Composites from Brazilian natural fibers with polypropylene: mechanical and thermal properties

Brazil has a well established ethanol production program based on sugarcane. Sugarcane bagasse and straw are the main by-products that may be used as reinforcement in natural fiber composites. Current work evaluated the influence of fiber insertion within a polypropylene (PP) matrix by tensile, TGA and DSC measurements. Thus, the mechanical properties, weight loss, degradation, melting and crystallization temperatures, heat of melting and crystallization and percentage of crystallinity were attained. Fiber insertion in the matrix improved the tensile modulus and changed the thermal stability of composites (intermediary between neat fibers and PP). The incorporation of natural fibers in PP promoted also apparent T _c and ΔH _c increases. As a conclusion, the fibers added to polypropylene increased the nucleating ability, accelerating the crystallization process, improving the mechanical properties and consequently the fiber/matrix interaction.     

Using dynamic mechanical spectroscopy to monitor the crystallization of PP/MAPP blends in the presence of wood

Crystal morphology of thermoplastics is known to be strongly influenced by the presence of solid substrates like fibers or fillers. For wood, this interphase development is governed by the chemical composition of the thermoplastic and substrate. The crystallization of PP/MAPP blends was observed using polarized light microscopy and quantified using DSC and DMA. Techniques are presented to assess degree of crystallinity and temperatures associated with the onset (T _o) and maximum rate (T _c) of crystallization using DMA. Strain history of the specimen during crystallization was evaluated and does not significantly influence either T _o or T _c. Crystallization temperatures of PP as assessed using DSC or DMA increase with the addition of MAPP or the presence of wood. Values for T _c are higher when measured by DMA than DSC. This difference appears to be related more to the relative interfacial dominance in the specimens, rather than to an inherent difference between techniques.     

Nonisothermal Crystallization of the Polypropylene/Organosilica Nanocomposite

Abstract

Nonisothermal crystallization of the neat isotactic polypropylene homopolymer (PP‐0) and of the nanocomposite containing 4.68 wt.% of organosilica (PP‐4.68) was studied in the standard differential scanning calorimetry (DSC) mode during constant‐rate cooling from the melt state. Analysis of the nucleation parameters derived from cooling rate dependencies of the temperatures for the onset of crystallization exotherms suggested a slight increase of the nucleation barrier for lamellar crystallization of PP within a confined space between neighboring nanoparticles of an infinite cluster of the nanocomposite, concomitant to stronger restrictions to transport of PP segments across the melt/lamellar crystal interface. The overall crystallization rate data for PP‐4.68 were consistent with the assumption of two separate contributions from the initial (unconstrained) and the subsequent (constrained) nucleation mechanisms, respectively. The obtained results were considered as evidence for a coexistence in an undercooled PP melt of the nanocomposite of initial nucleation sites characteristic for the neat PP‐0, and the basically different nucleation sites (presumably, PP chains anchored by both ends to the surfaces of two adjacent nanoparticles).     

Preparation,Morphology and Properties of Poly(Trimethylene Terephthalate)/Thermoplastic Polyester Elastomer Blends

Poly(trimethylene terephthalate)(PTT)/thermoplastic polyester elastomer (TPEE) blends were prepared and their miscibility, crystallization and melting behaviors, phase morphology, dynamic mechanical behavior, rheology behavior, spherulites morphology, and mechanical properties were investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), parallel-plate rotational rheometry, polarized optical microscopy (POM), wide angle X-ray diffraction (WAXD), universal tensile tester and impact tester, respectively. The results suggested that PTT and TPEE were partially miscible in the amorphous state, the TPEE rich phase was dispersed uniformly in the solid matrix with a size smaller than 2 μm, and the glass transition temperatures of the blends decreased with increasing TPEE content. The TPEE component had a good effect on toughening the PTT without depressing the tensile strength. The blends had improved melt viscosities for processing. When the blends crystallized from the melt state, the onset crystallization temperature decreased, but they had a faster crystallization rate at low temperatures. All the blends’ melts exhibited a predominantly viscous behavior rather than an elastic behavior, but the melt elasticity increased with increasing TPEE content. When the blends crystallized from the melt, the PTT component could form spherulites but their morphology was imperfect with a small size. The blends had larger storage moduli at low temperatures than that of pure PTT.     

Relationship between Microstructure and Mechanical Properties of Ethylene-Octene Copolymer Reinforced and Toughened PP

Polypropylene (PP)/ethylene-octene copolymer (POE) blends with 10–50wt% POE composition were prepared using a twin-screw extruder in the melt state. Mechanical properties of PP and PP/POE blends were tested and the effect of POE content on the crystalline morphology and structure, melting and crystallization behavior, compatiblilty, phase morphology, and the interface cohesiveness of the blends were investigated by polarizing optical microscope (POM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and scanning electron microscopy (SEM). The relationship between mechanical properties and microstructure of the PP/POE blends is discussed. The results showed that POE had a dual function of both reinforcing and toughening PP in the range from 10–40wt%, which was attributed to the integrated functions of the degree of crystallinity of the PP phase, phase morphology, and interface cohesiveness of the blend.     

Relationship between Peroxide Initiators and Properties of Styrene Grafted Polypropylene via Reactive Extrusion

To understand the relationship between the initiators and the properties of grafted polypropylene (PP), and provide guidance for designing polymers with different performance through selecting appropriate initiators, a series of styrene (St) grafted PP was prepared by modifying commercial linear PP via reactive extrusion using two different peroxide initiators, dicumyl peroxide (DCP) and benzoyl peroxide (BPO). Fourier transform infrared spectra indicated that the use of DCP led to a higher St grafting degree compared to the system using BPO. The melt flow index and rheological characteristics suggested the existence of short chain branching (SCB) structures in the St grafted PP using DCP, and long chain branching (LCB) structures in the St grafted PP using BPO. Differential scanning calorimetry and polarized optical microscopy results showed that the degradation of the PP chains and the introduction of SCB structures hindered the crystallization process of the St grafted PP using DCP, and the existence of the LCB structures accelerated the crystallization process of the St grafted PP using BPO. We suggest this research can contribute to the understanding of methods to prepare grafted PP with special properties via reactive extrusion by using proper initiators.     

Polymer-Nanoparticle Composites Composed of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and Coated Silver Nanoparticles

The effects of addition of synthesized organic-suspension silver nanoparticles on the crystallization and thermal stability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were studied by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (XRD), UV-Vis absorption spectroscopy, polarized optical microscopy (POM), and thermal gravimetric analysis (TGA). The TEM images showed the average primary size of the as-synthesized silver nanoparticles, coated with a monolayer of the surfactants consisting of oleic acid and an alkylamine, was about 5 nm with narrow distribution, and that they were uniformly dispersed in n-heptane. PHBV/silver nanocomposites were prepared by melt mixing in an internal mixer and then injection molded into rectangle-shaped specimens by a labscale injection molding device. The coated silver nanoparticles showed a homogenuous dispersion in the PHBV matrix when the content of coated silver nanoparticles was about 1%. Both the DSC and POM data showed the efficient heterogeneous nucleation by the coated silver nanoparticles for facilitating PHBV crystallization. The thermal stability of the PHBV/silver nanocomposites improved with the increase in the content of the coated silver nanoparticles.     

Nonisothermal Crystallization Behavior of Polypropylene-C60 Nanocomposites

The nonisothermal crystallization behavior of polypropylene (PP) and PP-fullerene (C₆₀) nanocomposites was studied by differential scanning calorimetry (DSC). The kinetic models based on the Jeziorny, Ozawa, and Mo methods were used to analyze the nonisothermal crystallization process. The onset crystallization temperature (T_c), half-time for the crystallization (t_1/2), kinetic parameter (F(T)) by the Mo method and activation energy (ΔE) estimated by the Kissinger method showed that C₆₀ accelerates the crystallization of PP, implying a nucleating role of C₆₀. Furthermore, due to the reduced viscosity of PP by adding 5% C₆₀, the parameters of crystallization kinetics for the PP-5%C₆₀ nanocomposites changed remarkably relative to that of neat PP and when lower contents of C₆₀ were added to PP.     

Effects of Montmorillonite on the Nonisothermal Crystallization Behavior of the Poly(trimethylene terephthalate)/Polypropylene/Montmorillonite Nanocomposites

Organic montmorillonite (MMT) reinforced poly(trimethylene terephthalate) (PTT)/ polypropylene (PP) nanocomposites were prepared by melt blending. The effects of MMT on the nonisothermal crystallization of the matrix polymers were investigated using differential scanning colorimetry (DSC) and analyzed by the Avrami equation. The DSC results indicated that the effects of MMT on the crystallization processes of the two polymers exhibited great disparity. The PTT's crystallization was accelerated significantly by MMT no matter whether PTT was the continuous phase or not, but the thermal nucleation mode and three-dimensional growth mechanism remained unchanged. However, in the presence of MMT, the PP's crystallization was slightly retarded with PP as the dispersed phase, and was influenced little with PTT as the dispersed phase. When the MMT content was increased from 2_wt% to 7_wt%, the crystallization of the PTT phase was slightly accelerated, whereas the crystallization of the PP phase was severely retarded, especially at lower temperatures. Moreover, the nucleation mechanism for the PP's crystallization changed from a thermal mode to an athermal one. In the polypropylene-graft-maleic anhydride (PP-g-MAH) compatibilized PTT/PP blends, with the addition of 2_wt% MMT during melt blending, the T _c (PTT) shifted 7.8°C to lower temperature and had a broadened exotherm, whereas the T _c (PP) shifted 17.1°C to higher temperature, with a narrowed exotherm. TEM analysis confirmed that part of the PP-g-MAH was combined with MMT during blending.     

Properties of Polypropylene/Antibacterial Glass Composites

Polypropylene (PP)/antibacterial glass composites were prepared by melt blending PP and silver-doped glass. The antibacterial activity of the PP composites was examined by the method of plate counting, and the crystallization behaviors of pure PP and antibacterial glass/PP composites were compared via hot-stage polarized optical microscopy (POM), X-ray diffraction (XRD), and differential scanning calorimeter (DSC). The results revealed that the antibacterial PP composites had effective antibacterial activity with antibacterial rates more than 90%. The antibacterial agent in the antibacterial glass/PP composites acted as nucleating agents, increasing the crystallization temperature and crystallization rate of PP, but not changing the crystalline modification of PP. The mechanical properties of antibacterial glass/PP composites were also studied, and the results showed that the antibacterial glass improved the stiffness and modulus but decreased the notched impact strength of the PP composites.     

Preparation and Characterization of Composites Based on Poly (Butylene Succinate) and Poly (Lactic Acid) Grafted Tetracalcium Phosphate

Tetracalcium phosphate (TTCP, Ca₄(PO₄)₂O) was functionalized by poly (l-lactic acid) (PLLA) in order to improve the dispersion of TTCP particles in poly (butylene succinate) (PBS) matrices, and then a series of the PLLA grafted TTCP/PBS (g-TTCP/PBS) composites were prepared via melt processing. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), tensile analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (DTG/TGA) and melt rheological analysis were used to investigate the structure and properties of the g-TTCP/PBS composites. The results revealed that l-lactide could be grafted onto the surface of TTCP, and the g-TTCP/PBS composites showed the best mechanical properties when the content of g-TTCP was 10 wt%. The crystallization temperature of g-TTCP/PBS composites tended to increase with the increase of g-TTCP contents. The functionalized particles played an important role in augmenting the thermal degradation rate and the complex viscosity of the composites due to their unique structure and the reasonable interfacial interaction between the particles and PBS matrix.     

Phase Structure of Compatibilized Poly(Lactic Acid)/Linear Low-Density Polyethylene Blends

Blends of PLA and linear low-density polyethylene (LLDPE) were compatibilized with glycidyl methacrylate (GMA)–grafted poly(ethylene-octene) copolymer (mPOE). Effects of compatilizer on phase structure of compatibilized PLA/LLDPE were studied by spreading coefficient calculation prediction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD) analysis. The spreading coefficient calculations, based on experimental and calculated surface tension data, show that mPOE spreads on LLDPE extensively to encapsulate LLDPE completely, which is in good agreement with the results of DSC, SEM, and WAXD analysis. The chemical reaction between the end carboxyl groups or end hydroxyl groups of PLA and epoxy groups of mPOE, which is suggested as the driving force leading to an ideal interfacial adhesion between PLA and the dispersed phase, was confirmed by Fourier transform infrared ray (FT-IR) spectroscopy analysis.     

Crystallization Behavior of Poly(Trimethylene Terephthalate)/Polycarbonate Blends

The crystallization behavior of poly(trimethylene terephthalate (PTT) in compatibilized and uncompatibilized PTT/polycarbonate (PC) blends are investigated in the research reported in this paper. The differential scanning calorimetry (DSC) results showed that the crystallization behaviors of PTT/PC blends were very sensitive to PC content. The onset (T_ci) and the peak (T_c) crystallization temperatures shifted to lower temperatures whereas the area of the exotherm decreased quickly as the PC content was increased. The Avrami exponent, n, decreased from 4.32 to 3.61 as the PC content was increased from 0 to 20 wt %, and the growth rate constant, Z _c , decreased gradually as well. This suggests that the nucleation mechanism exhibits the tendency of changing gradually from a thermal nucleation to an athermal mode although the growth mechanism still remains three‐dimensional. When epoxy (2.7 phr) was added as a compatibilizer during melt blending, the T_ci and T_c shifted slightly to higher temperature (≤2°C), and the crystallization enthalpy, however, exhibited an increased crystallinity with the exception of the 90/10/2.7 phr PTT/PC/Epoxy. This suggests that the epoxy make a positive contribution to the PTT crystallization. Moreover, the influences of epoxy on the crystallization behaviors of PTT/PC blends are related to the epoxy content. By contrast, the compatibilizer of ethylene‐propylene‐diene copolymer graft glycidyl methacrylate (EPDM‐g‐GMA, ≤6.3 phr) had little effect on the crystallization behavior of PTT/PC blends. For PTT/PC/Epoxy (2.7 phr) blends, the Avrami exponent, n, decreased to near 3, while the growth rate constant, Z _c , increased slightly as PC content was increased from 0 to 20 wt %. It is suggested that epoxy accelerated the process of the nucleation mechanism changing from thermal nucleation to an athermal mode. The EPDM‐g‐GMA had little effect on the nucleation mode and spherical growth mechanism. The PTT spherulite morphologies in PTT/PC blends were very sensitive to blend composition. Completely different morphologies were observed in pure PTT, PTT/PC, PTT/PC/Epoxy, and PTT/PC/EPDM‐g‐GMA blends.     

Reactive Compatibilization of Poly(trimethylene terephthalate)/Polypropylene Blends by Polypropylene‐graft‐Maleic Anhydride. Part 1. Rheology,Morphology, Melting,and Mechanical Properties

Poly(trimethylene terephthalate)/polypropylene (PTT/PP) blends were prepared by melt blending. The rheology, morphology, melting, and mechanical properties of PTT/PP blends were investigated with and without the addition of polypropylene‐graft‐maleic anhydride (PP‐g‐MAH). The melt viscosity results showed that the fluid behavior of PTT/PP blends exhibited great disparity to that of PTT but similar to that of PP; the dispersed flexible PP phase in the blends served as a “ball bearing effect” under shear stress, which made the fluid resistance markedly reduced; by contrast, the relatively rigid PTT dispersed phase made only a small contribution to the viscosity. With 5 wt.% PP‐g‐MAH addition during melt processing, both the shear viscosity and the non‐Newtonian index of 70/30 PTT/PP blend were increased over that of the corresponding uncompatibilized one, whereas the shear viscosity of the 30/70 PTT/PP melt decreased slightly indicating that a considerable amount of PP‐g‐MAH did not act as compatibilizer but probably served as plasticizer.

With the increasing of the other component, the melting temperature of the PTT phase showed a slight decrease while the melting temperature of the PP phase showed a slight increase. 5 wt.% PP‐g‐MAH addition had little influence on the melting temperatures of the two components. When PP≤20 wt.%, the cold crystallization temperature of the PTT phase (T_cc (PTT‐phase)) showed little change with the composition; however, it shifted to higher temperature when PP≥30 wt.%. The variations of the T_cc (PTT‐phase), with and without PP‐g‐MAH, suggested that, when PTT was a minor component, the excess PP‐g‐MAH which did not act as compatibilizer might serve as a plasticizer that made the PTT's cold crystallization process to be easier. The SEM results indicated that, for the uncompatibilized blends, the interfaces from particles pulling‐out are clear and smooth, while, for compatibilized blends, the reactive products are at the interfaces. The mechanical properties suggested that PP‐g‐MAH did not result in significant improvement of the toughness of the blend, but the tensile strength increased markedly.     

Synthesis and characterization of thermotropic liquid crystalline polyester/multi-walled carbon nanotube nanocomposites

Thermotropic liquid crystalline polyester (TLCP) was synthesized via low-temperature solution polycondensation from 1,4-Bis(4-Hydroxybenzoyloxy)butane and terephthaloyl dichloride. Polymer nanocomposites based on a small quantity of multi-walled carbon nanotubes (MWNTs) were prepared by in situ polymerization method. The wide-angle X-ray diffraction (WAXD) results suggested that the addition of MWNTs to TLCP matrix did not significantly change the crystal structure of TLCP. The interactions between the molecules of the TLCP host phase and the carbon nanotubes were investigated through Raman spectroscopy investigations. We detected a distinct wave number shift of the radial breathing modes, confirming the carbon nanotubes interacted with the surrounding liquid crystal molecules, most likely through aromatic interactions (π-stacking). The interactions between liquid crystal host and nanotube guests were also evident from a polarizing microscopy (POM) study of the liquid crystal-isotropic phase transition in the proximity of nanotubes. The thermal properties and the morphological properties of the TLCP/MWNTs nanocomposites were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). TGA data demonstrated the addition of a small amount of MWNTs into TLCP matrix could improve the thermal stability of TLCP matrix. DSC results revealed that melt transition temperatures and isotropic transition temperatures of the hybrids were enhanced.     

The interface structure of nano-SiO2/PA66 composites and its influence on material's mechanical and thermal properties

The PA66-based nanocomposites containing surface-modified nano-SiO₂ were prepared by melt compounding. The interface structure formed in composite system was investigated by thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The influence of interface structure on material's mechanical and thermal properties was also studied. The results indicated that the PA66 chains were attached to the surface of modified-silica nanoparticles by chemical bonding and physical absorption mode, accompanying the formation of the composites network structure. With the addition of modified silica, the strength and stiffness of composites were all reinforced: the observed increase depended on the formation of the interface structure based on hydrogen bonding and covalent bonding. Furthermore, the differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) showed that the presence of modified silica could affect the crystallization behavior of the PA66 matrix and lead to glass transition temperature of composites a shift to higher temperature.     

In situ Grafting onto Silica Surface with Epoxidized Natural Rubber via Solid State Method

An in situ solid state grafting reaction between epoxidized natural rubber (ENR) and silica was performed in a Haake internal mixer. Resulting ENR‐grafted silica was characterized by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) measurements. Based on these results, it was concluded the silanol groups (Si‐OH) of silica caused the ring opening of ENR oxirane rings so that ENR was grafted onto the silica surface. Transmission electron microscopy (TEM) photographs showed ENR‐grafted silica had better dispersibility and smaller aggregates compared with the original silica. Dynamical mechanical analysis (DMA) of vulcanized rubber compounds contained ENR‐grafted silica showed the glass transition temperature (T _g) of grafted ENR molecules shifted to higher temperature, from ?3°C to 20°C, indicating the mobility of ENR was greatly restricted. As a result, the compounds containing ENR‐grafted silica have higher hysteresis, and can be applied in a much wider field, such as damping materials, tires of racing cars, and so on.     

Effect of Filler Treatment on Crystallization,Morphology and Mechanical Properties of Polypropylene/Calcium Carbonate Composites

Pimelic acid (PA) was used as a new surface modifier for CaCO₃. The effects of PA treatment on the crystallization, morphology, and mechanical properties of PP/CaCO₃ composites were investigated. Fourier transform infrared (FTIR) spectroscopy analysis revealed that PA bonded to CaCO₃ and formed a calcium pimelate surface layer after reacting with CaCO₃. The results of wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and polarized light microscopy (PLM) proved that the PA treated CaCO₃ induced a large amount of β -iPP and decreased the spherulitic size of PP. The results of scanning electron microscopy (SEM) showed that the PA treatment enhanced the interfacial adhesion between the filler and the matrix, indicating the improvement of the compatibility between PP and CaCO₃. The toughness of the composites was improved by the more ductile β -form spherulites. When 1% of PA treated CaCO₃ was added, the notched impact strength reached its maximum, a value of 19.79 kJ/m², which was 3.64 times greater than that of the pure PP.     

Nonisothermal Crystallization Behavior of Polypropylene Grafted Silane and Styrene Using γ-Ray Irradiation

Polypropylene grafted silane and styrene (named PP-g-Si/St in this article) was successfully prepared by radical graft polymerization initiated by γ-ray irradiation. The influence of total absorbed dose on the graft ratio of vinyltrimethoxysilane onto PP and the melt flow rate (MFR) of the PP-g-Si/St product were studied. The effect of graft ratios of vinyltrimethoxysilane on the melting point and nonisothermal crystallization kinetics of PP-g-Si/St was investigated by the method of differential scanning calorimetry (DSC). With increasing vinyltrimethoxysilane and styrene (used as viscosity modifier and free radical source) grafted on PP, the melting point of PP-g-Si/St became lower. Several different analysis methods, including those of Avrami, Jeziorny, and Mo and colleagues, were employed to describe the nonisothermal crystallization process of the grafted samples. The results indicate that the peak temperature of crystallization of PP-g-Si/St sample was lower than that of virgin PP. Crystallization kinetics revealed that the rates of nucleation and growth were affected differently by the graft ratio of vinyltrimethoxysilane onto PP. The activation energy was calculated on the basis of the method of Kissinger, and the values were 253.6 and 215.7 kJ/mol for virgin PP and PP-g-Si/St, respectively.     

Synthesis of Polypropylene/Attapulgite Nanocomposites and Their Crystallization Behavior Studied by Step-Scan DSC

Attapulgite (AT) was modified by grafting with butyl acrylate (BA) via polymerizations initiated by Gamma radiation. Polypropylene (PP)/AT nanocomposites were synthesized via melt extrusion in a twin-screw extruder. Fourier transform infrared (FTIR) spectroscopy and thermogravimetry (TG) were used to assess the structure of the hybrid materials and the dispersion of AT was verified by transmission electron microscopy (TEM). The crystallization kinetics of PP/AT nanocomposites were investigated by differential scanning calorimetry (DSC) and analyzed by using the Avrami method. The isothermal crystallization kinetics showed that the addition of AT increased both the crystallization rate and the isothermal Avrami exponent of PP. Step-scan differential scanning calorimetry (SDSC) was used to study the influence of AT on the crystallization and subsequent melting behavior. The results revealed that PP and PP/AT nanocomposites experienced multiple melting and secondary crystallization processes during heating. The melting behaviors of PP and PP/AT nanocomposites varied with the variation of crystallization temperature and AT content.