Single Polymer Composites Research Articles

Interfacial crystallization of isotactic polypropylene surrounding macroscopic carbon nanotube and graphene fibers

A comparative study on interfacial crystallization of isotactic polypropylene (iPP) surrounding macroscopic carbon nanotube and graphene fibers has been carried out in single fiber polymer composites by means of in situ polarized optical microscope, scanning electron microscope and X-ray diffraction. Ordered interfacial microstructures of iPP nucleate on both nanocarbon fibers in the form of a transcrystalline interphase. Nanotube fibers tend to promote negative birefringence transcrystals whereas graphene fibers induce positive birefringence transcrystals. The microstructures of transcrystals are strongly dependent on the thermal history and the double-layered transcrystals consisting of a negative inner layer and a positive outer layer occur under certain conditions. Transcrystallization kinetics has been studied and the Lauritzen–Hoffman theory of heterogeneous nucleation used to analyze the dynamic crystallization process. While the fold surface energy of iPP transcrystals surrounding both nanocarbon fibers shows little difference, the nanotube fiber promotes shorter induction time than the graphene fiber. Thermal resistance test demonstrates that the ordered interfacial microstructures possess higher melting temperature in the nanotube fiber composites than those in the graphene fiber composites. Under appropriate conditions, the β-form transcrystals of iPP are observed. The amount of the β-form iPP surrounding the nanotube fiber is much higher than that surrounding the graphene fiber. A theoretical model is proposed to interpret the difference between the nanotube and graphene fiber composites and the mechanisms behind its influence on interfacial crystallization.

The effect of draw ratio on the mechanical properties and crystalline structure of single polymer polypropylene composites

The properties of self-reinforced single polymer composites produced by the Leeds hot compaction process are highly dependent on the compaction temperature as well as the constituent oriented elements used to produce the compacted sheets. In this paper, the variation in tensile mechanical properties of uniaxial hot compacted sheets manufactured from drawn polypropylene (PP) tapes with change in compaction temperature have been investigated, for a range of different draw ratio tapes. It is shown that there is a measureable difference between the optimum compaction temperatures required for obtaining the highest modulus and strength in the compacted sheets. The compaction temperature required to achieve the maximum tensile modulus was seen to increase with increasing draw ratio. The compaction temperature to obtain the maximum tensile strength was found to be both independent of the draw ratio and a few degrees higher than that for obtaining the maximum modulus. Peak modulus and peak tensile strength was shown to be dependent on the draw ratio of the drawn tape.Differential scanning calorimetry measurements on the compacted sheets were also performed in order to investigate the change in crystalline structure with compaction temperature and draw ratio. This has shown that the changes in structure within the oriented phase (i.e. tapes) during the compaction process itself are directly related to the final properties of the hot compacted sheets.

Interfacial crystallization and mechanical property of isotactic polypropylene based single-polymer composites

Isotactic polypropylene (iPP) based single-polymer composites (SPCs) were prepared by introducing iPP fibers into the molten or supercooled homogeneous iPP matrix. The influences of fiber introduction temperature (Ti) on the resultant morphology of transcrystallinity (TC) and mechanical properties of SPCs were investigated via a polarized optical microscopy (POM) and a universal tensile test machine. The effects of interfacial crystallization on mechanical properties were also studied. The tensile strength of SPCs was observed to increase firstly and to reach a maximum value at Ti = 160 °C, and then to decrease with further increasing the Ti. Wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM) and POM were employed to understand the mechanical enhancement mechanism. It is found that the enhanced tensile strength of SPCs was strongly dependent on the synergistic effects of TC, high orientation degree of iPP fibers and good adhesion between the iPP fiber and the matrix.

Novel high-temperature-resistant single-polymer composites based on self-reinforced phthalonitrile end-capped polyarylene ether nitrile

A series of phthalonitrile end-capped polyarylene ether nitrile (PEN-Ph) with different structures has been synthesized by adjusting the molar ratio of biphenyl (BP) to hydroquinone (HQ). Furthermore, based on the PEN-Ph, self-toughened and self-reinforced single-polymer composites were successfully prepared. The relationship between structure, morphology, and properties of the PEN-Ph system was also investigated in detail. From the polarizing micrographs, it is concluded that the sample-1# (molar ratio of BP to HQ is 10:93) possesses larger size spherocrystal. Moreover, the Tg decreases from 206.1 to 178.2 with the increasing HQ content. The mechanical measurement demonstrates that the sample-2# (molar ratio of BP to HQ is 20:83) shows the best tensile strength. Most importantly, the polarizing micrographs which illustrated the morphologies of PEN-Ph as a function of temperature, provide the direct evidence for the PEN-Ph crystals solidification by crosslinking reaction. Hence, taking the thermal and mechanical properties in consideration, the sample-2# will be a good candidate for the high-temperature-resistant single-polymer composites.

Insert injection molding of high‐density polyethylene single‐polymer composites

A process for making high‐density polyethylene (HDPE) single‐polymer composites (SPCs) by insert injection molding was investigated. HDPE SPCs with relatively good tensile and interfacial properties were prepared within a short cycle time within a temperature range of 40°C. Melt‐spun HDPE fibers were made from the same resin as the matrix. The fibers were heat treated in silicone oil, with and without tension, to study the changes of fiber properties upon exposure to high temperature. HDPE SPCs containing about 30 wt% lab‐made HDPE fabric achieved a tensile strength of 50 MPa, 2.8 times that of neat HDPE. The peel strength of HDPE SPCs increased with increasing injection temperature and achieved a maximum value of 16.7 N/cm. Optical micrographs of polished transverse cross‐sections of the SPC samples showed that higher injection temperature is beneficial to the wetting and permeation properties of the matrix. Scanning electronic microscope photographs suggested good bonding and compatibility between the fibers and the matrix. POLYM. ENG. SCI., 55:2448–2456, 2015. © 2015 Society of Plastics Engineers

Graphene-Induced Oriented Interfacial Microstructures in Single Fiber Polymer Composites.

Interfacial interactions between the polymer and graphene are pivotal in determining the reinforcement efficiency in the graphene-enhanced polymer nanocomposites. Here, we report on the dynamic process of graphene-induced oriented interfacial crystals of isotactic polypropylene (iPP) in the single fiber polymer composites by means of polarized optical microscopy (POM) and scanning electron microscopy (SEM). The graphene fibers are obtained by chemical reduction of graphene oxide fibers, and the latter is produced from the liquid crystalline dispersion of graphene oxide via a wet coagulation route. The lamellar crystals of iPP grow perpendicular to the fiber axis, forming an oriented transcrystalline (TC) interphase surrounding the graphene fiber. Various factors including the diameter of graphene fibers, crystallization temperature, and time are investigated. The dynamic process of polymer transcrystallization surrounding the graphene fiber is studied in the temperature range 124-132 °C. The Lauritzen-Hoffman theory of heterogeneous nucleation is applied to analyze the transcrystallization process, and the fold surface free energy is determined. Study into microstructures demonstrates a cross-hatched lamellar morphology of the TC interphase and the strong interfacial adhesion between the iPP and graphene. Under appropriate conditions, the β-form transcrystals occur whereas the α-form transcrystals are predominant surrounding the graphene fibers.

Development and characterization of insert injection moulded polypropylene single-polymer composites with sandwiched woven fabric

Abstract Polypropylene (PP) single-polymer composites (SPCs) with sandwiched woven fabric were successfully produced by insert injection moulding. The woven fabric was set in the middle of the mould cavity and fixed by the clamping force. The injected melt could fill and permeate the fibres from both sides of the woven fabric, so both improved mechanical properties and good appearance could be obtained. A processing temperature window (160–200 °C) with a short cycle time (less than 30 s) could be realized. Orthogonal experimental method was used. The tensile strength of the PP SPCs could reach up to 38.22 MPa, 45% higher than that of the non-reinforced PP. The effects of different processing parameters including nozzle temperature, injection pressure, holding pressure and holding time were discussed. Among the processing parameters, the nozzle temperature is the most important influence factor. The morphological properties were also observed using camera and microscope. It confirmed the processing temperature window and good interfacial adhesion.

Is the use of correct terms and definitions important in creation of new materials?

and widely applied term is a case in composite community, where the thermodynamic term ‘phase’ is used instead of the term ‘component’. Obviously, the misuse of the term ‘phase’ is a remnant from the time when the colloid chemistry was formulated (second half of 19th century, i.e. long before the polymer science was defined). The confusion of this misuse can be easily demonstrated by poly(vinylidene fluoride) (PVDF) exhibiting five crystalline polymorphic modifications (phases!) and one amorphous phase but PVDF is still a one-component system. While this example does not have a direct effect on the creation of new materials, the next one, the definition of the relatively new type of polymer composites, the single polymer composites (SPCs), does. SPCs have also been called: one polymer composites (R. Porter), homocomposites, self-reinforced composites, one-phase composites, homogeneous composites, or all-polymer composites. The concept of SPCs has been formulated by R. Porter some 40 years ago (DOI: 10.1007/BF00554928) as attempt to solve the basic problem in polymer science and technology, namely, the low adhesion quality between matrix and reinforcement due to their different chemical composition. The approach is quite simple – the matrix and the reinforcement have to be of the same polymer, i.e. to be chemically identical. The idea attracted the attention of academia and industry during the last decade when patents were registered and products were commercialized; nanofibrillar SPCs with superior mechanical properties were also created (DOI: 10.1002/mame.201200226). What is more, similar products were prepared and called also SPCs (DOIs: 10.1007/s10853-009-3792-1, and 10.1016/j.compscitech.2013.12.006) using highly oriented poly propylene (PP) (as reinforcement) and the random copolymer of PP (usually with polyethylene) as a matrix thus neglecting the basic requirement (R. Porter) for identical chemical composition of matrix and reinforcement. Strictly speaking, such composites belong to the category of polymer–polymer composites. The same holds for thermoplastic copolyesters reinforced with ‘homo’-poly(ethylene terephthalate). The argument that the two chemically different components belong to the same polymer family (DOI: 10.1016/j.compscitech.2013.12.006) could hardly be seriously considered – it only smears the boundary between the two types of composites, the polymer-polymer ones and the SPCs and makes the clear definition of single polymer composites hardly possible affecting in this way negatively their further development! In order to make use of the unique properties of SPCs we should not forget that they could be multi-phase but always remain one-component systems!

Charakterystyka i zastosowania kompozytow jednopolimerowych

Charakterystyka i zastosowania kompozytow jednopolimerowych

Properties of polypropylene single-polymer composites produced by the undercooling melt film stacking method

Abstract Polypropylene (PP) single-polymer composites (SPCs) were produced by the undercooling melt film stacking method within a large usable processing temperature window from 125 to 150 °C. Samples with good stiffness and strength could be made using 145 ± 5 °C. The undercooling compaction temperatures were all lower than the hot compaction temperatures in traditional processing. Tensile and peel tests were carried out. The effects of compaction temperature, holding time and compaction pressure on mechanical properties of the PP SPCs were investigated. The compaction temperature is the main factor in influencing the properties of the PP SPCs. At different compaction temperature, both holding time and compaction pressure have different influences. Especially, the holding time at undercooling temperature showed different effects compared with the traditional SPCs processing. The morphological properties of the PP SPCs were also examined, good interfacial adhesion were shown.

Insert injection molding of polypropylene single-polymer composites

Abstract A process for making polypropylene (PP) single-polymer composites (SPCs) by insert injection molding was investigated. PP SPCs with relatively good tensile and interfacial properties were prepared with a relatively short cycle time. Melt-spun PP fibers from the same resin as the matrix were treated in heated silicone oil, with and without tension, to study the changes of fiber properties upon exposure to high temperature. PP SPCs containing 36 wt% lab-made fabric achieved a tensile strength of 70 MPa, 2.3 times that of neat PP. Polarized light microscopy of PP SPCs with uniaxial fibers indicated that different crystalline regions formed from partial melting of fibers along the fiber surface. Differential scanning calorimetry results showed that most fibers could maintain the thermal properties after molding. Voids were not observed in the scanning electron microscopy images of the fracture surface after tensile failure indicating good bonding between the matrix and fibers.

Sposoby wytwarzania kompozytow jednopolimerowych

This paper constitutes a review of the literature on the single polymer composites (SPC), an interesting and useful group of new polymer materials. They are fully recyclable and have mechanical properties comparable to heterogeneous polymer composites. The most important preparation methods of these composites (hot compaction of polymer foils, fibres and tapes, infusion of polymer solution or powder, film-stacking method, co-extrusion technology, injection moulding) are presented.

Polymer–Polymer and Single Polymer Composites Involving Nanofibrillar Poly(vinylidene Fluoride): Manufacturing and Mechanical Properties

Nanofibrillar polymer–polymer composites (NFCs) and single polymer composites (SPCs) were produced using linear low density polyethylene (LLDPE) and poly(vinylidene fluoride) (PVDF). The NFCs were fabricated by means of a microfibrillar composite concept comprising melt blending, cold drawing, and compression molding retaining the highly oriented PVDF reinforcing nanofibrils (diameter of approximately 250 nm) dispersed without any agglomeration in the isotropic LLDPE matrix. The SPC films were prepared by partial surface premelting of neat PVDF nanofibrils (diameter of about 130 nm) using hot compaction at 148°C (about 20°C below the complete melting of PVDF), thus preserving the PVDF nanofibrillar identity. Tensile testing of NFCs based on LLDPE and PVDF showed an increase in the tensile modulus by 135% and in the tensile strength at break by 211%, as compared to those of an isotropic LLDPE film. Furthermore, the PVDF SPCs showed an enhancement of tensile modulus of 30% and strength at break of 305% when compared to those of an isotropic PVDF film.

Hybrid carbon fibre/nylon 12 single polymer composites

This paper describes the production and properties of hybrid single polymer composites made from co-mingled tows of carbon and oriented nylon 12fibres using the Leeds hot compaction process. For 22% volume fraction of carbon fibres, a well consolidated UD sample was made at a temperature of 176°C, 2°C below the temperature at which major melting of the oriented PA12 fibres, and loss of molecular orientation, occurs. For braided cloth a higher temperature of 178°C was required to give a good sample, which is too close to the melting point of the PA12 multifilaments. Reducing the carbon fraction to 13% allowed a well consolidated sample (braided cloth) to be made at a lower temperature of 175°C, giving a wider temperature processing window. In tension the hybrid samples were found to fail in a brittle manner while in bending the behavior was ductile as long the molecular orientation was retained.

Single-Polymer Composites: Concepts, Realization and Outlook: Review

Manufacturing, properties and applications of single-polymer composites (SPCs) have been surveyed. SPCs composed of amorphous or semicrystalline matrices and semicrystalline reinforcements were only considered because of their present and future relevance. Various concepts to enlarge the temperature difference between the matrix- and reinforcement-giving materials were listed and those applied commercially were discussed. The development of SPCs is fueled by the demand for various products which have low density and “ultimate” recyclability, namely reprocessing via remelting. At present SPC, parts are mostly used in the automotive, and sport/leisure sectors. Research activities target the production productivity, novel shaping technologies of SPCs, and ensuring their multifunctionality.

Structure and properties of β-polypropylene reinforced by polypropylene fiber and polyamide fiber

Matrix/fiber composites of β-form isotactic polypropylene (iPP) matrix and α-iPP or PA6 fibers were prepared by laminating technique under different preparation temperatures. The mechanical properties and interfacial morphologies of these composites were studied by tensile test, optical microscopy and scanning electron microscopy, respectively. The experimental results show that the tensile yield load and tensile modulus of β-iPP/PA6 matrix/fiber systems increased significantly at the expense of elongation at break. These mechanical properties show essentially no dependence on the sample preparation temperature. On the other hand, the mechanical properties of iPP matrix/fiber single polymer composites depend strongly on the sample preparation temperature. At low sample preparation temperature, e.g., 172 °C, the solid α-iPP fiber induces α-iPP crystallization, leading to the formation of α-iPP transcrystalline layer around the fiber. This results in a remarkable increment of the tensile yield load and tensile modulus. The elongation at break is also much better than that of the iPP/PA6 matrix/fiber system. It reflects a better interfacial adhesion of the single polymer composite compared with the iPP/PA6 composite. At higher sample preparation temperature, e.g., 174 °C or 176 °C, the partial surface melting of the oriented fiber allows interdiffusion of iPP molecular chains in the molten fiber and matrix melt. The penetration of matrix chains into the molten iPP fiber results in some iPP molecular chains being included partially in the recrystallized fiber and the induced β-transcrystalline layers. This kind of configuration leads to an improvement of interfacial adhesion between the fiber and matrix, which causes a simultaneous increase of the tensile yield load, tensile modulus and elongation at break of β-iPP.

Biodegradability of all-cellulose composite laminates

The high mechanical properties of single-polymer composites based on degradable non-derivatised cellulose, aka all-cellulose composites, have recently captured the attention of researchers. All-cellulose composites possess the intriguing combination of high strength and biodegradability. However, the biodegradation behaviour of all-cellulose composites has so far not been reported. In this work, soil burial experiments were carried out to compare the biodegradation behaviour of all-cellulose composites with conventional biocomposites in order to investigate the end-of-life disposal of this relatively new class of bio-based composite materials. All-cellulose composites are characterised by exceptional biodegradability with mass losses of up to 73% following a soil burial time of 70days. An investigation of the mechanisms of biodegradation of all-cellulose composites is undertaken for the first time.

Single-polymer composites (SPCs): Status and future trends

Preparation, properties and applications of single-polymer composites (SPCs), representing an emerging family within the polymeric composite materials, have been surveyed. SPCs were classified in respect to their composition (one- and two-constituents), and preforms (non-consolidated and consolidated). SPCs composed of amorphous or semicrystalline matrices and semicrystalline reinforcements were considered. Methods to widen the temperature difference between the matrix- and reinforcement-giving materials of the same polymer (one-constituent) or same polymer type (two-constituent approach) have been introduced and discussed. Special attention was paid to the unsolved questions related to the interface/interphase in SPCs. It was emphasized that the development of SPCs is fuelled by the need of engineering parts in different applications which have low density and “ultimate” recyclability (i.e. reprocessing via remelting). Recent development of SPCs is supported by novel preform preparation, consolidation and production possibilities.

Single Polymer Composites of Poly(Butylene Terephthalate) Microfibrils Loaded with Carbon Nanotubes Exhibiting Electrical Conductivity and Improved Mechanical Properties

Applying the concept of microfibrillar composites, microfibrils of poly(butylene terephthalate) (PBT) loaded with 5 wt% multi-walled carbon nanotubes are prepared by extraction of polypropylene (PP) from drawn PP/PBT blends and shaped into single polymer composites (SPCs). SPCs show superior mechanical performance with up to 300–600% improvement in modulus and tensile strength as compared to neat isotropic PBT. In addition, the microfibrillar SPCs (MF-SPCs), as well as the single microfibrils, have electrical volume conductivity of 8 × 10−3 S cm−1 demonstrating electrical conductive behavior.

Polymer‐Based Resistive Memory Materials and Devices

Due to the advantages of good scalability, flexibility, low cost, ease of processing, 3D-stacking capability, and large capacity for data storage, polymer-based resistive memories have been a promising alternative or supplementary devices to conventional inorganic semiconductor-based memory technology, and attracted significant scientific interest as a new and promising research field. In this review, we first introduced the general characteristics of the device structures and fabrication, memory effects, switching mechanisms, and effects of electrodes on memory properties associated with polymer-based resistive memory devices. Subsequently, the research progress concerning the use of single polymers or polymer composites as active materials for resistive memory devices has been summarized and discussed. In particular, we consider a rational approach to their design and discuss how to realize the excellent memory devices and understand the memory mechanisms. Finally, the current challenges and several possible future research directions in this field have also been discussed.