAnanofiller masterbatches. After melt processing of these materials, PLA molecular weight, thermal stability, film transparency, morphology, and permeability characteristics were determined. Direct addition of LDH-C 12 drastically reduced the PLA molecular weight. Although this reduction in molecular weight was still very significant, it was less when a PLA/ LDH-C 12 masterbatch was processed. In contrast, there was no significant reduction in PLA molecular weight when processing with CloisiteV R 30B. However, film transparency was compromised when either LDH or MMT nanofillers were used. Evidence from DSC analyses showed a significant increase in heat of fusion when LDH-C 12 was dispersed in PLA compared with CloisiteV R 30B, likely indicating a difference in nucleating properties. Complementary optical purity analyses suggested that racemization as a result of processing could influence the PLA crystallinity as determined by DSC in certain cases. A reduction in thermal stability when incorporating LDH-C 12 could be a direct result of PLA molecular weight reduction. XRD and TEM analyses showed that both CloisiteV R 30B-and LDH-C 12 -based PLA composites yielded exfoliated and intercalated morphologies, but nanofiller agglomeration was also seen when LDH-C 12 was used. PLA/ CloisiteV R 30B nanocomposite films exhibited significant enhancement in oxygen and water vapor barrier properties, but no such improvement was found in PLA/LDH-C 12 nanocomposite films.

Layered double hydroxides as fillers in poly(l-lactide) nanocomposites, obtained by in situ bulk polymerization

“…For other hand, the lowest value of this parameter was found for the nanocomposite containing 2 wt% of Zn/Al sebacate. These observations can indicate that some fillers exhibited, at certain concentrations, higher nucleation tendencies, giving rise to more uniform crystal sizes [1] .…”

“…This finding might be due to variations in the molecular weight of PLA since it is known that the PLA melting point is influenced by polymer chain length [12] . Some authors [1,10,12] reported the decrease in molecular weights of PLLA nanocomposites containing LDHs. This reduction in molecular weight could arise due to release of tightly bound water in the LDH interlayer spacing which would cause hydrolytic degradation of PLA chains.…”

“…For such applications nontoxic, biodegradable and derived from a renewable source polymers have been studied. Among the polymers in this category, poly(lactic acid) (PLA) has been identified as a good candidate to partially substitute petroleum-derived polymer such as polypropylene, polystyrene, or polyethylene(terephthalate) in some uses [1] . Typical PLA medical applications include suture materials, drug delivery systems and oral and orthopaedic internal fixation devices.…”

“…In order to compensate this charge excess and stabilize the structure, exchangeable hydrated anions are inserted in the interlayer spacing, generating the LDHs. The LDHs can be represented by the general formula: [M Few groups investigated the properties of the nanocomposites of PLLA filled with LDHs [1,2,[5][6][7][8][9][10][11][12] , but in these researches the produced LDHs were composed by only two pairs of divalent-trivalent cations: Mg/Al [1][2][5][6][7][9][10][11][12] and Zn/Al [8,11] . Besides, nanocomposites of PLLA filled with LDH intercalated by the anions evaluated in the present study (salicylate and sebacate) were not found.…”

Effect of Rare Earth Hypophosphite Salts on the Fire Performance of Biobased Polylactide Composites

“…The melting enthalpy of 100% crystalline PLA was taken as ΔH m°= 93 J/g. 25 After considering the effect of flame retardant loading (ϕ), crystallinity was calculated with eq 1: 26,27 Thermogravimetric analysis−infrared spectrometry (TG− IR) was conducted using the TGA Q500 IR thermogravimetric analyzer that was linked to the Nicolet 6700 FTIR spectrophotometer. About 5−10 mg of the sample was put in an alumina crucible and heated from 30 to 700°C.…”