Journal of Polymers and the Environment

Green composites of polypropylene (PP) and corncob (CCB) agricultural residue with CCB content ranging from 5 to 30 wt% were compounded by melt extrusion and their properties investigated by density measurements, thermogravimetric analyses, differential scanning calorimetry, scanning electron microscopy (SEM) and tension, flexural and impact properties. Properties were dependent on CCB content. SEM micrographs showed that PP/CCB composites are composed of all layers of the corncob, but with a higher content of woody ring and pith. Composites with CCB up to 20 wt% presented particles evenly dispersed into PP matrix and density values ranging from 0.929 to 1.026 g/cm3. Thermal analyses showed that CCB is thermally stable up to 200 °C, ensuring that no degradation took place during processing, and PP/CCB composites are more crystalline than neat PP. Tensile strength and elongation at break of the composites decreased respectively from 30 to 20 MPa, and 22.7 to 3.7%, and the elastic modulus increased while the impact strength remained practically constant at 14 J/m for the filling contents tested. Elastic and flexural moduli increased respectively from 906 MPa to 1.1 GPa and from to 1.26 to 1.81 GPa with corncob addition.

In this work, the optimum condition for the adsorption of Reactive Blue 19 dye onto Fe3O4 functionalized with hyperbranched polyethylenimine (Fe@HPEI) was determined using response surface methodology. The properties of synthesized magnetic Fe@HPEI nanoparticles were ascertained using FTIR, SEM, TEM, VSM and zeta potential measurement. The experimental adsorption data indicating the positive effect of adsorbent dose and contact time, and the negative effect of pH, initial dye concentration and ionic strength on dye adsorption. At optimal condition; pH 3.4, contact time 25 min, adsorbent dose 0.4 g/L and initial dye concentration 113 mg/L, Fe@HPEI nanoparticles removed dye up to 99.27%. The maximum experimental dye adsorption was near to the predicted value of 100%, which confirmed the reliability of the selected statistical model. The dye adsorption data were fitted well to Langmuir isotherm and pseudo-second-order kinetic, and the maximum adsorption capacity was 500 mg/g. Totally, Fe@HPEI as an effective superadsorbent can be repeatedly utilized for the adsorption of dye from the aqueous environment.

Bacterial cellulose (BC), a green biopolymer synthesized by certain bacteria, has been widely used for supporting different metal or their oxide nanoparticles which were utilized for different purposes. In this article, we report on using BC as a support for transition metal nanoparticles for catalysis purpose of organic pollutants. BC was synthesized using Gluconacetobacter xylinum. Then the copper (Cu) nanoparticles were synthesized by a quick procedure of microwave heating of the CuSO4 and hydrazine mixed aqueous solution in the presence of carboxymethyl cellulose (CMC). Typically, 10 μL suspension of the CMC stabilized Cu nanoparticles was coated on the BC nanofibers (CMC-Cu-BC) and further used for the catalytic reductions of methylene blue, 4-nitrophenol and in their mixed solution by sodium borohydride. All the samples were also characterized by X-ray diffraction, thermogravimetric analysis, and field emission scanning electron microscope. Our finding suggests that supported Cu nanoparticles catalyst performance was slower than its suspension. However, the ease of separation of the supported CMC-Cu-BC was appealing to be used.

In this study we investigated the role of the water content of extrudates had in foaming capacity and searched for the water content giving the greatest expansion of starch extrudates. Porous structures based on potato amylopectin starch were prepared by extrusion followed by a microwave foaming process. Starch was first extruded with water, in order to incorporate water in the granular structure and achieve gelatinization. Extrudates were conditioned at humidities ranging from 11% to 97%. The water content in the starch extrudates was studied by a water vapor sorption isotherm study. Extrudates were analyzed with light microscopy and wide angle X-ray scattering studies to determine degree of crystallinity. In the second step, extrudates were foamed in a microwave oven. As the water started to boil, it acted as a blowing agent, leaving a porous closed-cell starch structure. The densities and the expansion ratios of the foamed samples are determined. Porosity was studied with environmental scanning electron microscopy. Mechanical properties as a function of the surrounding humidity were analyzed with dynamic mechanical analysis. We found that the maximal degree of expansion was in extrudates conditioned at 33% and 54% RH and having water content of 11.2% and 13.4%, respectively. This level of water is sufficient to expand the extrudate to a maximum level but not high enough to plasticize the starch and cause cell collapse after treatment.

The utilization of forest auxiliary products and their conversion into products with higher added value is important for the use of renewable resources. For this purpose, acorns belonging to the Q. coccifera species were collected in November, which is their ripening period, and dried and ground in the laboratory. Then, acorn starch (AS) was isolated from the sieved acorn flour. For 5 g of this isolated AS, hydroxypropyl acorn starch (HPAS) with the highest molar substitution (MS = 0.319) was synthesized by optimizing at 45 °C for 5 h with 30 g of propylene oxide and 1.88 g of NaOH. The structures of HPASs synthesized were characterized by FT-IR, XRD and 1H (13C)-NMR spectroscopy, and their MS values were determined. In addition, surface morphologies with SEM images and thermal stability with DTA-TG thermograms were examined. Since hydroxypropyl acorn starch has not been synthesized from acorn starch before, this study contributed to the literature and science. It has been understood that HPASs can also be used in many areas where hydroxypropyl starch is used.

In this study, the biodegradation of PLA films using microorganisms from Lake Bogoria (Kenya) were investigated. The biodegradation tests done using certain strains of thermophilic bacteria showed faster biodegradation rates and demonstrated temperature dependency. The biodegradation of the PLA films was studied using Gel Permeation Chromatography (GPC) and light microscopy. The biodegradation of PLA was demonstrated by decrease in molecular weight. The preparation and characterization of PLA/Gum Arabic blends were also investigated using DSC, TGA, TMA and NMR. In summary, the results obtained in this research show that PLA films undergo fast biodegradation using thermophiles isolated from Lake Bogoria. The PLA/GA blends studies show it is possible to prepare films of varying hydrophobic–hydrophilic properties for various applications.

Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were used to study the effect of talc on the crystallization properties and morphology of PVA/talc composite films from the perspective of heterogeneous nucleation effect. The Mo Zhishen equation and Avrami equation were used to study the crystallization kinetics behavior, and successive self-nucleation annealing (SSA) method was used to analyze the wafer thickness at various melting temperatures. PVA films were prepared by flow-casting method, and talc was added as inorganic nucleating agent to improve the crystallinity of PVA. The results show that the addition of talc to the PVA film promotes its crystallization, and as the content of the nucleating agent increases, the crystallinity tends to increase. Due to the increase of nucleation point, the proportion of thinner wafers increases, and the gap of wafer thickness becomes smaller, and the wafer thickness becomes uniform. These results show that talc regulates the crystallization of PVA, improves the crystallinity and crystallization rate of PVA. Talc has heterogeneous nucleation effect on PVA films.

Novel thermoresponsive polymer conjugates based on microbial polyesters and poly-N-isopropyl acryl amide, PNIPAM, have been reported. The unsaturated poly-3-hydroxy alkanoates, poly (3-hydroxy undecenoate), PHU, and 1:1 mixture of 10-undecenoic acid and soy oil acids, PHU-Sy, were brominated by using bromine in the dark, at room temperature. Brominated PHAs were transformed to macro reversible addition–fragmentation chain transfer (RAFT) agents via the substitution reaction with potassium ethyl xanthate. RAFT polymerization of N-isopropyl acryl amide, NIPAM, was initiated by the PHA-derivative containing xanthate pendant groups in order to obtain brush type PHA-g-PNIPAM thermo responsive amphiphilic graft copolymers. The water uptake of the PHU-g-PNIPAM and PHU-Sy-g-PNIPAM amphiphilic graft copolymers changed from 50 % to completely soluble in water. Structural and thermal characterization of the novel conjugates were carried out by using 1H NMR, GPC, DSC and TGA techniques.

Nanocomposites based on waterborne poly(urethane-urea)s (NWPUU) containing hydrophilic montmorillonite (MMT) clay, reduced graphene oxide (rGO) or MMT/rGO hybrids were produced by a green synthesis method. Polymer matrices were based on poly(ethylene glycol-block-propylene glycol) (PEG-b-PPG) (with different contents of PEG-based segments), poly(propylene glycol) (PPG), isophorone diisocyanate (IPDI), dimethylolpropionic acid (DMPA) and hydrazine. Aqueous dispersions were characterized in terms of particle hydrodynamic diameter (DH) and rheological parameters and respective cast films were investigated by X-ray diffraction (XRD), low-field nuclear magnetic resonance (NMR) relaxometry and Fourier-transform infrared spectrometry (FTIR). Pseudoplastic dispersions with DH < 200 nm were stable for more than 12 months. The formation of exfoliated structures suggested the homogeneous nanodispersion of MMT silicate layers and rGO nanosheets. MMT/rGO synergism and layer-to-layer interactions suggested segregation of phases. Hydrogen bonds between polar groups of nanoloads and rigid segments of WPUU influenced the structure and molecular dynamics of the chains.