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Because of its low thermal stability and brittleness, both the drawbacks of poly(l-lactide) (PLLA) were solved by forming stereocomplex (ST) and its copolymer with poly(butylene adipate-co-terephthalate) (PLLA–PBAT). In this study, we synthesized PLLA and PLLA–PBAT copolymer by ring-opening polymerization. Both polymers were blended with poly(d-lactide) to form ST crystals. Multi-walled carbon nanotubes (MWCNTs) were added into the polymer matrix at 5 phr by the solvent casting method. The surface resistance of the composite was ≅106 Ω, which is appropriate for electrostatic dissipative purposes. The copolymer and its ST crystallites were confirmed by the peaks in infrared spectra at 922 and 908 cm−1, respectively. The PLLA–PBAT copolymer had 60% lower tensile strength than PLLA and its stereocomplex, but 10% higher elongation at break. The elongation at break of the PLLA–PBAT copolymer/MWCNT composite decreased by 17% while its thermal stability slightly increased when compared to the unfilled copolymer. The melting temperature for both ST PLLA–PBAT copolymers, with and without MWCNTs, was around 225°C, which is 50°C higher than that of the homocrystals. Moreover, the glass transition temperature and crystallinity of the ST PLLA–PBAT copolymer also increased by adding MWCNTs.

A new computer geometric modeling approach for 2 × 1 and 3 × 1 twill woven fabric structures is proposed. The precise geometrical description is presented by taking the skewness property into account. In the 2 × 1 and 3 × 1 twill weaves, the twill fabrics are formed of asymmetric floatings in which the length of floating sections was not equal on both surfaces and therefore the equilibrium condition was different from symmetric floatings. The proposed algorithm has three main parts: the first part describes the two-dimensional model of yarn cross-section for twill woven fabric structure, the second part consists of a modeling method for a three-dimensional model in warp/weft yarn, and the third part contains the CAD model. Examples of this approach are demonstrated and compared with a single line of yarn path model and the filament assemble model that excludes the skewness property. The model simulated in this study can improve the visual simulation of the real twill woven fabric and also this geometric model necessary as an input to many computational models for the prediction of the properties of the fabrics.

The formation of polylactide stereocomplex (sc-PLA), involving the blending of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), enhances PLA materials by making them stronger and more heat-resistant. This study investigated the competitive crystallization behavior of homocrystals (HCs) and stereocomplex crystals (SCs) in a 50/50 PLLA/PDLA blend with added polyethylene glycol (PEG). PEG, with molecular weights of 400 g/mol and 35,000 g/mol, was incorporated at concentrations ranging from 5% to 20% by weight. Differential scanning calorimetry (DSC) analysis revealed that PEG increased the crystallization temperature, promoted SC formation, and inhibited HC formation. PEG also acted as a plasticizer, lowering both melting and crystallization temperatures. The second heating DSC curve showed that the pure PLLA/PDLA blend had a 57.1% fraction of SC while adding 5% PEG with a molecular weight of 400 g/mol resulted in complete SC formation. In contrast, PEG with a molecular weight of 35,000 g/mol was less effective, allowing some HC formation. Additionally, PEG consistently promoted SC formation across various cooling rates (2, 5, 10, or 20 °C/min), demonstrating a robust influence under different conditions. [ABSTRACT FROM AUTHOR]

A new computer geometric modeling approach for 2 × 1 and 3 × 1 twill woven fabric structures is proposed. The precise geometrical description is presented by taking the skewness property into account. In the 2 × 1 and 3 × 1 twill weaves, the twill fabrics are formed of asymmetric floatings in which the length of floating sections was not equal on both surfaces and therefore the equilibrium condition was different from symmetric floatings. The proposed algorithm has three main parts: the first part describes the two-dimensional model of yarn cross-section for twill woven fabric structure, the second part consists of a modeling method for a three-dimensional model in warp/weft yarn, and the third part contains the CAD model. Examples of this approach are demonstrated and compared with a single line of yarn path model and the filament assemble model that excludes the skewness property. The model simulated in this study can improve the visual simulation of the real twill woven fabric and also this geometric model necessary as an input to many computational models for the prediction of the properties of the fabrics. [ABSTRACT FROM AUTHOR]

Poly(lactide) (PLA) is an interesting biodegradable polymer but has limited application because of its brittleness and low thermal stability. We found that both drawbacks of PLA were solved by forming stereocomplexes augmented with natural rubber (NR). Equal amounts of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) stereoisomers were blended to form a stereocomplex (St-PLA). Varying amounts of NR (5-30% by weight) were added simultaneously to equal amounts of the stereo isomers by melt blending. FTIR and XRD spectra demonstrated that, despite the added NR, the stereocomplex structures were still generated and complete. Stereocomplex crystallinity decreased with increasing NR content, verified by DSC and XRD, as well as polarizing optical micrographs which showed fewer spherulites at higher NR content. Measured glass transition temperatures ([T.sub.g]) of St-PLA/NR blends were significantly lower than for neat St-PLA, exhibiting shifts to as low as 46[degrees]C at 30% wt NR content, because of rubber dispersed in St-PLA segments expanding the free volume and enhancing chain mobility. Thermal stability of the blends, estimated by TGA, showed desired results, for example, at the 50% weight loss point, the temperature of all St-PLA/NR blends moved to higher temperatures than neat St-PLA., INTRODUCTION Since pollution from plastic production and waste has become a significant problem, biodegradable polymers, derived from renewable sources such as corn, potato, cassava, cane, etc. [1] has become the [...]

The high cost, low heat resistance, and brittleness of poly(L-lactide) (PLLA) is a significant drawback that inhibits its diffusion into many industrial applications. These weaknesses were solved by forming a polylactide stereocomplex (ST) and blending it with thermoplastic starch (TPS). We blended poly (L-lactide)(PLLA), up to 30% thermoplastic starch, and a chain extender (2%) in an internal mixer, which was then hand-mixed with poly (D-lactide)(PDLA) and injection molded to form specimens, in order to study mechanical, thermal, and crystallization behavior. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (XRD) demonstrated that the stereocomplex structures were still formed despite the added TPS and showed melting points ~55 °C higher than neat PLLA. Furthermore, stereocomplex crystallinity decreased with the increased TPS content. Dynamic mechanical analysis revealed that ST improved PLLA heat resistance, and tensile testing suggested that the TPS improved the elongation-at-break of ST. Moreover, the chain extender reduced the degradation of ST/TPS blends and generally improved ST/TPS composites' mechanical properties. [ABSTRACT FROM AUTHOR]

The effects of annealing time and temperature on the crystallinity of injection-molded poly(lactic acid) (PLA) were investigated using differential scanning calorimetry and wide-angle x-ray diffraction. Differential scanning calorimetry, tensile test, and dynamic mechanical analysis showed that an increase in crystallinity in the PLA parts from the annealing treatment offers several benefits such as a higher glass transition temperature, better heat resistance, and greater storage modulus and tensile strength. Based on the experimental data, the degree of crystallinity, annealing time, and annealing temperature were found to closely follow the time-temperature superposition relationship. Namely, a master curve could be constructed based on either the Wil-liams-Landel-Ferry equation or the Arrhenius relationship by shifting the crystallinity isotherms in the logarithmic scale horizontally along the log-time axis. This relationship provides a quantitative guideline for annealing postinjection-molded PLA parts to improve the heat resistance and mechanical properties. An increase of over 17% and 26% in tensile strength was achieved at an annealing temperature of 80 °C for 30 min and 65°C for 31 h, respectively. POLYM. ENG. SCI., 53:580-588, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION Poly(lactic acid) or polylactide (PLA) is a biodegradable thermoplastic polyester obtained by synthesis of lactic acid (or lactide), which can be produced from renewable resources such as corn or [...]

The effects of incorporating hyperbranched polymers (HBPs) and different nanoclays [Cloisite ® 30B and halloysite nanotubes (HNT)] on the mechanical, morphological, and thermal properties of solid and microcellular poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) were investigated. According to the X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses, Cloisite 30B exhibited a combination of exfoliation and heterogeneous intercalation structure for both solid and microcellular PHBV-12% HBP-2% Cloisite 30B nanocomposites. TEM images indicated that HNTs were uniformly dispersed throughout the PHBV matrix. The addition of 2% nanoclays improved the thermal stability of the resulting nanocomposites. The addition of HBP+poly(maleic anhydride-a/t-1-octa-decene) (PA), Cloisite 30B, and HNT reduced the average cell size and increased the cell density of the microcellular components. The addition of (HBP+PA), Cloisite 30B, and HNT also increased the degree of crystallinity for both solid and microcellular components in comparison with neat PHBV. Also, with the addition of 12% (HBP+PA), the area under the tan - δ curve, specific toughness, and strain-at-break of the PHBV-HBP nano-composite increased significantly for both solid and microcellular specimens, whereas the storage modulus, specific Young's modulus, and specific tensile strength decreased. The addition of 2% nanoclays into the PHBV-HBP nanocomposites improved the storage modulus, specific Young's modulus, and specific tensile strength of the PHBV-HBP-nanoclay-based nanocomposites, but they were still lower than those of the neat PHBV. POLYM. ENG-SCI., 51:1815-1826, 2011. © 2011 Society of Plastics Engineers, INTRODUCTION Broadening the use of biobased and biodegradable polymers such as poly(hydroxyalkanoates) (PHA) can reduce our dependence on petroleum-based polymers, which can have an adverse impact on the environment [1-3]. [...]

Poly(ethylene terephthalate) (PET) resin is one of the most widely used thermoplastics, especially in packaging. Because thermal and hydrolytic degradations, recycled PET (RPET) exhibits poor mechanical properties and lacks moldability. The effects of adding elastomeric modifiers, chain extenders (CE), and poly(butylene adipate-co-terephthalate), PBAT, as a toughener to RPET on its moldability and mechanical property were investigated. Melt blending of RPET with CE, thermoplastic elastomer (TPE), and/or PBAT was performed in a thermokinetic mixer (K-mixer). The blended materials were then injection molded to produce tensile specimens. Various techniques were used to study the mechanical properties, rheological properties, compatibility, and crystallization behavior of the RPET blends. By melt blending with proper additives, recycled PET regained its moldability, thereby enabling the recycling of RPET. Furthermore, the addition of CE greatly enhanced the mechanical properties of RPET. While the RPET and TPE blends also showed improved mechanical properties, the improvement was less significant and the blends were often immiscible due to the difference in polarities between RPET and TPE. Finally, it was found that the mechanical properties of RPET blends depended on the prior thermal history of the material and could be improved with an extra annealing step that increased the degree of crystallinity. POLYM. ENG. SCI., 51:1023-1032, 2011. [C] 2011 Society of Plastics Engineers, INTRODUCTION Poly(ethylene terephthalate) (PET) is one of the most widely used thermoplastic polyesters. PET is extensively used in various applications, such as beverage bottles, fibers, moldings, and sheets because of [...]

Poly(L-lactic acid)/poly(D-lactic acid) (PLLA/PDLA) blends were prepared by hand mixing, followed by injection molding at 210°C to produce tensile specimens. Thermal properties, crystalline structure, and mechanical properties were measured by differential scanning calorimetry (DSC), thermogravimetric analysis, wide-angle X-ray diffraction (XRD), and tensile testing. From the DSC tests of blends ranging from 10% to 30% PDLA in PLLA, the PDLA melting peak was absent and was replaced by a stereocomplex melting peak at 210°C, which was ~50°C higher than that for neat PLLA or PDLA. The reverse blending of PLLA into PDLA showed a similar behavior. Surprisingly, three melting peaks (for PLLA, PDLA, and the complex crystal) appeared in the 1:1 PLLA:PDLA pellet blends. However, the PLLA and PDLA powders (ground to less than 200 μm) and hand mixed, prior to injection molding, showed only small amounts of homocrystals and much higher fractions of stereocomplex crystals (18–44%). Compared to the hand mixed un-ground pellets, molded specimens from the PLLA and PDLA powders also exhibited higher tensile strengths (33–48 MPa) and moduli (1100–1250 MPa). Moreover, the stereocomplex formation was found to enhance the thermal stability compared with those of the pure PLLA and PDLA. [ABSTRACT FROM AUTHOR]

Poly(vinyl alcohol) (PVOH) resin is one of the most widely used water-soluble biodegradable polymer. Because of thermal degradation, PVOH exhibits limited melt processing and lacks moldability. The effects of adding glycerol as plasticizer and banana fibers (BF) to PVOH on its moldability and mechanical property were investigated. Melt blending of PVOH with glycerol and/or BF was performed in an internal mixer. The blended materials were then compression molded to produce tensile specimens. Various characterization techniques were employed to study the mechanical properties, compatibility, and crystallization behavior of the PVOH blends. By melt blending with glycerol, PVOH could be processed but decreased the tensile modulus, tensile strength, and crystallization temperature. Furthermore, the addition of BF enhanced the mechanical and thermal properties and crystallization temperature of plasticized PVOH due to compatibility between the two components. Apart from enhancing the mechanical properties and thermal stability, the incorporation of BF can reduce the production cost. [ABSTRACT FROM AUTHOR]

The effects of poly( d-lactide) (PDLA), nanoclay, talc, and stereocomplex formation were investigated in blends where these materials were added as a minor phase in a major phase of poly( l-lactide) (PLLA). Blends containing 2% PDLA, nanoclay, or talc as nucleants were prepared via melt blending and showed a strong increase in the crystallization rate as revealed by isothermal and nonisothermal crystallization measurements. The blending of 2% PDLA with PLLA led to the highest crystallization rate. Moreover, a stereocomplex formation was observed in a PLLA/PDLA blend (50:50). Wide-angle X-ray diffraction and differential scanning calorimetry verified that complete stereocomplex crystallites that do not form homocrystallites can be achieved. Compared with pure PLLA, the stereocomplex had a higher melting temperature and a higher crystallization temperature, by more than 50°C and 25°C, respectively. [ABSTRACT FROM AUTHOR]

Microcellular injection molding is capable of fabricating light weight, dimensionally stable plastic parts while using less material and energy. Two kinds of blowing agents, namely, supercritical nitrogen and expandable thermoplastic microspheres, were employed to produce foamed polylactic acid parts. The surface characteristics were evaluated with a two-dimensional surface roughness analyzer and a three-dimensional white-light interferometer surface profiler. Through surface roughness comparisons, injection molded American Society for Testing Material tensile test bars with expandable thermoplastic microspheres exhibited better surface quality than their supercritical nitrogen counterparts. The tensile properties of injection molded polylactic acid tensile bars with nitrogen and expandable thermoplastic microspheres at various weight concentrations were investigated. The results showed that the polylactic acid/nitrogen parts possessed a better Young’s modulus and tensile strength. The microstructure on the fractured cross-sectional surfaces was characterized using a scanning electron microscope. As reflected by the testing results, the cell microstructure – such as cell size and cell density, and multi-layered structure with a foamed core sandwiched by skin layers – played an important role in the surface quality and mechanical properties. In addition, while an appropriate expandable thermoplastic microspheres content had a positive effect on the cell microstructure and weight reduction, too high of a concentration of expandable thermoplastic microspheres adversely affected the tensile properties and surface roughness of the microcellular polylactic acid tensile test bars. [ABSTRACT FROM PUBLISHER]