Elastomers show improved properties when reinforced with nanoclay at low filler loadings, but dispersion of the clay is difficult in non‐polar polymers, such as ethylene propylene diene monomer (EPDM). In this work several compatibilization approaches were studied, including the addition of EPDM modified with maleic anhydride (EPDM‐g‐MA) and the use of organoclay modified with maleic anhydride‐grafted liquid vinyl polybutadiene (LVPB‐g‐MA). The use of LVPB‐g‐MA‐modified organoclay increased the degree of dispersion as measured by X‐ray diffraction, giving increased thermal stability and modulus, and decreased swelling. Flame resistance was poorer for the EPDM/LVPB‐g‐MA‐modified organoclay system compared to the unmodified EPDM/organoclay compound. The resistivity of the nanoclay‐filled composites was lower than the reference EPDM compound, but dielectric properties for the LVPB‐g‐MA modified organoclay were similar to the reference.
New talc/PBAT hybrid materials were prepared through reactive extrusion. First, PBAT was free‐radically grafted with MA to improve the interfacial adhesion between PBAT and talc. Then, the resulting MA‐g‐PBAT was reactively melt‐blended with talc through esterification reactions of MA moieties with the silanol functions from talc. Sn(Oct)2 and DMAP were used as catalysts. Interestingly, the tensile properties for these compatibilized composites were improved due to a better interfacial adhesion between both partners. XPS showed the formation of covalent ester bonds between the silanol functions from talc particles, and the MA moieties grafted onto the polyester backbones.
PLLA and stereocomplexed polylactide (sc‐PLA) nanofibers were formed by electrospinning solutions of the polymers in HFIP. A highly semi‐crystalline sc‐PLA nanofiber having only sc crystallites was confirmed by WAXD analysis. The diameters of the nanofibers of both polymers decreased slightly when they were annealed at 60 °C, which was near Tg. Enzyme degradation of both as‐spun PLLA and sc‐PLA nanofibers by proteinase K from Tritirachium album was carried out. The rate of degradation of the nanofibers can be controlled by varying annealing conditions, hence the extent of crystallinity.
PP‐g‐MA‐layered EGO composites were prepared directly by solution blending. Two types of PP‐g‐MA/EGO composites were prepared using different mixing methods: distributive and dispersive. In this study, the effects of the mixing method of EGO on the crystalline structure and thermo‐mechanical properties of PP‐g‐MA/EGO composites are reported. WAXD exhibited a shift in 2θ of the monoclinic (α) phase of PP‐g‐MA and (002) EGO peaks for PP‐g‐MA/EGO layered composites, which indicated a modification of the crystalline structure of PP‐g‐MA in the layered composites. DSC exhibited a single characteristic melting peak of monoclinic (α) crystalline phase PP‐g‐MA. The incorporation of EGO increased Tc indicating that the EGO acted as a nucleating agent for PP‐g‐MA. The crystallinity of the PP‐g‐MA/EGO composites was found to be dependent on the mixing method. Thermogravimetry demonstrated that PP‐g‐MA in the presence of EGO has higher degradation temperature, suggesting that the graphite particles acted as a thermal barrier material for PP‐g‐MA. DMA indicated that incorporation of EGO into PP‐g‐MA increased the storage modulus, due to the hydrogen bonding between EGO and MA of PP‐g‐MA.
PLA biodegradable composites reinforced with various silk fibroin powder contents (0, 1, 3, 5 and 7 wt.‐%) were prepared by solution processing technique using CH2Cl2 as solvent. After that the composites and virgin PLA were foamed by using supercritical CO2. The influence of silk contents on PLA/silk fibroin powder composite foams were investigated by using SEM, XRD and DSC. Compared with PLA foam, the composite foams exhibited a reduction in cell size and increase in cell density at high silk content. With an increase in saturation temperature and pressure, the cell size was increasing and both the cell density and foam density were decreased simultaneously.
The influence of talc loading on phase morphology of PLA/PCL/talc composites and improvement in resulting properties are reported. Talc‐based composites of PLA/PCL blends were prepared by melt blending. SEM analysis demonstrates that PLA appears as discrete domain phase, while PCL acts as a bulk phase in the blend. Talc addition decreases PLA domain sizes and voids in the matrix. This results in significant improvement of oxygen and water vapor barrier properties of composite by 33 and 25%, respectively, at 3 wt.‐% talc loading. DSC shows that talc acted as nucleating agent for PCL phase in the composite and improves its crystallinity. Various theoretical models based on dispersion and filler geometry are used to predict the tensile modulus and oxygen permeability.
A two‐level factorial experimental design was used to examine the combined effects of o‐MMT gallery polarity, surface modification of MDH, MA‐g‐PP and antioxidant addition, together with processing variables, on the burning behaviour and thermal stability of ternary composites based on PP, MDH and o‐MMT. Regression equations highlighted the detrimental effect of o‐MMT intercalants and possible improvement in the dispersion of o‐MMT at higher MDH levels. A polar gallery environment (providing quat OH groups) led to increased char formation, and MA‐g‐PP combined with o‐MMT led to a higher oxidation onset temperature. Addition of o‐MMT to PP/MDH composites can lead to a reduction in the level of MDH required for effective flame retardation.
Aluminum‐oxide‐coated PLA pellets, particles derived from aluminum oxide sol‐gel, and calcinated α‐Al2O3 powders were used to fabricate PLA/AlOx composites. The formation of aluminum oxide was confirmed by FTIR and EDS. SEM images suggested the melt compounding system provided a fairly homogeneous dispersion of AlOx particles in the PLA matrix. XRD analysis showed PLA and PLA/AlOx composites were both amorphous. The incorporation of AlOx particles did not alter the melting temperature of PLA. However, the shape and intensity of the melting endotherms was significantly changed, suggesting bimodal melting behavior. UV‐Vis transmission spectra suggested that PLA/AlOx composites may act as a better UV barrier than neat PLA.
Biofibers such as soy hull, switchgrass, miscanthus, and their hybrids are used as reinforcements to engineer green composites in poly(3‐hydroxybutyrate‐co‐valerate) and polylactide blends through melt mixing. The physico‐mechanical performance of the composites is evaluated by means of mechanical testing, DSC and SEM. The combination of agricultural residues as hybrids is shown to reduce supply chain concerns for injection‐molded green composites. The use of inexpensive biofibers and their hybrids proves an alternate way of getting cheap sustainable materials with better performance.
Boehmite alumina nanoparticles are added to PP‐g‐MAH‐compatibilized blends of PA 12 and PP to study the effects of nanoparticle loading in the resulting composites. WAXD and SEM data suggest that the nanoparticles enhanced the coalescence of PP. DSC, DMA, and TGA reveal that the final properties such as crystallization temperature, flexural storage modulus, thermal degradation temperature, etc., improve with increasing nanoparticle loading for blend/based composites. FTIR results show that the nanoparticles interfere with the interfacial activity at 5 wt% nanoparticle loading. All results are compared between the neat polymers and the compatibilized blend and show that despite a slight increase in dispersed‐phase domain size, all other properties improve with the addition of AlO(OH).
A comparative study of the preparation and properties of composites of PCL with cellulose microfibres (CFs) containing butanoic‐acid‐modified cellulose (CB) or PCL grafted with maleic anhydride/glycidyl methacrylate as compatibilizers, is reported. The composites are obtained by melt mixing and analyzed using SEM, DSC, TGA, XRD, FT‐IR, NMR and tensile tests. An improved interfacial adhesion is observed in all compatibilized composites, as compared to PCL/CF. The crystallization behavior and crystallinity of PCL is largely affected by CF and CB content. Composites with PCL‐g‐MAGMA display higher values of tensile modulus, tensile strength and elongation at break.
In recent years TPS has attracted more and more research interest as a promising replacement for commodity polymers in some applications. In this paper, a novel manufacturing technology to produce PLA fiber reinforced biodegradable TPS composite, and the microstructure and tensile properties of the composite, were first reported. PLA micro/sub‐micro fibers were generated in situ by elongational flow during die extrusion and subsequent hot stretching. The addition of 10% PLA significantly increased the drawability of TPS. Compared to direct extrusion, hot stretching tripled the tensile strength of the composite to 34 MPa. Extensive PLA fibrillation was evident in the composite. The generated PLA fibers measured ca. 400 nm in diameter with a large L/D ratio.
This paper analyzes the thermal and thermo‐oxidative degradation behavior, phase separation, melting, and crystallization of blends consisting of isotactic poly(propylene) (IPP) and poly(propylene) grafted with maleic anhydride (PP‐g‐MA). It has been established that, depending on the blend composition and crystallization/preparation procedure, the blends of IPP and PP‐g‐MA can either co‐crystallize or evidence phase separation. This conclusion has been attained by comparing the DSC results of crystallization under dynamic and isothermal conditions with X‐ray diffraction results. On the basis of the obtained results, the optimum mixing ratios have been established as 95–85 wt.‐% IPP/5–15 wt.‐% PP‐g‐MA. Thermo‐oxidative behavior has been studied by thermogravimetry and differential thermal analysis.
Factorial design analyses and numerical optimization are performed to establish material compositions (wood flour content, particle size, and impact modifier content) and mechanical property relationships for PLA/wood flour composites. Numerical optimization produces two scenarios based on materials compositions to manufacture composites with similar mechanical properties as unfilled PLA. High wood flour and impact modifier contents are required for composites made with fine wood flour particles, whereas the formulation requires low wood flour content and excludes impact modifiers for composites with coarse wood flour particles. These optimization solutions are validated experimentally.
A blend composition of poly(3‐hydroxybutyrate‐co‐valerate) and polylactide is used as a bioplastic matrix and reinforced with soy hull to engineer novel green composites. A comparative study with soy‐hull‐reinforced polypropylene composite system is performed. A compatibilizer is used to engineer the novel class of green composites with a balanced stiffness and toughness performance with the target to substitute PP‐based composites. The flexural and impact strength along with hydrophobicity of compatibilized composites are improved significantly over the noncompatibilized counterpart. The fiber/matrix interaction is investigated by SEM. These green composites have the potential to substitute PP‐based composites in some applications.
The fabrication of tissue engineering scaffolds based on the polymerization of crosslinked polylactide using leaching and batch foaming to generate well‐controlled and interconnected biodegradable polymer scaffolds is reported. The scaffold fabrication parameters are studied in relation to the interpore connectivity, pore morphology, and structural stability of the crosslinked PLA scaffold. In vitro cell culture and in vitro degradation are used to analyze the biocompatibility and biodegradability of the scaffolds. The new crosslinked PLA thermoset scaffolds are highly suitable for bone tissue engineering applications due to their complex internal architecture, thermal stability, and biocompatibility.
Novel silver/polymer composites based on thiol‐ene chemistry are prepared by an in situ bottom‐up approach. The in situ synthesis of silver particles inside the polymer matrix is achieved in one pot by photoreduction reaction in presence of a silver precursor and the concurrent crosslinking reaction. XPS analysis confirms the formation of silver particles; TEM morphological investigation shows a very good dispersion and distribution of the nanometric silver particles within the thiol‐ene network. Antimicrobial properties of the photocured hybrids are also evaluated.
A new completely biodegradable shape‐memory elastomer consisting of PLLCA reinforced by in situ PGA fibrillation is described. The manufacturing processes and shape‐memory effects of the composites are discussed. DMA results reveal a strong interface interaction between in situ PGA fibrillation and PLLCA. Compared with the SMP‐based composites that are commonly used, the shape‐memory test shows that in situ PGA fibrillation can improve the recovery properties of PLLCA; in fact, the shape‐recovery rate increases from 80.5 to 93.2%.
PLA/PBAT blends and PLA/PBAT/MWNT nanocomposite systems were prepared via a melt mixing process to examine their thermal and rheological properties. To compare the polymer blend/MWNT nanocomposite with a pure polymer/MWNT nanocomposite, PLA/MWNT, PBAT/MWNT, and PLA/PBAT/MWNT nanocomposite systems were prepared. TEM and SEM were used to observe that one phase has better affinity with the MWNT, while the MWNT was found to increase both the thermal properties of the PLA/PBAT blends and rheological properties of the PLA/PBAT/MWNT nanocomposite with distinct shear‐thinning behavior due to the addition of the MWNT. An increase in the storage (G′) and loss (G″) moduli for the PLA/PBT/MWNT nanocomposite was also observed.
PHBV is produced by bacteria as intracellular carbon storage. It is advantageous concerning biocompatibility and biodegradability, but its low crystallization rate hinders the melt‐processing of fibers. This problem can be overcome by combining PHBV with PLA in a core/sheath configuration and introducing a new spin pack concept. The resulting PHBV/PLA bicomponent fibers show an ultimate tensile stress of up to 0.34 GPa and an E‐modulus of up to 7.1 GPa. XRD reveals that PLA alone is responsible for tensile strength. In vitro biocompatibility studies with human fibroblasts reveal good cytocompatibility, making these fibers promising candidates for medical therapeutic approaches.
