Physical and mechanical properties of PLA, and their functions in widespread applications - A comprehensive review.

Fundamentals, processes and applications of high-permittivity polymer–matrix composites

Poly(lactic acid) (PLA), so far, is the most extensively researched and utilized biodegradable aliphatic polyester in human history. Due to its merits, PLA is a leading biomaterial for numerous applications in medicine as well as in industry replacing conventional petrochemical-based polymers. The main purpose of this review is to elaborate the mechanical and physical properties that affect its stability, processability, degradation, PLA-other polymers immiscibility, aging and recyclability, and therefore its potential suitability to fulfill specific application requirements. This review also summarizes variations in these properties during PLA processing (i.e. thermal degradation and recyclability), biodegradation, packaging and sterilization, and aging (i.e. weathering and hygrothermal). In addition, we discuss up-to-date strategies for PLA properties improvements including components and plasticizer blending, nucleation agent addition, and PLA modifications and nanoformulations. Incorporating better understanding of the role of these properties with available improvement strategies is the key for successful utilization of PLA and its copolymers/composites/blends to maximize their fit with worldwide application needs.

Physical and mechanical properties of PLA, and their functions in widespread applications — A comprehensive review

Thermal Conductivity of Polymer-Based Composites: Fundamentals and Applications

Supramolecular materials, dynamic materials by nature, are defined as materials whose components are bridged via reversible connections and undergo spontaneous and continuous assembly/disassembly processes under specific conditions. On account of the dynamic and reversible nature of noncovalent interactions, supramolecular polymers have the ability to adapt to their environment and possess a wide range of intriguing properties, such as degradability, shape-memory, and self-healing, making them unique candidates for supramolecular materials. In this critical review, we address recent developments in supramolecular polymeric materials, which can respond to appropriate external stimuli at the fundamental level due to the existence of noncovalent interactions of the building blocks.

Stimuli-responsive supramolecular polymeric materials.

Dispersion state of carbon black(CB) was studied in polymer blends which are incompatible with each other. It was found that CB distributes unevenly in each component of the polymer blend. There are two types of distribution. (1) One is almost predominantly distributed in one phase of the blend matrix, and in this phase fillers are relatively homogeneously distributed in the same manner as a single polymer composite. (2) In the second, the filler distribution concentrates at interface of two polymers. As long as the viscosities of two polymers are comparable, interfacial energy is the main factor determining uneven distribution of fillers in polymer blend matrices. This heterogeneous dispersion of conductive fillers has much effect on the electrical conductivity of CB filled polymer blends. The electrical conductivity of CB filled polymer blends is determined by two factors. One is concentration of CB in the filler rich phase and the other is phase continuity of this phase. These double percolations affect conductivity of conductive particle filled polymer blends.

Dispersion of fillers and the electrical conductivity of polymer blends filled with carbon black

Electrical conductivity of carbon black (CB) filled polymer blends which are incompatible with each other was studied as a function of the polymer's blend ratio Transmission electron microscope (TEM) analysis shows that CB distributes unevenly in each component of a polymer blend TEM photographs of phase structure of solvent extracted HDPE/PMMA blend and solvent extraction experiments of PMMA/PP blend detect the blend ratio at which the structural continuity of filler rich phase is formed The electrical conductivity of polymer blends is found to be determined by two factors One is the concentration of CB in the filler rich phase and the other is the structural continuity of this phase This double percolation affects the conductivity of conductive particle filled polymer blends

Double percolation effect on the electrical conductivity of conductive particles filled polymer blends

Crystalline structure and morphology of poly(l-lactide) (PLLA) formed under high-pressure CO2 were studied by comparing the CO2-treated PLLA and the annealed one in terms of the crystallization behavior, crystalline forms, and crystalline superstructures. The crystallization temperature dependence of the diffraction peak position (2θ ≈ 16°) and crystallinity for the CO2-treated PLLA indicates that the crystal modification changes continuously from the disorder α (α′′) to α forms not through the α′ one with increasing temperature. By using light scattering technique, we clarified that the morphological transition from spherulites on a micrometer scale to rodlike crystalline superstructures on a nanometer scale occurs around 15 °C under 7−15 MPa CO2 and around 30 °C under 3 MPa CO2. By introducing the parameters η and Δ in the theoretical calculation for Vv light scattering from spherulites, it is indicated that there is a distinct difference in the arrangement of crystalline lamellae within spherulite betw...

Crystalline Structure and Morphology of Poly(l-lactide) Formed under High-Pressure CO2

By screening examinations for a wide variety of organic solvents, we found that poly(l-lactide) (PLLA) forms the crystalline complex (e-form) with the specific organic solvents such as tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) below room temperature. It was revealed that PLLA has high selectivity for low molecular weight compounds to form the e-crystals. By fiber diagram analyses for the e-forms, it was found that PLLA chains take the 107 (left-handed 103) helical conformation and are packed in the orthorhombic lattice (a = 1.5–1.6 nm, b = 1.2–1.3 nm, c = 2.8–2.9 nm, and α = β = γ = 90°). Based on R-factor and packing energy calculations, the plausible crystal structure of PLLA–DMF complex was proposed, in which four PLLA chains and eight guest solvents are packed in the unit cell.

Complex Crystal Formation of Poly(l-lactide) with Solvent Molecules

This work attempts to clarify the influence of surface roughness on the thermodynamic interactions between carbon particles and polymer melts. The surface energy of carbon black (CB) and short carbon fibers (VGCF) having different surface roughnesses was estimated by inverse gas chromatography (IGC) and highly sensitive isothermal calorimeter (HS−ITC) measurements using low-molecular-weight analogues of polymers as probes. We confirmed that the carbon surfaces possess energetic heterogeneity with the most active sites at the graphite crystalline edges, and the interactions in play are van der Waals in nature. Competitive adsorption of two chemically different polymers by incorporation of the carbon particles into the polymer blends was investigated based on SEM and TEM observations. We found that the selective location of CB in the polymer blends does not always depend on the surface tension of polymers but seems to be governed largely by the flexibility of the polymer chains. In VGCF-filled HDPE/PMMA com...

Shigeo Asai

Papers

Dispersion of fillers and the electrical conductivity of polymer blends filled with carbon black

Double percolation effect on the electrical conductivity of conductive particles filled polymer blends

Crystalline Structure and Morphology of Poly(l-lactide) Formed under High-Pressure CO2

Complex Crystal Formation of Poly(l-lactide) with Solvent Molecules

Entropy Penalty-Induced Self-Assembly in Carbon Black or Carbon Fiber Filled Polymer Blends