Polypropylene Block Copolymer Research Articles

The role of recycling in UV and thermal ageing of polypropylene block copolymer

While polypropylene (PP) copolymers containing small amounts of polyethylene are greatly used in automotive, packaging, healthcare and pipe applications an understanding on how their properties are affected with recycling and subsequent ageing is limited. This study involves a characterization of a PP block copolymer that has been recycled three times and has been subjected to thermal and UV ageing. The materials have been characterized by Differential Scanning Calorimetry (DSC), Thermogravimetric analysis (TGA), Fourier Transform Infrared Analysis (FTIR) and micro-indentation. Qualitative differences between the non-recycled, recycled and aged materials are discovered and discussed. The results showed that with recycling only the crystallinity of the polyethylene (PE) fraction is affected. Thermal ageing affected the crystallinity of both PP and PE fractions while UV ageing affected only the crystallinity of the PP fraction. The connection between crystallinity, oxidation and hardness changes with recycling and ageing of the material is discussed.

Enhancement of mechanical properties of high modulus polypropylene grade for multilayer sewage pipes applications

AbstractAdvances in technology have provided fresh generations of stiff polypropylene block copolymers for gravity sewerage applications. The aim of this study is to further enhance the stiffness of these materials through the incorporation of inorganic fillers. In this study, three talc filled PP and one glass fiber filled PP composites were characterized in order to be used as a middle layer in a three‐layer sewage pipe. The obtained results showed an increase of approximately more than 100% and 250% in tensile and flexural moduli by the use of 30%–50 wt% talc‐filled PP and 30 wt.% glass fiber‐filled PP, respectively. This high increase in the rigidity of the material would allow manufacturing pipes with improving ring stiffness. Composites filled with 30 wt% talc or glass fiber showed good filler‐matrix interaction and good filler distribution and dispersion. However, reduced filler‐matrix interaction was observed in the case of the composite filled with 50 wt% talc. In addition, the use of Differential Scanning Calorimetry analysis revealed that the addition of fillers enhanced the crystallization temperature of the polypropylene matrix. Furthermore, Thermogravimetric Analysis showed that the high modulus PP grade retained its thermal stability in the various composites.

Double Crystallization and Phase Separation in Polyethylene-Syndiotactic Polypropylene Di-Block Copolymers.

Crystallization and phase separation in the melt in semicrystalline block copolymers (BCPs) compete in defining the final solid state structure and morphology. In crystalline–crystalline di-block copolymers the sequence of crystallization of the two blocks plays a definitive role. In this work we show that the use of epitaxial crystallization on selected crystalline substrates allows achieving of a control over the crystallization of the blocks by inducing crystal orientations of the different crystalline phases and a final control over the global morphology. A sample of polyethylene-block-syndiotactic polypropylene (PE-b-sPP) block copolymers has been synthesized with a stereoselective living organometallic catalyst and epitaxially crystallized onto crystals of two different crystalline substrates, p-terphenyl (3Ph) and benzoic acid (BA). The epitaxial crystallization on both substrates produces formation of highly ordered morphologies with crystalline lamellae of sPP and PE highly oriented along one direction. However, the epitaxial crystallization onto 3Ph should generate a single orientation of sPP crystalline lamellae highly aligned along one direction and a double orientation of PE lamellae, whereas BA crystals should induce high orientation of only PE crystalline lamellae. Thanks to the use of the two selective substrates, the final morphology reveals the sequence of crystallization events during cooling from the melt and what is the dominant event that drives the final morphology. The observed single orientation of both crystalline PE and sPP phases on both substrates, indeed, indicates that sPP crystallizes first onto 3Ph defining the overall morphology and PE crystallizes after sPP in the confined interlamellar sPP regions. Instead, PE crystallizes first onto BA defining the overall morphology and sPP crystallizes after PE in the confined interlamellar PE regions. This allows for discriminating between the different crystalline phases and defining the final morphology, which depends on which polymer block crystallizes first on the substrate. This work also shows that the use of epitaxial crystallization and the choice of suitable substrate offer a means to produce oriented nanostructures and morphologies of block copolymers depending on the composition and the substrates.

Failure Analysis of the Propylene Parts Used in Trucks

The paper provides the results of failure analysis of the air intake pipe in the truck compressor. The thermal studies were carried out to identify a material, and to analyze the thermal oxidative degradation caused by excessively high operating temperatures. The study of the vehicle component part showed that it was made from polypropylene block copolymer. Analysis of the thermo-physical properties of the warranty polypropylene part showed that the thermal degradation led to a higher polymer crystallization and, as a result, a lower molecular mass due to high temperatures. The results of the thermal studies showed that the polypropylene part was subjected to excessively high operating temperatures which caused the thermal degradation and, as a result, catastrophic failure of the material.

Comparisons of different polypropylene copolymers as potential recyclable HVDC cable insulation materials

The potential recyclable thermoplastic materials represent the future trend of the HVDC cable insulation material to replace crosslinked polyethylene (XLPE). Polypropylene block copolymer (PPB) and polypropylene random copolymer (PPR) with different weight-averaged molecular weight (Mw) were used to investigate the influence of different structure on their properties. The morphology, thermal, mechanical and electrical properties of the PP copolymers were comprehensively studied. The results show that PPB has good thermal properties, but its poor mechanical properties of low breaking elongation and low DC breakdown strength make it not suitable for recyclable HVDC cable insulation application. While PPR has relatively good thermal properties, high breaking elongation and high breakdown strength, which is significantly higher than XLPE and its space charge behavior is much better than PPB and XLPE. So PPR is more potentially suitable for recyclable cable insulation application.

Polipropilen Kopolimerinde (PPB) Kalsiyum Karbonat Tane Boyutunun Kısa Süreli Çekme Sürünme Özellikleri Üzerine Etkisi

Polipropilen blok kopolimer (PPB) kompozit malzemeler, polipropilen ve mikro tane boyutlu mineral dolgulu malzemelerinden, yani kalsiyum karbonattan (CC) oluşur. Testlerde kullanılacak numuneler, üç farklı tane boyutunda kalsiyum karbonat (CC) mineralinin eklenmesiyle oluşturulmuştur. Farklı ticari CC minerallerinin ortalama tane boyutları 1.65 um, 2.15 um, 5 um'dir. PPB kompozit malzemeler, hacim oranının % 17.5'i (veya ağırlıkça % 38.89) içeriğinde sabit miktarda CC ile hazırlandı. Bu çalışmada, hacimce %17,5 olan ve farklı boyutlarda CC katkılı PPB kompozit malzemelerin kısa süreli çekme tip sürünme özellikleri farklı gerilme seviyeleri için incelenmiştir. Gerilme seviyeleri, akma dayanımının altındaki gerilmelerden seçilmiştir. Gerilme seviyeleri 8 MPa ve 16 MPa'dır. Sonuç olarak, katkısız PPB malzemeye göre CC katkılı PPB malzemelerde, sürünme uzaması veya uzama düşüşü (∆ε) değerleri azaldığı tespit edilmiştir. Ayrıca, tane büyüklüğü arttıkça depolanan enerji seviyelerinin azaldığı da bulunmuştur.

Thermal properties of spray-dried cellulose nanofibril-reinforced polypropylene composites from extrusion-based additive manufacturing

Polypropylene block copolymer (PPco) is easier to process in extrusion-based additive manufacturing compared to isotactic PP homopolymer because it shrinks and warps less during printing. This study investigated the thermal properties of PPco and spray-dried CNF (SDCNF)-PPco composite pellet formulations. Thermogravimetric analysis data showed that the addition of SDCNF lowered the thermal degradation onset temperature and increased the residual mass content (at 450 °C) of PPco pellets. The peak degradation temperatures of SDCNF and PPco remained the same. The peak crystallization temperature and relative crystallinity of PPco were increased by the addition of SDCNF and MAPP. The peak melting temperature of PPco was not significantly changed. Printed specimens showed three melting peaks (β, β′ and α crystals) while injection molded PPco only showed one (α crystal) melting peak. Dynamic mechanical analysis results showed that the heat deflection temperatures of printed SDCNF-PPco composites were higher than injection molded PPco. SEM micrographs showed that the addition of SDCNF increased the number of voids inside the printed parts.

Constitutive model and failure locus of a polypropylene grade used in offshore intake pipes

BorECO®™ BA212E is a polypropylene block co-polymer which has become a common material in the manufacturing of large diameter non-pressurized gravity offshore intake pipelines. These lines are used for transportation of sea water for cooling of petrochemical process plants. The pipe sections are joined by butt heat fusion welding to create the pipeline. Recently a few premature failures of such pipelines have been reported in the field. Hence, there is a need to characterize the constitutive behavior of the pipe and weld material in order to properly design these pipes. The aim of this work is to determine the material constitutive behaviors of the pipe material and the welded joint material. Uniaxial tensile tests of both the pipe and weld joint material are conducted at various strain rates. Both the pipe and weld material show a rather high strain rate dependency, with the weld material having about half the yield strength than that of the pipe material. An analytical constitutive material model is developed for both the pipe and weld material, incorporating the effect of strain rate. The failure locus, expressed in terms of the equivalent plastic strain at failure vs. the stress triaxiality, for both materials is also determined as part of the constitutive model using notched dumbbell specimens. The constitutive model and failure loci for the pipe and weld material are implemented in a finite element model (FEM) and are validated by conducting a series of independent four-point bend experiments on both material types. The validation is carried out by comparing the FEM results of the four-point bend model with the experimental results, which show a rather good agreement.

Rapid disintegrating tablets of simvastatin dispersions in polyoxyethylene-polypropylene block copolymer for maximized disintegration and dissolution.

The objective of this research was to improve the dissolution of simvastatin and to incorporate it in rapid disintegrating tablets (RDTs) with an optimized disintegration and dissolution characteristics. Polyoxyethylene–polypropylene block copolymer (poloxamer 188) was employed as a hydrophilic carrier to prepare simvastatin solid dispersions (SDs). Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC) and X-ray diffractometry were employed to understand the interaction between the drug and the carrier in the solid state. The results obtained from Fourier transform infrared spectroscopy showed absence of any chemical interaction between the drug and poloxamer. The results of differential scanning calorimetry and X-ray diffractometry confirmed the conversion of simvastatin to distorted crystalline state. The SD of 1:2 w/w drug to carrier ratio showed the highest dissolution; hence, it was incorporated in RDT formulations using a 32 full factorial design and response surface methodology. The initial assessments of RDTs demonstrated an acceptable flow, hardness, and friability to indicate good mechanical strength. The interaction and Pareto charts indicated that percentage of croscarmellose sodium incorporated was the most important factor affecting the disintegration time and dissolution parameter followed by the hardness value and their interaction effect. Compression force showed a superior influence to increase RDT’s porosity and to fasten disintegration rather than swelling action by croscarmellose sodium. On the other hand, croscarmellose sodium was most important for the initial simvastatin release. The results suggest the potential use of poloxamer 188-based SD in RDT for the oral delivery of poor water-soluble antihyperlipidemic drug, simvastatin.

Promoting effect of crystallization on the foaming behavior in polypropylene homopolymer/polypropylene block copolymer blends

Polypropylene (PP) is a kind of semi-crystalline polymer so it is hard to foam with supercritical carbon dioxide (SCCO2). We used polypropylene block (PP-B) copolymer as a modifier to improve the crystallization behaviors and foaming performance of polypropylene homo polymer (HPP). HPP, PP-B, and a series of HPP/PP-B blends were characterized by differential scanning calorimeter (DSC), X-ray diffraction, and polarized optical microscope. Results show that both the crystallization behaviors and melt strength have influence on the cell structure. The crystallization temperature of PP-B is about 7°C higher than that of HPP and that the crystallization behavior of HPP/PP-B blends is similar to that of PP-B. Much denser and smaller size spherulites are observed in PP-B and HPP/PP-B blends than in HPP, and the crystal structure is unchanged after blending. Scanning electron microscope results show that much more uniform, smaller cells can be obtained for the HPP/PP-B blends. The crystal nuclei formed earlier can act as physical cross-link points, increasing the melt strength and improving dramatically the cell structure and morphology of the HPP/PP-B blends. Furthermore, the best cell structure and morphology was achieved for HPP/PP-B blends with the ratio of 70/30 under the same foaming conditions. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

Novel Solar Thermal Collector Systems in Polymer Design – Part 3: Aging Behavior of PP Absorber Materials

A novel, accelerated aging test method was used to characterize the long-term stability of commercial black-pigmented polypropylene (PP) model materials for solar thermal absorbers at elevated temperatures. The PP model materials investigated, PP-B1 and PP-B2, are based on carbon black pigmented PP block copolymer grades. Using an automatized planning technique, sliced 100 μm thick specimens were prepared, aged in hot air and heat carrier fluid (mixture of 60 vol.-% deionized water and 40 vol.-% commercial propylene glycol) at 95 ̊C, 115 ̊C and 135 ̊C for up to 15,000 hours, and characterized in terms of various aging indicators (i.e., remaining primary stabilizer content, oxidation temperature, carbonyl index and ultimate mechanical properties). In general two major trends were discerned. First, the aging processes of the PP compounds depend on the stabilizer system, but even more heavily on the interaction of the stabilizers with the carbon black pigments and the structure and morphology of the polymer. Although the compound PP-B2 exhibited much faster stabilizer loss and an associated drop in oxidation temperature than PP-B1, mechanical investigations proved a better long-term stability for PP-B2. Second, it was shown for the compounds investigated that exposure to hot air causes harsher aging than exposure to hot heat carrier fluid. This is, presumably related to the reduced quantity of dissolved oxygen and triazole-based corrosion inhibitors used in the heat carrier fluid. While PP-B1 is use for absorbers in unglazed collectors and overheating-protected glazed collectors, the investigations clearly revealed that PP-B2 is a promising alternative.

Migration of Stabilizers from Polypropylene into Simulated Food

ABSTRACTThis study has investigated the migration of stabilizers from three polypropylene materials: a polypropylene homopolymer, a polypropylene block copolymer, and a polypropylene random copolymer in 10% ethanol, 3% acetic acid, 20% ethanol, 50% ethanol, and isooctane according to Regulation (EU) No. 10/2011. Measurements were performed at 20, 40, and 70°C and migration was evaluated from 10 min to 10 days. Measurements were performed by high-performance liquid chromatography (HPLC) with external calibration. The HPLC method provided high correlation coefficients, good precision, good accuracy, and suitable reproducibility. Diffusion coefficients for stabilizers were obtained using a rigorous model based on Fick’s second law and the values were between 6.1 × 10−13 and 3.8 × 10−9 cm2 s−1. By applying an Arrhenius-type equation to the diffusion coefficients, an estimation of activation energy of the diffusion was obtained. The activation energies were from 39.97 to 98.75 kJ mol−1 for the stabilizers. The results indicate that the polypropylene material structure influenced the migration rate, which decreased in the order of the increasing crystallinity in the materials. The diffusion coefficients for stabilizers in the polypropylene random copolymer were higher than in the polypropylene block copolymer and polypropylene homopolymer. The random polypropylene copolymer had the lowest activation energy. These results show that a higher diffusion coefficient indicates a higher migration rate, and a system with a lower activation energy allows more migration.

Characterisation of quasi-brittle fatigue crack growth in pipe grade polypropylene block copolymer

The aim of this work was to characterise quasi-brittle fatigue crack growth in a pipe grade polypropylene block copolymer. Cyclic cracked round bar specimen tests have been identified as a possible way to induce cyclic quasi-brittle crack growth within a reasonable amount of time. To ensure quasi-brittle failures, fracture surfaces have been examined using scanning electron microscopy. For further acceleration of the tests, higher temperatures with adapted load ranges have been applied. For 50 °C and 80 °C, a decrease in testing times of approx. 60% and 80% was achieved without significant changes in failure behaviour (e.g. cyclic crack opening displacement (Δδ) curves or fracture surfaces) of the tested specimens. Relationships between applied load and testing times, as well as between crack initiation and failure have been examined. A change in ratio of crack initiation to total failure time was observed at higher temperatures. This has to be considered in future tests, especially when comparing different types of polypropylene at temperatures, differing from the real application.

Performances of Blends Between Poly(pentabromobenzyl acrylate) and Magnesium Hydroxide as Flame Retardants for Polypropylene Block Copolymers

Combinations between poly(pentabromobenzyl acrylate), and highly pure and surface treated magnesium hydroxide offer improved flame retardant systems for polypropylene block copolymers enabling to reduce significantly the need for high loadings of antimony trioxide used as synergist. According to a series of bench-scale tests, these flame retardant blends are contributing to good melt flow properties, significant increase of thermal dimensional stability and ease to recycle scraps online or at the end of life of plastic parts. Drastic smoke reduction is benefit provided by the presence of magnesium hydroxide. The high molecular weight of poly(pentabromobenzyl acrylate) makes it unlikely to leach out or migrate from plastic parts or to penetrate through the cell membranes of living tissue. The use of ethylene/1-octene copolymers is recommended if high impact properties are required.

Fracture behavior of boehmite‐filled polypropylene block copolymer nanocomposites as assessed by the essential work of fracture concept

ABSTRACTThe essential work of fracture (EWF) method was adapted to determine the fracture toughness of poly(propylene‐block‐ethylene) (EPBC) based nanocomposites with different amounts (from 0 up to 5 wt %) of synthetic boehmite alumina (BA). The dispersion of BA in the matrix was studied by transmission and scanning electron microscopies. Agglomerated micronscale along with well dispersed nanoscale BA particles were present in the EPBC matrix. By contrast to the neat EPBC, all nanocomposites failed by unstable necking. Therefore the energy partitioning concept of the EWF was adapted and attention paid to the yielding‐related term. Both specific yielding‐related essential and nonessential work of fracture parameters increased linearly with the product of the yield stress and elongation at yield derived from static tensile tests. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40447.

Effect of the Mandrel Rotation Speed and Inner Wall Cooling Rate on the Performance and Structure of Polypropylene Block-Copolymer Pipe

Abstract Polypropylene block-copolymer (PP-B) pipes were prepared using a self-designed rotational extrusion processing system. The experimental results showed that though the crystal morphology in the prepared PP-B pipes did not change compared to conventional extrusion, the molecular chains in amorphous region apparently deviated from the axial direction. As a result, in comparison with the conventional extrusion pipes, the mechanical properties in hoop direction and the resistance to crack growth of rotation extrusion PP-B pipes were greatly improved. Furthermore, both the two mechanical properties improved monotonously with increasing mandrel rotation speed and inner wall cooling rate.

On the toughness of thermoplastic polymer nanocomposites as assessed by the essential work of fracture (EWF) approach

The essential work of fracture (EWF) approach is widely used to determine the plane stress fracture toughness of highly ductile polymers and related systems. To shed light on how the toughness is affected by nanofillers EWF-suited model polymers, viz. amorphous copolyester and polypropylene block copolymer were modified by multiwall carbon nanotube (MWCNT), graphene (GR), boehmite alumina (BA), and organoclay (MMT) in 1 wt% each. EWF tests were performed on deeply double-edge notched tensile-loaded specimens under quasistatic loading conditions. Data reduction occurred by energy partitioning between yielding and necking/tearing. The EWF prerequisites were not met with the nanocomposites containing MWCNT and GR by contrast to those with MMT and BA. Accordingly, the toughness of nanocomposites with homogeneously dispersed and low aspect ratio fillers may be properly determined using the EWF. Results indicated that incorporation of nanofillers may result in an adverse effect between the specific essential and non-essential EWF parameters.

Crystallization behavior of sorbitol derivative nucleated polypropylene block copolymer under high pressure

The preparation of γ-phase in polypropylene is still an interesting issue in a long-term. In this work, we introduced a highly effective α-phase nucleating agent 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol derivatives (DMDBS) into polypropylene block copolymer (PPB) and investigated the crystallization behaviors of nucleated PPB sample under high pressure. The crystallization and melting behaviors of samples were characterized by differential scanning calorimetry, and the crystalline structure as well as the relative fraction of γ-phase in the sample was characterized by wide-angle X-ray diffraction (WAXD) and two-dimensional WAXD. Scanning electron microscope was used to characterize the supermolecular structure of samples. The results show that the effects of DMDBS and high pressure on crystallization behavior of PPB were dependent on the content of DMDBS. When the content of DMDBS is smaller than the critical value, there is a synergistic effect between DMDBS and high pressure to promote the formation of γ-phase. Specifically, the critical pressure under which γ-phase dominates completely is also decreased dramatically. When the content of DMDBS is higher than the critical value, there is a competition between the effect of DMDBS, which promotes the formation of α-phase and the effect of high pressure which promotes the formation of γ-phase.

Foaming of Homogeneous Polypropylene and Ethylene-Polypropylene Block Copolymer Using Supercritical Carbon Dioxide

A new process was used to foam homogeneous polypropylene (HPP) and ethylene-polypropylene block copolymer (CPP). Many different foaming behaviors of these two kinds of PP were observed. The HPP and CPP were characterized by Differential Scanning Calorimetry (DSC), and Capillary Rheometry. We find that the melt shear viscosity of CPP is more sensitive to the temperature variation than that of HPP, thus leading to larger change of cell diameter of CPP with foaming temperature. Cell size of CPP is the result of competition between cell nucleation and cell growth. When the saturation pressure is lower or higher than 25 MPa, cell nucleation or cell growth plays a dominant role, which leads to the increase or decrease of cell size, respectively. Because of its low melting temperature and crystallinity, cell diameter of CPP increases with the infiltration temperature increasing, which is opposite to those of HPP. And at the foaming temperature of 152°C or 158°C, cell diameter of CPP increases or decreases with an increase in foaming time, while that of HPP decreases with foaming time increasing at both foaming temperatures.

Degradation Profiles of Injection-molded Polypropylene Block-copolymer after Outdoor and Artificial Weathering

Degradation Profiles of Injection-molded Polypropylene Block-copolymer after Outdoor and Artificial Weathering