Structures and properties of low‐shrinkage polypropylene composites

The high shrinkage and the low impact strength severely limit the applications of the isotactic polypropylene (iPP). In this article, we studied the shrinkage, microstructure, and mechanical properties of the composites consisted of iPP, short glass fiber (GF), maleic anhydride grafted polypropylene (MPP), maleic anhydride grafted polypropylene/polyolefin elastomer (MPPPOE) or composite toughening agents (CTAs). The results show that the shrinkage of the composite with 40% GF reduces to 0.0754% (24 h) and 0.0893(48 h), respectively, under room temperature, which is far lower than the shrinkage [1.782% (24 h) and 1.821% (48 h)] of the pure iPP. For the composite of PP/GF/MPPPOE/CTAs (55/30/5/10), the tensile strength increases to 65.53 MPa (33.8 MPa for pure iPP), the tensile modulus is 1445 MPa which is 136% higher than pure iPP, and the izod impact strength reaches 22.72 kJ/m² (only 5.28 kJ/m² for pure iPP). Not only the scale stability of iPP is remarkably improved, but also the comprehensive mechanical properties are enhanced drastically. This work may generate potential opportunities for iPP in those applications demanding high scale stability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44275.     

Preparation and properties of dynamically vulcanised blends of isobutylene–isoprene rubber and isotactic polypropylene

Abstract

Dynamic vulcanisation was employed to prepare blends of isobutylene–isoprene rubber (IIR) and isotactic polypropylene (iPP) with superior properties. The preparation technology, the effects of the presence of IIR on the crystallisation properties of iPP and the mechanical properties of the IIR/iPP thermoplastic vulcanisates (TPVs) were investigated. It was revealed that, under regular shearing at 180°C, dynamic vulcanisation for 10 min produced IIR/iPP TPVs of excellent properties; while degradation occurred when the duration of vulcanisation was extended to 15 min. Incorporation of IIR into iPP dramatically reduced the size of the iPP spherulites, and thus decreased the melting temperature and the degree of crystallinity of the iPP. When the IIR content was 50 wt-%, maximally balanced mechanical properties of IIR/iPP TPVs were obtained with a Charpy impact strength of 53·6 kJ m^?2 and a tensile strength of 31·3 MPa.     

Preparation and balanced mechanical properties of solid and foamed isotactic polypropylene/SEBS composites

This study presents a self-designed foaming apparatus and routes to manufacture foamed isotactic polypropylene (iPP) blends with uniform and dense cells, using styrene-ethylene-butadiene-styrene (SEBS) block copolymer as toughening additive. The addition of SEBS can clearly enhance the impact strength of solid iPP, iPP blends with a 20 wt% SEBS has obtained high notched impact strength of 75 kJ/m², which is ca. 16 times larger than that of neat iPP. Relatively fine microcellular iPP-SEBS foams with the average cell size of several micrometers, and the cell density of 10⁹ cells/cm³ were fabricated using a batch foaming procedure. Moreover, using our self-designed mold and compression foaming method, iPP-SEBS foams with balanced mechanical properties were produced. With the increasing of SEBS, tensile strength and flexural strength were slightly decreased, but the impact strength was increased clearly. The balanced mechanical properties between stiffness and toughness were achieved after compression foaming.     

Essential work of fracture of polypropylene and polypropylene blends over a wide range of test speeds

The mechanical properties of extruded films of isotactic polypropylene (iPP) and ethylene‐propylene rubber toughened iPP (iPP/EPR) have been analyzed in terms of the specific essential and non‐essential work of fracture using high speed tensile test apparatus modified for quasi‐static testing in the range 0.0001 to 3 ms^?1. Three iPP/EPR grades with modifier contents of 15, 21 and 30 vol% were investigated. As the deformation rate increased, relatively uniform necking of the whole ligament and extensive plastic deformation were progressively replaced by more localized plastic deformation in the blends, and by fully brittle fracture in the unmodified iPP. The non‐essential work of fracture and the total fracture energy were highly sensitive to these changes in deformation mechanism. However, the essential work of fracture, although dependent on the test speed, was less correlated with the extent of global plasticity.     

Greatly improved toughness of isotactic polypropylene blends with traces of carbon nanotubes

In this work, the β‐nucleated isotactic polypropylene (iPP)/ ethylene‐octene copolymer (POE) blends demonstrated greatly enhanced impact toughness by adding traces of carbon nanotubes (CNTs) (only 0.05 wt%). When the POE content was 30 wt%, the impact strength of β‐nucleated iPP/POE blends with CNTs was as high as 51.7 kJ/m², about 5.6 kJ/m² higher than β‐nucleated iPP/POE blends, 15.2 kJ/m² higher than CNTs‐filled iPP/POE blends, and almost 19 times of pure iPP sample. This significantly improved impact toughness was considered to be attributed to the shear yielding and multiple‐crazing, originating from the presence of abundant β‐crystals in the iPP matrix, the enhanced mobility of the molecular chains in the confined amorphous region of iPP lamellae and the homogenous distribution of POE dispersed phase with a small size, indicating the synergistic effect of CNTs, β‐nucleating agent and POE on the toughness of iPP. POLYM. ENG. SCI., 59:757–764, 2019. © 2018 Society of Plastics Engineers     

Mechanical,thermal, and water uptake characteristics of woodflour‐filled polyvinyl chloride/acrylonitrile butadiene styrene blends

Woodflour‐filled composites based on polymeric blends of polyvinyl chloride (PVC) and super high‐impact grade ABS were developed. Mechanical, thermal, and water uptake characteristics of the PVC/ABS matrix and their wood composites were evaluated. In the case of PVC/ABS matrix, the blend at a mass ratio of 50/50 rendered the impact strength with a very high value of up to 65 kJ/m², noticeably higher than those of the parent resins, that is, 6 kJ/m² of PVC and 35 kJ/m² of ABS. Dynamic mechanical analysis thermograms showed two distinct glass transition temperatures (T_gs) that shifted toward each other indicating partial miscibility of the blends. Water absorption of the blends after 24 h immersion was low, that is, within the range of 0.04–0.2 wt % and exhibits a behavior closed to pseudo‐Fickian type. The obtained PVC/ABS wood composites exhibited an increase of flexural modulus as well as T_gs with an increase of woodflour content. Finally, impact strength of the PVC/ABS composites was significantly higher than those of PVC composites or polyethylene composites comparing at the same woodflour content. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of fluorinated poly(etherimide)s toughening for carbon fiber‐reinforced epoxy composites

Novel‐fluorinated poly(etherimide)s (FPEIs) with controlled molecular weights were synthesized and characterized, which were used to toughen epoxy resins (EP/FPEI) and carbon fiber‐reinforced epoxy composites (CF/EP/FPEI). Experimental results indicated that the FPEIs possessed outstanding solubility, thermal, and mechanical properties. The thermally cured EP/FPEI resin showed obviously improved toughness with impact strength of 21.1 kJ/m² and elongation at break of 4.6%, respectively. The EP/FPEI resin also showed outstanding mechanical strength with tensile strength of 91.5 MPa and flexural strength of 141.5 MPa, respectively. The mechanical moduli and thermal property of epoxy resins were not affected by blending with FPEIs. Furthermore, CF/EP/FPEI composite exhibited significantly improved toughness with Mode I interlaminar fracture toughness (G_IC) of 899.4 J/m² and Mode II interlaminar fracture toughness (G_IIC) of 1017.8 J/m², respectively. Flexural properties and interlaminar shear strength of the composite were slightly increased after toughening. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Experimental Investigation of Mechanical and Morphological Properties of Flax-Glass Fiber Reinforced Hybrid Composite using Finite Element Analysis

The use of cellulosic fibers as reinforcing materials in polymer composites has gained popularity due to an increasing trend for developing sustainable materials. In the present experimental study, flax and glass fiber reinforced partially eco-friendly hybrid composites are fabricated with two different fiber orientations of 0° and 90°. The mechanical properties of these composites such as tensile, flexural and impact strengths have been evaluated. From the experiments, it has been observed that the composites with the 0° fiber orientation can hold the maximum tensile strength of 82.71 MPa, flexural strength of 143.99 MPa, and impact strength of 4 kJ/m². Whereas the composites with 90° fiber orientation can withstand the maximum tensile strength of 75.64 MPa, flexural strength of 134.86 MPa, and impact strength of 3.99 kJ/m². Morphological analysis is carried out to analyze fiber matrix interfaces and the structure of the fractured surfaces by using scanning electron microscopy (SEM). The finite element analysis (FEA) has been carried out to predict the resulting important mechanical properties by using ANSYS 12.0. From the results it is found that the experimental results are very close to the results predicted from FEA model values. It is suggested that these hybrid composites can be used as alternate materials for pure synthetic fiber reinforced polymer composite materials.     

Fabrication of polypropylene blends with excellent low‐temperature toughness and balanced toughness‐rigidity by a combination of EPR and SEEPS

To overcome serious rigidity depression of rubber‐toughened plastics and fabricate a rigidity‐toughness balanced thermoplastic, a combination of styrene‐[ethylene‐(ethylene‐propylene)]‐styrene block copolymer (SEEPS) and ethylene‐propylene rubber (EPR) was used to toughen polypropylene. The dynamic mechanical properties, crystallization and melting behavior, and mechanical properties of polypropylene (PP)/EPR/SEEPS blends were studied in detail. The results show that the combination of SEEPS and EPR can achieve the tremendous improvement of low‐temperature toughness without significant strength and rigidity loss. Dynamic mechanical properties and phase morphology results demonstrate that there is a good interfacial strength and increased loss of compound rubber phase comprised of EPR component and EP domain of SEEPS. Compared with PP/EPR binary blends, although neither glass transition temperature (T_g) of the rubber phase nor T_g of PP matrix in PP/EPR/SEEPS blends decreases, the brittle‐tough transition temperature (T_bd) of PP/EPR/SEEPS blends decreases, indicating that the increased interfacial interaction between PP matrix and compound rubber phase is also an effective approach to decrease T_bd of the blends so as to improve low‐temperature toughness. The balance between rigidity and toughness of PP/EPR/SEEPS blends is ascribed to the synergistic effect of EPR and SEEPS on toughening PP. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45714.     

Properties of electropolymerized polycarboxyphenylmethacrylamide matrices/graphite fiber composites: Crosslinking effect

Imide formation from -CONH and -COOH functional groups of 2-carboxyphenylmethacrylamide (2-CPM), 4-carboxyphenylmethacrylamide (4-CPM), 4-carboxyphenyl methacrylamide/methylmethacrylate (4-CPM/MMA) and 4-carboxyphenylmethacrylamide/N-phenylmalemide (4-CPM/NPMI) electropolymerized matrices was investigated. It was found that 2-CPM polymers undergo intramolecular imidization and anhydride formation, which result in a small amount of crosslinked network. On the other hand, the thermally cured 4-CPM polymer demonstrates a significant increase in gel fraction. T_g and dynamic storage modulus, owing to crosslinked network formation. T_gs of 4-CPM/MMA and 4-CPM/NPMI composites measured by thermomechanical analysis after thermal heating were increased and were correlated very well with the preheating time. The 4-CPM/MMA composites with a particle crosslinking (T_g increased to 245°C) maintained a higher Izod impact strength than a typical epoxy composite (200 kJ/m² vs. 100 kJ/m²). Upon heating to promote crosslinking, a lower shear strength (65 MPa) of a 4-CPM/MMA composite increased to a strength of 78 MPa, close to the 80 MPa of an epoxy composite at 67% fiber volume fraction. A lower water absorption of around 1% was associated with the increased crosslinking. The mechanical properties of the 4-CPM/NPMI composites showed a similar trend upon preheating.     

Partial replacement of EPR by GTR in highly flowable PP/EPR blends: Effects on morphology and mechanical properties

This research analyzes the effect of ground tire rubber (GTR) and a novel metallocene‐based ethylene–propylene copolymer (EPR), with high propylene content, on the morphology and mechanical behavior of ternary polymer blends based on a highly flowable polypropylene homopolymer (PP). The PP/EPR blends morphology, with very small domains of EPR dispersed in the PP matrix, indicates a good compatibility among these materials, which leads to a significant improvement on elongation at break and impact strength. The incorporation of EPR on the rubber phase of thermoplastic elastomeric blends (TPE) based on GTR and PP (TPE^GTR) has a positive effect on their mechanical performance, attributed to the toughness enhancement of the PP matrix and to the establishment of shell‐core morphology between the rubber phases. The mechanical properties of the ternary blends reveal that TPE^GTR blends allow the upcycling of this GTR material by injection molding technologies. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42011.     

Simultaneously enhanced fracture toughness and flame‐retardant property of poly(l‐lactic acid) via reactive blending with ammonium polyphosphate and in situ formed polyurethane

The preparation of poly(l ‐lactic acid) (PLLA) with high mechanical and ideal flame‐retardant properties is a great challenge. Herein, a simultaneous toughness and flame‐retardant PLLA composite was successfully fabricated by using a one‐step process which introduces 4,4′‐methylenediphenyl diisocyanate and ammonium polyphosphate (APP) into PLLA/poly(ε‐caprolactone) blends. SEM, Fourier transform infrared spectroscopy and TGA were adopted to confirm that APP participated in the in situ reaction during the melt process. The impact strength was increased to 13.5 kJ m^?2 from 1.0 kJ m^?2 for L8P2A5 composite, indicating the toughening effect of reactive blending. The cone calorimeter test, limiting oxygen index and vertical burning test results indicate that the flame‐retardant properties of the composites are enhanced with increasing APP content. This work provides a method to prepare PLLA with high mechanical properties and enhanced flame retardancy. © 2020 Society of Chemical Industry     

Room temperature and low temperature toughness improvement in SAN/ASA blends by blending with CPE,HNBR, and BR

Styrene‐acrylonitrile copolymer (SAN)/acrylonitrile‐styrene‐acrylate terpolymer (ASA) blends (75/25, wt/wt) was toughened by blending with impact modifiers including chlorinated polyethylene (CPE), hydrogenated nitrile butadiene rubber (HNBR), and butadiene rubber (BR) and the impact property was tested at four temperatures (–30, ?15, 0, and 25 °C). The combination of CPE and HNBR was imported to toughen the SAN/ASA blends, indicating that CPE and HNBR had similar toughening effect at room temperature but HNBR exhibited a better performance at low temperature. When a little HNBR was substituted by BR, the impact strength improved dramatically with the total content of impact modifiers keeping at 30 phr. After 15 phr CPE, 10 phr HNBR and 5 phr BR were employed into blends together, the impact strength reached to a peak of 14 kJ/m² at ?30 °C while the impact strength of the blends individually toughened by 30 phr CPE or 30 phr HNBR was 5 or 12 kJ/m², respectively. The toughening mechanism showed that the low glass‐transition temperature (–108 °C) of BR and the compatibilization between BR and matrix accounted for the improvement of toughness. Simultaneously, scanning electron microscopy, dynamic mechanical analysis, flexural and tensile properties, heat distortion temperature, and Fourier transform infrared spectroscopy were measured. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45364.     

Isothermal crystallization behavior and properties of polypropylene/EPR blends nucleated with sodium benzoate

The effect of sodium benzoate on the isothermal crystallization behavior of isotactic polypropylene (iPP)/ethylene–propylene rubber(EPR) blends was investigated using differential scanning calorimetry. Dynamic mechanical and physical properties of the iPP/EPR blends nucleated with sodium benzoate were also measured. It was found that the crystallization behavior and physical properties such as heat deflection temperature (HDT), flexural modulus, and impact strength were strongly affected by the competition between the nucleating effect of EPR attributed to its partial compatibility with iPP and the simple addition of the amorphous component, as well as the nucleating effect of sodium benzoate. High impact strength was achieved by addition of EPR and sodium benzoate to iPP. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 201–211, 2002     

Effect of γ-Radiation on the Mechanical Performance of Hybrid Rice Straw/Seaweed-Polypropylene Composites

Hybrid composites of rice straw (Rs)/seaweed (Sw) and polypropylene (PP) were prepared at a fixed filler ratio of 30:70 and variable ratio of the two reinforcements, viz. 30:0, 25:5, 20:10, 10:20, 0:30 by weight. Mechanical properties of the composites such as tensile strength (TS), bending strength (BS), impact strength (IS) and elongation at break (Eb%) were investigated and the composite formulation of 20:10:70 (Rs:Sw:PP) was found to be optimum that showed TS = 2.8 MPa, BS = 68 N/mm², IS = 2.5 kJ/mm² and Eb = 50%. For better compatibility, Rs and Sw were subjected to surface treatment using various intensities of γ-radiation to prepare improved hybrid composites. γ-irradiated filler hybrid composites significantly enhanced mechanical properties and the composite in which fillers were irradiated at 100 krad achieved maximum enhancement with TS = 35 MPa, BS = 75 N/mm², IS = 2.7 kJ/mm² and Eb = 68%. Water absorption capacity of the different composites was also studied and irradiated filler composites showed less water uptake.     

Effect of N,N′‐diphenyl adipamide on the formation of the β‐crystalline form in isotactic polypropylene

The polymorphic compositions and mechanical properties of isotactic polypropylene (iPP) samples nucleated by a selective β‐nucleating agent [N,N′‐diphenyl adipamide (DPA)] were investigated with wide‐angle X‐ray diffraction, polarized light microscopy, scanning electron microscopy, and mechanical tests. It was found that β‐phase crystals emerged with the addition of DPA, and the relative proportion of the β‐crystalline form reached the maximum value of 0.97 with the addition of 0.1 wt % DPA. The curved lamellae in the β spherulites were like flowers. The β spherulites were etched more easily than α spherulites because amorphous regions were distributed inside the β spherulites. The Izod notched impact strength increased sharply with the addition of DPA and attained the maximum value of 7.30 kJ/m² (the value of blank iPP was 3.13 kJ/m²) with the addition of 0.1 wt % DPA. An analysis of the misfit factors between DPA and β‐iPP showed that β‐iPP could epitaxially crystallize on the DPA crystal well. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Nitrile rubber/sliding graft copolymer damping material with significantly improved strength and damping performance

Nitrile rubber (NBR)/sliding graft copolymer (SGC) composites with significantly improved strength and damping property are successfully prepared. SGC is a novel kind of supramolecular material with sliding crosslink junctions. The micromorphology analyses of NBR/SGC composites indicate that the SGC phase with particle size less than 500 nm is fairly uniformly dispersed in the NBR matrix. As SGC content increases, the loss factors (tan δ) of NBR/SGC composites increase gradually. Specifically, the tan δ of NBR/SGC (100/40) is about 1.2 times higher than that of pristine NBR rubber. The tensile strength and elongation at break of NBR/SGC composites are unexpectedly improved after the addition of SGC. The significantly improved damping performance and tensile strength can be ascribed to the pulley effect of SGC and the strong interfacial hydrogen bonds between SGC and NBR. The high damping performance and good mechanical strength make the NBR/SGC composite a promising high-performance damping material. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47188.     

Effect of conductive polyaniline in thermoplastic natural rubber blends on the mechanical,thermal stability,and electrical conductivity properties

This research was conducted to fabricate thermoplastic natural rubber/polyaniline (TPNR/PANI) blends via melt blending method using an internal mixer and followed by compression molding. The effects of PANI contents between 1 and 5 wt % PANI in the TPNR blends on the mechanical properties, thermal stability, electrical conductivity (impedance), and morphology observation were investigated. The TPNR/3 wt % PANI sample exhibited the highest tensile strength (3.7 MPa), elongation at break (583%), flexural strength (1.8 MPa), flexural modulus (37.0 MPa), and impact strength (7.1 kJ m⁻²). From the aspect of thermal properties, it was found that with the addition of PANI, the thermal stability of the TPNR/PANI increased. Comparing to nonconductive TPNR sample, the incorporation of PANI promoted the electrical conductivity characteristic to PANI-filled TPNR blends which showing a magnitude order of 10⁻⁹ S cm⁻¹. Scanning electron microscopy micrograph revealed the good distribution of PANI at the optimum content (3 wt % PANI) in the TPNR blends and the good interaction between TPNR and PANI. It can be concluded that the TPNR blends incorporated with a low loading of PANI could be a newly good conductive material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47527.     

In situ fibrillation of isotactic polypropylene in ethylene-vinyl acetate: Toward enhanced rheological and mechanical properties

In situ microfibrillar reinforced composites with ethylene-vinyl acetate (EVA) as matrix and isotactic polypropylene (iPP) as dispersed fibrils were successfully fabricated by multistage stretching extrusion with an assembly of laminating-multiplying elements (LMEs). Four types of EVA with different apparent viscosity were utilized to study the influence of viscosity ratio on the morphology and mechanical properties of EVA/iPP in situ microfibrillar blends. The scanning electron micrographs revealed that the dividing–multiplying processes in LMEs could effectively transform the morphology of iPP phase into microfibrils and the morphology of iPP microfibrils strongly depended on the viscosity ratio. Higher viscosity ratio was favorable for formation of finer microfibrils with narrower diameter distribution. The morphology development of iPP with different viscosity ratio greatly affected the rheological and mechanical properties of EVA/iPP blends. The dynamic rheological results shown that the iPP microfibrils were helpful to increase the storage modulus and loss modulus. The tensile test indicated that the mechanical properties of EVA/iPP blends were controlled by the morphology of iPP phase and the polarity of EVA matrix. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47557.