polymer in processes involving melt stretching (film extrusion, blow molding, foaming, and the like) have been limited due to disadvantages such as intrinsic brittleness, slow crystallization rate, low melt strength, narrow processing window, and low thermal stability. [7][8][9][10][11][12][13] The low melt strength of PLA is due to the inherent degradation behavior of polyesters. PLA degrades at temperatures above its melting point, similar to other polyesters. The degradation reactions include hydrolysis, inter-chain transesterification, and depolymerization by back-biting (intramolecular transesterification). Depending on the process conditions, one of these undesirable reactions overcomes the others. For example, the chain scission, at temperatures above the melting point, is responsible for the degradation of the polymer that leads to a decrease in molecular weight and rheological properties. [1,14,15] To obtain a wider processing window for PLA and thus make the range of its applications broader, improved melt strength is postulated. [16,17] For increasing the melt strength, the modification of PLA is an effective method to achieve a branched high molecular weight structure. Several ways exist for the branching of PLA, including solution polymerization, using the free radical initiator, and functional groups reaction. Due to environmental problems, high costs, low effectiveness, and issues associated with process convenience, solution reactions are not the best choices. Furthermore, as the free radical reaction is a random one, it is more difficult to control the molecular weight when utilizing this method. On the contrary, compared to the free radical branching, reactions of functional groups tend to give rise to long chain branching (LCB) more readily, leading to controlled structures. [18] Chainextension reactions are exploited to increase the melt strength of linear polymers. The advantage of using the chain extenders with functional groups includes re-bonding the degraded chains together and as a result, increasing the molecular weight and the melt strength. For polyesters such as PET and PLA, chain-extension occurs by increasing the molecular weight due to bridging the hydroxyl or carboxyl reactive-end groups using bi-or multi-functional molecules. [1,9] Some researchers have investigated the effect of different chain extenders with different functional groups such as diand multi-functional epoxides, [19][20][21][22][23][24][25][26][27] diisocyanate, [28][29][30] dianhydride, [31][32][33] and so forth. Among these, chain extenders constituted of multi-functional epoxy groups such as Joncryl are highly This research considers a two-step chain extension reaction in the presence of two chain extenders, Joncryl and Pyromellitic dianhydride (PMDA), as a solution for poor melt properties of poly (lactic acid) (PLA). The aim of adding PMDA is to increase the carboxyl groups via the anhydride ring-opening reaction so that the reaction between PLA and Joncryl could be facilitated since the reactivity between t...

Nanocomposites were prepared by adding 1-3 vol % multiwalled carbon nanotubes (MWCNTs) to polyamide 6 (PA6), polypropylene (PP), and their co-continuous blends of 60/40 and 50/50 volume compositions. Because of the good interaction and interfacial adhesion to the PA6, nanotubes were disentangled and distributed evenly through nanocomposites containing PA6. In contrast, lack of active interactions between the matrix and the CNTs resulted in poor tube dispersion in PP. These observations were then verified by studying the rheology and electrical conductivity of their respective nanocomposites. Absence of percolated CNT clusters and possible wrapping of the tubes by PA6 resulted in low electrical conductivity of PA6/CNT nanocomposites. On the other hand, despite the weak dispersion of the tubes, electrical conductiv-ities of PP/CNT nanocomposites were much higher than all other counterparts. This could be the result of good threedimensional distribution of the agglomerated bundles and secondary aggregation of tubes in PP. Adding CNTs to blends of PA6/PP (60/40 and 50/50) resulted in almost full localization of carbon nanotubes in PA6, leading to their higher effective concentration. At the same CNT loadings, the blend nanocomposites had three to seven orders of magnitude higher electrical conductivity than pure PA6.

Nanocomposites of polycarbonate (PC)/multiwalled carbon nanotubes (MWCNTs) containing 0.5-3 wt% of MWCNTs were prepared via two methods of melt mixing and solution mixing. The effect of CNT content and processing methods on electrical and electromagnetic properties of nanocomposite samples were investigated. TEM microphotographs revealed that the PC/ MWCNT composites prepared by the solution method, have better dispersion and distribution of CNTs in the PC matrix. Electrical measurements indicated an electrical percolation threshold of less than 1 wt% of CNTs for this system. Also, it was found that PC/MWCNT composites prepared by the solution method, exhibit higher electrical conductivity and lower electrical percolation threshold. The electromagnetic interference shielding effectiveness (EMI SE) measurements in the X-band (8.2-12.4 GHz) indicated that EMI SE is increased by increasing the amount of CNTs in the samples, and also the thickness of specimens. In addition, the results showed that the composites prepared by the solution method, have higher SE values. Finally, in order to reach an acceptable value for commercial applications of EMI shielding materials (20 dB), thicker samples were produced and it was found that the 3.5 mm thick samples containing 2 wt% CNTs, have a 19.6 dB shielding effectiveness. POLYM. COMPOS., 38:E269-E276,

Polypropylene/polylactic acid (PP/PLA) blends containing 5 wt% of nanoclay in presence and absence of an ethylene‐butylacrylate‐glycidyl methacrylate terpolymer as compatibilizer were prepared by melt‐mixing process. A matrix‐droplet–type morphology confirmed by transmission electron microscope (TEM) and scanning electron microscopy (SEM) studies is formed in presence and absence of the compatibilizer in which the clay platelets were mainly localized in the polylactic acid (PLA) dispersed phase. Degradation studies by means of thermogravimetry analysis (TGA) and analysis of degradation activation energy (Ea), Tmax (maximum degradation temperature), and ΔT (difference between initial and final degradation temperatures) parameters for each polymer component of the system revealed that incorporation of less stable PLA phase to polypropylene (PP) decreases Ea and Tmax parameters, and hence, reduces the thermal stability of PP phase, while incorporation of clay nanoplatelets to the neat blend further reduces its thermal stability attributed to their lack of localization in PP phase. Compatibilization of the filled system results in migration of clay nanoplatelets toward PP and improves Ea and Tmax of PP phase. On the other hand, the Ea and Tmax of PLA phase of the blend were increased with incorporation of clay and its localization within that phase, while compatibilization of the filled system slightly reduces thermal stability of PLA phase due to migration of clay toward PP. A correlation was found between Ea and intensity of the thermogravimetry analysis Fourier‐transform infrared spectroscopy (TGA‐FTIR) peaks of the evolved products. Using the Criado method, a detailed analysis on degradation mechanism of each component was performed, and the changes in the degradation mechanism of the developed systems were determined.

In the present study, the effectiveness of paclitaxel nanocrystals (PTX NCs) encapsulated in carboxymethyl chitosan (CMCS) nanoparticles (CMCS−PTX NPs) as an anticancer drug is evaluated. The CMCS nanoparticles are produced via a cross‐junction microfluidic device where the PTX/CMCS concentration and flow rates in the device are optimized. The dynamic light scattering data show that the PTX NCs have a median diameter size of 230±90 nm, while the size of CMCS−PTX NPs is roughly 270±30 nm. The zeta‐potential result indicates less negative surface charge for the CMCS−PTX NPs as compared to the PTX NCs. Moreover, scanning electron microscopy micrographs, differential scanning calorimetry thermograms, and X‐ray diffraction patterns reveal that the physicochemical properties of the drug remain unaltered after perfusion through the microfluidic device. Cytotoxicity and cell endocytosis of PTX NCs and CMCS−PTX NPs are evaluated in vitro using G361 melanoma‐positive skin cells. The results reveal that the CMCS−PTX NPs increase the cellular uptake and cytotoxicity compared to the PTX NCs alone. In addition, the antitumor effect of CMCS−PTX NPs on B16 melanoma indicates the great potential of CMCS as a promising nano‐carrier for PTX NCs drug with potent inhibitory effect on the tumor growth.