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A universal method for determining the modulus of the interlamellar amorphous phase of semicrystalline polymers was proposed. The basics of the method were presented on the example of high-density ...

Surface morphology and bulk structure of polylactide (PLA) modified with halloysite nanotubes (HNT) treated with N,N’-ethylenebis(stearamide) (EBS) and untreated, as well as reference materials – PLA, EBS, and a blend of PLA with EBS, were examined. HNT is known to improve PLA properties, including mechanical and barrier properties. The materials were cold crystallized and tested using DSC, TGA, PLM, SALS, SEM, AFM. The additives affected nucleation and crystallization of PLA, but did not influence crystallinity, which was of approx. 37–40 %. In bulk, PLA crystallized in the form of spherulites in all materials. However, on surfaces of EBS-containing materials, a thin EBS layer with domain morphology was found. The EBS layer induced epitaxial crystallization of PLA in the form of parallel stacks of edge-on lamellae, the phenomenon reported for this polymer pair for the first time. It was observed in PLA with EBS modified HNT and in the PLA blend with EBS. Moreover, the EBS layers imparted hydrophobicity to the EBS-containing materials.

The influence of macromolecular architecture on shear-induced crystallization of poly(L-lactide) (PLLA) was studied. To this aim, three star PLLAs, 6-arm with Mw of 120 and 245 kg/mol, 4-arm with Mw of 123 kg/mol, and three linear PLLAs with Mw of 121, 240 and 339 kg/mol, were synthesized and examined. The PLLAs were sheared at 170 and 150 °C, at 5/s, 10/s and 20/s for 20 s, 10 s and 5 s, respectively, and then cooled at 10 or 30 °C/min. Shear-induced crystallization during cooling was followed by a light depolarization method, whereas the crystallized specimens were examined by DSC, 2D-WAXS, 2D-SAXS and SEM. The effect of shear depended on the shearing conditions, cooling rate and polymer molar mass but it was also affected by the macromolecular architecture. The shear-induced crystallization of linear PLLA with Mw of 240 kg/mol was more intense than that of the 6-arm polymer with similar Mw, most possibly due to its higher Mz. However, the influence of shear on the crystallization of the star polymers with Mw close to 120 kg/mol was stronger than on that of their linear analog. This was reflected in higher crystallization temperature, as well as crystallinity achieved during cooling.

Ternary blends of polylactide (PLA, 90 wt.%) and poly(methyl methacrylate) (PMMA, 10 wt.%) with functionalized polysilsesquioxanes (LPSQ-R) were obtained by solution blending. R groups in LPSQ containing hydroxyethyl (LPSQ-OH), methylglycolic (LPSQ-COOMe) and pentafluorophenyl (LPSQ-F5) moieties of different chemical properties were designed to modify PLA blends with PMMA. The effect of the type of LPSQ-R and their content, 1–3 wt.%, on the structure of the blends was studied with scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (SEM-EDS), dynamic mechanical thermal analysis (DMTA) and Raman spectroscopy. Differential scanning calorimetry (DSC) and tensile tests also showed various effects of LPSQ-R on the thermal and mechanical properties of the blends. Depth-sensing indentation was used to resolve spatially the micro- and nano-scale mechanical properties (hardness and elastic behaviour) of the blends. The results showed clearly that LPSQ-R modulate the structure and properties of the blends.

Linear ladder polysilsesquioxanes (LPSQ-R) bearing fluoroaryl groups [R: p-fluorophenyl (F), p-trifluoromethylphenyl (F3) or pentafluorophenyl (F5)] were used to modify polylactide (PLA). Vibrational spectroscopy analysis suggested specific, non-covalent interactions between C O of PLA and fluoroaryl groups of LPSQ-R while quantum-chemical modelling performed for representative models indicated that the pattern of possible preferred contacts differs for LPSQ-F3 in respect to LPSQ-F and LPSQ-F5 (H····F hydrogen bonding against n→π* attractive interactions). It may affect interface phenomena in PLA/LPSQ-R systems. Thermal characteristics of PLA/LPSQ-R depended on the type of R and LPSQ-R content. Dielectric relaxation spectroscopy (DRS) studies revealed one relaxation process present in PLA and related to the glass transition. However, for PLA/LPSQ-R blends two processes were identified: glass transition and normal–mode relaxation. The modification with fluorinated macromolecules increased hydrophobicity of amorphous PLA and improved its mechanical and gas barrier properties, which can be of importance for packaging applications.

Three star-shaped poly(ʟ-lactide)s (PLLAs) were synthesized, two 6-arm with Mw of 120 and 245 kg/mol and one 4-arm with Mw of 123 kg/mol. Linear PLLAs with Mw of 121 and 339 kg/mol were also prepared. Crystallization, both isothermal and nonisothermal, of all PLLAs was studied by means of DSC. The growth rate of spherulites was measured in a broad range of crystallization temperature using PLM. At Mw close to 120 kg/mol the star architecture slowed down the spherulite growth above 120 °C, up to 145 °C. The spherulite growth in PLLAs with Mw > 200 kg/mol was slower than that in the other polymers and unaffected by the macromolecule architecture. The differences in the spherulite growth rate were reflected in overall crystallization kinetics in isothermal conditions and also in crystallization peak temperature and crystallinity developed during cooling. The highest crystallinity developed during isothermal crystallization in linear and 6-arm PLLAs with Mw close to 120 kg/mol, whereas the lowest in PLLAs with Mw > 200 kg/mol. For Mw > 200 kg/mol the star architecture decreased the melting temperature. The glass transition temperature of all PLLAs was the same, at 61–62 °C, regardless of Mw and macromolecule architecture.

Composites of syndiotactic polypropylene (sPP) with 5 to 17 vol.° of halloysite and 2.5 to 7.5 vol.° of stearic acid modified nano-calcium carbonate, having an average grain size of 80 nm, were prepared and examined. The effect of fillers on thermal properties of sPP was different; halloysite increased markedly peak crystallization temperature. The composites with the highest filler contents, 7.5 vol.° of calcium carbonate and 17 vol.° of halloysite, exhibited a solid-like behavior at 170 °C, with the storage modulus exceeding the loss modulus in the entire frequency range, that is 512 to 0.1 rad s−1. The composites with halloysite exhibited decreased Izod impact strength compared to neat sPP. On the contrary, 2.7 fold improvement of the impact strength was found for the composites with nano-calcium carbonate. Moreover, nano-calcium carbonate did not worsen the drawability of the materials during uniaxial drawing. It was found that debonding at calcium carbonate/sPP interface occurred both during the impact test and tensile drawing facilitating the plastic deformation of the polymer.

Poly(lactide)/halloysite nanotubes (PLA/HNT) nanocomposites with crystalline matrix were obtained by cold crystallization and examined. Neat HNT and HNT treated with N,N′- ethylenebis(stearamide) (EBS) were used as nanofillers. Reference materials, PLA and PLA/EBS blend, prepared in the same way, were also considered. The influence of HNT and/or EBS content on the crystallinity and morphology of PLA matrix, as well as on the dynamic mechanical and optical properties of the materials, was determined. The nanocomposites contained well-distributed HNT, with only occasional agglomerates. HNT, EBS-treated HNT and EBS influenced the morphology of the crystalline PLA matrix and the amounts of the disorder α’ (termed also δ) and order α crystallographic forms of PLA. Crystallinity increased stiffness of the materials compared to their counterparts with the amorphous matrix. Owing to the crystallinity and the presence of the nanofillers, the storage modulus at 20 °C and 60 °C increased by up to 30 and 60%, respectively, compared to neat amorphous PLA. Interestingly, at lower nanofiller content the crystalline nanocomposites with EBS were more transparent than neat crystalline PLA.

Thermal and mechanical properties of polylactide (PLA) composites with different grades of calcium carbonate, 40 nm and 90 nm nanoparticles, and also with submicron particles, unmodified and modified with calcium stearate or stearic acid, obtained by melt mixing, were compared. Films with amorphous and crystalline matrices were prepared and examined. Tg of PLA in the composites remained unaffected whereas its cold crystallization was enhanced by the fillers and predominantly depended on filler content. Filling decreased thermal stability of the materials but their 5% weight loss temperatures well exceeded 250 °C, evidencing stability in the temperature range of PLA processing. The amorphous nanocomposites with modified nanoparticles exhibited improved drawability and toughness without a significant decrease of tensile strength; nearly two-fold increase of the elongation at break and tensile toughness was achieved at 5 wt% content of the modified nanofiller. Lack of surface modification of the filler, larger grain size with an average of 0.9 μm, and matrix crystallinity had a detrimental effect on the drawability. However, the presence of nanofillers and crystallinity improved tensile modulus of the materials by up to 15% compared to neat amorphous PLA.

Amorphous polylactide/halloysite nanotube (PLA/HNT) nanocomposites were prepared and examined. Neat HNT and HNT treated with N,N' - ethylenebis(stearamide) (EBS) were used as nanofillers. The role of HNT and/or EBS content on the cold crystallization of amorphous PLA matrix, HNT dispersion, as well as on the dynamic mechanical and optical properties of the materials was determined. The PLA/HNT-based nanocomposites contained well-distributed nanotubes and occasionally micron-sized aggregates, especially at high loading. HNT, EBS treated HNT and EBS influenced the cold crystallization of PLA, therefore the formation of the disorder α′ and the order α crystallographic forms of PLA. The nanocomposites exhibited increased stiffness and decreased transparency compared to the neat PLA. Due to the reinforcing effect and additional specific features of HNT, the addition of the nanofiller allows tuning of the properties of the nanocomposites with amorphous PLA matrix.

Shear-induced nonisothermal crystallization of two commercial polylactides (PLAs) differing in optical purity was studied. The molten polymers were sheared at selected temperatures (Ts) and subsequently cooled. The crystallization was followed by a light depolarization method, whereas the specimens were analysed ex-situ by DSC, 2D-WAXS and SEM after etching. It was found that the effect of shear, especially on the crystallinity developed during post-shearing cooling, intensified with a decrease of Ts from 160 to 146 °C, and with increasing shear rate and strain. Moreover, the effect of shear on PLA1.5 with d -lactide content of 1.5% was stronger than PLA2.8 with 2.8% of d -lactide, although maximum crystallinity of both polymers was practically the same. A decrease of cooling rate from 30 to 10 °C/min increased crystallinity of both PLAs, except for those shearing conditions which induced high crystallinity even during faster cooling. Although SEM examination revealed some row-nucleated forms, no significant crystal orientation was detected by 2D-WAXS, indicating that, under the experimental conditions, the shear induced predominantly point-like nuclei.

Oligomeric ladder silsesquioxanes (LPSQ-R) with side substituents (R = COOH, COOMe, OH) capable of acceptor/donor interactions through hydrogen bonds were used for the preparation of blends with polylactide (PLA). Depending on the strength of their interactions with the PLA, LPSQ-R were differently dispersed in the polyester matrix. The blends exhibited different properties and crystallization behaviour depending on the type and content of LPSQ-R. PLA/LPSQ-COOMe exhibited good transparency. Owing to very good dispersion of the modifier, PLA with 5 wt% of LPSQ-COOMe was ductile, which was reflected in nearly 230% elongation at break, retaining however relatively high yield strength of nearly 40 MPa. Moreover, the spherulite growth rate was accelerated in PLA/LPSQ-COOMe, which caused enhancement of the cold-crystallization. In turn, cold-crystallization of PLA/LPSQ-OH was enhanced by strong nucleation.

The influence of shear on non-isothermal crystallization of commercial poly(butylene adipate-co-terephthalate) (PBAT) was investigated. PBAT melt was sheared at 130 and 150 °C at rates of 10–100/s, and then cooled. The crystallization was followed by a light depolarization technique, whereas the crystallized specimens were analyzed by DSC, 2D-SAXS, 2D-WAXS, PLM and SALS. Shear flow shifted crystallization to higher temperature, and the effect was augmented by lower temperature of shearing as well as by higher shear rate and strain. Crystallization peak rate temperature of PBAT, sheared at 130 °C for 5 min at 100/s, increased by up to 12 °C. However, no evidence of crystal orientation due to shear was found, indicating that the shear induced the point-like nucleation. Only a small increase of melting peak temperatures, by up to 2–5 °C, was observed for the specimens sheared at the highest rates (≥50/s).

Hybrid blends of poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) and hydrogen bonds donating/accepting oligomeric ladder silsesquioxanes (LPSQ-R; R OH, (OH)2, COOH, COOMe) exhibited higher thermal stability at T > 533 K. Temperature of decomposition (Td) increased by 20–30 K comparing to neat PLLA/PDLA, even when small amounts of the additives were used. Stereocomplexation in PLLA/PDLA blends was improved with the addition of H-bond donating LPSQ-R, even in the presence of substantial amounts of the additives, and only slightly disturbed by LPSQ-COOMe. Vibrational spectroscopic analysis was used to follow the crystal structure evolution at 448 K. The modes characteristic of 31 β-helical structures were observed in the studied samples. LPSQ-R grafted with thioglycerol moieties, significantly increased the stereocomplexation rate. Nuclear magnetic resonance spectroscopy (NMR) and wide-angle X-ray scattering (WAXS) measurements confirmed the stereocomplex structure of the hybrid blends. All the observed effects may be related to the specific structure of polysilsesquioxanes and R groups.

We hypothesized that polymer crystal anisotropy is advantageous for toughening of polymer composites involving easy slip network of oriented crystalline layers around filler particles. To this end, composites of syndiotactic polypropylene (sPP) with high concentration of submicrometer calcium carbonate particles were prepared and examined because usual sPP crystals exhibit high packing anisotropy. The specific orientation of sPP lamellae around chalk grains was found, which is supposed to facilitate the plastic deformation of polymer matrices. The compression molded bars of the composite exhibited markedly higher Izod impact strength than those of neat sPP. Toughening was even enhanced in the injection molded composite, for which 4.5-fold increase in the impact strength was achieved. Injection-induced orientation of the disordered form I sPP crystals was enhanced in the composite. The injection molded tensile specimens exhibited also a good drawability. Debonding at chalk–sPP interface occurred both during the impact and tensile tests facilitating the plastic deformation of sPP matrix. Chalk did not have any significant influence on the thermal properties of the composites but it affected the rheological behavior, increasing the loss and storage moduli, and the viscosity. Highly filled sPP composite exhibited solid-like behavior in a molten state with the storage modulus exceeding the loss modulus in the entire frequency range. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43651.