A polyethylene (PE)/starch copolymer was prepared by a grafting technique in the presence of benzoyl peroxide as a catalyst and xylene as a solvent. The ratio of PE grafted onto starch was in ratio 1:5, respectively. The obtained grafted copolymer was characterized by Fourier transform infrared (FTIR) spectroscopy. The obtained grafted copolymer was mixed with rice and wheat straw as well as calcium carbonate (CaCO3) as a filler to form biodegradable films. Various analyses such as viscosity, tensile strength, elongation at break, water contact angle, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and solubility tests have been used to study the properties of biodegradable films in water and soil. CaCO3 and rice and wheat straws improved the biodegradability of the grafted copolymer. The presence of CaCO3 in the presence of rice and wheat straws increased the viscosity, tensile strength, thermal stability, and weight loss of the film in the soil. While elongation at break, the water contact angle and solubility in water decreased. According to the study, samples that were between 380°C and 400°C showed the highest polymer breakdown values and adding CaCO3 resulted in the lowest water contact angle.
We present efficiency and lifetime results for solar cells composed of blends of poly(3‐hexylthiophene‐2,5‐diyl) and N,N′‐bis(3‐pentyl)perylene‐3,4,9,10‐bis(dicarboximide) or P3HT:PDI. This combination represents a baseline system for future studies of PDIs as electron acceptors. Poor performance in the fabricated devices was correlated with unusual sample morphologies. Large aggregates in the form of rods and crossbones were observed using both optical and electron microscopy. Energy dispersive X‐ray elemental analysis was used to identify the composition of the structures. These results illustrate the critical connection between polymer organization and solar cell efficiency, providing insights into the structure‐function interaction between PDI and P3HT.
In this chapter, the fundamental science of polymer crystallization has been discussed. The chemical composition and thermal histories, such as cooling conditions during the fabrication process and post-thermal treatment, the size of the structural units, or the molecular orientation, in addition to the degree of crystallinity of the starting melt, paths of nucleation, organization of lamellar crystals, and evolution of the final crystalline structures, affect the mechanical, thermal, and optical final performance of semi-crystalline polymer materials. An understanding of the complex processing of polymers from their amorphous states to their crystalline states for a variety of applications is provided by addressing the fundamentals of polymer crystallization via a combination of unique thoughts, concepts, and sophisticated methodologies.
Molecular simulation is an effective and powerful method to study the microscopic mechanisms of polymer crystallization. Firstly, based on molecular simulation, some new theories about polymer crystallization were proposed, such as the intramolecular crystal nucleation mode. Secondly, some specific polymer crystallization processes can be detected at the molecular scale. For instance, the molecular mechanism for the nanohybrid shish-kebab structure can be revealed. The influences of some factors on stereocomplex crystallization can also investigated. Besides, the simulation results can provide strong microscopic evidence for the multi-scale and multi-step process of polymer crystallization induced by flow field.
Polypropylene has developed into one of the most relevant thermoplastic polymers, both technically and commercially, since its development in the 1950s. Both the far more relevant isotactic variety and the syndiotactic polymer are crystalline with an interesting polymorphism, and they can be modified by copolymerization and blending to cover a wide range of mechanical and optical properties. The different crystal polymorphs can be controlled by chain structure and nucleation, allowing either higher stiffness or toughness and facilitated processing. In multiphase systems with amorphous and crystalline inclusions, especially polyethylene shows relevant epitactic interaction. Processing effects related to cooling rate and flow further determine crystalline morphology and performance. A wide variety of characterization methods are available today to study the related phenomena.
Shape memory polymers (SMPs) are intelligent class of polymers that change shape in response to an appropriate stimulus. Or, in other words, SMPs are highly deformable materials that can be pre-programmed to memorize and recover from a temporary shape and return to their original form when triggered with an external stimulus. Due to their attractive properties, such as minimal toxicity, biocompatibility, biodegradability, and tunable properties, SMPs find great application in biomedical field. This chapter details the different types of SMPs and the factors that determine and influence the shape memory effect of polymers. Moreover, the molecular mechanism underlying the shape memory effect, the steps of shape memory cycle, and the biomedical and other applications of the SMPs are discussed in detail with suitable examples.
The state of polymeric crystalline phase is significant for its final thermal, optical, and mechanical properties. However, polymeric 3D ordered regions (crystallites) are more complicated than the crystalline structure of other materials because of the chain folding and structural disorder. To reveal and control the crystalline phase and crystallization mechanisms of polymers has attracted more and more attention. Various technologies have been applied to characterize the crystallization of polymers, such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), RAMAN, differential scanning calorimetry (DSC), and so on. Among various technologies, DSC method can easily provide thermal-kinetic mechanism to characterize polymer crystallization. In this chapter, we are aiming to present the characterization of polymer crystallization by using DSC method. The basic principle of thermal-kinetic mechanism and common variants are discussed.
Crystalline polymer composites have been an emerging class of composite materials with their novel physical, chemical, and mechanical features. Semi-crystalline polymers, the most common crystalline polymer type, are usually reinforced with several kinds of organic, inorganic, or natural fillers to boost the crystallinity and mechanical features of the resultant materials used in many applications in automotive, electrical, energy, defense, aerospace, military, textile, and biomedical fields. However, the growing interest in the extensive utilization of polymer composites has brought the accumulation of waste that threatens the human health and the environment. Due to environmental and economic concerns, waste management has become compulsory and to this end, recycling has been applied to the ultimate disposal in order to meet the demands of environmental legislation, and waste management regulations. Based on the related knowledge and current studies, this chapter focuses on the understanding of crystalline polymer composites in terms of the reinforcing agent types. In addition, a comprehensive review of the automotive, biomedical, defense, and aerospace applications of crystalline polymer composites is presented. The recycling, environmental, and safety issues of crystalline polymer composites are comprehended based on the different filler types existing in their structure. Furthermore, as a last stage, future aspects of crystalline polymer composites are discussed in detail.
In situations where the stereoregularity of the polymer chains permits, crystals can form in synthetic or natural polymers. These crystals have an immense impact on the properties of the polymeric material. Typically polymers crystallized from a quiescent melt form spherulites, but where the melt exhibits a level of anisotropy, the crystalline morphology, is quite different to the spherulitic structure, although it may well contain chain-folded lamellar crystals. We consider a number of different systems in which the anisotropy has developed in different ways. Despite these differences, there are strong features in common within the semi-crystalline polymer morphology. We consider the strain-induced crystallization in deformed natural rubber, in sheared melts containing both self-assembling nanoparticles and engineered nanoparticles, and during extrusion as part of fused granular deposition-based 3D printing.
Over the past 10 years, thermoplastic polymer poly(lactic acid) or PLA, which is bio-based and biodegradable, has increasingly become a key component of competing products. This bioplastic is able to replace petroleum-derived polymers not only in applications that require just one use but also in those that need greater durability and technical performance. Controlling the PLA degradation rate, heat resistance, and optical, mechanical, and barrier characteristics requires a thorough understanding of crystallization dynamics. Crystal growth follows initial crystal nucleation during the crystallization process. Both processes, as described in this chapter, have different temperature and cooling-rate requirements and require chain segment mobility at different length scales. Controlling the polymer's crystallinity grade is crucial for stabilizing PLA and enhancing its mechanical properties, and using nucleating agents (both inorganic and organic) for this purpose is an efficient method. Blending systems based on PLA, PLLA, PDLA, and other thermoplastics, generate stereocomplex crystals, as well as binary immiscible/miscible blends. To produce multifunctional ternary blends, which give rise to high-performance materials, a third polymer or fillers like nanoparticles (NPs) can be added. This chapter summarizes all of these studies and examines the processing-morphology-properties correlations within the created PLA-based blends, as well as their many applications.
Poly(ϵ-caprolactone) (PCL) is known for its biodegradability, mechanical properties, processability, and compatibility with other polymers. The biodegradability of PCL mainly depends on the crystallinity and molecular weight, along with the different degradation mechanisms under different conditions. Studies on the kinetics of crystallization are important in designing suitable polymers for various applications and for obtaining desired morphology, which is of utmost importance to achieve the required properties. In this chapter, factors affecting the crystallization behavior of PCL are discussed. The change in the crystalline behavior of PCL in multiphase polymer systems such as PCL-based blends and composites is discussed. The influence of crystalline behavior on the properties of PCL is also outlined in this book chapter.
Poly (lactic acid) (PLA) has gained attention due to its mechanical performance, optical transparency, renewability, biocompatibility and biodegradability in recent past. The slow crystallization kinetics, poor thermal stability, brittleness and process complexity limit its practical applications. Hence, crystallization behavior of PLA was studied enormously in past to improve its performance. Here, in particular, crystallization behavior of poly ( l -lactic acid) (PLLA) and its different forms (in blends, in composites, and after adding nucleating agents, etc.) are described.
Lignin is the second most abundant pollution-free biomass material. However, most of lignin is discarded as waste in river or burned as fuel, which results in serious environmental pollution problems and low utilization efficiency of lignin at present. Thus, high-value utilization of lignin has become a hot research field. Herein, nanolignin (nano-Lig) is prepared successfully by the self-assembly method, and then nano-Lig and isotactic polypropylene (iPP) are mixed to prepare a series of nano-Lig/iPP composites by the solution blending method. Nano-Lig not only enhance thermostability of iPP but also improve crystallization properties of iPP. When 1.0 wt% nano-Lig was added in iPP, the crystallinity of iPP increased by 6.39% compared to iPP. Nano-Lig can increase the crystallization rate of iPP through investigation of kinetics of nonisothermal crystallization, suggesting nano-Lig can be used as a nucleating agent for iPP.
We investigated the effect of the chemical structure of alkylammonium salt on the crystallization behavior of poly(vinylidene fluoride) (PVDF) by DSC, optical microscopy, light scattering, and FT-IR. The nonisothermal and isothermal crystallizations of PVDF were accelerated by adding alkylammonium salt consisting of short alkyl chains and small anion species, and the spherulite size and the ordering in the spherulite became smaller due to the nucleation agent effect. The FT-IR spectra revealed that electroactive γ-phase was preferentially formed by adding alkylammonium salts though the accelerated crystallization was suppressed due to the steric hindrance effect by the long alkyl chain and large anion species. On the other hand, the formation of the γ-phase was suppressed when the dispersion of the salt in the PVDF matrix was poor due to the high melting temperature.
The β-nucleating agent (β-NA), zinc phthalate (ZnPht), was prepared from a mixture of zinc oxide (ZnO) and phthalic anhydride (Pht) during the extrusion of isotactic polypropylene (iPP). To establish the relationship between the crystalline characteristic of ZnO and the crystallization of iPP, single-crystalline ZnO (ZnO(S)) and polycrystalline ZnO (ZnO(P)) were selected and mixed with Pht, respectively, to in situ inducing the β-crystal form of iPP (β-iPP). Compared to ZnO(S)/Pht, ZnO(P)/Pht has the selectivity of β-crystal nucleation during the crystallization of iPP; indeed, the relative content of β-crystal ( k β ) improved from 18.0% for ZnO(S)/Pht/iPP to 84.6% for ZnO(P)/Pht/iPP. Moreover, the impact strength of the ZnO(P)/Pht/iPP was nearly 2.0 times greater than pure iPP; for ZnO(S)/Pht/iPP, it was approximately 1.4 times greater than pure iPP. To explain these phenomena, we propose a mechanism that the content of ZnPht generated by ZnO(P)/Pht is more than that of ZnO(S)/Pht during its in situ reaction; evidence from Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, and thermogravimetric infrared spectroscope analysis was consistent with this mechanism. This study may provide a new perspective to control the crystal type of polymorphic polymer by adjusting the crystalline characteristic of the nucleating agent.
It is well known that the processing conditions in polymer processing have a high impact on the resulting material morphology and consequently the component's mechanical behavior. However, especially for semicrystalline polymers, the tools available for predicting the final morphology of injection molding parts still have significant limitations. In order to investigate the potential of injection molding simulation for the prediction of the morphology, POM homopolymer specimens were injection molded. The crystallization kinetics data were measured, and simulations in 3D and 2.5D with and without crystallization analysis were conducted in Autodesk Moldflow. The simulations are found to be good accordance with the experiments. Predicted spherulite size and crystalline orientation factor reveal a good qualitative correlation with optical micrographs. Also, the evolution of these parameters along the flow path is plausible. The simulation is found to be a powerful tool for morphology prediction in polymeric parts. Its applicability, however, is still limited to 2.5D models in Autodesk Moldflow, which, of course, is insufficient for complex, thick-walled 3-dimensional parts.
Composites of polylactide containing graphite nanoplates as a filler in the concentration range 1–20 wt% were prepared in methylene chloride using the sonication technique. The thermal characteristics and phase transitions were studied by DSC and TGA methods. The temperatures and heats of glass transition, crystallization, and melting were determined, and the degree of crystallinity during primary and secondary heating was calculated. It is shown that the introduction of graphite nanoplates leads to an increase in the elastic modulus and a decrease in the breaking stress and elongation at break. These changes are especially pronounced at 20% GNP content in the composition, when the corresponding mechanical parameters are characteristics of brittle polymer systems. The study of the electrical properties of the composites showed that the percolation threshold in these materials is close to 7 wt%, which is significantly lower than in the case of spherical particles of comparable density. The SEM study of the filled composites showed a system of pores, which were apparently formed during the evaporation of solvent in the process of their preparation. Diverse structures of PLA/GNP composites films after hot pressure were established by the SEM method.
Many grades of homopolymer polypropylene (HPP) and impact copolymer PP (ICPP) with a wide range of mechanical properties have been developed for a variety of applications in different industrial sectors. Management of this wide range of materials is a challenge for material suppliers and manufacturers and product developers. This research was to provide insights for managing material supplies through formulating PP with specific mechanical properties using melt compounding of ICPP and HPP. ICPP and HPP were compounded with an internal mixer at different ratios and then the mixtures were injection molded into specimens for characterization. The mechanical behaviors, fracture surfaces, and thermal properties of the mixtures were then characterized. The fracture surface results indicated that the morphologies of the rubber particles in ICPP changed after compounding with HPP, leading to different mechanical and thermal behaviors of the mixtures. Notched and unnotched impact strengths increased linearly with increasing ICPP contents. The crystallization peak temperatures increased linearly with increasing ICPP contents while the degrees of crystallinity of the mixtures decreased linearly. The thermal compounding process and the original material properties mainly determine the final mixture behaviors, and the mixture properties can be predicted based on the weight ratios of the two components.
