Poly(lactic Acid): A Versatile Biobased Polymer for the Future with Multifunctional Properties—From Monomer Synthesis, Polymerization Techniques and Molecular Weight Increase to PLA Applications

Environmental problems, such as global warming and plastic pollution have forced researchers to investigate alternatives for conventional plastics. Poly(lactic acid) (PLA), one of the well-known eco-friendly biodegradables and biobased polyesters, has been studied extensively and is considered to be a promising substitute to petroleum-based polymers. This review gives an inclusive overview of the current research of lactic acid and lactide dimer techniques along with the production of PLA from its monomers. Melt polycondensation as well as ring opening polymerization techniques are discussed, and the effect of various catalysts and polymerization conditions is thoroughly presented. Reaction mechanisms are also reviewed. However, due to the competitive decomposition reactions, in the most cases low or medium molecular weight (MW) of PLA, not exceeding 20,000–50,000 g/mol, are prepared. For this reason, additional procedures such as solid state polycondensation (SSP) and chain extension (CE) reaching MW ranging from 80,000 up to 250,000 g/mol are extensively investigated here. Lastly, numerous practical applications of PLA in various fields of industry, technical challenges and limitations of PLA use as well as its future perspectives are also reported in this review.

Solid-State Polymerization of Poly(Ethylene Furanoate) Biobased Polyester, III: Extended Study on Effect of Catalyst Type on Molecular Weight Increase

In this study, the synthesis of poly(ethylene furanoate) (PEF), catalyzed by five different catalysts—antimony acetate (III) (Sb Ac), zirconium (IV) isopropoxide isopropanal (Zr Is Ip), antimony (III) oxide (Sb Ox), zirconium (IV) 2,4-pentanedionate (Zr Pe) and germanium (IV) oxide (Ge Ox)—via an industrially common combination of melt polymerization and subsequent solid-state polymerization (SSP) is presented. In all reactions, proper amounts of 2,5-dimethylfuran-dicarboxylate (DMFD) and ethylene glycol (EG) in a molar ratio of DMFD/EG= 1/2 and 400 ppm of catalyst were used. Polyester samples were subjected to SSP procedure, under vacuum application, at different reaction times (1, 2, 3.5, and 5 h) and temperatures of 190, 200, and 205 °C. Carboxyl end-groups concentration (–COOH), intrinsic viscosity (IV), and thermal properties, via differential scanning calorimetry (DSC), were measured for all resultant polymers to study the effect of the used catalysts on the molecular weight increase of PEF during SSP process. As was expected, it was found that with increasing the SSP time and temperature, the intrinsic viscosity and the average molecular weight of PEF steadily increased. In contrast, the number of carboxyl end-groups content showed the opposite trend as intrinsic viscosity, that is, gradually decreasing during SSP time and temperature increase. It is worthy to note that thanks to the SSP process an obvious and continuous enhancement in the thermal properties of the prepared PEF samples was attained, in which their melting temperatures (Tm) and degree of crystallinity (Xc) increase progressively with increasing of reaction time and temperature. To predict the time evolution of polymers IV, as well as the hydroxyl and carboxyl content of PEF polyesters during the SSP, a simple kinetic model was developed. From both the theoretical simulation results and the experimental measurements, it was demonstrated that surely the Zr Is Ip catalyst shows the best catalytic characteristics compared to all other used catalysts herein, that is, leading in reducing—in a spectacular way—the activation energy of the involved both transesterification and esterification reactions during SSP.

Determination of some characteristics of comet’s gases by photometry method for comet Hyakutake

The present paper focuses on the study of some characteristics ofcomets ions by photometry method which represent by CCD camerawhich it provide seeing these images in a graded light. From 0-255when Zero (low a light intensity) and 255 (highlight intensity). Thesedifferences of photonic intensity can be giving us a curve whichappear from any line of this image.From these equations the focus is concentrating on determine thetemperature distribution, velocity distribution, and intensity numberdistribution which is give number of particles per unit volume.The results explained the interaction near the cometary nucleuswhich is mainly affected by the new ions added to the density of thesolar wind, the average molecular weight increase and result in manyunique characteristics of the cometary tail.

Effect of catalyst type on molecular weight increase and coloration of poly(ethylene furanoate) biobased polyester during melt polycondensation

The effect of several catalysts on the synthesis of poly(ethylene furanoate) (PEF) was studied during a two-stage melt polycondensation process.

Morphologic Modification in ABS by the Incorporation “in Situ” of Nano-ZnO: Study of the Effect on Characteristics and Final Properties

The synthesis of poly(acrylonitrile-butadiene-styrene) (ABS) was carried out using the mass-suspension process, high cis polybutadiene (PB), benzoyl peroxide (BPO) as the initiator and modified and unmodified nanoparticles of zinc oxide (nano-ZnO). X-ray diffraction (XRD) and Fourier transform infrared (FTIR) were used to characterize the ZnO nanoparticles. A Universal tensiometer, Brokfield viscosimeter and transmission electronic microscopy (TEM) were used to characterize ABS. The employment of nano-ZnO induced an impressive morphologic modification and transformed the highly occluded salame morphology of poly(styrene-acrylonitrile) (SAN) to a highly dispersed one in its matrix. During the reaction, a decrease in the total production of SAN was observed due to the interaction between radicals produced by the initiator and nano-ZnO, causing a molecular weight increase of SAN. The nano-ZnO also induced a decline in the phase inversion and extended the period of occurrence. ABS without nano-ZnO yielded higher mechanical properties than one without any nanoparticles.

Convenient Synthesis and Characterization of Silane-Capped Polysiloles for the Fabrication of Luminescent OLED

Catalytic dehydropolymerization and subsequent silane-capping with R2 SiHCl (R = Ph, Me)of 1,1-dihydrotetraphenylsilole (1) using various inorganic hydrides produces electroluminescent silane-capped polysiloles (2)in high yield. The polymerization yield and molecular weight increase in the order LiB[CH(CH3)C2H5]3H < NaB[CH(CH3)C2H5]3H < KB[CH(CH3)C2H5]3H. The molecular weights increase in the order Na[H2Al(OCH2CH2OCH3)2] < KB[CH(CH3)C2H5]3H < LiB(C2H5)3H. The silane-capped polysiloles 2 emit at 521 nm and are electroluminescent at 522 nm. The fluorescence quantum yield of 2 in toluene is (1.67 ± 0.31) × 10−2. The emission color is green and the maximum brightness of the device is 2,900 cd/m2 with a luminous efficiency of 0.69 lm/W. The substituent type of silyl end group showed no appreciable effect on the luminescent properties of polysilole backbone. Thus, the silane-capped polysiloles are found to be a good material for OLED fabrication. A possible mechanism for the formation of 2 was suggested.