The crystallization behavior of poly(L ‐lactide) (PLLA) was investigated in the presence of benzenetricarboxylamide (BTA) derivatives as crystal nucleators. BTA‐cyclohexyl (BTA‐cHe) was the most effective nucleating agent, but induced a complete loss of transparency of the processed material. On the other hand, BTA‐n‐hexyl (BTA‐nHe) enhanced crystallization with little increase in haze. PLLA containing BTA‐cHe enhanced PLLA crystallization in α‐form crystal whereas BTA‐nHe enhanced α′‐form (incomplete α‐form) with forming smaller spherulites. TEM revealed BTA‐nHe had completely dissolved in the PLLA matrix in melt and recrystallized during the thermal annealing process. It was also found that the size of the recrystallized BTA‐nHe was in the nanometer range to effectively nucleate the PLLA crystals.
In the present work, the functionalisation of oxidised SWCNTs and MWCNTs is studied. The functionalised fillers are characterised by Raman spectroscopy and TGA. The functionalised fillers are dispersed in a PBT‐PTMO thermoplastic elastomer matrix via in situ polymerisation. The functionalisation causes a fine filler dispersion right at beginning of nanocomposite manufacturing. The fillers act as nucleating agents for crystallisation and evidences for a grafting from PBT at the surface of the functionalised nanotubes are found. An outstanding reinforcement effect by the functionalised CNTs is confirmed by tensile tests.
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.
The effects of incorporated nano/micro‐diamond (NMD) on the physical properties, crystallization, thermal/hydrolytic degradation of poly(L ‐lactic acid) (PLLA) were investigated for a wide NMD concentration range of 0–10 wt.‐%. Incorporated NMD increased the tensile modulus and strength of PLLA films but decreased the elongation at break of PLLA films. Incorporated NMD accelerated the crystallization of PLLA during heating and cooling and increased the absolute crystallization enthalpy of PLLA films (except for an NMD concentration of 10 wt.‐% during cooling) but did not alter the crystallization mechanism. Incorporated NMD increased and decreased the thermal stability of PLLA films for NMD concentrations of 1–5 and 10 wt.‐%, respectively, and increased the hydrolytic degradation resistance of PLLA films.
Polyurethanes were prepared from poly(tetramethylene oxide) end‐capped with MDI and PBT extenders. The PBT extenders were random‐disperse in length and their length varied from three to seven repeating units. The structure of the polyurethanes was studied by FT‐IR and AFM, their thermal and thermomechanical responses were measured by DSC and DMTA, and their elastic behavior was assessed by compression set measurements. The MDI‐PBT‐MDI hard segments had a ribbon‐like crystalline morphology. Increasing the PBT length gave rise to an increase of the storage modulus at room temperature and the melting point. The storage modulus depended strongly on temperature.
The supramolecular structure in pipe walls of isotactic PP‐R is a function of compound composition and processing parameters, which both influence the mechanical properties of the pipes. µFTIR shows a gradient of the crystallinity across the pipe wall, with a lower‐crystalline outer layer, and a higher‐crystalline core layer. The rate of extrusion has an influence on the thickness of the outer layer. The nucleating effect on the morphological profile throughout the pipe wall can be visualised. µFTIR shows a homogeneous distribution of the primary antioxidant in the pipe wall. Both the spectral crystallinity and the antioxidant concentration distribution are calculated.
The pressure and cooling rate dependence of the phase diagram of isotactic polypropylene (iPP) with the nucleating agent 1,3:2,4‐bis(3,4‐dimethylbenzylidene)‐sorbitol (DMDBS) is investigated. A custom designed dilatometer is used to measure the specific volume of the blends for a wide range of cooling rates and elevated pressures. The crystallization line in the phase diagram shifts to higher temperatures with increase in the pressure and decrease in the cooling rate, independent of the concentration. The influence of cooling rate and pressure is related to the final morphology determined from X‐ray diffraction. Dilatometry can be used as an interesting alternative to extract information on the phase behavior and crystallinity, for conditions hard or not at all obtainable with standard techniques like DSC or SALS.
This study explored the combined influence of shear flow and nucleating agents on isotactic polypropylene (iPP) crystallisation. The study showed that oriented α‐iPP crystals were not necessary to form β‐iPP crystals, contrary to the accepted view that the surface of oriented α‐iPP crystals provides nucleation sites for an α‐iPP to β‐iPP growth transition. Instead it was proposed that flow‐induced mesomorphic point‐like nuclei preferentially nucleates β‐iPP. The combined effect of shear flow and nucleant was found to promote γ‐iPP crystals. The surprising γ‐iPP nucleation effect was explained by the high density of flow‐induced and heterogeneous nuclei present at the start of crystallisation.
Blends of PET, PTT and PBT with the corresponding MCOs have lower melt viscosities than the pure polymers. This effect of MCOs on viscosity has the potential for exploitation in polymer fabrication and especially in the processing of composite materials. Thus, the blends can be more easily melt‐processed than the pure polymers, and the MCOs can then subsequently be converted in situ into high‐molar‐mass polymers by ED‐ROPs. No catalyst is needed for the ED‐ROPs. It was shown that suitable polymer/MCO blends can be obtained directly by carrying out cyclo‐depolymerizations at appropriate concentrations. Suitable polymer/MCO blends can also, almost certainly, be obtained by carrying out the original polyester syntheses at lower concentrations than normally used.
In the general processing temperature range of poly(L ‐lactic acid) (PLLA) articles (210–240 °C), PLLA/poly(D ‐lactic acid) (PDLA) stereocomplex (SC) crystallites melted just above the endset temperature of SC melting (228–238 °C) and recrystallized during cooling were found to act as the most effective nucleating agents for enhancing the crystallization of PLLA compared to partially melted SC crystallites (211–227 °C) or those melted far above the endset temperature of SC melting (240 and 250 °C) and recrystallized during cooling. The high nucleating effect of the SC crystallites melted in the temperature range of 228–238 °C was found to be caused by their smaller sizes or the larger number of SC crystallites per unit mass. The incorporation of such SC crystallites facilitates the processing of PLLA articles having high crystallinity and, therefore, high heat‐resistance in a shorter period to reduce the production cost.
The effects of nucleobases, especially uracil, on the nonisothermal and isothermal crystallization, melting behavior, spherulite morphology, and crystalline structure of bio‐based and biodegradable PLLA are studied. The melt‐ and cold‐crystallization rates of PLLA increase with increasing uracil loading. The melting behavior of nonisothermally melt‐ and cold‐crystallized PLLAs depends on the uracil content. The isothermal crystallization kinetics is analyzed based on an Avrami model. The incorporation of uracil changes the t1/2/Tc profile of PLLA due to the more distinct heterogeneous nucleation effects at small supercooling. The crystalline structure of PLLA is not affected by uracil presence. The nucleation density increases and the spherulite size decreases by uracil incorporation.
The present work provides a critical review of polymer crystallization studies using SALS; experimental methods, analysis techniques, observations and their relations with respect to other techniques are discussed. Furthermore, the fact that nucleation might be accompanied by large scale density fluctuations has been investigated for the flow‐induced crystallization of iPB. SALS was applied to measure density and orientation fluctuations, whereas complementary results were obtained from optical microscopy. The observations from both crystallization and melting experiments seem to indicate that the detected density fluctuations result from the presence of weakly anisotropic structures, rather than being an indication of densification before the onset of crystallization.
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.
xGnP‐Reinforced LLDPE nanocomposites have been prepared using co‐, counter‐ and modified co‐rotating screw systems. The highest tensile strength and modulus were shown in the case of composites made by counter‐rotating screws. The percolation threshold of exfoliated graphite nanoplatelet/LLDPE nanocomposites was between 12 and 15 wt.‐%. The change of crystallinity caused by exfoliated graphite nanoplatelet loading was monitored using DSC and XRD. It was found that solution mixing showed better dispersion of exfoliated graphite nanoplatelets than melt mixing, and counter‐rotating screws produced better dispersion of the exfoliated graphite nanoplatelets than co‐ and modified co‐rotating screws even though bubbling appeared during mixing in the barrel.
PCL‐based nanoclay (layered silicate) nanocomposites are prepared using a small scale intermeshing co‐rotating twin‐screw extruder. Improving the level of nanoclay dispersion in PCL nanocomposites is obtained by changing the extrusion parameters. Increasing the screw speed and decreasing the throughput leads to an improved dispersion quality, as observed from the improved mechanical properties of the nanocomposites as well as from their clearly affected rheological and crystallization behavior. Furthermore, a commercially available software that simulates the twin‐screw extrusion process (LUDOVIC) is used to asses the processing parameters applied for making the nanocomposites.
The spherulitic morphology and growth, overall isothermal crystallization kinetics and hydrophilicity of PBSU were investigated by POM, DSC and WCA measurements in its miscible blends with PEO. The Hoffman‐Lauritzen equation was employed to analyze the spherulitic growth rates of neat and blended PBSU, which show a crystallization regime transition between regime II and III. The overall crystallization rates of PBSU decreased with increasing crystallization temperature, regardless of blend composition, while the crystallization mechanism does not change. A significant improvement in the hydrophilicity of PBSU can be achieved by blending with different weight fractions of PEO, which may be essential for the practical application of PBSU/PEO blends.
Spherical silica particles with pseudo‐inverse opal structure are synthesized by using pomegranate‐like polymer microparticles as templates. A micro‐dispersion polymerization occurring in the suspended monomer droplets in the presence of a silica precursor leads to the formation of nearly monodisperse polymer sub‐particles of about 1 µm size, randomly‐packed within a 30–100 µm polymer particle. The polymerization is followed by an acid‐catalyzed reaction that induces formation of silica in the interstices between the sub‐particles within a polymer particle. Spherical PIOS particles are eventually produced by selectively removing the polymer template by pyrolysis. The PIOS particles show large specific surface areas with unique pore geometry and pore size distribution.
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.
The influence of Ca‐stearate‐coated CaCO3 and talc on the quiescent and flow‐induced crystallization of iPP is studied using different methods. Comparison of rheometry and DSC shows that rheometry is an interesting tool to monitor crystallization kinetics. It is observed that the Ca‐stearate coating degrades at commonly used annealing temperatures, influencing the crystallization behavior of the CaCO3‐containing polymer. WAXD indicates that the CaCO3 does not significantly influence the degree of crystallinity. As shear intensifies, both the pure and particle‐containing polymers crystallize faster; however, their behavior also becomes increasingly similar. There are indications that shear influences the organization of the CaCO3 aggregates.
A photoresponsive fluorinated azobenzene homopolymer is synthesized via TERP. UV irradiation of the surface based on a fluorinated azobenzene homopolymer with micro/nanostructures induces a tunable/switchable water droplet mobility. Water droplets can easily roll off the pristine surface at a small tilt angle (≈14°). The apparent water CA changes from 150 to 135° after UV illumination of the surface. Thus, water drops stick on the surface when the substrate is turned vertically or even upside down, indicating a very high adhesion force. Interestingly, the water droplet rolls off again under visible‐light irradiation. The as‐prepared surface may be useful for applications requiring switchable mobility of water droplets.
