Supramolecular polypropylene with self-complementary hydrogen bonding system

The accurate prediction of scientific and statistical parameters depends, largely, on the functional correlation between the variables involved, as well as their definite and predictable behaviour around the line of best fit (the regression line). Hence, an accurate and reliable prediction of the fracture toughness and mechanical properties of glass fibre reinforced polypropylene (GFPP) composites is very important in order to prevent sudden failure of components fabricated from them. It also gives the opportunity to save cost on experimentation. Three grades of polypropylene (PP) of different molecular weights (MW) had glass fibre reinforcements each. The incorporation of maleic anhydride grafted PP (MA-g-PP) into the composites was for compatibilisation between the matrix and reinforcements. There was tensile testing on both the un-notched and notched dumbbell samples. The use of J-Integral analysis was to investigate the fracture toughness of the composites. There was an evaluation of the effect of different MW of PP on the fracture toughness and impact properties of the composites. The examination of the morphology of the materials was by (SEM), while charge coupled device (CCD) camera monitored crack propagation behaviour under tensile loading. There was further morphology study to analyse the fibre length distribution and interfacial shear strength of the composites. Investigations revealed that the composite with the lowest MW PP consistently showed better mechanical, impact and fracture toughness properties than those with higher MW PP. It was also observed that incorporating MA-g-PP as compatibilisers had greater interfacial bonding effects, resulting in higher interfacial shear strength in GFPP of lower MW and high melt flow rates than those of higher MW and low melt flow rate. The investigation further revealed that as the MW of PP decreased, the fracture toughness and other mechanical properties increased in a linear correlation. Crack propagation trailed the interface between PP matrix and GF because of weak bonding in the composite with higher MW PP. This study revealed that incorporating MA-g-PP into GFPP composites achieved better properties with PP of lower MW and higher melt flow rate. Hence the mechanical and fracture properties of GFPP depend largely on the MW of the polymer PP matrix. There was a strong linear correlation observed between the MW of PP, fracture toughness and other impact properties thereby making it possible to make a reliable prediction of any property of the composites from another.

Novel C1-symmetric group 4 ansa-metallocene complexes Me2Si(C5Me4)(2-R-Ind)MCl2 (R = H, M = Ti (5a), Zr (5b); R = Me, M = Ti (6a), Zr (6b)) were prepared from the reaction of dilithium salt of the corresponding ligands Me2Si(C5Me4H)(2-R-IndH) (R = H, Me) with appropriate group 4 metal halides. Crystal structures of 5a, 6a, and 6b determined by X-ray diffraction studies reveal chiral C1-symmetric nature irrespective of the type of metal and ligand. The complexes 5a, 5b, 6a, and 6b were tested for the polymerization of propylene in the presence of methylaluminoxane (MAO) at various temperatures. All of them exhibit good activity and afford moderate to high isotactic polypropylenes. In the case of titanocenes (5a and 6a), polymerization activity, molecular weight, and isotacticity of polypropylene sharply increase as the polymerization temperature decreases, while the increase of polymerization activity and the decrease of isotacticity and molecular weight of polypropylene were observed upon increasing the polymerization temperature in the case of zirconocenes (5b and 6b). The effect of a 2-Me substituent at the indenyl ring on propylene polymerization was apparent in terms of polymerization activity and molecular weight of polypropylene, especially for zirconocenes, but was minor for titanocenes.

Isolation of mesophilic bacterium for biodegradation of polypropylene

A single-step method that produces percolated, dynamic covalent cross-links integrated into the PP homopolymer has not been previously demonstrated. Here, we synthesized covalent adaptable networks (CANs) from polypropylene (PP) homopolymers using 180 °C, radical-based, reactive processing with a free-radical initiator, dicumyl peroxide (DCP), and resonance-stabilized, aromatic disulfide cross-linkers, one methacrylate-based and another phenyl acrylate-based. Both cross-linkers yielded networks when reactively processed at 4 wt % with relatively high molecular weight (MW) PP (melt flow index (MFI) = 12) and 4 wt % DCP. The phenyl acrylate-based cross-linker also yielded PP networks at other studied DCP/cross-linker concentrations and with relatively low MW PP (MFI = 35). Notably, our highest cross-link density PP CAN exhibited full recovery of cross-link density after three reprocessing steps by compression molding; that PP CAN also exhibited full cross-link density recovery within experimental uncertainty after reprocessing by melt extrusion.

Polypropylene (PP) contains promising application prospects in thermoplastic cables for high voltage direct current (HVDC) power transmission because of its outstanding thermal and dielectric properties. However, the problem of poor toughness and space charge has restricted the application of pure PP in HVDC cables. In this paper, polyolefin elastomer (POE) and nano-silica were blended thoroughly and added into a PP mixture by a melting method. Scanning electron microscopy (SEM) was employed to observe the dispersion of POE and nanoparticles. Thermal properties were characterized by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Mechanical properties were evaluated by tensile tests. The elastomeric properties of composites were improved as the dispersed POE could transfer and homogenize external mechanical forces. DC breakdown results showed that the fail strength of composite with 10 phr POE and 1 phr nano-silica was obviously enhanced. The pulsed electro-acoustic (PEA) results showed that the injection and accumulation of space charge was increased by the introduction of POE, while it was restrained by the collective effect caused by nano-silica filling. X-ray diffraction (XRD) spectrograms showed that secondary ordered structures existed in the composites of PP, POE, and nano-silica, and that the ordered structure around the nanoparticles contributed to the enhancement of breakdown strength. The mechanical and dielectric properties were modified synergistically, which made the modified PP a propitious insulation material for HVDC cables.

Stabilization of polypropylene, polypropylene blends with poly (styrene-b-(ethylene-co-butylene)-b-styrene) under irradiation: A comparative investigation

Polyvinylidene fluoride (PVDF) has been considered as an alternative suture material to replace polypropylene (PP) due to its superior biocompatibility and mechanical properties, but it has never been examined for use in barbed sutures, particularly for tendon repair. This study fabricated size 2–0 PVDF and PP bidirectional barbed sutures and compared their mechanical properties and anchoring performance in patellar tendons. The mechanical properties were evaluated via tensile testing, and the anchoring performance of the barbed sutures was assessed by a tendon suture pullout test. Sixty porcine patellar tendons were harvested, transected to mimic a full‐thickness injury, and repaired using a cross‐locked cruciate suturing technique. The ultimate tensile force was 60% higher for the PVDF barbed sutures (22.4 ± 2.1 N) than for the PP barbed sutures (14.0 ± 1.7 N). The maximum pullout force was 35% higher for PVDF barbed sutures (70.8 ± 7.8 N) than for PP barbed sutures (52.4 ± 5.8 N). The force needed to form a 2‐mm gap, indicative of repair failure, was similar between the PVDF (29.2 ± 5.0 N) and PP (25.6 ± 3.1 N) barbed sutures, but both were greater than the 2‐mm‐gap forces for non‐barbed sutures of the same size. In this study, PVDF barbed sutures provided better mechanical properties and improved tissue anchoring performance compared to the barbed PP sutures for porcine patellar tendon repair, demonstrating that PVDF monofilament sutures can be barbed and used effectively for tendon repair.

Mechanical properties of the weld line defect in micro injection molding for various nano filled polypropylene composites

This work investigates the possibility of obtaining the molecular weight distribution (MWD) of linear ultrahigh molecular weight (UHMW) polypropylene (PP) through rheology. To this end, the linear viscoelastic response of a set of UHMWPP samples is measured over the largest possible frequency range. The terminal relaxation is achieved by running creep experiments and converting the compliance in dynamic moduli. A time–temperature concentration principle, recently validated for UHMW polyethylene, is also applied to obtain the terminal relaxation of the sample with the largest molecular weight. The linear rheological response is correlated with gel permeation chromatography (GPC) results by means of the mixing rule based on the relaxation modulus. The implementation of such a rule requires the knowledge of some material parameters governing the stress relaxation of the polymer. Since they are unknown in literature for PP, they are estimated from the comparison between the viscoelastic spectra and the GPC distributions of three lab-made UHMWPPs with narrow polydispersity. Such parameters are then used as a basis to predict the MWDs of two UHMWPP samples with large polydispersity. The variability of the parameters upon molecular weight and polydispersity is assessed by applying the mixing rule to two different PP samples with lower molecular weights, one with narrow polydyspersity and another one with broad polydispersity. As the GPC curves of the samples are available, first the direct problem of estimating the rheological response from MWD and then the inverse problem of obtaining the MWD from the rheological data are solved. An overall satisfactory agreement is found between the calculated and measured MWD for the two samples, with both the direct and inverse approach.

Geocell is widely used in the treatment of poor roadbed, which can restrain soil laterally and improve the stability of soil. In cold area engineering, a change in temperature can influence the mechanical properties of geocell of different materials. To study the mechanical response of geocell at low temperatures, three types of geocell strips commonly used in engineering, namely the polyethylene (HDPE), polypropylene (PP), and polyester (PET), were studied via the uniaxial tensile test at the ambient temperatures of −5 °C, −20 °C, and −35 °C, respectively. Meanwhile, the tensile strength, fracture mode, and temperature sensitivity of geocell specimens were compared. It is concluded that: (1) at low temperatures, the tensile strengths of HDPE and PET geocell strips are significantly improved, while that of the PP geocell strip is less sensitive to the temperature. (2) The PP geocell is subject to a brittle failure at all ambient temperatures. The PET geocell strip experiences a hard-ductile failure at normal temperatures of −5 °C and −20 °C. While in the tensile test at −35 °C, it is prone to brittle failure and hard-ductile failure. The HDPE geocell strip suffers from ductile failure at all ambient temperatures. (3) At low temperatures, overall, the tensile properties of the PET geocell strip is better than those of the PP and HDPE geocell strips.

Despite the popularity of fiber reinforced polypropylene (PP) composites both in academia and industry, the research on basalt fiber (BF) reinforced thermoplastic PP composites is quite limited. Due to their superior properties, BFs have a great commercial potential for industrial applications. In this study, six different silane coupled BF/PP composites were prepared with fiber contents up to 15wt% using a twin-screw extruder. Maleic anhydride grafted PP (MA-g-PP) coupling agent content was fixed at 10wt%. Mechanical properties were investigated by tensile, flexural, and Izod impact tests. Thermal, viscoelastic, and morphological properties were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM), respectively. The results showed that BFs have substantial effect on the mechanical and viscoelastic properties of the composites. The considerable increase in the tensile strength, flexural strength, and Izod impact strength was attributed to the higher interfacial adhesion between the BF and PP matrix in the presence of MA-g-PP coupling agent. The SEM images proved the increased interfacial adhesion between the fibers and the PP matrix. The improved interfacial adhesion was also affected the crystallization behavior of PP.

Polymerization of propylene was conducted at 40 °C with the catalytic system of TiCl4/MgCl2/ Al (C2H5)3/ethyl benzoate using hydrogen as a chain transfer agent, and the effect of hydrogen on the molecular weight was examined separately with the soluble and insoluble fractions in boiling n-heptane. It was found that the chain transfer reaction of the atactic and isotactic polymers took place via an atomic hydrogen and a molecular hydrogen, respectively. The result strongly supports the previous mechanism that there exist two types of polymerization centers, one having two vacancies which gives the atactic polymer and the other having one vacancy which gives the isotactic polymer.

Polypropylene/starch blends were prepared using starch of different botanical source. The influence of starch type and starch content on thermal properties and morphology of polypropylene/starch blends was studied. Corn and potato starches were used as starch source. The starch content in the blends was 7 and 15 wt-%. Characterization of PP and PP/starch blends by (DSC), (TGA), and (SEM) was carried out to obtain information on miscibility among PP and starch. The starch domains exhibited characteristic voids be due to thermal degradation.

This study investigates the influence of incorporating 30 wt.% polyolefin elastomer (POE) on the physical, mechanical, and microstructural properties of 3D printed three widely used thermoplastic: acrylonitrile butadiene styrene (ABS), low density polyethylene (LDPE), and polypropylene (PP). Three ABS-POE, LDPE-POE, and PP-POE blends were prepared by melt mixing method and printed by direct granule-based material extrusion, and finally the printability, microstructure, thermal, and mechanical properties aiming for potential usage in various applications were investigated. Dynamic Mechanical Thermal Analysis (DMTA) results revealed a notable shift in the glass to rubber phase to a higher temperature range and an increase in the glass transition temperature due to the presence of POE elastomers. Mechanical properties of the 3D printed samples were meticulously examined and compared with prior research. All blend samples containing 30 wt.% POE exhibited significantly enhanced ductility, attributed to aligned polymer chain reactions. ABS-POE samples demonstrated superior mechanical properties compared to PP-POE and LDPE-POE samples, likely attributed to fewer potential failure points, as evidenced by Scanning Electron Microscope (SEM) analysis of fractured cross-sections of 3D-printed samples immersed in liquid nitrogen. Additionally, 3D-printed samples with combined infill orientations (0° and 90°) were generated and subjected to tensile strength testing. Furthermore, samples 3D-printed specimens by honeycomb filling pattern for compression tests were included in the study. Microstructure analyses identified common 3D printing defects responsible for failure modes in the printed samples.

In this work, cetyltrimethyl ammonium bromide and methacryloyloxyethyhrimethyl ammonium chloride were used to prepare organophilic montmorillonite (O‐MMT). Then, polypropylene (PP)–clay nanocomposites were prepared by the in situ grafting polymerization of styrene (St)‐containing O‐MMT onto PP with tert‐butyl perbenzoate as an initiator in the solid state. Fourier transform infrared spectroscopy, gel permeation chromatography, transmission electron microscopy, and X‐ray diffraction were applied to study the structure of the layered silicate and modified PP. The surfaces of the composites and, thus, the distribution of the clay in the PP matrix were characterized by scanning electron microscopy. The rheology and mechanical properties were studied and are discussed. According to the characterization results, OMMT and St were already grafted onto the PP main chain. Also, the intercalated structure of montmorillonite could be stabilized, and a stable exfoliated structure could be attained. Namely, intercalated PP/OMMT nanocomposites were obtained. The rheological results clearly show that these PP/OMMT nanocomposites had long‐chain‐branched structures. The peroxide modification of PP had minor effects on the tensile and bending strengths of the modified PP; however, this modification resulted in a significant reduction in the impact strength. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012