Search

The aim of this project was to study the efficacy of current methods of quality control and quality assurance for ultra-high molecular weight polyethylene (UHMWPE) products, and find improvements where possible. Intrinsic viscosity (IV) tests were performed on three grades of polyethylene with weight average relative molar masses M ̅ $̅{M}$ w of about 6 × 105, 5.0 × 106 and 9.0 × 106. Results from three laboratories showed substantial scatter, probably because different methods were used to make and test solutions. Tensile tests were carried out to 600 % extension at 150 °C under both constant applied load and constant Hencky strain rate, on compression mouldings made by a leading manufacturer of ultra-high molecular weight polyethylene. They gave low values of M ̅ $̅{M}$ w, suggesting incomplete entanglement at ‘grain boundaries’ between powder particles. Results from conventional melt-rheology tests are presented, and their relevance to quality control and assurance is discussed. Attempts to calculate molecular weights from these data met with limited success because of extended relaxation times. Suggestions are made for improving international standards for IV testing of UHMWPE, by investigating the various factors that can cause significant errors, and by introducing methods for checking the homogeneity (and hence validity) of the solutions tested. Part 2 addresses characterization of crystallinity and structure. Part 3 covers mechanical properties, and Part 4 focuses on the sporadic crack propagation behaviour exhibited by all three grades of UHMWPE in fatigue tests on 10 mm thick compact tension specimens.

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.

The influence of the crystallization temperature and the pressure on the crystallization kinetics, structure and compression strength of γ-polypropylene was investigated. Samples were produced in a custom-made high-pressure crystallization cell and characterized by differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM). It could be shown that the strength is mainly affected by the mean lamellar thickness. The strength of γ-PP is at least 40% higher than α-PP at the same mean lamellar thickness. This confirms the hypothesis that the arrangement of non-parallel chains restricts the number of possible slip systems so that almost no mobile dislocations are generated. The mode of nucleation is only slightly affected by the crystallization pressure. The Avrami coefficient is n = 2.5 ± 0.1 at the beginning of crystallization and largely independent of pressure.

Electrically conductive composite polypropylene and poly(ethylene terephtalate) fabrics were obtained by coating with organo-silicon sol containing dispersed graphene particles. The graphene-modified coating was deposited on the fabric using the sol-gel method and the padding technique. To improve bonding of the coating to the fiber surfaces, the latter were activated with atmospheric pressure plasma in the form of corona discharge. The activation resulted in chemical and structural changes of the surfaces, roughening, and the formation of oxygen-containing functional groups, as evidenced by SEM with 3D analysis, EDS and XPS, and also measurements of contact angles with liquids. The padding with graphene-containing organo-silicon sol imparted electrical conductivity to the polymer fabrics. It was found that the pre-coating activation improved durability of the coating and stability of the electrical properties due to better bonding between the conducting coating and the fiber surfaces.

Electrical conductivity was imparted to a cotton fabric through thermal reduction of graphene oxide. The reduction was enhanced by commercial antioxidants used in the plastics industry. The cotton fabric was coated with GO by the padding method and dipped in antioxidant solution. After drying, the antioxidant assisted reduction of GO was conducted at 220 °C in air. The electrical properties and hydrophobicity of thus-modified fabric were examined. The structure of materials was analyzed by atomic force microscopy and scanning electron microscopy. Application of the antioxidants permitted to reach lower values of surface electrical resistivity of the fabric. After the reduction all fabric samples became hydrophobic.

Dual-component fibrous materials were produced by co-extrusion and multiplication technology in combination with a water jet procedure. High density polyethylene/poly(vinylidene fluoride) (HDPE/PVDF) and polypropylene/high density polyethylene (PP/HDPE) systems were obtained. Modification of these fibrous materials with multiwall carbon nanotubes imparted electrical conductivity. Methyltrichlorosilane treatment permitted to reach superhydrophobicity reflected in a water contact angle (WCA) ≥ 160°. Both types of modification decreased a pore size of HDPE/PVDF fibrous material and strongly increased its surface area. The material subjected to both treatments possess pore size of 3.1 μm. This electrically conductive and superhydrophobic HDPE/PVDF fibrous material is characterized by WCA of 164° and low surface resistivity of 87.4 Ω/sq. Electrochemical modification using cyclic voltammetry resulted in the formation of silver nanoparticles (Ag°) on surfaces of the fibers, which imparted antibacterial properties against Staphylococcus aureus and Escherichia coli. Keywords: Smart materials, Dual-component fibrous materials, Lotus effect, Multiwall carbon nanotubes, Cyclic voltammetry

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.

Electrospun nonwovens of poly(L-lactide) (PLLA) modified with multiwall carbon nanotubes (MWCNT) and linear ladder-like poly(silsesquioxane) with methoxycarbonyl side groups (LPSQ-COOMe) were obtained. MWCNT and LPSQ-COOMe were added to the polymer solution before the electrospinning. In addition, nonwovens of PLLA grafted to modified MWCNT were electrospun. All modified nonwovens exhibited higher tensile strength than the neat PLA nonwoven. The addition of 10 wt.% of LPSQ-COOMe and 0.1 wt.% of MWCNT to PLLA increased the tensile strength of the nonwovens 2.4 times, improving also the elongation at the maximum stress.

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.

1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS) is highly effective in nucleation of the &alpha, form of isotactic polypropylene (iPP). However, its role in high-pressure crystallization of iPP, facilitating the formation of the &gamma, polymorph, has not been explored. The present paper focuses on the influence of DMDBS on nucleation of high-pressure crystallization of iPP. iPP with 0.2&ndash, 1.0 wt.% of the DMDBS was crystallized under elevated pressure, up to 300 MPa, in various thermal conditions, and then analyzed by PLM, WAXD, SEM, and DSC. During cooling, crystallization temperatures (Tc) were determined. It was found that under high-pressure DMDBS nucleated crystallization of iPP in the orthorhombic &gamma, form. As a consequence, Tc and the &gamma, form content increased for the nucleated iPP, while the size of polycrystalline aggregates decreased, although the effects depended on DMDBS content. The significant increase of Tc and the decrease of grain size under high pressure of 200&ndash, 300 MPa required higher content of DMDBS than the nucleation of the &alpha, form under lower pressure, possibly due to the effect of pressure on crystallization of DMDBS itself, which is a prerequisite for its nucleating activity.

Three grades of polyethylene, with weight-average relative molar masses, M ‾ W ${\bar{M}}_{\text{W}}$ , of approximately 0.6 × 106, 5 × 106, and 9 × 106, were supplied as compression mouldings by a leading manufacturer of ultra-high molecular weight polyethylene (UHMWPE). They were code-named PE06, PE5, and PE9, respectively. Specimens cut from these mouldings were subjected to a wide range of mechanical tests at 23 °C. In tensile tests, deformation was initially elastic and dominated by crystallinity, which was highest in PE06. Beyond the yield point, entanglement density became the dominant factor, and at 40 % strain, the rising stress–strain curves for PE5 and PE9 crossed the falling PE06 curve. Fracture occurred at strains above 150 %. Differences in stress–strain behaviour between PE5 and PE9 were relatively small. A similar pattern of behaviour was observed in wear tests; wear resistance showed a marked increase when M ‾ W ${\bar{M}}_{\text{W}}$ was raised from 0.6 × 106 to 5 × 106, but there was no further increase when it was raised to 9 × 106. It is concluded that the unexpected similarity in behaviour between PE5 and PE9 was due to incomplete consolidation during moulding, which led to deficiencies in entanglement at grain boundaries; they were clearly visible on the surfaces of both tensile and wear specimens. Fatigue crack growth in 10 mm thick specimens was so severely affected by inadequate consolidation that it forms the basis for a separate report – Part 4 in this series.

Test methods including OM, SEM, TEM, DSC, SAXS, WAXS, and IR were used to characterise supra-molecular structure in three batches of polyethylene (PE), which had weight-average relative molar masses M ¯ w ${\overline{M}}_{\text{w}}$ of approximately 0.6 × 106, 5 × 106, and 9 × 106. They were applied to compression mouldings made by the polymer manufacturer. Electron microscopy showed that powders formed in the polymerization reactor consisted of irregularly shaped grains between 50 and 250 μm in diameter. Higher magnification revealed that each grain was an aggregate, composed of particles between 0.4 and 0.8 μm in diameter, which were connected by long, thin fibrils. In compression mouldings, lamellar thicknesses ranged from 7 to 23 nm. Crystallinity varied between 70 and 75 % in reactor powder, but was lower in compression mouldings. Melting peak temperatures ranged from 138 to 145 °C, depending on processing history. DMTA showed that the glass transition temperature θ g was −120 °C for all three grades of polyethylene. IR spectroscopy found negligibly small levels of oxidation and thermal degradation in mouldings. Optical microscopy revealed the presence of visible fusion defects at grain boundaries. It is concluded that relatively weak defects can be characterized using optical microscopy, but there is a need for improved methods that can detect less obvious fusion defects.

Fatigue tests were carried out on compression mouldings supplied by a leading polymer manufacturer. They were made from three batches of ultra-high molecular weight polyethylene (UHMWPE) with weight-average relative molar masses, M ¯ W ${\overline{M}}_{\mathrm{W}}$ , of about 0.6 × 106, 5 × 106 and 9 × 106. In 10 mm thick compact tension specimens, crack propagation was so erratic that it was impossible to follow standard procedure, where crack-tip stress intensity amplitude, ΔK, is raised incrementally, and the resulting crack propagation rate, da/dN, increases, following the Paris equation, where a is crack length and N is number of cycles. Instead, most of the tests were conducted at fixed high values of ΔK. Typically, da/dN then started at a high level, but decreased irregularly during the test. Micrographs of fracture surfaces showed that crack propagation was sporadic in these specimens. In one test, at ΔK = 2.3 MPa m0.5, there were crack-arrest marks at intervals Δa of about 2 μm, while the number of cycles between individual growth steps increased from 1 to more than 1000 and the fracture surface showed increasing evidence of plastic deformation. It is concluded that sporadic crack propagation was caused by energy-dissipating crazing, which was initiated close to the crack tip under plane strain conditions in mouldings that were not fully consolidated. By contrast, fatigue crack propagation in 4 mm thick specimens followed the Paris equation approximately. The results from all four reports on this project are reviewed, and the possibility of using fatigue testing as a quality assurance procedure for melt-processed UHMWPE is discussed.

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.

Microbial infections lead to elevated inflammatory responses, which usually result in prolonged and incomplete wound healing. Therefore, there is an increasing demand for biodegradable fibres that are effective against a different range of microorganisms, especially those with antibiotic resistance. Herein, quercetin-(Q)-loaded polylactide-based fibres were developed using the electrospinning technique. Since Q exhibits low chemical stability, we used star-shaped polylactides (PLAs) with a β-CD core to host Q by inclusion complexation. To enhance the stability of the fibres and additionally entrap the Q between polymeric chains, we adapted supramolecular cross-linking by the stereocomplexation of PLAs with opposite configurations. As a control, we prepared an additional formulation of star-shaped/commercial PLA/Q for the preparation of nonwovens in which the β-CD moiety was not present. All developed fibres were smooth and continuous, with an average diameter of 37 μm. Although nonwovens did not possess diffusible activity, good antibacterial effects against Staphylococcus aureus (S. aureus), Escherichia coli (E.coli) and Klebsiella pneumoniae (K. pneumoniae) were observed. All these features validate the proposed approach, in which different supramolecular interactions were used to modify the properties of PLA-based fibres and, most importantly, show their great potential usefulness against microbial infections.

Pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), an antioxidant widely applied in the plastic industry, was used to assist thermal reduction of graphene oxide (GO) on a cotton fabric in air. l-ascorbic acid was also applied for comparison. GO was deposited on the fabric by the padding method. Reduction of GO deposited on fiber surfaces at 180 and 220 °C in air imparted electrical conductivity. For all the materials the conductivity worsened after the reduction during cooling and during the first hours of storage at room conditions. However, the most stable effect of GO reduction was achieved using pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), which assisted the reduction of GO at both 180 and 220 °C, and allowed to obtain the cotton fabric with a stable surface resistivity of 6.6 and 3.7 MΩ/sq, respectively. Moreover, superhydrophobicity of the conductive fabric was achieved by modification with methyltrichlorosilane in an anhydrous environment.

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.

The relations between crystalline structure and micromechanical properties of α-, β- and γ-phase of isotactic polypropylene (iPP) were investigated. The iPP samples with various crystalline phase compositions were prepared by a controlled high-pressure crystallization that enabled us to obtain not only α-iPP and β-iPP modifications, but also a series of almost pure γ-iPP samples with gradually changing morphology, crystallinity and lamellar thickness. The micromechanical properties were assessed by instrumented microindentation hardness testing (MHI), from which we determined indentation hardness (HIT), indentation modulus (EIT), indentation creep (CIT) and elastic part of the indentation work (ηIT). It was demonstrated that γ-iPP does not necessarily exhibit better mechanical performance than α- and β-iPP, as suggested by some previous studies, because the final properties are strongly influenced not only by the phase composition (i.e. by the content of α-, β- and γ-phase), but also by the overall crystallinity.

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.

Cotton fabrics were modified by xerogel coatings with dispersed particles of graphene (Gr) or reduced graphene oxide (RGO). To obtain a stable dispersion of Gr or RGO in organo-silicon sol, sodium lauryl sulfate as an anionic surfactant was used. The fabrics were padded with the organo-silicon sol containing dispersed Gr or RGO, forming a thin xerogel coating after drying. The fabrics coated with the xerogel containing 0.5–1.5 wt% of RGO or Gr were prepared and examined. The best anti-static properties were obtained for the coating with 1.5 wt% of Gr, whose surface resistance and volume resistance were on the order of 105 and 103 Ω, respectively. Such properties make the fabric suitable for protective cloths in the environment with explosive atmosphere.

Awareness of the environmental issues results in increasing attention paid to biobased polymers as their development and commercialization can help to limit exploitation of fossil resources and global warming. The article presents an overview of biobased polymers comprising most abundant natural polymers, bio-engineered polymers, and polymers synthesized fully or partially from biobased substrates, including analogs of petrochemical resins. The structure, important properties, synthesis, and applications are addressed.

Polylactide (PLA) composites with 10–30 wt% of commercial fine grain filler of native cellulose were prepared by melt-mixing, and examined. The composite films had esthetic appearance, glossy surface, creamy color and density close to that of neat PLA. Good dispersion of the filler in PLA matrix was achieved. The composites were stiffer than neat PLA; in the glassy region the storage modulus increased by approx. 30 %. The tensile strength of the composite materials in the temperature range from 25 to 45 °C was similar to that of neat PLA. No marked decrease in molar mass of PLA in the composites occurred during processing in comparison to neat PLA. Moreover, thermogravimetry experiments demonstrated good thermal stability of the composites; 5 % weight loss occurred well above 300 °C.

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.

The influence of gold nanoparticle morphology on nucleation of isotactic polypropylene (PP) crystallization was investigated. Previous experiments indicated certain nucleation activity of gold nanoparticles, varying with their size. In this work, eight types of gold micro/nanoparticles were used: vacuum-sputtered nanostructures (nanoparticles, nanoislands, and nanolayers), chemically prepared isometric gold nanocrystals (5, 20, and 100 nm diameters), and two types of gold microcrystals with well-developed crystal facets [with (100) and (111) facets, respectively]. To minimize the effect of particle agglomeration, we used our recently introduced sandwich method, in which the nucleating agent was deposited between thin PP films and the nucleation was evaluated by polarized light microscopy (PLM), X-ray scattering (WAXS), and differential scanning calorimetry (DSC). The nucleation activity of Au particles in PP was lower than it might be expected from the previous studies and depended on their morpho...

Nonwovens of commercially available polylactide (PLA) were produced by electrospinning using laboratory scale equipment. The nonwovens were subsequently coated with an aqueous dispersion of multiwall carbon nanotubes (MWCNT), using the padding technique. MWCNT formed 3D networks on fiber surfaces making the nonwovens electrically conducting, with surface electrical resistivity of 77 Ω/sq – 680 Ω/sq. Modification of the nonwovens with methyltrichlorosilane made them superhydrophobic, what was reflected in the water contact angles of 160 − 175°. In turn, electrochemical deposition of silver particles (Ag°) on the conductive nonwovens imparted antibacterial activity against Staphylococcus aureus (gram-positive) and Escherichia coli (gram-negative).

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).