Polypropylene Block Copolymer Research Articles

High strain rate behaviour of polypropylene microfoams

Microcellular materials such as polypropylene foams are often used in protective applications and passive safety for packaging (electronic components, aeronautical structures, food, etc.) or personal safety (helmets, knee-pads, etc.). In such applications the foams which are used are often designed to absorb the maximum energy and are generally subjected to severe loadings involving high strain rates. The manufacture process to obtain polymeric microcellular foams is based on the polymer saturation with a supercritical gas, at high temperature and pressure. This method presents several advantages over the conventional injection moulding techniques which make it industrially feasible. However, the effect of processing conditions such as blowing agent, concentration and microfoaming time and/or temperature on the microstructure of the resulting microcellular polymer (density, cell size and geometry) is not yet set up. The compressive mechanical behaviour of several microcellular polypropylene foams has been investigated over a wide range of strain rates (0.001 to 3000 s −1 )i n order to show the effects of the processing parameters and strain rate on the mechanical properties. High strain rate tests were performed using a Split Hopkinson Pressure Bar apparatus (SHPB). Polypropylene and polyethylene-ethylene block copolymer foams of various densities were considered.

Collagen-based packaging films for nonfood applications and their comparison with commercial polyolefin (polypropylene block copolymer) films

The potential use of collagen as packaging film was investigated. Various chemical properties (permeability, resistance to chemicals, and weathering) and physical properties (resistance to puncture impacts, tearing, and temperature) of cast films were compared with those of a polyolefin (polypropylene block copolymer) car body paint protection film. The collagen films showed excellent resistance to nonpolar substances (oil and fuel mix) and they had tensile strengths (27 N/mm2) similar to those of polyolefin films (38 N/mm2). The collagen films tested, however, were brittle (elongation at break = 34%) and exhibited a high solubility in polar substances like deionized water (total soluble matter = 20 wt% at 20°C, 40 wt% at 60°C after 1 h). Due to the low water resistance their usage as packaging films is anticipated to be restricted to indoor applications or to applications which require water solubility.

Characterization of Polypropylene blockcopolymer by Temperature Dependent Scanning Probe Microscope and Dynamic Mechanical Analysis

Characterization of Polypropylene blockcopolymer by Temperature Dependent Scanning Probe Microscope and Dynamic Mechanical Analysis

The use of the load separation parameter Spb method to determine the J– R curves of polypropylenes

The characterization of the fracture behaviour of polypropylenes following standard procedures is a complex task due to the difficulties encountered in the experimental measurement of the crack length. The load separation parameter S pb method is capable of determining J– R curves by testing a single pre-cracked specimen and a single blunt notched specimen. This work examines several aspects of the method, such as load separation property, its sensitivity to the initiation criterion, the influence of the blunt notched specimen used as reference and the calibration procedure. A polypropylene homopolymer and an ethylene–polypropylene block copolymer (REPSOL YPF) were analyzed. The results have shown that load separation property can be applied to both materials. Also, the initiation crack growth energy, J IC, is very sensitive to the point chosen as crack growth onset. For that reason, a criterion is proposed. Finally J– R curves are modified depending on the number of calibration points used.

Mechanical Properties and Morphology of LDPE/PP Blends

Two types of polypropylene (PP) with different molecular structure, namely, homogeneous PP (PPH) and PP block‐copolymer (PPC), were blended with a long chain, branched, low density polyethylene (LDPE) in a twin screw extruder and then injection moulded into test specimens; the mechanical properties and morphology of the blends are reported. The tensile strength, elastic modulus, flexural strength, and flexural modulus of the blends increased monotonically with increasing PP content, although exhibiting a slightly negative deviation from the rules of mixtures due to the relatively poor compatibility of the components, which caused the blends to separate into individual phases. Comparatively, these mechanical properties of the LDPE/PPH blend were much higher than that of the LDPE/PPC blend, which was attributable mainly to the fact that the mechanical properties of neat PPH are stronger than that of neat PPC. With respect to the impact strength of the blends, a maximum value appeared in LDPE/PPH blends when PPH content was about 20% and also in LDPE/PPC blends when PPC content was about 40%.

Failure characterization of polypropylene block copolymer welded joints

AbstractThe failure behavior of polypropylene block copolymer double‐V welded joints was investigated. Joints were prepared using the hot‐gas welding technique at varying gas temperatures in the range of 230–260°C. Uniaxial tensile tests, fracture mechanics experiments, several microscopy techniques, and complementary FEM analysis were carried out to assess the quality of filler rods and welding interfaces. The developed interfaces were weaker than the parent material as a consequence of polymer chains segregation during the welding process. The hot‐gas temperature had a marked effect on the failure behavior of the welds. The highest interface toughness was attained at the highest gas welding temperature used at which, polymer chains were able to quickly diffuse into the parent material enlarging the distance of penetration and hence the micro‐deformation capability of the joint. POLYM. ENG. SCI., 47:1062–1069, 2007. © 2007 Society of Plastics Engineers

Interfacial adhesion enhancement of polyethylene–polypropylene mixtures by adding synthesized diisocyanate compatibilizers

AbstractImmiscible and incompatible binary blends of commercial polypropylene (PP)/polyethylene (PE) display poor mechanical properties. The addition of compatibilizer to reinforce and enhance an adhesion at the interfaces between PE–PP mixtures has been conducted. The compatibilizer chosen was in the group of Ziegler–Natta's PE–PP block copolymer with diisocyanate linkage. The effects of adding the compatibilizers were assessed by morphology studies, thermal analysis, and mechanical testing. DSC curves of crystallization and FTIR provided evidences to support the formation of PP/PE block copolymer. Significant improvements in the mechanical properties of 50/50 PE/PP blends containing compatibilizer have been noted. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3766–3773, 2007

High rate toughness of ductile polymers

Impact toughness of two highly ductile polymers: acrylonitrile–butadiene–styrene (ABS) terpolymer and polypropylene block copolymer (PPBC) – was evaluated using the essential work of fracture (EWF) – and a J– R resistance single specimen curve – S pb techniques. The EWF has proved to be capable of determining toughness from the total fracture energy of several samples differing in initial ligament length and the linear regression of the data. On the other hand, the S pb method, which is based on the load separation principle, is able of constructing J– R curves by inferring instantaneous crack growth length from the sole comparison between one sharp and one blunt-notched load–displacement traces. Results show that both methodologies can be used under impact conditions when evaluating ABS polymers. However, ABS impact fracture toughness value yielded by the EWF method, w Ie, was larger than the J 0.2 value obtained from the S pb method. This difference was imputed to the more progressive development of the necking zone in front of the crack tip under plane strain conditions. On the contrary, for very ductile fracture behavior like that demonstrated by PPBC in which J-controlled conditions were not achieved and hence J– R curves could not be built the EWF appeared as a valuable alternative to characterize impact toughness.

Synthesis of polypropylene block copolymers from brominated styrene-terminated isotactic polypropylene

Isotactic polypropylene block copolymers, isotactic-polypropylene- block-poly (methyl methacrylate) ( i-PP- b-PMMA) and isotactic-polypropylene- block-polystyrene ( i-PP- b-PS), were prepared by atom transfer radical polymerization (ATRP) using a brominated styrene-terminated isotactic polypropylene macroinitiator synthesized from bromination of styrene-terminated isotactic polypropylene. The styrene-terminated isotactic polypropylene can be obtained by polymerization of propylene in the presence of styrene and hydrogen chain transfer agents using a rac-Me 2Si[2-methyl-4-(1-naphyl)Ind] 2ZrCl 2 as catalyst. The molecular weights of isotactic polypropylene block copolymers were controlled by altering the amount of hydrogen used in the polymerization of propylene and the amount of monomer used in the blocking reaction. The effect of i-PP- b-PS block copolymer on PP–PS blends and that of i-PP- b-PMMA block copolymer on PP–PMMA blends were studied by scanning electron microscopy.

分散相の構造がブロックポリプロピレンのタフネスに及ぼす影響

ブロックポリプロピレン (PP) のランダムコポリマ一部の分率と共重合比により分散相の構造を調整し, それがタフネスに及ぼす効果について, ひずみの拘束の解放によるタフニングのメカニズムを基に検討した. ブロックPPのぜい性破壊はランダムコポリマーから形成される分散相から発生する多数のボイドにより抑制されたが, ボイドの形成に寄与する分散相の体積分率は, 重合時におけるラソダムコポリマーの分率の半分以下であった. ランダムコポリマー部のエチレン共重合比を増加させると, 分散相の体積分率が増加するため, 低温でのタフネスは向上した. 一方, エチレン共重合比を増加させると常温での破断伸びは低下するため, ねらいとする耐衝撃性によって適するエチレソ共重合比があることがわかった.

PP-Blends with Tailored Foamability and Mechanical Properties

The optimisation of physical foaming of branched Daploy™ WB130HMS polypropylene foam resin and corresponding blends with a Polypropylene Blockcopolymer are described in this paper. The resulting foam morphologies of blends consisting of linear and branched polypropylene materials produced at various processing temperatures were studied using a single-screw tandem foam extrusion system and their volume expansion behaviours were compared. Three different die geometry's were tested for physical foaming of PP-blends using 5 and 10 wt% of butane. A correlation between extensional rheology and lower limit of foam density for blends was found. Depending on die geometry the use of different concentrations of branched polypropylene resin in the blends was required to achieve foam densities < 50 kg/m3. The influence of foam density and blend ratio on mechanical properties of foams will be discussed on a model and representative samples.

PP/PEのせん断流動下でのモルフォロジー変化と粘弾性に関する研究

The morphology change and viscoelastic behavior of polypropylene/polyethylene blend systems under shear flow was investigated. Polypropylene homo-polymer (PP-A), polypropylene block-copolymer including ethylene-propylene copolymer part (PP-B) and linear low density polyethylene (PE) were used for this study. The steady and dynamic viscoelasticities under shear flow were measured. Mix rule was not adapted for the rheological properties at long times. The relaxation modulus of PP-A and PP-B decreased as a function of the time, but that of both PP/PE blends showed 2-step relaxation mode. The swelling ratio of PP-A and PP-B increased according to the increase of shear rate. On the other hand, shear rate dependence of the swelling ratio of PP became small by addition of PE. The morphology of capillary strands after shear flow was observed by TEM. As a result, the morphology change of PP-B was small for wide range of shear rate. The droplets size was large and it strongly orientated to flow direction at low shear rate region for both PP/PE blends. Then, the size and orientation of droplets were reduced due to the increase of the shear rate. It was concluded that the swelling behavior of both PP/PE blends was affected by morphology change according to the shear rate.

Thermal and mechanical properties of the polymers synthesized by the sequential polymerization of propylene and 1‐hexadecene

AbstractThe block copolymer of poly(1‐hexadecene) (PHD) and polypropylene (PP) was effectively synthesized by the sequential polymerization of propylene and 1‐hexadecene by using highly isospecific TiCl3/Cp2Ti(CH3)2 (Cp = cyclopentadienyl). The block copolymers had two separate melting temperatures of constituent blocks. The modulus of PHD–PP block copolymer was enhanced as the content of sequentially polymerized PP block was increased. The elongation at break showed positive deviation at the intermediate compositions from the simple additive values of constituent homopolymers. Shape memory effect which utilizes the crystalline PHD block as a reversible phase and the crystalline PP block as a fixed structure was examined. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1709–1715, 2002; DOI 10.1002/app.10551

ON THE DEPENDENCE OF IMPACT BEHAVIOR ON THE CRYSTALLINE MORPHOLOGY IN POLYPROPYLENES

The correlation between impact resistance and crystalline morphology was studied on specimens prepared from three different polypropylene (PP) homo- and copolymers, obtained by injection molding. The crystalline morphology was varied using three different nucleating agents. Linear elastic fracture mechanics was applied for the description of fracture resistance. The results indicate that morphological characteristics strongly influence the mechanical performance of the polymers. According to Young's theory for yielding, the resistance to crack initiation, represented by K Ic, correlates with the thickness of the lamellae. This suggests that the onset for yield can be described by a dislocation mechanism. The total energy absorbed during impact, G Ic, is a complex function of the morphology with no single identifiable morphological characteristic that dominates its value. The heterogeneous, dispersed morphology of the PP block copolymer initiates an additional energy absorption mode compared to the homo-polymer and the random-copolymer.

Polypropylene filled with flame retardant fillers: mechanical and fracture properties

Two grades of isotactic polypropylene (homopolymer and block copolymer) were filled with magnesium and aluminium hydroxides, and studied focusing the mechanical and fracture characteristics of the composites. As expected, dispersion of such fillers in PP resulted in improved stiffness and reduced tensile yield strength. By one hand, the composites fracture resistance was characterised at low strain rate applying the J-integral concept; the resistance to crack growth initiation (J IC ) was found decreasing as the Mg(OH) 2 concentration was raised in the copolymer PP matrix. By the other hand, the linear-elastic fracture mechanics (LEFM) parameters were determined by means of instrumented impact tests at 1 m/s on the homopolymer PP filled with uncoated Al(OH) 3 particles. The higher the Al(OH) 3 mean particle size, the lower the composite fracture energy (G IC ). In the opposite, with commercial surface-coated filler grades it was not possible to achieve LEFM conditions to characterise the fracture toughness of filled PP at 1 m/s, because the Mg(OH) 2 surface coating, which is applied in practice to improve the melt processing, acts increasing the composite plasticity and reducing the tensile yield strength.

Low-rate fracture behaviour of magnesium hydroxide filled polypropylene block copolymer

This paper presents the fracture behaviour of injection-moulded magnesium hydroxide filled polypropylene block copolymer (PP) as a function of the filler content, and it is compared to that of the unfilled PP. The J-integral concept was applied from tests carried out on SENB specimens according to the European Structural Integrity Society (ESIS) protocol for plastics. The results show lower fracture toughness (J IC ) as the filler content increases in the composite, what is explained on the basis of morphological details.

Predictions of the Thermodynamic Properties of Multicomponent Polyolefin Blends from Measurements on Two-Component Systems

Scattering experiments were conducted on a critical, binary mixture of polyethylene (PE) and head-to-head polypropylene (PP), and a symmetric PE−PP diblock copolymer melt. The binary mixture exhibited a liquid−liquid phase transition at 143 °C, while the block copolymer exhibited an order−disorder transition at 149 °C. Estimates of the Flory−Huggins interaction parameter between PE and PP, and the statistical segment lengths of the chains were obtained by fitting neutron scattering profiles from the PE/PP blends and the PE−PP block copolymer, in the single-phase regime, to theoretical predictions based on the random phase approximation (RPA). These estimates were used to compute the scattering profiles of multicomponent blends comprising PE, PP, and PE−PP. A phase diagram for these blends was constructed on the basis of the computed scattering profiles. In the paper that follows this one, we compare the theoretical computations with experimental data from multicomponent PE/PP/PE−PP blends.

5618886 Olefin polymerization catalyst and process for preparing polypropylene and propylene block copolymers

The present invention provides olefin polymerization catalysts and processes for preparing a polypropylene and a propylene block copolymer using the olefin polymerization catalysts. The olefin polymerization catalyst (1) of the invention is formed from: (I-1) a contact product obtained by contacting: (A) a solid titanium catalyst component, (B) an organometallic compound catalyst component, and (C) a specific organosilicon compound; (II-1) (D) a specific polyether compound; and optionally, (III) an organometallic compound catalyst component. The olefin polymerization catalyst (2) of the invention is formed from: (I-2) a contact product obtained by contacting: (A) a solid titanium catalyst component, (B) an organometallic compound catalyst component, and (D) a specific polyether compound; (II-2) (C) a specific organosilicon compound; and optionally, (III) an organometallic compound catalyst component. The propylene is polymerized in the presence of the above-mentioned olefin polymerization catalysts to prepare highly isotactic polypropylene. The propylene block copolymer is prepared by the steps of polymerizing propylene to form a polypropylene component and copolymerizing ethylene and an α-olefin of 3 to 20 carbon atoms to form an ethylene/α-olefin copolymer component in the presence of the polymerization catalysts.

Influence of mechanical properties in carbon black (CB) filled isotactic polypropylene (iPP) and propylene-ethylene block copolymer

The mechanical properties of isotactic polypropylene (iPP) and propylene-ethylene block copolymer (Co-PP) with carbon black (CB) were added as a filler. By mixing appropriate amounts of the two components through melt-blending in a twin-screw extruder, the blended pellets were prepared to a series of test specimens by injection molding. A scanning electron microscopic study was performed of the morphologies of the impact fractured surfaces. The blending of CB in Co-PP not only improves the impact strength, but also improves the flexural modulus and tensile strength; however, the heat distortion temperature (HDT) of the Co-PP/CB blends decreased with greater filler content. Furthermore, the filler of CB improves the tensile yield strength only at low filler content in iPP/CB blends, and the heat distortion temperature (HDT) and flexural modulus of the iPP/CB blends increased with greater filler content. The impact behavior is not good for the iPP/CB blends. Overall, Co-PP/CB has better interaction of molecules than iPP/CB. © 1996 John Wiley & Sons, Inc.

Novel polypropene materials derived from vinylidene‐terminated oligopropenes

AbstractMetallocene‐based homogeneous Ziegler–Natta catalysts produce mono‐olefin‐terminated oligopropenes with narrow molecular weight distributions, controlled stereoregularities, and molecular weights ranging from 100 to 30,000 g/mole in high yield slurry and solution processes. Steric and molecular weight control are influenced by metallocene structures, and by polymerization conditions such as temperature and propene concentration. Predominantly mono‐vinylidene‐terminated oligopropenes are attractive intermediates, and feedstock for the synthesis of a variety of polypropylene materials, including blends, block and graft copolymers. The key step is the chain end functionalization of the vinylideneterminated oligopropenes via double bond conversion reactions, followed by the controlled synthesis of polypropylene block and graft copolymers. In melt and solution processes the olefinic end groups have been converted into a variety of polar functional groups, e.g. hydroxy, carboxy, succinic anhydride, thiol and acrylic groups. The thiol‐terminated oligopropenes are chain transfer agents in radical methylmethacrylate polymerization with chain transfer constant measured to be 0.2. Acrylic monomers and styrene are grown onto the thiol end group via a chain transfer reaction, thus producing a family of block copolymers, e.g. poly(propene‐b‐methylmethacrylate) and poly(propene‐b‐styrene). As demonstrated by SEM fracture surface analysis, the poly(propene‐b‐styrene) block copolymers are efficient dispersing agents for compatibilizing polystyrene/polypropene (70/30) blends. Homo‐ and copolymerization of acrylic oligopropene macromonomers yield novel classes of graft copolymers with pendant isotactic or atactic oligopropene chains. Hydroxy‐terminated oligopropenes are useful initiators in caprolactone polymerization to form poly(propene‐b‐caprolactone) block copolymers. IR spectroscopic studies demonstrate that succinic anhydride‐terminated oligopropenes, obtained by ene‐type addition of maleic anhydride to the olefinic oligopropene end group, react with oligomeric diamine‐terminated polyamide‐6,6 in the melt to yield polypropene‐b‐polyamide‐6,6‐b‐polypropene triblock copolymers.