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Linear poly(d-lactide) (PDLA) with various molecular weights is synthesized and incorporated into commercial poly(l-lactide) (PLLA) with different optical purities. And then, the crystallization, mechanical and thermal properties of the PLLA and PLLA/PDLA cast films are investigated. In the PLLA and PDLA/PLLA specimens with lower optical purity, few homochiral crystallites (HC) form in all the specimens and only a small amount of PLA stereocomplex crystallites (SC) are observed in the blends. The elongation at break of all the specimens is extraordinary high, >300%. Dynamic mechanical analyses indicate that the destruction temperature increases at first, and then depresses as enlarging the molecular weight of PDLA in these blends. For the PLLA and PLLA/PDLA with higher optical purity, more content of HC develops in neat PLLA, and both SC and HC produce in the PLLA/PDLA specimens. However, the strains of neat specimens and binary blends are much lower than that of specimens with lower optical purity. The specimens with higher optical purity exhibit higher destruction temperatures and lower loss factors. The high content of crystals (SC and HC) would act as the physical cross-linking points and provide a key factor to impede the deformation of neat PLLA and binary blends during stretching, which should result in the fragile behavior of the PLLA and PLLA/PDLA blends with higher optical purity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44730.

Poly(l-lactide-co-e-caprolactone-diOH) (PCLA) with (ABA)n type is synthesized using poly(lactic acid) (PLA) and poly(e-caprolactone) di-OH (PCL-diOH) via chain extending method. FT-IR, 1H-NMR, and GPC data demonstrate that PLA and PCL-diOH have reacted completely. The product is electrospun into ultrafine fibers subsequently. The optimum electrospinning parameters obtain from an orthogonal experiment are a solvent ratio (DMF/DCM) of 5/5, a polymer concentration of 28 wt %, a collector distance of 20 cm and a voltage of 18 kV. As a result, the average diameter of fibers is 0.77 µm and the uniformity is above 80%. Via range analysis, it is found that the order of the influence on diameter is solvent ratio, applied voltage, collector distance, and polymer concentration, successively. Single effect of the four governing factors on diameter and morphology is also experimentally investigated. This may provide clues for obtaining fibers with various structures by controlling the parameters. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3600–3610, 2013

Synthetic l-lactide random copolymers can be employed as controlled release materials when prepared using supercritical carbon dioxide (scCO2), since they are biodegradable via hydrolysis. To determine the effects of thermal properties on polymer performance following scCO2 processing, three types of poly(l-lactide) having different properties were assessed. The Tm of one poly(l-lactide) sample (H-100) was found to be approximately 170 °C over the processing pressure range from 8 to 18 MPa, while a second sample (H-440) also showed a constant value of approximately 152 °C. In contrast, the poly(l-lactide) REVODE exhibited a Tm of 146 °C prior to processing but a higher value of 147 °C following treatment at 8 MPa. Unlike the H-100 and H-440, the Tm value of the REVODE tended to decrease with increasing pressure. The Tg values increased greatly under mild conditions of 8 MPa pressure and a temperature of 40 °C. In particular, the Tg values for the H-440 and REVODE increased by 4 °C and 5 °C, respectively. All Tg values were lowest at 12 MPa and increased with increasing processing pressure, although the effect of processing temperature was minimal. The Χc DSC of the H-100 was 18% initially but increased to 20% upon scCO2 processing at 40 °C and 14 MPa, and showed further increases at higher processing temperatures. Although the relationship between processing temperature and Χc DSC values for the H-440 showed the same trend as observed with the H-100, a different trend was seen for the REVODE. The Χc XRD values obtained from the XRD analyses differed from the values generated by DSC analysis, and showed a maximum degree of crystallinity following processing at 80 °C both with and without scCO2 treatment. ATR FT-IR analyses identified peaks due to semicrystalline regions in poly(l-lactide) samples treated with scCO2, even when applying low temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44006.

Poly(l-lactide) (PLLA)/TiO2 composite membranes were fabricated by immersion precipitation method. The resulting membranes were characterized using various methods including XRD, ATR-FTIR, TGA, DSC, SEM, goniometer, and molecular weight cut-off. The antifouling performance of the membrane was investigated through the filtration experiments of the oil/water emulsion. XRD, SEM, and ATR-FTIR results indicated that TiO2 was successfully introduced into the membrane, while DSC and TGA indicated the enhancement of thermal stability of membrane. The improvement of membrane hydrophilicity was confirmed by goniometer. In addition, the pore size and porosity on the membrane surface varied obviously with increasing the TiO2 loading. It was concluded that PLLA/TiO2 composite membranes had better antifouling and recycling performance compared with the pure PLLA membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43542.

Electrospraying is a one-step technique for fabricating polymeric microspheres/nanospheres, and the surface characterization of polymeric microspheres fabricated under high voltage is different from an emulsion method. In this study, biodegradable poly(l-lactide) (PLLA) microspheres were successfully fabricated by electrospraying, and electrospraying parameters were used to investigate the size and ζ potential of the electrosprayed PLLA microspheres. The results demonstrate that electrospraying was a one-step method for fabricating monodispersed PLLA microspheres with a size of 1.92 ± 0.35 μm and that the enrichment of methyl groups on the surface of the microspheres contributed to the strong hydrophobicity of electrosprayed PLLA microspheres. Of all the electrospraying parameters investigated, the size and ζ potential of the PLLA microspheres increased with increasing solution concentration and flow rate and decreased with increasing injection voltage and collecting distance. The results provide a theoretical basis for preparing electrosprayed polymeric microspheres as drug carriers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The cold crystallization behavior of poly (L-lactide) (PLLA) blend films modified by small amount of acrylic rubber particles (ACR) have been investigated by in situ Fourier-transform infrared (FTIR) spectroscopy. During the isothermal cold crystallization, the crystallization rate of PLLA is greatly improved with addition of only 1 wt % ACR. However, for PLLA with 8 wt % ACR, the crystallization rate is slower than that of neat PLLA. The relative crystallinity of PLLA with the addition of 1–5 wt % ACR is obviously higher than that of the neat PLLA. For the PLLA blend film with 3 % ACR, the relative crystallinity reaches a maximum. It was found that the addition of ACR particles below 5% accelerated the cold crystallization nucleation process and made the cold-crystallization rate of PLLA/ACR be quicker than that of neat PLLA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Accelerated crystallization of poly(L-lactide) (PLLA) homo-crystallites occurred in the presence of poly(L-2-hydroxybutyrate) [P(L-2HB)], poly(D-2-hydroxybutyrate) [P(D-2HB)], and the mixture of P(L-2HB) and P(D-2HB) [P(L-2HB)/P(D-2HB)]. The accelerating effect of incorporated polymers decreased in the following order: P(L-2HB)/P(D-2HB) > P(D-2HB) > P(L-2HB) > none, for heating and isothermal crystallization for Tc of 130 and 135°C and P(D-2HB) > P(L-2HB)/P(D-2HB) > none > P(L-2HB), for cooling. The P(L-2HB)/P(D-2HB) homo-stereocomplex (HMSC) crystallites, P(D-2HB)/PLLA hetero-stereocomplex (HTSC) crystallites, and P(L-2HB) or P(D-2HB) homo-crystallites are found to be promising biodegradable nucleating agents for PLLA homo-crystallization. The P(L-2HB)/P(D-2HB) HMSC crystallites are most effective during isothermal crystallization and nonisothermal crystallization with heating, whereas the P(D-2HB)/PLLA HTSC crystallites are most effective during nonisothermal crystallization with cooling from the melt. In addition to the nucleating effect, the plasticizing effect of free P(2HB) chains increases both G and the PLLA spherulite number per unit mass. These effects result in accelerated crystallization of PLLA homo-crystallites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

A series of biodegradable poly(L-lactide-co-ϵ-caprolactone) (PCLA) copolymers with different chemical compositions are synthesized and characterized. The mechanical properties and shape-memory behaviors of PCLA copolymers are studied. The mechanical properties are significantly affected by the copolymer compositions. With the ϵ-caprolactone (ϵ-CL) content increasing, the tensile strength of copolymers decreases linearly and the elongation at break increases gradually. By means of adjusting the compositions, the copolymers exhibit excellent shape-memory effects with shape-recovery and shape-retention rate exceeding 95%. The effects of composition, deformation strain, and the stretching conditions on the recovery stress are also investigated systematically. A maximum recovery stress around 6.2 MPa can be obtained at stretching at Tg − 15°C to 200% deformation strain for the PCLA70 copolymer. The degradation results show that the copolymers with higher ϵ-CL content have faster degradation rates and shape-recovery rates, meanwhile, the recovery stress can maintain a relative high value after 30 days in vitro degradation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The effect of thermal history on the nonisothermal crystallization of poly(L-lactide) (PLA) was studied. The cold crystallization of PLA by heating from the glassy state was dominated by the heating rate. However, the temperature to which PLA was cooled before crystallization markedly affected the crystallization kinetics. The lower the temperature was to which PLA was cooled, the lower the nonisothermal crystallization peak temperature was and the larger the crystallization enthalpy was, which indicated enhanced nucleation of spherulites. Fast heating from the glassy state reduced the time available for the growth of spherulites and also suppressed the number of nuclei stable at elevated temperatures by limiting the recrystallization of nuclei formed at low temperatures and their overgrowth by thicker and more perfect crystals. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 282–290, 2007

Montmorillonite (MMT) was modified with dodecylamine, 1,12-diaminododecane, and 1,11-aminoundecanoic acid to prepare CHMMT, NHMMT, and COMMT, respectively. The three clays were mixed with poly(L-lactide) (PLLA) with the aid of chloroform. Depending on the modifiers, PLLA/MMT composites exhibited different mechanical properties and morphology. A completely exfoliated morphology was observed in the PLLA/COMMT composite (PLACO). The PLACO exhibited the best tensile properties among the tested composites because of the finest dispersion of the clay layers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4983–4988, 2006

A mathematical model to describe the molecular weight and polydispersity index (Q) in poly(L-lactide) (PLLA) thermal degradation has been developed. Based on the random chain scission mechanism, effects of temperature and time on the molecular weight and polydispersity index are included in this model. It incorporates the degradation and recombination reaction of PLLA thermal degradation, while taking into account the equal probability assumption. The developments of molecular weight and polydispersity index of PLLA polymer in the thermal degradation process were investigated at temperature ranging from 180–220°C, the experimental data show PLLA reaches its thermal degradation equilibrium in 2 h. The simulated results of this model are compared with the measured molecular weight and polydispersity index of the PLLA polymer. The changes of the molecular weight and polydispersity index in the PLLA thermal degradation can be predicted by this model. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2557–2562, 2003

Triacetin (TAC) is known as a lubricant of poly(L-lactide) (PLLA), and it is used to improve the mechanical properties of PLLA. However, the compatibility of TAC with PLLA and the morphological changes induced by the addition of TAC to PLLA have not been clarified. This study investigates the effects of the addition of TAC on the morphological changes and physical properties of PLLA. We prepared the PLLA films containing a given amount of TAC by solvent-cast blending with chloroform under a low temperature. From the investigation of the mechanical properties of the blends, it is found that the glass-transition temperature of PLLA is remarkably decreased with an increasing amount of TAC, the blend films exhibit high elastic recovery, and the degree of the recovery increases linearly with the amount of TAC. The morphological changes exhibiting high elastic recovery are discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 474–480, 2003

Two biodegradable polymers, poly(L-lactide) (PLLA) and cellulose acetate (CA), were solvent-cast-blended with chloroform. Macrophase separation took place without a compatibilizer. However, homogeneous blend films were obtained with the addition of tetraisopropyl titanate (TP) as a compatibilizer to the blend. We investigated the reasons for the blends exhibiting homogeneity and measured the physical properties of the blends. We reached the following conclusions: (1) the addition of TP produces small PLLA crystallites in the PLLA/CA blends, (2) the addition of TP reduces the thermal decomposition temperature of PLLA/CA blends, (3) Young's modulus of the blends is almost independent of the blend ratio, and (4) the introduction of TP assists with the hydrolysis of the blends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1219–1226, 2002

Poly(l-lactide) (PLLA) is a bioabsorbable polymer with high stiffness and strength compared to the other commercially available bioabsorbable polymers. The properties of PLLA can be improved by straining, causing deformation-mediated molecular orientation. PLLA tubes were biaxially strained above their Tg for improvement of their strength, in a two-step process (sequential straining). Mechanical properties and crystal morphology were investigated as a function of processing strain rate and temperature. DSC revealed that a low processing strain rate allows molecular chain relaxation in the direction of strain and the crystallization is suppressed. Faster strain rates on the other hand suppress chain relaxation, and results in crystalline tubes. The mechanical properties are influenced by both processing strain rate and temperature. Low strain rates allow chain relaxation resulting in the lowest strength and stiffness, whereas a larger stiffness and strength is achieved by increasing strain rate and temperature. Isotropic mechanical properties are only observed at high processing strain rates. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45192.

The influence of processing conditions during melt extrusion on the degradation of poly(L-lactide) (PLLA) has been investigated. PLLA polymer was processed by melt extrusion in a double screw extruder at 210 and 240°C. For each extrusion temperature, two screw rotation speeds, 20 and 120 rpm, were used. To investigate the influence of moisture on the thermal degradation during processing, the PLLA granules were dried at 100°C for 5 h and then either extruded directly or conditioned at 65% RH, 20°C for 24 h prior to extrusion. The results show that a decrease in molecular weight measured as number-average (Mn) molecular weight occurs for all combinations of process parameters used. At processing temperature of 210°C, the change in molecular weight for the dry granules was shown to be dependent on the residence time (i.e., screw rotation speed) in the melt. By changing the screw rotation speed from 120 to 20 rpm at 210°C, Mn decreased from 33,600 to 30,200 g/mol. When the processing temperature was increased to 240°C, the dry granules showed an Mn of 25,600 and 13,600 g/mol when extruded at 120 and 20 rpm, respectively. Mn for the conditioned specimens extruded at 210°C was 18,400 g/mol when processed at 120 rpm and 12,300 g/mol at 20 rpm. When processed at 240°C, 20 rpm, Mn is independent of whether the granules were dry or moist prior to extrusion. It is probably due to the fact that the degradation at 240°C is so extensive that the presence of moisture in the polymer does not contribute further to the degradation process. The stress and strain at break decreased due to degradation and were dependent on the molecular weight of the samples. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2128–2135, 2001

Copolymer of L-lactide and e-caprolactone [P(LLA-CL)] (50/50) was synthesized using stannous octoate and was stored at room temperature. The change in physical properties occurring during this storage at room temperature was investigated by differential scanning calorimetry (DSC), X-ray diffractometry, polarizing optical microscopy, tensile and bending tests, and light absorbance measurements. It was concluded that the increase in mechanical properties and light absorbance during storage can be ascribed to gradual selective crystallization of the L-lactide sequence in P(LLA-CL) at room temperature. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 947–953, 2000

The low-temperature physical aging of amorphous poly(L-lactide) (PLLA) at 25–50°C below glass transition temperature (Tg) was carried out for 90 days. The physical aging significantly increased the Tg and glass transition enthalpy, but did not cause crystallization, regardless of aging temperature. The nonisothermal crystallization of PLLA during heating was accelerated only by physical aging at 50°C. These results indicate that the structure formed by physical aging only at 50°C induced the accelerated crystallization of PLLA during heating, whereas the structure formed by physical aging at 25 and 37°C had a negligible effect on the crystallization of PLLA during heating, except when the physical aging at 37°C was continued for the period as long as 90 days. The mechanism for the accelerated crystallization of PLLA by physical aging is discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Variation of the ambient temperature of the spinline during dry spinning of PLLA solutions induced variation of the extrudate swell of the spinline, affected by the rate of solidification of the PLLA. By way of phase separation, porous filaments were achieved in which the morphology depended on the applied ambient temperature. Hot drawing of these filaments led to tensile strengths varying between 1.1 and 2.2 GPa. An optimal tensile strength of 2.2 GPa was achieved by hot drawing of a filament which was spun into a surrounding of 25 o C

This paper is concerned with the influences of the extrusion speed and the winding speed during dry spinning of 4 wt % solutions of poly(L-lactide) (PLLA) in mixtures of chloroform and toluene, on the ultimate fiber tenacities after hot drawing. It was found that high-strength PLLA fibers (1.5 GPa) can be produced at high spinning rates (> 180 m/min) if rupturing of the entanglement network and oriented crystallization during spinning is suppressed. This could be accomplished by avoiding spinline stretching and applying low elongational deformation rates in the spinneret during spinning.

Fibers of poly(L-lactide) (PLLA) with a tensile strength up to 1.2 GPa and Young's modulus in the range of 12–15 GPA were obtained by a hot drawing of fibers spun from solution of PLLA in good solvents such as dichloromethane and trichloromethane. The tensile strength of fibers was strongly dependent on the molecular weight of PLLA and on polymer concentrations in the spinning solution. Changing of the polymer concentration in the spinning solution gives rise to formation of fibers with different shape and porosity. Fibers spun from 10–20% solutions at room temperature exhibit a regular structurization, due to the melt fracture. These fibers had knot strengths up to 0.6 GPa, whereas fibers with a smooth surface spun from more dilute solutions had weaker square knots up to 0.3 GPa.