Mechanical, Hydrophobic, and Barrier Properties of Nanocomposites of Modified Polypropylene Reinforced with Low-Content Attapulgite.

Attapulgite (ATT) has never been used as a barrier additive in polypropylene (PP). As a filler, ATT should be added in high content to PP. However, that would result in increased costs. Moreover, the compatibility between ATT and the PP matrix is poor due to the lack of functional groups in PP. In this study, carboxylic groups were introduced to PP to form a modified polypropylene (MPP). ATT was purified, and a low content of it was added to MPP to prepare MPP/ATT nanocomposites. The analysis from FTIR indicated that ATT could react with MPP. According to the results of oxygen and water permeability tests, the barrier performance of the nanocomposite was optimal when the ATT content was 0.4%. This great improvement in barrier performance might be ascribed to the following three reasons: (1) The existence of ATT extended the penetration path of O2 or H2O molecules; (2) O2 or H2O molecules may be adsorbed and stored in the porous structure of ATT; (3) Most importantly, -COOH of MPP reacted with -OH on the surface of ATT, thereby the inner structure of the nanocomposite was denser, and it was less permeable to molecules. Therefore, nanocomposites prepared by adding ATT to MPP have excellent properties and low cost. They can be used as food packaging materials and for other related applications.

Enhancing Performance of Thin-Film Nanocomposite Membranes by Embedding in Situ Silica Nanoparticles.

In this work, silica nanoparticles were produced in situ, to be embedded eventually in the polyamide layer formed during interfacial polymerization for fabricating thin-film nanocomposite membranes with enhanced performance for dehydrating isopropanol solution. The nanoparticles were synthesized through a sol-gel reaction between 3-aminopropyltrimethoxysilane (APTMOS) and 1,3-cyclohexanediamine (CHDA). Two monomers-CHDA (with APTMOS) and trimesoyl chloride-were reacted on a hydrolyzed polyacrylonitrile (hPAN) support. To obtain optimum fabricating conditions, the ratio of APTMOS to CHDA and reaction time were varied. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) were used to illustrate the change in morphology as a result of embedding silica nanoparticles. The optimal conditions for preparing the nanocomposite membrane turned out to be 0.15 (g/g) APTMOS/CHDA and 60 min mixing of APTMOS and CHDA, leading to the following membrane performance: flux = 1071 ± 79 g∙m-2∙h-1, water concentration in permeate = 97.34 ± 0.61%, and separation factor = 85.39. A stable performance was shown by the membrane under different operating conditions, where the water concentration in permeate was more than 90 wt%. Therefore, the embedment of silica nanoparticles generated in situ enhanced the separation efficiency of the membrane.

Barrier Properties and Hydrophobicity of Biodegradable Poly(lactic acid) Composites Reinforced with Recycled Chinese Spirits Distiller's Grains.

Adding natural biomass to poly(lactic acid) (PLA) as a reinforcing filler is a way to change the properties of PLA. This paper is about preparing PLA/biomass composites by physically melting and blending Chinese Spirits distiller's grains (CSDG) biomass and PLA to optimize the composite performance. Composites of modified PLA (MPLA) with varying amounts of CSDG were also prepared by the melt-mixing method, and unmodified PLA/CSDG composites were used as a control group for comparative analysis. The functional groups of MPLA enhanced the compatibility between the polymer substrate and CSDG. The composite water vapor/oxygen barrier and mechanical properties were studied. It was found that the barrier and mechanical properties of MPLA/CSDG composites were significantly improved. SEM was adopted to examine the tensile section structure of the composites, and the compatibility between the filler and the matrix was analyzed. An appropriate amount of CSDG had a better dispersibility in the matrix, and it further improved the interfacial bonding force, which in turn improved the composite mechanical properties. X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry were conducted to determine the crystalline properties and to analyze the stability of the composites. It was found that the CSDG content had a significant effect on the crystallinity. Barrier and biodegradation mechanisms were also discussed.

Barrier performance and biodegradability of antibacterial poly(butylene adipate-co-terephthalate) nanocomposites reinforced with a new MWCNT-ZnO nanomaterial.

A new nanomaterial or nano-filler in the form of multiwalled carbon nanotube-zinc oxide (MWCNT-ZnO) was synthesized for the purpose of modifying poly(butylene adipate-co-terephthalate) (PBAT) and its derivative (modified PBAT or MPBAT) through a melt-blending method (MPBAT was obtained by introducing maleic anhydride groups into PBAT). The effect of the new nano-filler on the properties of resultant nanocomposites was determined from the characterization of mechanical properties, morphology, crystallinity, thermal stability, barrier properties, hydrophilicity, conductivity, antibacterial property, and biodegradability. The results showed that MPBAT nanocomposites had stronger mechanical properties, better barrier properties, and higher electrical conductivity than PBAT nanocomposites. Scanning electron microscopy illustrated that MWCNT-ZnO had better compatibility with MPBAT than with PBAT. At 0.2% MWCNT-ZnO, the MPBAT/MWCNT-ZnO nanocomposite film exhibited the greatest mechanical properties (17.74% increase in tensile strength, 22.17% in yield strength, and 14.29% in elongation at break). When the MWCNT-ZnO content was 0.4%, the nanocomposite film demonstrated the best water vapor barrier ability (an increase of 30.4%). The MPBAT/MWCNT-ZnO film with 0.6% MWCNT-ZnO turned out to have the best oxygen barrier performance (an increase of 130% relative to pure PBAT). It was shown from the results of antibacterial evaluation that the new nanomaterial could impart PBAT and MPBAT with antibacterial activity. The biodegradability tests indicated that an MWCNT-ZnO content of 0.2% could slightly reduce the biodegradability, and when the content was higher than 0.2%, the weight loss rate would increase.

Cosolvent-Driven Interfacial Polymerization for Superior Separation Performance of Polyurea-Based Pervaporation Membrane.

A thin-film composite (TFC) polyurea membrane was fabricated for the dehydration of an aqueous tetrahydrofuran (THF) solution through interfacial polymerization, wherein polyethyleneimine (a water-soluble amine monomer) and m-xylene diisocyanate (an oil-soluble diisocyanate monomer) were reacted on the surface of a modified polyacrylonitrile (mPAN) substrate. Cosolvents were used to tailor the membrane properties and increase the membrane permeation flux. Four types of alcohols that differed in the number of carbon (methanol, ethanol, isopropanol, and tert-butanol) were added as cosolvents, serving as swelling agents, to the aqueous-phase monomer solution, and their effect on the membrane properties and pervaporation separation was discussed. Attenuated total reflection Fourier transform infrared spectroscopy confirmed the formation of a polyurea layer on mPAN. Field emission scanning electron microscopy and surface water contact angle analysis indicated no change in the membrane morphology and hydrophilicity, respectively, despite the addition of cosolvents for interfacial polymerization. The TFC membrane produced when ethanol was the cosolvent exhibited the highest separation performance (permeation flux = 1006 ± 103 g·m-2·h-1; water concentration in permeate = 98.8 ± 0.3 wt.%) for an aqueous feed solution containing 90 wt.% THF at 25 °C. During the membrane formation, ethanol caused the polyurea layer to loosen and to acquire a certain degree of cross-linking. The optimal fabrication conditions were as follows: 10 wt.% ethanol as cosolvent; membrane curing temperature = 50 °C; membrane curing time = 30 min.

Optimal Performance of Thin-Film Composite Nanofiltration-Like Forward Osmosis Membranes Set Off by Changing the Chemical Structure of Diamine Reacted with Trimesoyl Chloride through Interfacial Polymerization.

Thin-film composite (TFC) polyamide membranes formed through interfacial polymerization can function more efficiently by tuning the chemical structure of participating monomers. Accordingly, three kinds of diamine monomers were considered to take part in interfacial polymerization. Each diamine was reacted with trimesoyl chloride (TMC) to manufacture TFC polyamide nanofiltration (NF)-like forward osmosis (FO) membranes. The diamines differed in chemical structure; the functional group present between the terminal amines was classified as follows: aliphatic group of 1,3-diaminopropane (DAPE); cyclohexane in 1,3-cyclohexanediamine (CHDA); and aromatic or benzene ring in m-phenylenediamine (MPD). For FO tests, deionized water and 1 M aqueous sodium sulfate solution were used as feed and draw solution, respectively. Interfacial polymerization conditions were also varied: concentrations of water and oil phases, time of contact between the water-phase solution and the membrane substrate, and polymerization reaction time. The resultant membranes were characterized using attenuated total reflectance-Fourier transform infrared spectroscopy, field emission scanning electron microscopy, atomic force microscopy, and surface contact angle measurement to identify the chemical structure, morphology, roughness, and hydrophilicity of the polyamide layer, respectively. The results of FO experiments revealed that among the three diamine monomers, CHDA turned out to be the most effective, as it led to the production of TFC NF-like FO membrane with optimal performance. Then, the following optimum conditions were established for the CHDA-based membrane: contact between 2.5 wt.% aqueous CHDA solution and polysulfone (PSf) substrate for 2 min, and polymerization reaction between 1 wt.% TMC solution and 2.5 wt.% CHDA solution for 30 s. The composite CHDA-TMC/PSf membrane delivered a water flux (Jw) of 18.24 ± 1.33 LMH and a reverse salt flux (Js) of 5.75 ± 1.12 gMH; therefore, Js/Jw was evaluated to be 0.32 ± 0.07 (g/L).

Characterization of network bonding created by intercalated functionalized graphene and polyvinyl alcohol in nanocomposite films for reinforced mechanical properties and barrier performance.

Graphene that consists of less than 10 layers is expensive; moreover, it tends to agglomerate. These disadvantages restrict its utility. In this regard, the present study aimed to reduce the number of layers of a functionalized graphene (FG) with 10-30 layers to less than 10 layers by using an ultrasonic processor. We prepared nanocomposite films of polyvinyl alcohol (PVA) incorporated with FG by a simple hydrothermal method and ultrasonic dispersion. Oxygen transmission rate and water vapor permeability were considerably increased on account of modifying PVA with FG. Furthermore, the mechanical properties, thermostability, and barrier properties were improved. The barrier efficiency of the nanocomposites at different temperatures remained high for long periods of operation because of the network bonding. A simple procedure involving relatively low-cost nanomaterials could unlock the potential of nanocomposite FG/PVA films in the fields of coating, packaging, and semiconductor materials.

Antibacterial Property and Cytotoxicity of a Poly(lactic acid)/Nanosilver-Doped Multiwall Carbon Nanotube Nanocomposite.

A novel method was used to synthesize a nanosilver-doped multiwall carbon nanotube (MWCNT-Ag), and subsequently, the novel poly(lactic acid) (PLA)- and MWCNT-Ag-based biocompatible and antimicrobial nanocomposites were prepared by melt blending. Based on energy dispersive X-ray spectrometry images, an MWCNT-Ag was successfully synthesized. The effect of the MWCNT-Ag on the PLA bionanocomposites was investigated by evaluating their thermal and mechanical properties, antifungal activity, and cytotoxicity. The nanocomposites exhibited a high degree of biocompatibility with the MWCNT-Ag content, which was less than 0.3 phr. Furthermore, tensile strength testing, thermogravimetric analysis, differential scanning calorimetry, and antibacterial evaluation revealed that the tensile strength, thermostability, glass transition temperature, and antibacterial properties were enhanced by increasing the MWCNT-Ag content. Finally, hydrolysis analysis indicated that the low MWCNT-Ag content could increase the packing density of PLA.

Biocompatibility and characterization of polylactic acid/styrene-ethylene-butylene-styrene composites.

Polylactic acid (PLA)/styrene-ethylene-butylene-styrene (SEBS) composites were prepared by melt blending. Differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WXRD) were used to characterize PLA and PLA/SEBS composites in terms of their melting behavior and crystallization. Curves from thermal gravimetric analysis (TGA) illustrated that thermostability increased with SEBS content. Further morphological analysis of PLA/SEBS composites revealed that SEBS molecules were not miscible with PLA molecules in PLA/SEBS composites. The tensile testing for PLA and PLA/SEBS composites showed that the elongation at the break was enhanced, but tensile strength decreased with increasing SEBS content. L929 fibroblast cells were chosen to assess the cytocompatibility; the cell growth of PLA was found to decrease with increasing SEBS content. This study proposes possible reasons for these properties of PLA/SEBS composites.

Preparation and Characterization of Bioplastic-Based Green Renewable Composites from Tapioca with Acetyl Tributyl Citrate as a Plasticizer.

Granular tapioca was thermally blended with poly(lactic acid) (PLA). All blends were prepared using a plasti-corder and characterized for tensile properties, thermal properties and morphology. Scanning electron micrographs showed that phase separation occurred, leading to poor tensile properties. Therefore, methylenediphenyl diisocyanate (MDI) was used as an interfacial compatibilizer to improve the mechanical properties of PLA/tapioca blends. The addition of MDI could improve the tensile strength of the blend with 60 wt% tapioca, from 19.8 to 42.6 MPa. In addition, because PLA lacked toughness, acetyl tributyl citrate (ATBC) was added as a plasticizer to improve the ductility of PLA. A significant decrease in the melting point and glass-transition temperature was observed on the basis of differential scanning calorimetry, which indicated that the PLA structure was not dense after ATBC was added. As such, the brittleness was improved, and the elongation at break was extended to several hundred percent. Therefore, mixing ATBC with PLA/tapioca/MDI blends did exhibit the effect of plasticization and biodegradation. The results also revealed that excessive plasticizer would cause the migration of ATBC and decrease the tensile properties.

Multilayered poly(vinylidene fluoride) composite membranes with improved interfacial compatibility: correlating pervaporation performance with free volume properties.

A spin-coating process integrated with an ozone-induced graft polymerization technique was applied in this study. The purpose was to improve the poor interfacial compatibility between a selective layer of poly(2-hydroxyethyl methacrylate) (PHEMA) and the surface of a poly(vinylidene fluoride) (PVDF) substrate. The composite membranes thus fabricated were tested for their pervaporation performance in dehydrating an ethyl acetate/water mixture. Furthermore, the composite membranes were characterized by field emission scanning electron microscopy (FE-SEM) for morphological change observation and by Fourier transform infrared spectroscopy equipped with attenuated total reflectance (ATR-FTIR) for surface chemical composition analysis. Effects of grafting density and spin-coating speed on pervaporation performance were examined. The composite membrane pervaporation performance was elucidated by means of free volume and depth profile data obtained with the use of a variable monoenergy slow positron beam (VMSPB). Results indicated that a smaller free volume was correlated with a higher pervaporation performance of a composite membrane consisting of a selective layer of spin-coated PHEMA on a PHEMA-grafted PVDF substrate (S-PHEMA/PHEMA-g-PVDF). The composite membrane depth profile illustrated that an S-PHEMA layer spin-coated at a higher revolutions per minute (rpm) was thinner and denser than that at a lower rpm.

Solving the charging effect in insulating materials probed by a variable monoenergy slow positron beam.

A variable monoenergy slow positron beam (VMSPB) operating at a high vacuum on insulating materials encounters a problem of significant surface charging effect with time. As a result, positronium formation is inhibited, and the positron annihilation radiation counting rate is reduced; these consequently distorted the experimental positron annihilation and results. To solve such problems, a technique of depositing an ultrathin layer of sputtering noble metals on insulators is developed. We report a successful method of sputtering a few atomic layers of platinum (∼1 nm) on a polyamide membrane to completely remove the charging effect for VMSPB applications in insulators.

Effects of surface properties of different substrates on fine structure of plasma-polymerized SiOCH films prepared from hexamethyldisiloxane (HMDSO).

In this study, Doppler broadening energy spectroscopy (DBES) combined with slow positron beam was used to discuss the effect of substrate types on the fine structure of a plasma-polymerized SiOCH layer as a function of depth. From the SEM pictures, the SiOCH films formed on different substrates showed hemispherical macrostructures, and the deposition rate was dependent on the mean pore size. It appears that the morphology of the plasma-polymerized SiOCH films was associated with the porosity-related characteristics of the substrate such as the size/shape of pores. As deposited on the MCE-022 substrate (mixed cellulose esters membrane with a mean pore size of 0.22 µm) with a nodular structure, the SiOCH films had pillar-like structures and high gas permeabilities. DBES results showed that the SiOCH films deposited on different substrates were composed of three layers: the SiOCH bulk layer, the transition layer, and the substrate. It was observed that the microstructure of the SiOCH films was affected layer by layer; a higher surface pore size in the substrates induced thicker transition layers with higher microporosities and led to thinner bulk layers having higher S parameter values during the plasma polymerization. It was also observed that the change in O(2)/N(2) selectivity was consistent with the DBES analysis results. The gas separation performance and DBES analysis results agreed with each other.