Spherulite Size Research Articles

Glass Fiber-Reinforced Polypropylene Composites with High Solar Reflectance for Thermal Insulation Applications

Reflective thermal insulation layers can offer an energy-efficient strategy for preventing temperature rises by reflecting sunlight on surfaces. Our previous study presented a novel solvent-based method to prepare porous polypropylene (PP) with high solar reflectivity. However, the stiffness and strength of the neat porous PP were insufficient for thermal insulation applications, as mechanical loads from installation and environmental factors limit the applicability of such products. This paper addresses this gap by applying our solvent-based surface modification technology to glass fiber (GF)-reinforced PP composite sheets, creating a previously unexplored system. While the enhanced modulus and strength aligned with expectations, the micro- and nano-structured porous outer layers situated below the skin layer of the sheets, the refractive index mismatch between the PP matrix and the GF, and the size of the GF delivered a notable advancement in reflective thermal insulation performance. The combined effect of 30 wt% GF, nucleating agents, and surface modification resulted in a highly porous surface layer featuring spherulite sizes of 0.5–2.0 μm. With these combined effects, we achieved a modulus value of ~4 GPa, a tensile strength of 60 MPa, and an average solar reflectance of up to 94%. Thermal insulation performance measurements demonstrated that the registered inner temperature was lower by 24.1 °C compared to neat PP sheets. These combined effects demonstrate the potential of our solvent-based surface modification technology to develop cost-effective, porous PP composite sheets for efficient reflective thermal insulation.

Double Spherulite Formation via Two-Step Crystallization in PTT/PET Blends.

We investigated the crystallization kinetics and morphology evolution of miscible crystalline/crystalline blends of poly(trimethylene terephthalate) (PTT) and poly(ethylene terephthalate) (PET) during isothermal melt crystallization. The integrated light-scattering intensity and the spherulite size increased gradually and then steeply as crystallization progressed in 70/30 PTT/PET at 215 °C, indicating the two-step crystallization behavior. The compact PET spherulite grew in the first step, and the dendritic PTT spherulite grew in the second step, forming the double spherulite consisting of a PET component in the inner region and a PTT one in the outer region. The spherulite size of PET increased nonlinearly with time, suggesting the exclusion of PTT from the crystal growth front. Atomic force microscopy (AFM) observation revealed that the PTT fibrils were interfiled within the PET spherulite in the inner region and continued outward to the outer region consisting of the PTT spherulite. These results suggest that the excluded PTT crystallizes into fibrils by interfiling crystallization within the inner PET spherulite, and then the interfiled PTT fibrils continue to grow outward to form the outer dendritic PTT spherulite after the spherulite growth of PET stops due to the excluded PTT at the growth front.

Structure, morphology and crystallization behavior of PVDF/Co nanowire nanocomposites under horizontal and vertical magnetic fields

So far, very limited research has been carried out on the fabrication of polyvinylidene fluoride (PVDF) composited with anisotropic magnetic nanostructures such as nanowires or nanorods, which can potentially provide specific reactions to magnetic fields. Here, single crystal Co nanowires (CNWs) with an average length and diameter of about 220 and 12 nm, respectively, are synthesized using a solvothermal method, followed by adding them to PVDF matrix in order to prepare flexible PVDF/CNW nanocomposites by solvent casting and solution crystallization processes at room temperature. The nucleation and growth of PCNW nanocomposites are investigated in the absence and presence of horizontal and vertical magnetic fields. According to FESEM images, in addition to the direction of the applied magnetic field, the presence or absence of CNWs induces different effects on the size of spherulites and the configuration of polymer chains. By adding CNW to the PVDF matrix in the absence of a magnetic field and under a horizontal magnetic field, the size of the spherulites in the pure PVDF film increases about 67 % (from 3 to 5 μm) and 300 % (from 3 to 12 μm), respectively. Under a vertical magnetic field, the addition of CNW reduces the size of the spherulites to 1 μm, thereby forming a film with a combination of spherulites and filamentary structure likely due to the nanowire-nanowire, nanowire-chain and chain-chain interactions. Also non-contact flexible triboelectric nanogenerators of magnetic force are fabricated.

Design of toughed bio-based polylactide/polyamide 11 blends with regulatable size of dispersed phase and spherulites by interfacial stereocomplex crystallites

Enhancing the ductility of polylactide (PLA) through toughening modification to expand the application range of PLA aligns with the requirements of green development. In this study, eco-friendly bio-based plastic polyamide 11 (PA11) was chosen to modify poly(l-lactide) (PLLA). PA11 and poly(d-lactide) (PDLA) were grafted onto the main chain of ADR via simple reactive processing and utilized as reactive compatibilizers to improve toughening efficiency of PA11. The successful preparation of the graft copolymer was confirmed through 1H NMR, FT-IR and DSC, and a detailed investigation was conducted on how the composition and concentration of the compatibilizer influence the mechanical properties, phase morphology, crystallization, and nucleation behaviors of PLLA/PA11 blends. Elongation at break of the 5 % PDLA/PA11 graft copolymers toughed PLLA was as high as 222 % at 30 % PA11 content, which was 17 times greater than the PLLA toughened by pristine PA11 without compromising the strength. PLLA and PA11 were immiscible binary blends with PA11 droplet/PLLA matrix phase separated morphologies in the molten state. Based on the calculation of interfacial tension, the grafted copolymer would be mainly distributed at the interface between the two phases. The dispersion of PA11 droplet in PLLA matrix was improved since the interfacial interaction force was enhanced through in-situ reaction. The increase of the nucleation site and decrease of the spherulites size were worked synergistically by stereocomplex (SC) crystallites and PA11. Under the impact of reducing the size of the dispersed phase and spherulites, the toughness of blends was enhanced. This study provided valuable insights into the control of PLLA immiscible blend morphology and elucidated the relationship between the size of dispersed phase and spherulites and the ultimate mechanical performance of bio-based PLA materials.

Optimization of polypropylene high-strength injection molding welding and interface structure analysis

Secondary injection molding is an effective method for joining polymer parts, where the weld interface plays a critical role in the overall performance of the part. This study discusses the influence of injection molding parameters on the interface strength of polypropylene and polypropylene (PP-PP) secondary injection molding and analyzes the welding interface structure. The injection molding parameters for PP-PP were optimized using the Taguchi method and the signal-to-noise ratio (S/N). The optimal injection molding parameters were determined to be a mold temperature of 120°C, injection temperature of 350°C, and injection speed of 100 mm/s. The interface tensile strength was measured at 33.42 MPa, corresponding to 98.1% of the tensile strength of the base material. Among these parameters, mold temperature has the greatest influence on the strength of the welding interface. Secondly, polarizing microscopy, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) were employed to observe and analyze the crystal structure and fracture failure modes at the interface. The results indicate that elevated injection molding parameters promote the formation of crystal nuclei and spherulite growth at the secondary melt interface, with the spherulite size at the interface significantly affecting the interface strength. This study offers valuable reference for the welding of other polymers and fiber-reinforced materials.

How surface modification of cellulose nanocrystals affects the crystallization process of poly (β-hydroxybutyrate)

Hydroxyl groups on the surface of cellulose nanocrystals (CNC) are modified by chemical methods, CNC and the modified CNC are used as fillers to prepare PHB/cellulose nanocomposites. The absorption peak of carbonyl group of the modified CNC (CNC-CL and CNC-LA) appears in the FT-IR spectra, which proves that the modifications are successful. Thermal stability of CNC-CL and CNC-LA is better than that of pure CNC. Pure CNC is beneficial to the nucleation of PHB, while CNC-CL and CNC-LA inhibit the nucleation of PHB. The spherulite size of PHB and its nanocomposites increases linearly over time, and the maximum growth rate of PHB spherulite exists at 90 °C. Rheological analysis shows that viscous deformation plays the dominant role in PHB, PHBC and PHBC-CL samples, while the elastic deformation is dominant in PHBC-LA. According to the rheological data, the dispersion of CNC-CL and CNC-LA in PHB is better than that of CNC. This work demonstrates the impact of modified CNC on the crystallization and viscoelastic properties of PHB. Moreover, the interface enhancement effect of modified CNC on PHB/CNC nanomaterials is revealed from the crystallization and rheology perspectives.

Reinforcing and toughening poly (lactic acid) using cellulose nanocrystal grafted with epoxidized soybean oil

AbstractCurrently, toughening poly(lactic acid) (PLA) without reducing its strength and modulus is still challenging. Fortunately, this problem could be addressed by incorporating cellulose nanocrystals grafted with epoxidized soybean oil (CNCs‐g‐ESO) into the PLA matrix. The percolation threshold for uniform dispersion of the CNCs‐g‐ESO in the PLA matrix was about 0.8 wt%. The loading made the elongation at break and tensile fracture energy of the PLA composite film increase to 26.5 and 11.26 from 3.7% and 0.96 MJ.m−3, respectively, concerning the neat PLA. Meanwhile, it also resulted in a 4.7% and 12.4% increase in the tensile strength and Young's modulus, respectively. Additionally, the initial decomposition temperature (T5%) of the PLA composite increased to 334.9 from 316.1°C after incorporating the CNCs‐g‐ESO. Therefore, the CNCs‐g‐ESO, acting as an ESO‐like plasticizer and a CNCs‐like nucleating agent, is a potential nanofiller for reinforcing and toughening PLA.Highlights Cellulose nanocrystal grafted with epoxidized soybean oil (CNCs‐g‐ESO) The CNCs‐g‐ESO acting as both plasticizer and nucleating agent The CNCs‐g‐ESO decreasing the spherulite size, but increasing the CrI of PLA The CNCs‐g‐ESO enlarging the window for thermal process of PLA Simultaneous reinforcement and toughness of PLA

Impact of aromatic sulfonate derivative on the crystallization, thermal resistance, and hydrolytic properties of poly(lactic acid)

AbstractThe thermal, crystallization kinetics and hydrolysis properties of poly(lactic acid)‐based blends containing different concentrations of 5‐dimethylthioisosulfate salts (LAK) were systematically investigated and compared with those of poly(lactic acid) (PLA). PLA/LAK blends were prepared by melt blending method‐using LAK as a nucleating agent of PLA. During the isothermal crystallization process, the morphology of PLA crystal in the neat PLA and PLA/LAK blends showed spherical crystals. With an increase in the concentration of LAK, the nucleating density of the PLA spherulites increased and the size of the PLA spherulites decreased. Differential scanning calorimetry indicates that after the addition of LAK, both the crystallinity and crystallization rate of PLA have been enhanced. In situ X‐ray diffraction analysis also shows that the sample exhibits the same crystal structure as neat PLA and continues to strengthen, indicating that LAK enhances the crystallization properties of PLA. Moreover, the crystallinity of PLA increased and crystal size of PLA decreased with the increase in the LAK content. The Vicat softening temperatures of PLA/LAK blends increased, so the heat resistance improved. Through hydrolysis testing under identical conditions, the PLA/LAK blends exhibits better hydrolytic stability.

Influence of magnesium and calcium sulfate whisker on crystallization characteristics of poly (butylene adipate-co-terephthalate) and Poly(butylene succinate)

Inorganic fillers of whisker-like morphology are considered promising materials, and they have gained significant attention in recent years as a substitute for glass fibers due to their fibrous surface characteristics and extremely low bulk density. This study selected magnesium sulfate whiskers (MSWs) containing crystal water and pure calcium sulfate whiskers (CSWs) as fillers. They were physically blended with biodegradable polymers PBAT and PBS in a range of 0.1 wt.% to 2 wt.% to form composite materials. The non-isothermal crystallization behavior of the composite materials was studied using differential scanning calorimetry (DSC). The data indicated that with an increase in whisker content, the crystallization temperature (Tc) of composites increased, and the addition of a small amount of whiskers led to a reduction in the half-crystallization time of the composite materials, indicating the crystallization capacity of the materials has been enhanced to varying degrees. Analysis via POM unveiled a consistent pattern of decreased spherulite size and heightened spherulite count with the introduction of whiskers. This phenomenon is ascribed to the whisker fillers’ function as nucleating agents within the polymer matrices, thereby stimulating the crystallization process. Interestingly, the findings suggest that CSWs exert a more significant influence on crystallization than MSWs, likely due to the distinct single fiber morphology of the former filler.

Eco-friendly zinc-metal-organic framework as a nucleating agent for poly (lactic acid)

Eco-friendly poly(L-lactic acid) (PLA) can be made more versatile, and its crystallization rate is accelerated by adding Zinc-based metal-organic framework (Zn-MOF) particles. Using differential scanning calorimetry (DSC), the non-isothermal melt crystallization behavior of biodegradable PLA nucleated by 0.3 to 3 wt% of Zn-MOF was examined. The non-isothermal melt crystallization kinetics parameters were determined using a modified Avrami model and Mo approach. Zn-MOF dramatically accelerated the crystallization process, as evidenced by several non-isothermal crystallization metrics, including the crystallization half-time and crystallization rate constant. The melt crystallization temperatures of the PLA-Zn-MOF composites, with contents of 0.7 and 1 wt%, were increased by 21 °C compared to the neat PLA. Using the Friedman isoconversional kinetic method, the neat PLA and PLA-Zn-MOF composites' effective activation energy values, ∆E, were determined. The ∆E values of PLA-Zn-MOF from 0.3 to 1 wt% Zn-MOF composites were lower than that of neat PLA. Moreover, polarized optical microscopy revealed the formation of numerous small-sized PLA spherulites upon Zn-MOF addition. The results indicate that the Zn-MOF (at concentrations of 0.7 to 1.0 wt%) can be used as an efficient nucleating agent for PLA, where it increases the melt crystallization temperature, nucleation density, and crystallinity without changing the crystalline structure, while also significantly reduces the effective activation energy and the size of spherulites. Additionally, scanning electron microscopy confirms good dispersion of Zn-MOF (0.3 to 1 wt%) within the PLA matrix.

Enhancement of PLA crystallization, transparency, and strength by adding the long aliphatic chains grafted CNC

The combination of crystallization, transparency, and strength is still a challenge for broadening the application of polylactic acid (PLA) films, while it is also difficult to balance. In this work, the long aliphatic chains of octadecylamine (ODA) were grafted onto the surface of cellulose nanocrystal (CNC) by tannic acid oxidation self-polymerization and Michael addition/Schiff base reaction between polytannic acid and ODA. Furthermore, the ODA grafted CNC (g-CNC) was used as green reinforcement for the PLA matrix and a series of PLA/g-CNC nanocomposite films were prepared by the casting method. The DSC, WAXD, POM, UV–vis and stretching test were employed to examine the effect of g-CNC on the properties of the as-prepared PLA/g-CNC nanocomposite films. It shows that the g-CNC is effective to improve the melt crystallization rate of PLA from 11 min to 7.3 min. Most importantly, the crystal size of the PLA spherulites was significantly reduced due to the well dispersion in the amorphous PLA matrix, which would effectively improve the transmittance of the PLA films and synchronously realize the combination of crystallization (62 %) and transparency (80.6 %). Moreover, the improved crystallization could also enhance the heat deformation performance of the PLA films since the heat resistance is closely associated with the crystallinity. Besides, the grafted ODA long chains improve the compatibility between CNC and PLA, leading to the reinforcement of PLA matrix, where the tensile strength reaches 65.05 MPa from 44.31 MPa. Compared with the pristine CNC, the addition of g-CNC makes more comprehensive improvement in the properties of the PLA films.

Controlling the crystal morphology of high-hardness TPU through two pre-crystallization processes and its impact on physical foaming behavior

Clarifying the relationship between crystal evolution and the physical foaming behavior of high-hardness thermoplastic polyurethane (HD-TPU) is essential for preparing HD-TPU foams with controllable cellular morphology. In this study, two thermal treatment methods, isothermal annealing and isothermal crystallization, were utilized to control the crystal structure of HD-TPU. The effect of crystals on the physical foaming behavior of HD-TPU foams was examined. The annealing process produced mainly lamellae and Form Ⅰ structure, while isothermal crystallization primarily led to Form Ⅱ spherulites. Foams based on original and pre-treated HD-TPU were prepared by pressure quench foaming. The evolution of foam density and cell morphology was discussed. At low foaming temperatures, crystals induced the heterogeneous nucleation. Realizing a uniform cell structure at high foaming temperatures could be challenging when the spherulite size was large. When the size of the spherulite was small but loosely distributed, larger cells with thinner cell walls could be obtained. However, if the spherulite distribution was dense, the spherulites hindered cell growth, resulting in unevenly distributed and deformed cells.

Effect of mechanical stretching and low amount of silica adding on gas transport properties of poly(butylene succinate-co-adipate) films

This work aimed at studying the influence of a post drawing process on the morphology and the gas permeability of a PBSA (Polybutylene succinate-co-adipate) film. Two films were studied, one of neat PBSA and one filled with 1%wt of silica. The influence of silica was also studied. Reference films of PBSA and PBSA + Si presented a spherulitic morphology despite a difference of spherulites sizes and long period. After stretching, this isotropic morphology changed to an oriented one, as shown by WAXS measurements. SAXS analysis revealed that stretching led to a lamellae organization in the stretching direction, with lamellae oriented perpendicular to the stretching direction. Thermal characterizations have shown that stretching did not modified the degree of crystallinity for both systems. The helium, carbon dioxide and oxygen permeability increased with stretching, mainly due to the orientation of crystalline lamellae, decreasing the diffusion path. Moreover, for PBSA + Si stretched films, small non-percolating voids were evidenced around the silica particles which could also make gas transport easier. Thus, for both systems, this increase in gas permeability happened in a different way.

Optimizing bonding performance in CF/PEKK composites: The role of IR heating and press consolidation

Bonding performance of carbon fiber/polyetherketoneketone (CF/PEKK) laminates is closely related to crystallinity and is influenced by growth, formation, and density of spherulites. Press consolidation, with its ability to adjust pressure, exhibits superior quality compared to oven consolidation. However, bonding and production of CF/PEKK laminates using Press consolidation exhibit significant variations in quality depending on forming conditions. While research on producing CF/PEKK laminates using press consolidation is currently active, there is a lack of studies on co-consolidation for CF/PEKK laminates. Thus, in this study, establishment of forming process variables for press consolidation was conducted to achieve excellent bonding performance for CF/PEKK. Furthermore, IR heating-assisted surface heat treatment was employed to enhance bonding performance of CF/PEKK laminates by controlling crystallinity and spherulites. To analyze bonding performance, short bean shear testing was conducted to obtain interlaminar shear strength (ILSS). Results showed that surface modification through IR heating led to an increase in crystallinity and a noticeable growth in size of spherulites. In specific conditions, improved bonding performance was observed. This is judged to be primarily due to increase in spherulite size and crystallinity at bonding interface, attributed to specific conditions of both surface treatment through IR heating and Press consolidation.

The Crystallization and Melting Behavior of Neodymium-Based Butadiene Rubber Blends.

This study investigates the influence of poly(butadiene-isoprene) copolymer rubber (BIR) and TDAE oil on the crystallization and melting behavior of neodymium-based butadiene rubber (Nd-BR). The study demonstrates that the melting points of Nd-BR and its blends decrease with lower crystallization temperatures. Below the critical crystallization temperature (Tc,c), the melting behavior shows dual peaks in distinct temperature ranges, which are attributed to different spherulitic sizes. The addition of BIR or TDAE oil lowers the Tc,c, with TDAE oil exerting a more substantial effect. These diluents mainly influence the nucleation temperature and crystallinity level of Nd-BR while having a minimal effect on the crystallization mechanism. A master curve, which overlaps for various samples, is developed by correlating the peak melting temperature (Tm,peak) with the Tc. This curve facilitates a quantitative assessment of the effects of BIR and TDAE oil on Nd-BR, highlighting the greater influence of TDAE oil on the crystalline structure compared with BIR at equivalent mass fractions. By applying the Lorentz equation and multi-peak fitting, a relationship between the melting points and crystallization temperatures is established, enabling the calculation of the equilibrium melting points (Tm0) for different samples. The findings show a reduction in the Tm0 due to the diluents; specifically, the Tm0 is approximately 0 °C for pure Nd-BR, and it decreases to -4.579 °C and -6.579 °C for samples with 50 PHR TDAE oil and 60 wt.% BIR, respectively.

Influence of assisted electric field on the microstructure evolution and direct current electrical properties of low-density polyethylene

Low-density polyethylene (LDPE) is the basic material of the high-voltage direct current (DC) power cable insulation. The assisted electric field is a common way to regulate the microstructure of polymers, but its application in the field of electrical insulating polymers is rarely reported. In order to study the influence of the assisted electric field on the microstructure evolution and DC electrical properties of LDPE, the LDPEs without and with being treated with assisted electric field are prepared in the melting stage, cooling stage, and the whole stage (i.e. the melting stage and cooling stage), respectively. The influence of the assisted electric field applied in the different stages on the microstructure evolution of LDPE is characterized by the scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The DC electrical properties of the untreated LDPE and the treated LDPE are investigated via measuring their breakdown strengths, conductivities, space charges and surface potential decays. The results show that, compared with the untreated LDPE, the LDPE treated with the assisted electric field in the whole stage has the smallest spherulite size and the largest spherulite number, followed by the LDPE treated in the cooling stage and the melting stage. The assisted electric field applied in different stages can significantly improve the DC electrical properties of LDPE. Compared with the untreated LDPE, the LDPE treated in the melting stage, the cooling stage and the whole stage increases the breakdown strength but greatly reduces the conductivity and space charge accumulation. The DC electrical properties of LDPE treated with the assisted electric field in the whole-stage are the best. Compared with untreated LDPE, the LDOE treated in whole stage increases the breakdown field strength by 35.8%, reduces the conductivity by 72.0%, and the space charge accumulation by 20.2%. More and smaller spherulites lead to the formation of more interface paths and introduce more deep-traps, which contributes to improving the DC electrical characteristics of the electric field assisted LDPE. This work provides a new idea for improving the DC electrical properties of polymers.

Crystallinity, Rheology, and Mechanical Properties of Low-/High-Molecular-Weight PLA Blended Systems.

As semi-crystalline polyester (lactic acid) (PLA) is combined with other reinforcing materials, challenges such as phase separation, environmental pollution, and manufacturing difficulties could hinder the benefits of PLA, including complete biodegradability and strong mechanical properties. In the present investigation, melt blending is utilized to establish a mixture of low- and high-molecular-weight polylactic acids (LPLA and HPLA). The crystallinity, rheology, and mechanical properties of the combination were analyzed using rotational rheometry, differential scanning calorimetry, X-ray diffraction, polarized optical microscopy, scanning electron microscopy, and universal testing equipment. The results demonstrate compatibility between LPLA and HPLA. Moreover, an increase in LPLA concentration leads to a decrease in the crystallization rate, spherulite size, fractional crystallinity, and XRD peak intensity during isothermal crystallization. LPLA acts as a diluent during isothermal crystallization, whereas HPLA functions as a nucleating agent in the non-isothermal crystallization process, promoting the growth of LPLA crystals and leading to co-crystallization. The blended system with a 5% LPLA mass fraction exhibits the highest tensile strength and enhances rheological characteristics. By effectively leveraging the relationship between various molecular weights of PLA's mechanical, rheological, and crystallization behavior, this scrutiny improves the physical and mechanical characteristics of the material, opening up new opportunities.

A Comparative Study on Crystallisation for Virgin and Recycled Polyethylene Terephthalate (PET): Multiscale Effects on Physico-Mechanical Properties.

Poly(Ethylene Terephthalate) (PET) is one of the most used polymers for packaging applications. Modifications induced by service conditions and the means to make this matter circular have to be understood to really close the loop (from bottle to bottle for example). Physico-chemical properties, crystalline organisation, and mechanical behaviour of virgin PET (vPET) are compared with those of recycled PET (rPET). Using different combined experimental methods (Calorimetry, Small Angle X-ray Scattering [SAXS], Atomic Force Microscopy [AFM], Dynamic Mechanical Analysis [DMA], and uniaxial tensile test), it has been proven that even if there is no change in the crystallinity of PET, the crystallisation process shows some differences (size and number of spherulites). The potential impact of these differences on local mechanical characterisation is explored and tends to demonstrate the development of a homogeneous microstructure, leading to well-controlled and relevant local mechanical property characterisation. The main contribution of the present study is a better understanding of crystallisation of PET and recycled PET during forming processes such as thermoforming or Injection Stretch Blow Moulding (ISBM), during which elongation at the point of breaking can depend on the microstructure conditioned by the crystallisation process.

Planerite with aheylite and faustite from the Chala deposit, Spahievo Ore Field

Planerite, aheylite and faustite are minerals of the turquoise group. They were found in samples from the Chala deposit, Spahievo Ore Field. The samples consist of a small crystalline mass of the investigated mineral phases among quartz. Single spherulites up to 2 mm in size and aggregates of spherulites with a yellowish-greenish color are observed in small cavities. Transparent, colorless wavellite crystals and aggregates are crystallized on spherulites. For the first time in Bulgaria, the presence of aheylite was established.

Enhancement of flexural properties of carbon fiber-reinforced polyamide 6 via oriented crystallization of polyamide 6 among carbon fibers

The effect of the crystalline structure of polyamide 6 (PA6) among carbon fiber (CF) on the mechanical properties of PA6/CF composites was explored using two types of PA6 with different spherulite sizes. Infrared (IR) spectroscopy showed that intra/intermolecular interactions were nearly equivalent for the two types of PA6. The viscoelasticities in the molten state were almost identical; that is, the molecular weights of the PA6s were comparable. The mechanical properties of the PA6 matrix with smaller spherulites (PA6a) in PA6/CF were superior to those of the PA6 matrix with larger spherulites (PA6b). Polarized light microscopy, wide-angle X-ray scattering, and polarized Raman spectroscopy revealed oriented crystals of PA6a in the PA6a/CF composite and random crystals of PA6b in the PA6b/CF composite. Therefore, the superior mechanical properties of PA6/CF are due to the oriented crystal chains of PA6, which support the overall stress transfer in composites.