Annealing of polypropylene/poly(ethylene-co-propylene) blend. II. Influence of the structure and properties of poly(ethylene-co-propylene) and blended polyethylene on impact strength

The effect of annealing on the impact strength of PP/poly(ethylene-co-propylene) (PEP) and PP/PEP/PE blends was studied with regard to the structure of PEP and the polyethylene crystallinity. The tensile impact strength of annealed blends was remarkably affected by the PEP structure such as molecular weight and comonomer composition and the annealing temperature, while the brittle temperature was scarcely affected. For the PP/PEP/PE blends, annealing at temperatures above the melting point of PE lowers the tensile impact strength in a similar manner as the PP/crystalline PEP blend. These phenomena were explained on the basis of the deformation mechanism presented in the previous article, that is, a thicker interfacial layer of PP and PEP forms by means of annealing to increase the energy needed to deform the interface. By using a scanning electron microscope, the transition layer was observed at the interface between amorphous PEP and PE in the PP/amorphous PEP/PE blend after etching with nitric acid. The formation of a thicker transition layer between amorphous PEP and PE and a sizeable increase in PE particle size by annealing was observed. The phenomena should be correlated with the impact sensitivity, especially tensile impact strength, in the PP/crystalline PEP and PP/amorphous PEP/PE blends. A reasonable explanation of the microstructure in PP/PEP blends has been developed in terms of comonomer composition and melting property of PEP.     

Annealing of commercial block polypropylene. I. Thermal and physical properties

Investigations were carried out regarding the effect of annealing of ethylene–propylene block copolymer (block PP) moldings on their tensile impact strength (TIS), brittle temperature (Tb), and other mechanical properties. Annealing near the melting point improves TIS and Tb as the result of recrystallization. With a system in which a minute amount of talc is added as a nucleating agent, the degree of improving TIS through annealing is considerably less than that with a nonnucleated system. The effect of annealing on the impact strength is due to changes of fine texture and morphology of crystallites and is explicable by recrystallization and polymer diffusion. © 1992 John Wiley & Sons, Inc.     

Annealing of polypropylene–poly(ethylene-co-propylene) blends. I. Thermal and physical properties of blends

Annealing of polypropylene and blends of polypropylene and poly(ethylene-co-propylene) was studied. The structural and physical properties were determined from thermal, mechanical, physicochemical, and spectral investigations. The particular emphasis was on the characteristics of structure and thermal properties of relatively amorphous components segregated from the crystalline region by annealing. Annealing of polypropylene induced an increase in crystallinity resulting in a decrease in impact strength. In contrast, by annealing a blend of polypropylene and poly(ethylene-co-propylene), the impact strength and rigidity were significantly improved with an increase in annealing temperature. The effect of annealing in a binary system was ascribed to the formation of a thicker transitional layer at the interface of the two polymers owing to the increased mobility of amorphous polymer segments. The results of tensile impact strength and brittle temperature were correlated with a deformational mechanism involving the crazing of the matrix.     

Studies on binary and ternary blends of polypropylene with SEBS,PS, and HDPE. II. Tensile and impact properties

Studies are reported on tensile and impact properties of several binary and ternary blends of polypropylene (PP), styrene-b-ethylene-co-butylene-b-styrene triblock copolymer (SEBS), high-density polyethylene (HDPE), and polystyrene (PS). The blend compositions of the binary blends PP/X were 10 wt % X and 90 wt % PP, while those of the ternary blends PP/X/Y were 10 wt % of X and 90 wt % of PP/Y, or 10 wt % Y and 90 wt % PP/X (PP/Y and PP/X were of identical composition 90:10); X, Y being SEBS, HDPE, or PS. The results are interpreted for the effect of each individual component by comparing the binary blends with the reference system PP, and the ternary blends with the respective binary blends as the reference systems. The ternary blend PP/SEBS/HDPE showed properties distinctly superior to those of PP/SEBS/PS or the binary blends PP/SEBS and PP/HDPE. Differences in the tensile yield behavior of the different samples and their correlation with impact strength suggested shear yielding as the possible mechanism of enhancement of impact strength. Scanning electron microscopic study of the impact fractured surfaces also supports the shear yielding mechanism of impact toughening of these blends.     

Influence of an annealing treatment on the solid‐state grafting of styrene onto spherical isotactic polypropylene granules

The main place of solid‐state graft polymerization in polypropylene (PP) granules has been believed to be the amorphous region of PP. In this work, the solid‐phase morphology of nascent spherical PP (N‐PP) granules was found to be markedly changed by an annealing treatment. The crystallinity of PP granules was almost doubled after annealing at 150°C for 12 h, whereas the porosity of the granules was unchanged. Solid‐state grafting polymerizations of styrene initiated by tert‐butyl perbenzoate in both N‐PP and annealed polypropylene (A‐PP) granules were compared under different reaction conditions. The formation of gel in the product could be completely depressed at a low concentration of the initiator when A‐PP granules were used as the matrix and graft‐polymerized at 120°C. Both the introduction of styrene and the annealing treatment of the PP granules led to a depression of polymer degradation in the process of the grafting reaction. However, using A‐PP as the matrix caused an increase in the grafting degree at a relatively high concentration of the initiator. A reduction in the amorphous phase in the PP granules was thought to be the main reason for the effects of the annealing treatment on the structure of the graft polymerization products. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Characterization of polypropylene and ethylene–propylene copolymer blends for industrial applications

The crystalline structure and physico‐mechanical properties of polypropylene (PP) blended with ethylene–propylene copolymer (EPM) were investigated. WAXS diffractograms showed that the addition of EPM did not affect the crystalline structure of PP. DSC curves revealed the presence of two T_g peaks indicating the amorphous phases of EPM and PP. As EPM increased, the elastomeric domains cavitated from PP matrix increased while the tensile stress and modulus of elasticity decreased. Impact strength, on the other hand, increased, and showed a remarkable effect at 30% EPM/PP. The properties of the blended polymers were compared with the commercial PP impact copolymer, and it was found that polyblends containing 30% EPM was suited for applications on products requiring very high impact strength. Further addition of EPM from 40 to 50% produced very high impact strength, but the tensile stress and modulus of elasticity were very low. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1200–1208, 2000     

Laser annealing of polyetheretherketone (PEEK)

Changes in the crystalline morphology and thermal behavior of amorphous poly(etheretherketone) (PEEK) films have been effected by irradiation with a continuous wave CO₂ laser. At high laser scan rate and power, PEEK films melt and requench into amorphous transparent films. At a scanning velocity of 14 μm/s and incident intensities ≥ 4.8 W/cm² and a Gaussian beam radius of 1.63 mm, PEEK films crystallize “completely” above T_g on laser annealing. Irradiation of PEEK films on a quartz substrate reduces the cooling rate, allowing slower and more perfect recrystallization. Similar changes are effected by reducing the laser scan velocity or by increasing the laser power. Depending on the experimental conditions, laser induced recrystallization may occur on annealing above T_g or on cooling from the melt.     

Structure and properties of rubber-modified polypropylene impact blends

The state of dispersion of poly(ethylene-co-propylene) (PEP) rubber and high-density polyethylene (HDPE) in polypropylene (PP) blends was investigated using scanning electron microscopy to examine solvent-etched microtomed surfaces cut at low temperatures. The validity of the method was established by comparing the areal fraction of dispersed particles in micrographs with the volume fraction of PEP and HDPE in PP-rich blends. When small amounts of PEP and HDPE were added to PP, they combined to form composite PEP–HDPE particles with characteristic internal structures in a PP matrix. Changes in impact strength and flexural modulus with changes in mixing conditions and blend composition were determined and interpreted in terms of the size, composition, and internal structure of the dispersed particles. Particle growth in the melt limited the impact strength level achieved in molded articles. A simple model proposed for screening rubbers for toughening of brittle plastics successfully predicts that PEP rubber should be an excellent impact modifier for PP.     

Effect of heterophasic or random PP copolymer on the compatibility mechanism between EVA and PP copolymers

Compatibility mechanisms between EVA and PP copolymers (C‐PP) blends have been studied as a function of the type of copolymer, using a heterophasic PP copolymer (PP‐EP) and a random PP copolymer (PP‐r‐EP), with similar ethylene content. The morphology and thermal and mechanical properties of PP/EVA blends with different levels of EVA containing 28% vinyl acetate (VA) were determined. The obtained results indicated compatibility for both systems showing interactions at the amorphous interfaces; however, this interaction was higher for the PP‐r‐EP/EVA, which showed a single glass transition temperature and changes in the PP crystalline fraction (changes in the fusion temperature and in the diffraction patterns). The evolution of the morphology from isolated spherical domains (20% EVA) to elongated shapes (40% EVA) was related to the observed changes in thermal and mechanical properties. The impact strength and deformation properties showed significant improvement with increasing EVA content above 40% where the highest values of elongation for the PP‐r‐EPand of impact strength for the PP‐EP were obtained. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Novel method for fabrication of PP/HDPE/PP trilayer microporous membrane with a highly orientated structure

In this work, a highly orientated polopropelene/high-density polyethylene/polopropelene (PP/HDPE/PP) trilayer cast film was obtained from viscous encapsulation of HDPE and PP which involved of controlling the molecular factors and processing conditions. Consequently, a stable stratified flow was obtained as a result of phase-segregation through a single screw extruder under a high draw ratio (DR). Microporous HDPE, PP monolayer films as well as PP/HDPE/PP trilayer film have been successfully fabricated after a proper cold and hot stretching. The influence of DR and annealing process on crystalline structure and orientation of monolayer and trilayer membrane was investigated by differential scanning calorimetry, two-dimensional wide-angle X-ray diffraction and Fourier transform infrared. Both crystallinity and crystalline orientation increased with DR and annealing process. Additionally, the crystallinity in PP/HDPE/PP was lower than it in monolayer films but the orientation of PP/HDPE/PP was higher compared to monolayer films. The lamellae structure of HDPE, PP, and PP/HDPE/PP cast films prepared at different DR values and the influence of annealing process was also studied. The lamellae parameters, the long period (L_p ), the thickness of crystalline region (L_c ) and the thickness of amorphous region (L_a ) were obtained via 2D-small angle X-ray scattering. The long period (L_p ) of PP was 35% smaller than HDPE implying tight stacking in PP. The scanning electron microscopy micrographs of the membrane surface morphology and cross-section obtained from the cold and hot stretching of 30% and 150%, respectively. The results showed that the pore size of HDPE was greater than PP. Besides, the pore number and regularity of PP/HDPE/PP at DR = 90, which had a porosity of 0.48, was the best among all samples. The cross-section of PP/HDPE/PP trilayer membrane was found to be a multilayer structure. However, the majority of HDPE phase was in the middle of film while PP phase was absolutely at the edge of the film. The current work may open an entirely novel and simple way to fabricate PP/HDPE/PP trilayer microporous films. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47249.     

Morphology and mechanical properties of blends of isotactic or syndiotactic polypropylene with SEBS block copolymers

Blends of poly(styrene)-block-poly(ethene-co-but-1-ene)-block-poly(styrene) (SEBS) with isotactic polypropylene (PP) and syndiotactic PP, respectively, were investigated. The morphology was observed by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The cryofracture surfaces studied by SEM did not show any particles that were pulled out, so that a good compatibility between SEBS and different PPs could be assumed. The multiphase character of the blends could be well detected by TEM of RuO₄ stained samples. TEM micrographs of two-layer specimens revealed that SEBS tends to diffuse into the PP phase under formation of micelles. The block copolymer shows a reorientation phenomenon of large domains at the interface before the diffusion into the PP phase occurs. The interfacial strength as a function of annealing time was measured by a peel test of two-layer specimens. Mechanical properties are studied and related to the blend morphology. © 1996 John Wiley & Sons, Inc.     

The functions of crystallizable ethylene‐propylene copolymers in the formation of multiple phase morphology of high impact polypropylene

The functions of crystallizable ethylene‐propylene copolymers in the formation of multiple phase morphology of high impact polypropylene (hiPP) were studied by solvent extraction fractionation, transmission electron microscopy (TEM), selected area electron diffraction (SAED), nuclear magnetic resonance (¹³C‐NMR), and selected reblending of different fractions of hiPP. The results indicate that hiPP contains, in addition to polypropylene (PP) and amorphous ethylene‐propylene random copolymer (EPR) as well as a small amount of polyethylene (PE), a series of crystallizable ethylene‐propylene copolymers. The crystallizable ethylene‐propylene copolymers can be further divided into ethylene‐propylene segmented copolymer (PE‐s‐PP) with a short sequence length of PE and PP segments, and ethylene‐propylene block copolymer (PE‐b‐PP) with a long sequence length of PE and PP blocks. PE‐s‐PP and PE‐b‐PP participate differently in the formation of multilayered core‐shell structure of the dispersed phase in hiPP. PE‐s‐PP (like PE) constructs inner core, PE‐b‐PP forms outer shell, while intermediate layer is resulted from EPR. The main reason of the different functions of the crystallizable ethylene‐propylene copolymers is due to their different compatibility with the PP matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Polyester-Polyether Block Copolymers II. Thermal and Mechanical Properties of Poly(hexamethylene terephthalate)/Poly(oxytetramethylene) Block Copolymers

The melting and crystallisation behaviour of crystalline phases in poly (hexamethylene terephthalate)/poly(oxytetramethylene) block copolymers have been investigated in relation to copolymer composition and polyether block molecular weight (m.w.). In contrast to that in corresponding homopolymer blends, the polyester crystallinity in the block polymers is greatly reduced by incorporation of polyether units, though some persists even at low polyester contents. Concomitant changes in the glass transition temperatures show part of the polyester component to form a homogeneous component of the amorphous phase. The mechanical properties change with composition in parallel with the changes in copolymer crystallinity and T_g. Copolymers with 20-60 w % of poly(oxytetramethylene) units of m.w. 2000 are highly extensible elastomers. Those with higher m. w. polyether blocks have higher modulus and strength but suffer a serious loss of properties at 60d?C. The observations are interpreted in terms of a model in which polyester crystallites (and polyether crystallites also, for the higher m. w. polyether blocks) are supported within an amorphous matrix by tie-molecules whose nature changes with the copolymer compositions. The results are compared with those for analogous polyester-polyethers having different structural components.     

Maleic anhydride grafted polypropylene as a coupling agent for polypropylene composites filled with ink‐eliminated waste paper sludge flour

Ink‐eliminated sludge flour (IESF), a waste residue from the recycling treatment of waste paper, is a promising new kind of filler for thermoplastic polymers with a good price/performance ratio and advantages for environmental protection. In this study, high‐impact polypropylene (PP) and maleic anhydride grafted polypropylene (MAPP) were chosen as a polymer matrix and a coupling agent, respectively, for the preparation of IESF/PP composites, and the structures and properties of the obtained composites were also investigated. The experimental results revealed that IESF not only induced the crystallization orientation of PP along the b axis but also had a restraining effect on the formation of the β phase during the recrystallization of PP from the melt; the addition of MAPP further strengthened this effect to some extent. In addition, the proper addition of MAPP was helpful for improving the thermal stability of the IESF/PP composites. With the strengthening of the interfacial interaction between the IESF and PP matrix by MAPP, the resultant efficient stress transfer from the PP matrix to the IESF particles led to increased tensile and flexural strength. However, the original greater rigidity of MAPP, with respect to PP, reduced the toughness of the composites and caused some negative effects on the impact strength and the elongation at break. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2320–2325, 2004     

Compatibilization of polypropylene/Poly(acrylonitrile‐butadiene‐styrene) blends by polypropylene‐graft‐cardanol

The polypropylene‐graft‐cardanol (PP‐g‐cardanol) was prepared by reactive extrusion with polypropylene (PP) and natural renewable cardanol which could increase the interfacial energy of PP and inhibit the degradation of PP during the process of reactive extrusion and usage. In this article, PP‐g‐cardanol and polypropylene‐graft‐maleic anhydride (PP‐g‐MAH) were used as compatibilizers of the polypropylene (PP)/poly(acrylonitrile‐butadiene‐styrene) (ABS) blends. PP/ABS (70/30, wt %) blends with PP‐g‐cardanol and PP‐g‐MAH were prepared by a corotating twin‐screw extruder. From the results of morphological studies, the droplet size of ABS was minimized to 1.93 and 2.01 μm when the content of PP‐g‐cardanol and PP‐g‐MAH up to 5 and 7 phr, respectively. The results of mechanical testing showed that the tensile strength, impact strength and flexural strength of PP/ABS (70/30) blends increase with the increasing of PP‐g‐cardanol content up to 5 phr. The complex viscosity of PP/ABS (70/30) blends with 5 phr PP‐g‐cardanol showed the highest value. Moreover, the change of impact strength and tensile strength of PP/ABS (70/30) blends were investigated by accelerated degradation testing. After 4 accelerated degradation cycles, the impact strength of the PP/ABS (70/30) blends with 5 phr PP‐g‐cardanol decrease less than 6%, but PP/ABS (70/30) blends with 5 phr PP‐g‐MAH and without compatibilizer decrease as much as 12% and 32%, respectively. The tensile strength of PP/ABS (70/30) blends has a similar tendency to that of impact strength. The above results indicated that PP‐g‐cardanol could be used as an impact modifier and a good compatibilizer, which also exhibited better stability performance during accelerated degradation testing. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41315.     

Compatibilization efficiency of styrene–butadiene triblock copolymers in polystyrene–polypropylene blends with varying compositions

The compatibilization efficiency of two styrene‐butadiene‐styrene triblock copolymers with short (SB1) and long (SB2) styrene blocks was studied in polystyrene (PS)–polypropylene (PP) blends of composition 20, 50, and 80 wt % PS. The supramolecular structure of the blends was determined by small‐angle X‐ray scattering, and the morphology was studied with transmission electron microscopy and scanning electron microscopy. Structural changes in both the uncompatibilized and compatibilized blends were correlated with the values of tensile impact strength of these blends. Even though the compatibilization mechanisms were different in blends with SB1 and SB2, the addition of the block copolymers to the PS–PP 4/1 and PS–PP 1/4 blends led to similar structures and improved the mechanical properties in the same way. These block copolymers had a very slight effect on the impact strength in PS–PP 1/1 blends, exhibiting a nearly cocontinuous phase morphology. The strong migration of SB2 copolymers to the interface and of SB1 copolymers away from the interface were detected during the annealing of compatibilized PS–PP 4/1 blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2431–2441, 2004     

Phase morphology,thermomechanical, and crystallization behavior of uncompatibilized and PP‐g‐MAH compatibilized polypropylene/polystyrene blends

In this article, we discuss the phase morphology, thermal, mechanical, and crystallization properties of uncompatibilized and compatibilized polypropylene/polystyrene (PP/PS) blends. It is observed that the Young's modulus increases, but other mechanical properties such as tensile strength, flexural strength, elongation at break, and impact strength decrease by blending PS to PP. The tensile strength and Young's modulus of PP/PS blends were compared with various theoretical models. The thermal stability, melting, and crystallization temperatures and percentage crystallinity of semicrystalline PP in the blends were marginally decreased by the addition of amorphous PS. The presence of maleic anhydride‐grafted polypropylene (compatibilizer) increases the phase stability of 90/10 and 80/20 blends by preventing the coalescence. Hence, finer and more uniform droplets of PS dispersed phases are observed. The compatibilizer induced some improvement in impact strength for the blends with PP matrix phase, however fluctuations in modulus, strength and ductility were observed with respect to the uncompatibilized blend. The thermal stability was not much affected by the addition of the compatibilizer for the PP rich blends but shows some decrease in the thermal stability of the blends, where PS forms the matrix. On the other hand, the % crystallinity was increased by the addition of compatibilizer, irrespective of the blend concentration. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42100.     

Dynamic mechanical and mechanical properties of polypropylene/poly(vinyl butyral)/mica composites

Three-component composites consisting of polypropylene (PP) matrix, poly(vinyl butyral) (PVB) modifier, and mica filler at various ratios of matrix to modifies and a constant mica content (30 wt %) were prepared by using two different kinds of PVB, viz., PVB and PVB-P. By correlating with the morphology, the dynamic mechanical and mechanical properties of the composites are studied in detail. PVB component in PP/PVB/mica composites cannot display a reinforcing effect to PP/mica binary composites, while impact strength of the composites are reduced further. It associates with incompatibility between PP and PVB, and as well as higher glass transition temperature of PVB. For PP/PVB-P/mica composites, stiffness decreases and, meanwhile, impact strength increases when PVB-P content is 7 wt %. The improvement of impact strength on PP/mica binary composites at the composition is due to a little affinity between the PP matrix and the plasticizer of PVB-P. Moreover, a minor amount of PP-g-MA in the 63/7/30 PP/PVB/mica composites only acts as an adhesion promoter. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2003–2011, 1997     

Equilibrium disperse-dye sorption by isotactic polypropylene films of varied thermal histories

Spherulitic polypropylene (PP) films prepared by a melt-quenched process and then exposed to isothermal annealing treatments at various temperatures ranging from 120°C to 155°C have been dyed at 80°C with C.I. Disperse Yellow 7(Y-7) or p-aminoazobenzene. Different PP films as crystallized isothermally in the range of 60°C to 155°C have also been dyed with the same dyes. The equilibrium dye sorption (M_o) obtained for these films increased slightly with an increase in polymer volume crystallinity (C_u). Using fine structural data of these films, the change in M_o were analyzed in terms of the mosaic-block structural model; e.g., the values of M_o were divided into sorption by the amorphous end region (M_e) located between lamella surfaces and sorption by the amorphous side region (M_s) located between crystalline cores parallel to the molecular chain axis. The value of M_s increased with increasing C_v in both cases of the dyeing systems, while the value of M_e decreased monotonically in an opposite manner. The amorphous chains in the side region seem to have a strong affinity to a long rodlike dye molecule of Y-7; this feature is considered to be associated with the extended chain conformation of the side region which originates from distorted lattice chains.     

Toughening of PP/EPDM blend by compatibilization

To improve the mechanical properties of blends of polypropylene (PP) and terpolymer of ethylene–propylene–diene (EPDM), a triblock copolymer, (PP‐g‐MAH)‐co‐[PA‐6,6]‐co‐(EPDM‐g‐MAH), was synthesized by coupling reaction of maleic anhydride (MAH)‐grafted PP (PP‐g‐MAH), EPDM‐g‐MAH, and PA‐6,6. The newly prepared block copolymer brought about a physical interlocking between the blend components, and imparted a compatibilizing effect to the blends. Introducing the block copolymer to the blends up to 5 wt % lead to formation of a β‐form crystal. The wide‐angle X‐ray diffractograms measured in the region of 2θ between 10° and 50° ascertained that incorporating the block copolymer gave a new peak at 2θ = 15.8°. The new peak was assigned to the (300) plane spacings of the β‐hexagonal crystal structure. In addition, the block copolymer notably improved the low‐temperature impact property of the PP/EPDM blends. The optimum usage level of the compatibilizer proved to be 0.5 wt %. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1267–1274, 2000