Effects of reactive and nonreactive POSS types on the mechanical,thermal, and morphological properties of plasticized poly(lactic acid)

The aim of this study is to investigate the effects of the reactive and nonreactive polyhedral oligomeric silsesquioxane (POSSs) types and their composition on the mechanical, thermal, and morphological properties of poly(ethylene glycol) plasticized poly(lactic acid) (PLA) composites prepared with melt compounding. The results showed that the incorporation of POSS decreased the melt viscosity of the compounds regardless of POSS type. The lowest viscosity was obtained with epoxy‐POSS, which is the only one that is liquid at processing temperature in comparison to the others. It was revealed from the mechanical tests that the toughness‐related properties such as impact strength and elongation at break improved by the addition of POSS without remarkable deterioration in stiffness. The chemical structure of the POSS influenced the level of dispersion and hence the mechanical performance of the composites. Octaisobutyl‐POSS, being the nonreactive and nonpolar one, had the best dispersion among the other reactive and polar POSS types. The glass transition temperature of the matrix decreased in the presence of POSS types. In addition, the POSS particles also had an impact on the crystallization of PLA. The thermal stability of the composites improved in the presence of POSS particles with respect to the POSS content and the POSS type. POLYM. ENG. SCI., 54:264–275, 2014. © 2013 Society of Plastics Engineers     

Production of poly(lactic acid)/organoclay nanocomposite scaffolds by microcompounding and polymer/particle leaching

Organoclay reinforced poly(lactic acid) (PLA)/poly(vinyl alcohol) (PVA) blend based porous nanocomposite scaffolds are prepared by microcompounding/injection molding and subsequent polymer (PVA)/particle (NaCl) leaching method. The objective of the study is to investigate the effect of clay content on the properties of scaffolds for tissue engineering. It is revealed from X‐ray diffraction and TEM studies that incorporation of PVA to PLA matrix as a polymeric porogen enhance the state of dispersion of clay particles resulting in an exfoliated structure. The porosities of all the scaffolds are higher than 70% and the pores are well‐interconnected as observed by SEM. The addition of clay to the scaffolds improves the compressive modulus. Differential scanning calorimeter analysis shows that T_g of neat‐PLA is shifted to lower values when it is compounded with PVA. As a result, it is demonstrated that the method applied in this work can be a good candidate for production of polymeric scaffolds for tissue engineering applications. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Effects of polyamide 6 incorporation to the short glass fiber reinforced ABS composites: an interfacial approach

The properties of 30 wt% short glass fiber (SGF) reinforced acrylonitrile-butadiene-styrene (ABS) terpolymer and polyamide 6 (PA6) blends prepared with extrusion were studied using the interfacial adhesion approach. Work of adhesion and interlaminar shear strength values were calculated respectively from experimentally determined interfacial tensions and short beam flexural tests. The adhesion capacities of glass fibers with different surface treatments of organosilanes were evaluated. Among the different silanes tested, γ-aminopropyltrimethoxysilane (APS) was found to be the best coupling agent for the glass fibers, possibly, because of its chemical compatibility with PA6. Tensile test results indicated that increasing amount of PA6 in the polymer matrix improved the strength and stiffness of the composites due to a strong acid–base interaction at the interface. Incorporation of PA6 to the SGF reinforced ABS reduced the melt viscosity, broadened the fiber length distributions and increased the toughness of the composites. Fractographic analysis showed that the incorporation of PA6 enhanced the interactions between glass fibers and the polymeric matrix.     

Interfacial strength in short glass fiber reinforced acrylonitrile‐butadiene‐styrene/polyamide 6 blends

The purpose of this study is to derive the apparent interfacial shear strength of short glass fiber reinforced acrylonitrile‐butadiene‐styrene/polyamide 6 (PA6) blends with different PA6 contents. Tensile stress‐strain curves and fiber length distributions are utilized within a continuum micromechanics approach which involves a unified parameter for fiber length distribution efficiency represented as a function of strain. The unique combination of predicted micromechanical parameters is capable of accurately reproducing the mechanical response of the composite to applied strain. In this way, the influence of PA6 on interfacial zone is revealed by outcomes of the predictive method and validated by scanning electron microscopy observations. Favored intermolecular interactions in presence of PA6 chains result in the formation of a PA6 sheathing layer on glass fiber surfaces which in turn causes a drop in the apparent interfacial shear strength. The reason behind is shown to be the shift of the fracture zone from fiber/matrix interface to sheathing layer/matrixinterphase. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Thoughening of poly(lactic acid) with silicone rubber

In this study, poly(lactic acid) (PLA) was blended with silicone rubber (SR) to improve its impact strength and toughness by using dynamic crosslinking in the presence of peroxide during melt compounding. The SR to PLA ratio, peroxide and coagent concentrations were taken as experimental parameters. Blends were evaluated in terms of their thermal properties, tensile and impact strengths, dynamic mechanical properties, and micro‐structure. Results showed that PLA was successfully toughened with SR using dynamic crosslinking. Impact strength and energy of fracture in tensile test improved up to 4 and 10 times, respectively. On the other hand, yield strength and stiffness of blends deteriorated by the incorporation of SR. Thermal analysis pointed out that presence of SR decreased the cold crystallization temperature. It was observed from scanning electron microscopy (SEM) that the energy absorbing mechanism under impact loads in PLA/SR blends is tortuosity in the crack patterns. POLYM. ENG. SCI., 54:2029–2036, 2014. © 2013 Society of Plastics Engineers     

Compatibilization of PLA/PBAT blends by using Epoxy-POSS

Poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) blends were compatibilized using epoxidized polyhedral oligomeric silsesquioxanes (Epoxy-POSS). Three different Epoxy-POSS types were utilized having mono-, tri-, and multi-epoxides per POSS cage. In order to understand the localization of Epoxy-POSS types, wetting coefficients were calculated from surface energy measurements. According to scanning electron microscopy (SEM) and transmission electron microscopy (TEM), it was observed that Epoxy-POSS types mostly located at the interface of PLA/PBAT phases. The compatibilization of PLA and PBAT was shown through the decrease in dispersed particles size and the shifts in glass transition temperatures of phases. Mechanical properties of PLA/PBAT improved in the presence of Epoxy-POSS types. The Izod impact strength and elongation in tensile test values were maximized when 0.5% monoepoxy-POSS was used as compatibilizer. The reactions between Epoxy-POSS and polymers were monitored by Fourier transform infrared (FTIR) analysis and rheology. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47217.     

Overmolded polylactide/jute-mat eco-composites: A new method to enhance the properties of natural fiber biodegradable composites

Environmentally friendly, biodegradable composites were prepared via overmolding of poly(lactic acid) (PLA) onto PLA/jute-mat, named as “ecosheets,” reinforced continuous fiber composite sheets. Film stacking procedure was used to prepare ecosheets via using a hot-press. The fiber orientation was changed as −45°/+45° and 0°/0°. −45°/+45° orientation exhibited higher properties as compared to 0°/0° for ecosheets; therefore, this construction was used to produce overmolded composites (OMCs). The mechanical tests showed that flexural modulus and strength of OMCs were improved in comparison to neat PLA. The dynamic mechanical analysis exhibited that the thermomechanical resistance of PLA was enhanced for OMCs. Scanning electron microscopy investigation showed that the jute/PLA interphase needs to be improved to further increase the properties. It was concluded that one of the biggest advantages of this novel technique was the increase of mechanical properties of PLA without altering the density. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48692.     

The Potential Use of Epoxy-POSS as a Reactive Hybrid Compatibilizers for PLA/PBAT Blends: “Effect of PBAT Molecular Weight and POSS Type”

This article focuses on the effect of molecular weight of poly(butylene adipate-co-terephthalate) (PBAT) on the immiscible poly(lactic acid) (PLA)/PBAT blends compatibilized with epoxidized polyhedral oligomeric silsesquioxanes (Epoxy-POSSs) having different numbers of epoxy groups per molecule. Mechanical, thermomechanical, thermal, rheological, and morphological properties of the blends were investigated as a function of PBAT molecular weight and epoxy-POSS type. Mechanical tests revealed that all epoxy-POSS types significantly improved the performance of the blends containing low-molecular-weight PBAT. On the other hand, epoxy-POSS with three epoxy functional groups (TriEpPOSS) and Epoxy-POSS with multiple-epoxy functional groups (MuEpPOSS) only slightly improved the performance of blends with high-molecular-weight PBAT. Thermomechanical and thermal test results supported that the compatibilization effects of the epoxy-POSSs were more prominent in the PLA/PBAT blends with low-molecular-weight PBAT due to the observation of the shifts in the glass transition temperatures of the PLA phase. According to the rheological results, the addition of epoxy-POSSs increased the interactions between the PLA and PBAT phases much more effectively in the PLA/PBAT with low-molecular-weight PBAT. The dispersed phase size of the PBAT further decreased in the low-molecular-weight PLA/PBAT blend system due to the enhanced compatibility much better. POLYM. ENG. SCI., 60: 398–413, 2019. © 2019 Society of Plastics Engineers     

A modified method for processing and characterization of organoclay‐based poly(ethylene terephthalate) nanocomposite fibers

In the current study, in order to prepare poly(ethylene terephthalate) (PET)/organoclay nanocomposite fibers, a slurry‐compounding method (SCM) was applied and compared to conventional melt‐compounding method (CMM) in terms of the dispersion of organoclays and the performance of the spun and or drawn fibers. The organoclays were synthesized by using three different alkyl phosphonium salts and compared with commercially available alkyl ammonium‐modified organoclays in terms of thermal stability and basal spacing. It was found that the alkyl phosphonium salts exhibited higher thermal stability and basal spacing with respect to commercial alkyl ammonium organoclays. Among them, tributylhexadecylphosphonium bromide resulted in superior properties; therefore, it was used to prepare the nanocomposite PET fibers. The organoclay content of 0.1–1 wt% was taken as the material parameter. It was demonstrated that the SCM yielded better dispersion of organoclays with respect to CMM. The drawn nanocomposite fibers prepared via SCM exhibited improved tensile strength and modulus in comparison to the neat‐PET. The maximum tensile properties for fibers were obtained at 0.5% organoclay loading in SCM. The thermal properties and the percentage of crystallinity were investigated by differential scanning calorimetry analysis. In addition, Fourier transform infrared spectroscopy was utilized to obtain the percentage of crystallinity of the fibers. POLYM. COMPOS., 34:887–896, 2013. © 2013 Society of Plastics Engineers     

Effects of a diisocyanate compatibilizer on the properties of citric acid modified thermoplastic starch/poly(lactic acid) blends

In this article, for the first time in the literature effects of phenylene diisocyanate (PDI)‐based compatibilizer on the physical and chemical properties of citric acid (CA) modified thermoplastic starch (TPS)/poly(lactic acid) (PLA) blends were investigated with respect to PDI and CA content and blend composition. The blends were prepared by melt compounding in a laboratory microcompounder. Fourier transformation infrared spectroscopy results showed that CA interacted with starch and PDI interacted by both starch and PLA through the hydroxyl groups. It was revealed from SEM micrographs that combinatorial usage of CA and PDI resulted in an improved, finer distribution of TPS in PLA matrix. This improvement affected the mechanical properties of blend, especially the toughness related properties such as impact strength and elongation at break. The thermal properties such as T_g and T_m revealed from differential scanning calorimeter analysis were in line with the morphological structure of the blends by suggesting the compatibilization phenomena in the presence of PDI and CA together. Thermogravimetric analysis showed that compatibilization of two phases improved the thermal stability of the blends. As a general conclusion, the combinatorial usage of PDI and CA can be utilized to obtain tougher PLA/TPS blends‐based materials to overcome the brittleness problem. POLYM. ENG. SCI., 53:2183–2193, 2013. © 2013 Society of Plastics Engineers