scholarly journals Recent Developments in the Crystallization of PLLA-Based Blends, Block Copolymers, and Nanocomposites

2021 ◽  
Author(s):  
Amit Kumar Pandey ◽  
Shinichi Sakurai
Keyword(s):  
Block Copolymers ◽  
Liquid State ◽  
Triblock Copolymers ◽  
Nucleating Agent ◽  
The Third ◽  
Confined Crystallization ◽  
The Poor ◽  
The Matrix ◽  
Recent Developments ◽  
Poly Ethylene

Despite the extensive studies of poly(L-lactic acid)(PLLA), the crystallization of PLLA-based materials is still not completely understood. This chapter presents recent developments of crystallization of PLLA-based blends, block copolymers and nanocomposites. The first section of the chapter discusses the acceleration of PLLA crystallization by the inclusion of biobased (solid and liquid state) additives. It was found that the solid state additives work as a nucleating agent while the liquid-state additive works as a plasticizer. Both type of the additives can significantly enhance the crystallization of PLLA, as indicated by crystallization half-time (t0.5) values. Such composites are of great interest as they are 100% based on renewable resources. The second section talks about the enhanced formation of stereocomplex (SC) crystals in the PLLA/PDLA (50/50) blends by adding 1% SFN. It was found that the loading of SFN enhances the formation of SC crystals and it suppresses the formation of HC (homocrystal). The third section deals with confined crystallization of poly(ethylene glycol) (PEG) in a PLLA/PEG blend. The PLLA/PEG (50/50) blend specimen was heated up to 180.0°C and kept at this temperature for 5 min. Then, a two-step temperature-jump was conducted as 180.0°C → 127.0°C → 45.0°C. For this particular condition, it was found that PEG can crystallize only in the preformed spherulites of PLLA, as no crystallization of PEG was found in the matrix of the mixed PLLA/PEG amorphous phase. The last section describes the confined crystallization of PCL in the diblock and triblock copolymers of PLA-PCL. Furthermore, enantiomeric blends of PLLA-PCL and PDLA-PCL or PLLA-PCL-PLLA and PDLA-PCL-PDLA have been examined for the purpose of the improvement of the poor mechanical property of PLLA to which the SC formation of PLLA with PDLA components are relevant.

Morphology and thermal properties of clay based biocomposites

2018 ◽  
Vol 38 (8) ◽  
pp. 785-793 ◽  
Author(s):  
Leila Bounabi ◽  
Naima Bouslah Mokhnachi ◽  
Amar Djadoun ◽  
Nabila Haddadine ◽  
Regis Barille
Keyword(s):  
Crystallization Rate ◽  
Layered Silicate ◽  
Nucleating Agent ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Sem Images ◽  
Low Weight ◽  
The Matrix ◽  
Poly Ethylene ◽  
Temperature Melting

Abstract Carboxymethylcellulose/poly(ethylene glycol) (CMC/PEG) blend and CMC/PEG/montmorillonite (MMT) nanocomposites were produced by the solvent casting method. The clay, a sodium MMT, was incorporated in the polymer matrix at low weight loadings (from 1 wt% to 7 wt%). The MMT dispersion in the matrix was evaluated by X-ray diffraction, which revealed an intercalated structure of the nanocomposites. Different levels of intercalation have been detected. The changes in morphology caused by the addition of layered silicate on CMC/PEG blend were investigated by scanning electron microscopy (SEM). The SEM images of CMC/PEG blend containing 5% of MMT displayed more homogenous morphology than CMC/PEG blend. The compatibilizing performance of the filler was investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) spectroscopy. The effect of the introduction of the clay on the crystallization temperature, melting temperature and crystallization degree of CMC/PEG revealed that clay behaved as a nucleating agent and enhanced the crystallization rate of PEG. Furthermore, it was demonstrated that the addition of a small percentage of montmorillonite (1%) was enough to improve the thermal stability of the nanocomposites.

Antimicrobial activity of polystyrene particles coated by photo-crosslinked block copolymers containing a biocidal polymethacrylate block

e-Polymers ◽  
2005 ◽  
Vol 5 (1) ◽  
Author(s):  
Sandrine Lenoir ◽  
Christophe Pagnoulle ◽  
Christophe Detrembleur ◽  
Moreno Galleni ◽  
Robert Jérôme
Keyword(s):  
Antimicrobial Activity ◽  
Block Copolymers ◽  
Atom Transfer Radical Polymerization ◽  
Radical Polymerization ◽  
Triblock Copolymers ◽  
Hydroxyl Group ◽  
Cross Linking ◽  
Biocidal Activity ◽  
Poly Ethylene ◽  
End Group

AbstractA commercially available poly(ethylene-co-butylene) copolymer, endcapped by a short polyisoprene block and a hydroxyl group (PI-b-PEB-OH), has been derivatized into a macroinitiator for atom transfer radical polymerization (ATRP) by esterification of the hydroxyl end-group by an activated bromidecontaining acyl bromide. Two types of triblock copolymers, PI-b-PEB-b-poly- (dimethylaminoethyl methacrylate) (PDMAEMA) and PI-b-PEB-b-poly[2-(tert-butylamino) ethyl methacrylate] (PTBAEMA), have been synthesized and used to coat polystyrene particles. These coatings have been permanently immobilized by UV cross-linking of the isoprene units. They exhibit a biocidal activity against Gramnegative bacteria either intrinsically in case of the PTBAEMA block or upon quaternization of the PDMAEMA block by octyl bromide. The antimicrobial activity is directly related to the concentration of coated PS particles in the medium.

Functional Polyether-based Amphiphilic Block Copolymers Synthesized by Atom-transfer Radical Polymerization

2011 ◽  
Vol 64 (9) ◽  
pp. 1183 ◽  
Author(s):  
Hazrat Hussain ◽  
Elkin Amado ◽  
Jörg Kressler
Keyword(s):  
Block Copolymers ◽  
Atom Transfer Radical Polymerization ◽  
Radical Polymerization ◽  
Amphiphilic Block Copolymers ◽  
Atom Transfer ◽  
Coupling Reactions ◽  
Recent Developments ◽  
Broad Variety ◽  
Poly Ethylene ◽  
Poly Propylene

This review deals with the synthesis, physical properties, and applications of amphiphilic block copolymers based on hydrophilic poly(ethylene oxide) (PEO) or hydrophobic poly(propylene oxide) (PPO). Oligomeric PEO and PPO are frequently functionalized by converting their OH end groups into macroinitiators for atom-transfer radical polymerization. They are then used to generate additional blocks as part of complex copolymer architectures. Adding hydrophobic and hydrophilic blocks, respectively, leads to polymers with amphiphilic character in water. They are surface active and form micelles above a critical micellization concentration. Together with recent developments in post-polymerization techniques through quantitative coupling reactions (‘click’ chemistry) a broad variety of tailored functionalities can be introduced to the amphiphilic block copolymers. Examples are outlined including stimuli responsiveness, membrane penetrating ability, formation of multi-compartmentalized micelles, etc.

Self-Assembly of Hydrogels From Elastin-Mimetic Block Copolymers

2002 ◽  
Vol 724 ◽  
Author(s):  
Elizabeth R. Wright ◽  
R. Andrew McMillan ◽  
Alan Cooper ◽  
Robert P. Apkarian ◽  
Vincent P. Conticello
Keyword(s):  
Block Copolymers ◽  
Self Assembly ◽  
Triblock Copolymers ◽  
Variable Temperature ◽  
Inverse Temperature ◽  
Temperature Transition ◽  
Scanning Calorimetry ◽  
Design Synthesis ◽  
Inverse Temperature Transition ◽  
Functional Biomaterials

AbstractTriblock copolymers have traditionally been synthesized with conventional organic components. However, triblock copolymers could be synthesized by the incorporation of two incompatible protein-based polymers. The polypeptides would differ in their hydrophobicity and confer unique physiochemical properties to the resultant materials. One protein-based polymer, based on a sequence of native elastin, that has been utilized in the synthesis of biomaterials is poly (Valine-Proline-Glycine-ValineGlycine) or poly(VPGVG) [1]. This polypeptide has been shown to have an inverse temperature transition that can be adjusted by non-conservative amino acid substitutions in the fourth position [2]. By combining polypeptide blocks with different inverse temperature transition values due to hydrophobicity differences, we expect to produce amphiphilic polypeptides capable of self-assembly into hydrogels. Our research examines the design, synthesis and characterization of elastin-mimetic block copolymers as functional biomaterials. The methods that are used for the characterization include variable temperature 1D and 2D High-Resolution-NMR, cryo-High Resolutions Scanning Electron Microscopy and Differential Scanning Calorimetry.

No fear of George Kingsley Zipf

10.1558/37291 ◽  
2018 ◽  
Vol 2 (2) ◽  
pp. 242-263
Author(s):  
Stefano Rastelli ◽  
Kook-Hee Gil
Keyword(s):  
Minimalist Program ◽  
Classroom Research ◽  
Language Design ◽  
Efficient Computation ◽  
Generative Linguistics ◽  
The Third ◽  
Factor Effect ◽  
Language Classroom ◽  
Recent Developments ◽  
Insight Into

This paper offers a new insight into GenSLA classroom research in light of recent developments in the Minimalist Program (MP). Recent research in GenSLA has shown how generative linguistics and acquisition studies can inform the language classroom, mostly focusing on what linguistic aspects of target properties should be integrated as a part of the classroom input. Based on insights from Chomsky’s ‘three factors for language design’ – which bring together the Faculty of Language, input and general principles of economy and efficient computation (the third factor effect) for language development – we put forward a theoretical rationale for how classroom research can offer a unique environment to test the learnability in L2 through the statistical enhancement of the input to which learners are exposed.

Current trends in the structure of eye injuries

2020 ◽  
Vol 21 (3) ◽  
pp. 106-108
Author(s):  
M. N. Ponomareva ◽  
◽  
S. V. Sakharova ◽  
E. M. Pochinok ◽  
E. V. Fomina ◽  
...  
Keyword(s):  
Medical Records ◽  
Young Patients ◽  
Present Stage ◽  
Eye Injuries ◽  
Third Place ◽  
The Third ◽  
Eye Trauma ◽  
Current Trends ◽  
The Poor ◽  
Leading Position

Aim. To identify current trends in hospital eye trauma based on the materials of the specialized ophthalmology department of a round-the-clock hospital. Materials and methods. The analysis of medical records of patients treated in the round-the-clock specialized ophthalmology department of the state medical establishment OKB No. 2 in the period since January 2017-2019. Results. During the analyzed period, 4948 patients were treated, of which 218 patients (5.6%) were identified for nosologies belonging to the category of eye trauma. Men are most often exposed to eye injuries (84%), in addition, in 62% of cases, these are young patients (18-44 years). The structure of eye trauma is almost unchanged: the leading position is occupied by penetrating wounds of the eyeball and contusions, the third place is occupied by burns, through wounds of the eyeball are rare. Conclusions. Given the poor prognosis of the outcome of a severe eyeball injury, it requires the introduction of modern types of microsurgical intervention using endovitreal surgery at the present stage.

Structural engineering to control density, conformation, and bioactivity of the poly(ethylene glycol)-grafted poly(urethane urea) scaffolds

2018 ◽  
Vol 34 (2) ◽  
pp. 209-223
Author(s):  
Shideh Shaneh ◽  
Fatemeh Shokrolahi ◽  
Parvin Shokrollahi ◽  
Hamid Yeganeh ◽  
Hossein Omidian
Keyword(s):  
Stem Cells ◽  
Mesenchymal Stem Cells ◽  
Ethylene Glycol ◽  
Structural Engineering ◽  
Cell Attachment ◽  
Poly Ethylene Glycol ◽  
Salt Leaching ◽  
The Matrix ◽  
Diphenyl Tetrazolium Bromide ◽  
Poly Ethylene

Poly(urethane urea) scaffolds were fabricated through combined salt leaching and solvent casting methods. The scaffolds were then functionalized via aminolysis with poly(ethylene glycol) (PEG- g-PUU). To compare its bioactivity, gelatin was also grafted onto the aminolyzed poly(urethane urea) surface (Gel- g-PUU). Chemical changes at the surface were then monitored using quantitative/qualitative methods. Grafting with both gelatin and poly(ethylene glycol) remarkably enhanced the wettability of poly(urethane urea). Proliferation of human adipose–derived mesenchymal stem cells on poly(urethane urea) and the modified poly(urethane urea)s was evaluated by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide assay. The cell experiment results showed that both the modified poly(urethane urea)s enhanced the attachment and proliferation of human adipose–derived mesenchymal stem cells compared to pure poly(urethane urea). Based on previous reports, while a supportive role is observed at adequate poly(ethylene glycol) graft densities, cell adhesion and proliferation are inhibited at very high grafting densities. To correlate the cell data to poly(ethylene glycol) conformations, the surface tension was measured. Data on human adipose–derived mesenchymal stem cells’ attachment/proliferation and contact angle/surface free energy together showed that the grafting density of poly(ethylene glycol) was regulated by optimizing aminolysis conditions, careful selection of poly(ethylene glycol)’s molecular weight, and bulk properties of the matrix poly(urethane urea). As a result, surface overcrowding and brush conformation of the poly(ethylene glycol) chains were avoided, and human adipose–derived mesenchymal stem cell attachment and proliferation occurred on the PEG- g-PUU scaffold at a comparable level to the Gel- g-PUU.

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