Inorganic silica functionalized with PLLA chains via grafting methods to enhance the melt strength of PLLA/silica nanocomposites

The low melt strength greatly limits the application of PLA as biodegradable package materials produced by film blowing method. Modified silica nanoparticles are introduced into PLA matrix to solve this problem in this study. To build Poly (l-lactide) nanocomposites successfully, two kinds of convenient and efficient methods are conducted to synthesize well-defined topological PLLA grafted SiO₂ nanoparticle. One is the ring-opening of l-lactide (Grafting from), and another is nucleophilic addition reaction (Grafting to). The structure, molecular weight of grafted PLLA chains, grafting density, and the thermal decomposition behavior of the nanoparticles prepared by different methods are characterized. By varying the contents of the initiator SiO₂ and the molecular weight of the reacted PLA chains, high density-low molecular weight PLLA grafted SiO₂ are obtained in “grafting from” while high molecular weight-low grafting density PLLA grafted SiO₂ are synthesized in “grafting to”. It is exactly in good agreement with the theoretic model. The spatial distribution of nanoparticles as well as the interaction force between nanoparticles and matrix is critical important to structuring bionanocomposites with desirable properties. So the two kinds of synthesized nanoparticles are introduced into PLA matrix in our contribution to evaluate these two factors, respectively. The TEM and SEM results both reveal the uniform dispersion of nanoparticles after modified. While the extension and shear rheology results show that the long grafted chains covalently connected on the surface of the silica via “grafting to” contribute more to enhance the melt strength of PLA. Meanwhile, stabilized PLA nanocomposites films with modified silica via “grafting to” method are successfully blown base on these researches. The research in this work constitutes a robust way to design melt-strengthen PLA/SiO₂ nanocomposites.     

Surface-grafted silica linked with l-lactic acid oligomer: A novel nanofiller to improve the performance of biodegradable poly(l-lactide)

A new surface modification method by grafting l-lactic acid oligomer onto the surface silanol groups of silica nanoparticles has been developed. The surface-grafting reaction is confirmed by IR and ²⁹Si MAS NMR analyses. TEM and SEM results show that grafted SiO₂ (g-SiO₂) nanoparticles can be comparatively uniformly dispersed in chloroform or PLLA matrix, while the unmodified SiO₂ nanoparticles tend to aggregate. The loading of g-SiO₂ nanoparticles in poly(l-lactide) (PLLA) matrix greatly improves the toughness and tensile strength of this material. In contrast, the incorporation of un-grafted SiO₂ nanoparticles into PLLA leads to the deterioration of its mechanical properties. DSC analysis shows that g-SiO₂ nanoparticles can serve as a nucleating agent for the crystallization of PLLA in the composites. SEM characterization shows the tough characteristics and great interfacial combination strength for g-SiO₂ (5 wt%)/PLLA nanocomposites.     

Poly(L‐lactic acid)/silicon dioxide nanocomposite prepared via the in situ melt polycondensation of L‐lactic acid in the presence of acidic silica sol: Isothermal crystallization and melting behaviors

In a previous article, we reported the preparation and characterization of a nanocomposite of poly(L ‐lactic acid) (PLLA) and silica via the in situ melt polymerization of L ‐lactic acid in the presence of acidic silica sol. In this study, the isothermal crystallization and melting behaviors of a PLLA/silicon dioxide (SiO₂) nanocomposite with 5 wt % well‐dispersed SiO₂ nanoparticles (PLLASN5) and pure PLLA were comparatively studied with differential scanning calorimetry and polarized optical microscopy. The SiO₂ nanoparticles acted as nucleation agents in the PLLA matrix and enhanced its nucleation rate and overall crystallization rate, especially at high crystallization temperatures. However, no deleterious effect on the crystal morphology or crystallinity was observed. The crystals that formed at a low temperature were imperfect; therefore, double melting peaks occurred during the second heating scan because of melt recrystallization. With the crystallization temperature increasing, the crystals became increasingly perfect; as a result, the low melting peak increased and shifted to a higher temperature. The existence of SiO₂ nanoparticles had no effect on the equilibrium temperature of the PLLA matrix. Pure PLLA and PLLASN5 have the same equilibrium temperature of 171.5°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and characterization of PLLA–ESO/surface-grafted silica nanocomposites

Various amounts of surface-grafted silica (g-SiO₂) and un-grafted (SiO₂) nanoparticles were solution blended with a copolymer of l-lactide and epoxidized soybean oil (PLLA–ESO) or PLLA. Chemical reaction between the low molecular weight (LMW) PLLA and surface of silica nanoparticles is confirmed by FTIR and TGA analyses. The amount of grafted LMW PLLA investigated by thermal gravimetric analysis (TGA) was about 14.9%–28.2% in weight. g-SiO₂ nanoparticles can be easily dispersed into PLLA–ESO matrix to form a uniform PLLA–ESO/g-SiO₂ composite. Thermal properties of PLLA–ESO/g-SiO₂ and PLLA/g-SiO₂ nanocomposites were subsequently investigated by the differential scanning calorimeter measurements (DSC). DSC analyses indicated that g-SiO₂ nanoparticles can serve as a nucleating agent for the crystallization of PLLA–ESO in the composites, while the melting temperature (T _m) and the glass transition temperature (T _g) of PLLA–ESO/g-SiO₂ nanocomposites seemed to be independent of loading of g-SiO₂ particles. The DSC curves of PLLA/g-SiO₂ nanocomposite obviously showed double melting peaks, while that of PLLA–ESO/g-SiO₂ nanocomposites only a single melting peak. PLLA–ESO/g-SiO₂ composites exhibited a higher tensile strength and elongation than that of PLLA–ESO/SiO₂ composites.     

Poly(l‐lactide)/four‐armed star poly(l‐lactide)‐grafted multiwalled carbon nanotubes nanocomposites: Preparation,rheology, crystallization,and mechanical properties

Four‐armed star poly(l ‐ lactide)‐grafted multiwalled carbon nanotubes (CNTs‐g‐4PLLA) were synthesized through the nucleophilic substitution reaction between 4PLLA and acryl chloride of CNTs and then characterized by transmission electron microscope, X‐ray photoelectron spectroscopy, thermal gravimetric analysis (TGA), and ultraviolet visible spectrophotometer. The results indicated that 4PLLA was successfully grafted onto CNTs, and CNTs‐g‐4PLLA contained 37.7 wt% of 4PLLA. PLLA/CNTs‐g‐4PLLA nanocomposites were prepared by solution casting with different CNTs‐g‐4PLLA content. Rheological behavior of PLLA/CNTs‐g‐4PLLA nanocomposites was measured using a rheometer. The result showed that CNTs‐g‐4PLLA formed a network structure at percolation concentration, which improves obviously rheological properties of PLLA in the molten state. The crystallization behavior and crystal structure of the nanocomposites were comprehensive evaluated through differential scanning calorimetry, X‐ray diffraction, and polarizing optical microscope. The results found that CNTs‐g‐4PLLA played two roles in PLLA crystallization. The addition of CNTs‐g‐4PLLA acted as nucleating agent and obviously accelerated the spherulites growth under percolation concentration, while it inhibited the movement of PLLA chains at above percolation concentration, resulting in the decrease of crystallinity. Thermal stability and mechanical properties of the nanocomposites were also investigated using TGA, dynamic mechanical analysis, and tensile test. These results indicated that the incorporation of CNT‐g‐4PLLA into the PLLA matrix improved the thermal stability, storage modulus, and tensile strength of the nanocomposites. POLYM. COMPOS., 37:2744–2755, 2016. © 2015 Society of Plastics Engineers     

Antibacterial activity and antistatic composites of polyester/Ag‐SiO2 prepared by a sol–gel method

Poly(butylene adipate‐co‐terephthalate) (PBAT) composites containing silver‐silica (Ag‐SiO₂) were prepared using an in‐situ sol–gel process. Maleic anhydride‐grafted PBAT (PBAT‐g‐MA) and multihydroxyl‐functionalized Ag‐SiO₂ were used to improve the compatibility and dispersibility of Ag‐SiO₂ within the PBAT matrix. The composites were characterized morphologically using transmission electron microscopy and chemically using Fourier transform infrared spectrometry. The existence of Ag‐SiO₂ nanoparticles on the substrate was confirmed by the ultraviolet–visible absorption spectra. The antibacterial and antistatic properties of the composites were evaluated whether SiO₂ enhanced the electrical conductivity was tested as well as whether Ag enhanced the antibacterial activity of the PBAT‐g‐MA/SiO₂ or PBAT/SiO₂ composites. The PBAT‐g‐MA/SiO₂ or PBAT/SiO₂ composite that contained Ag had better antibacterial activity (more than 1.3‐fold). The functionalized PBAT‐g‐MA/Ag‐SiO₂ composite can markedly enhanced antibacterial and antistatic properties due to the carboxyl groups of maleic anhydride, which acted as coordination sites for the Ag‐SiO₂ phase, allowing the formation of stronger chemical bonds. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanical and crystalline properties of monomer casting Nylon‐6/Sio2 composites prepared via in situ polymerization

A series of monomer casting (MC) nylon‐6/SiO₂ composites were prepared via in situ polymerization. It was found that the tensile strength, storage modulus, and notched charpy impact strength of the composites were improved and reached maximum at 3–5 wt% loading of SiO₂. The α relaxation peak corresponding to the glass transition temperature (T_g) shifted to high temperature with increasing SiO₂ content. Addition of SiO₂ led to an increase of the melting and crystallization temperatures, and crystallinity. It also reduced the induction time of crystallization, advance the crystallization process of MC nylon‐6, and improve the crystal growth rate. The self‐nucleation crystallization analysis indicated that SiO₂ particles played the role of facilitating the crystallization of the matrix mainly via accelerating the generation of crystal nucleus. By addition of SiO₂ particles, the fracture surface of MC nylon‐6 changed to distant striations with many yield folds accompanied by a large number of stress whitening, displaying much obvious character of tough fracture. SiO₂ particles can be pulled‐out under stress by being covered with MC nylon‐6 resin due to strong interfacial interaction and presented a skin–core structure. © 2012 Society of Plastics Engineers.     

Crystallization behavior and isothermal crystallization kinetics of PLLA blended with ionic liquid, 1‐butyl‐3‐methylimidazolium dibutylphosphate

The crystallization behavior and isothermal crystallization kinetics of neat poly(l ‐lactic acid) (PLLA) and PLLA blended with ionic liquid (IL), 1‐butyl‐3‐methylimidazolium dibutylphosphate, were researched by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and wide angle X‐ray diffraction (WXRD). Similar to the non‐isothermal crystallization behavior of neat PLLA, when PLLA melt was cooled from 200 to 20°C at a cooling rate of 10°C min^?1, no crystallization peak was detected yet with the incorporation of IL. However, the glass transition temperature and cold crystallization temperature of PLLA gradually decreased with the increase of IL content. It can be attributed to the significant plasticizing effect of IL, which improved the chain mobility and cold crystallization ability of PLLA. Isothermal crystallization kinetics was also analyzed by DSC and described by Avrami equation. For neat PLLA and IL/PLLA blends, the Avrami exponent n was almost in the range of 2.5–3.0. It is found that t_1/2 reduced largely, and the crystallization rate constant k increased exponentially with the incorporation of IL. These results show that the IL could accelerate the overall crystallization rate of PLLA due to its plasticizing effect. In addition, the dependences of crystallization rate on crystallization temperature and IL content were discussed in detail according to the results obtained by DSC and POM measurements. It was verified by WXRD that the addition of IL could not change the crystal structure of PLLA matrix. All samples isothermally crystallized at 100°C formed the α‐form crystal. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41308.     

Effect of interfacial interaction on the crystallization and mechanical properties of PP/nano‐CaCO3 composites modified by compatibilizers

To investigate the effect of interfacial interaction on the crystallization and mechanical properties of polypropylene (PP)/nano‐CaCO₃ composites, three kinds of compatibilizers [PP grafted with maleic anhydride (PP‐g‐MA), ethylene–octene copolymer grafted with MA (POE‐g‐MA), and ethylene–vinyl acetate copolymer grafted with MA (EVA‐g‐MA)] with the same polar groups (MA) but different backbones were used as compatibilizers to obtain various interfacial interactions among nano‐CaCO₃, compatibilizer, and PP. The results indicated that compatibilizers encapsulated nano‐CaCO₃ particles, forming a core–shell structure, and two interfaces were obtained in the compatibilized composites: interface between PP and compatibilizer and interface between compatibilizer and nano‐CaCO₃ particles. The crystallization and mechanical properties of PP/nano‐CaCO₃ composites were dependent on the interfacial interactions of these two interfaces, especially the interfacial interaction between PP and compatibilizer. The good compatibility between PP chain in PP‐g‐MA and PP matrix improved the dispersion of nano‐CaCO₃ particles, favored the nucleation effect of nano‐CaCO₃, increased the tensile strength and modulus, but reduced the ductility and impact strength of composites. The partial compatibility between POE in POE‐g‐MA and PP matrix had little effect on crystallization and mechanical properties of PP/nano‐CaCO₃ composites. The poor compatibility between EVA in EVA‐g‐MA and PP matrix retarded the nucleation effect of nano‐CaCO₃, and reduced the tensile strength, modulus, and impact strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of interface and confinement size on the crystallization behavior of PLLA confined in coaxial electrospun fibers

Poly(l ‐lactide)/polyacrylonitrile (PLLA/PAN) core‐sheath composite fibers were fabricated by coaxial electrospinning. The crystallization behavior of PLLA within the coaxial electrospun fibers was studied by differential scanning calorimetry (DSC). The PLLA/PAN coaxial electrospun fiber with a PLLA diameter of ～32 nm (C1) exhibits a crystallization temperature (T_c) of 22.5 °C higher but a cold‐crystallization temperature (T_cc) of 10 °C lower than bulk PLLA. The crystallinity of C1 fiber is also higher than bulk PLLA. In both isothermal melt‐ and cold‐crystallization, PLLA in C1 fiber crystallizes faster than the bulk PLLA, as revealed by the smaller half crystallization times (t_1/2). The enhanced crystallizability of PLLA in the C1 fiber may be attributed to the increased nuclei number and crystal growth rate induced by the PAN surface, i.e., surface‐induction effect. However, PLLA also suffers a nano‐confinement effect exerted by PAN sheath in the coaxial electrospun fiber, which can suppress PLLA crystallization. When the diameter of PLLA is too small (< 32 nm), the nano‐confinement effect may prevail over the surface‐induction effect, leading to a slower crystallization rate and smaller crystallinity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45980.     

Effects of interfacial adhesion on properties of polypropylene/Wollastonite composites

Wollastonite reinforced polypropylene (PP/CaSiO₃) composites were prepared by melt extrusion. A silane coupling agent and a maleic anhydride grafted PP (PP‐g‐MA) were used to increase the interfacial adhesion between the filler and the matrix. The increased adhesion observed by scanning electron microscopy (SEM) resulted in improved mechanical properties. A model was applied to describe the relationship between the interfacial adhesion and tensile properties of PP/CaSiO₃ composites. There is stronger interfacial adhesion between silane‐treated CaSiO₃ and polymer matrix containing PP‐g‐MA as a modifier. Results of dynamic mechanical thermal analysis (DMTA) showed that stronger interfacial adhesion led to higher storage modulus. The influence of CaSiO₃ particles on the crystallization of PP was studied by using differential scanning calorimetry (DSC). The introduction of CaSiO₃ particles does not affect the crystallization temperature and crystallinity of PP matrix significantly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A novel method of hyperbranched poly(amide‐ester) modifying nano‐SiO2 and study of mechanical properties of PVC/nano‐SiO2 composites

A new method of surface chemical modification of nano‐SiO₂ was proposed in the paper. In the presence of catalyst, the active hydroxyl groups on the surface of nano‐SiO₂ reacted with AB₂‐type monomer (N,N‐dihydroxyethyl‐3‐amino methyl propionate) by one‐step polycondensation. And the product's Fourier transform infrared graphs and transmission electron microscopy (TEM) images proved that hyperbranched poly(amine‐ester) (HPAE) was grafted from nano‐SiO₂ surface successfully. Moreover, polyvinyl chloride (PVC)/modified nano‐SiO₂ composites were made by melt‐blending. The composites' structures and mechanical properties were characterized by TEM, scanning electron microscopy, and electronic universal testing machine. The results showed that nano‐SiO₂ grafted by HPAE increased obviously in dispersion in PVC matrix, and mechanical properties of PVC were effectively improved. Additionally, it was found that mechanical properties of PVC/nano‐SiO₂ composites reached the best when weight percent of nano‐SiO₂ in PVC matrix was 1%. Compared with crude PVC, the tensile strength of HPAE grafted nano‐SiO₂/PVC composite increased by 24.68% and its break elongation, flexural strength, and impact strength increased by 15.73, 4.07, and 184.84%, respectively. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Morphology,mechanical properties,and thermal stability of poly(L‐lactic acid)/poly(butylene succinate‐co‐adipate)/silicon dioxide composites

Poly(butylene succinate‐co‐adipate) (PBSA) and two types of SiO₂ (hydrophilic or hydrophobic) were used to modify poly(L ‐lactic acid) (PLLA). The mechanical properties, rheological and thermal behavior, phase morphology, and thermal stability of PLLA/PBSA/SiO₂ composites were investigated. The impact strength, flexural strength, and modulus of PLLA/PBSA blends increased after the addition of hydrophobic SiO₂ without decreasing the elongation at break, and the elongation at break monotonically decreased with increasing hydrophilic SiO₂ content. The melt elasticity and viscosity of the PLLA/PBSA blend increased with the addition of SiO₂. The hydrophilic SiO₂ was encapsulated by the dispersed PBSA phase in the composites, which led to the formation of a core–shell structure, whereas the hydrophobic SiO₂ was more uniformly dispersed and mainly located in the PLLA matrix, which was desirable for the optimum reinforcement of the PLLA/PBSA blend. The thermogravimetric analysis results show that the addition of the two types of SiO₂ increased the initial decomposition temperature and activation energy and consequently retarded the thermal degradation of PLLA/PBSA. The retardation of degradation was prominent with the addition of hydrophobic SiO₂. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Polypropylene-grafted nanoparticles as a promising strategy for boosting physical properties of polypropylene-based nanocomposites

SiO₂ nanoparticles grafted to terminally hydroxylated polypropylene (PP-g-SiO₂) with different molecular weights were melt mixed with PP to prepare a series of PP/PP-g-SiO₂ nanocomposites. PP/PP-g-SiO₂ offered several advantages over pristine PP and PP/unmodified SiO₂ such as highly uniform dispersion up to 10 wt.-%, +200–400% faster crystallization and +30% increments for both the Young's modulus and the tensile strength without largely sacrificing the melt viscosity of PP. We concluded that grafted chains act as crystallization nuclei and co-crystallize with matrix chains to make PP-g-SiO₂ nanoparticles as a physical cross-linker between lamellae, while the linkage disappears in melt and grafted chains minimize the cohesive attraction between nanoparticles.     

Mechanical properties of low nano‐silica filled high density polyethylene composites

Modification of nanoparticles through graft polymerization is able to change the chemical nature of the particles' surfaces and provides an effective means for the preparation of nano‐fillers specified for composites manufacturing. The present work focuses on the mechanical role of grafted nano‐SiO₂ particles in high density polyethylene composites prepared by melt compounding. The experimental results show that at a content of 0.75 vol%, the modified nano‐silica results in a rise in tensile stiffness, tensile strength and impact strength of the composites. The grafted nanoparticles can improve the mechanical performance of the matrix polymer more effectively than the untreated version. In addition, a further enhancement of the composites stiffness and strength can be achieved by crosslinking the concentrated masterbatches, which has not yet been revealed in the authors' previous works on grafted nano‐SiO₂ particles/polypropylene composites. It is thus revealed that the introduction of the grafting polymers onto the nanoparticles increases the tailorability of the composites.     

Cold Crystallization of PLLA Studied by Simultaneous SAXS and WAXS

Summary: The cold crystallization process of initially amorphous poly(L ‐lactic acid), PLLA, with two different molecular weights, during a heating at 2 °C/min, was investigated by DSC and time‐resolved simultaneous SAXS and WAXS, using synchrotron radiation. Equatorial scans of the isotropic 2D‐SAXS patterns showed that the average Bragg long period (L_B) of PLLA samples was approximately constant with the development of cold crystallization up to a temperature that corresponded to a melt/re‐crystallization process that took place before the nominal melting peak seen by DSC. L_B values were found to be higher for the high molecular weight material. This was in accordance with the higher melting temperature observed in the high molecular weight PLLA that implied the existence of thicker lamellae. WAXS results showed that the molecular weight did not apparently affect the crystal form and the final degree of crystallinity of PLLA. The Avrami parameters from WAXS and DSC were consistent, showing that the non‐isothermal cold crystallization of the two PLLA samples corresponded mainly to a three‐dimensional growth, although an imperfect crystallization process was involved at early times. The crystallization rate of PLLA, observed both by WAXS and DSC, decreased with increasing molecular weight.

SAXS profiles of PLLA2 as a function of temperature. The inset shows the 2D‐SAXS pattern obtained at 180 °C.     

Effect of compatibilizer on the dispersion of untreated silica in a polypropylene matrix

BACKGROUND: A new processing method for polypropylene–untreated precipitated silica (PP/SiO₂) composites based on the incorporation of a second polymer phase of polyamide 6 (PA6) is presented and compared with a more classic one making use of compatibilizers: glycerol monostearate (GMS), ethylene acrylic acid ionomer (IAAZE) and maleic anhydride grafted polypropylene (MA‐graft‐PP). The effects of processing methods and conditions on the microstructure and properties of PP/SiO₂ composites prepared by melt compounding are investigated with a view to reduce the size of aggregates of silica from the micrometre to the nanometre scale and to improve the link between filler and matrix. RESULTS: On the one hand, the presence of GMS and IAAZE compatibilizers significantly improves the dispersion of the silica particles. On the other hand, when using a PA6 second phase, the SiO₂ particles are dispersed in PA6 nodules. Within these nodules, SiO₂ appears dispersed at the nanoscale but with larger particles (‘aggregates’) of about 200 nm. Significant improvements in tensile strength and modulus are obtained using MA‐graft‐PP compatibilizer. An increase in impact strength is observed in the case of GMS compatibilizer. Thermal parameters indicate also that silica plays the role of nucleation agent for PP matrix. All improvements (tensile strength, modulus and impact strength) increase with the addition of compatibilized PA6 second phase. CONCLUSION: By the incorporation of masterbatch of silica in PA6 as a second polymer polar phase, a successful new production method for PP/SiO₂ nanocomposites has been developed. Interestingly, this method does not require any (expensive) pre‐treatment of the silica. Copyright © 2007 Society of Chemical Industry     

Interfacial effects in polypropylene–silica nanocomposites

Grafted inorganic nanoparticles can greatly improve the mechanical performance of polymers. To examine the effects of the interfacial characteristics generated by the grafting polymer bonded to nanoparticle surfaces, we chemically grafted nano‐silica with different polymers and then melt‐mixed it with polypropylene (PP). We extracted the homopolymers produced during the graft polymerization from the grafted products before the composites were manufactured to get rid of the side effects of the nongrafting polymers. We tailored the interfacial interaction between the grafted nano‐SiO₂ and PP matrix by changing the amount of the grafting polymers on the nanoparticles, that is, the grafting percentage. Mechanical tests indicated that all the composites incorporated with grafted nano‐SiO₂ particles possessed much higher impact strength than untreated SiO₂/PP composites and neat PP. The greatest contribution of the particles was made at a low grafting percentage. Tensile measurements showed that the treated nanoparticles could provide PP with stiffening, strengthening, and toughening effects at a rather low filler content (typically 0.8 vol %) because of the enhanced interfacial adhesion resulting from molecular entanglement and interdiffusion between the grating polymers on the nanoparticles and matrix macromolecules. The presence of grafting polymers on the nanoparticles provided the composites with a tailorable interphase. The tensile performance of the composites was sensitive to the nature of the grafting polymers. Basically, a hard interface was beneficial to stress transfer, whereas a soft one hindered the development of cavities in the matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1771–1781, 2004     

Mechanical properties and nonisothermal crystallization of polyamide 6/carbon fiber composites toughened by maleated elastomers

Polyamide 6/carbon fiber (PA6/CF) composites toughened with maleated elastomers were prepared by melt blending using twin‐screw extruder followed by injection molding. Three kinds of maleated elastomers, maleic anhydride (MAH)‐grafted ethylene‐vinyl acetate copolymer (EVA‐g‐MAH), MAH‐grafted ethylene‐propylene‐diene terpolymer (EPDM‐g‐MAH), and MAH‐grafted hydrogenated styrene‐butadiene‐styrene (SEBS‐g‐MAH), were used to toughen the PA6/CF composites. The mechanical properties, morphology, nonisothermal crystallization, and subsequent melting behavior of PA6 hybrid composites were investigated. Mechanical tests indicated that incorporation of elastomers improved the impact properties of CF‐reinforced PA composites accompanied with loss of tensile strength and modulus. It was observed from scanning electron microscope photographs that modification with maleated elastomers improved the interfacial adhesion between the CFs and PA6 matrix. Nonisothermal crystallization behavior showed that three kinds of elastomers had negative effect on crystallization and retarded crystallization of PA6. Kissinger's analysis illustrated that addition of CF slightly increased the crystallization activation energy of PA6, whereas incorporation of elastomers reversed it compared with pure PA6. Furthermore, a slight decrease in crystallinity and melting peak of the composites after incorporation of elastomers was observed compared with pure PA6. Polarizing optical microscope results showed that the transcrystallinity phenomenon seemed to be also affected when the matrix was added by the elastomers. POLYM. COMPOS., 35:2170–2179, 2014. © 2014 Society of Plastics Engineers     

Modification of polyethylene–octene elastomer by silica through a sol–gel process

In this study, tetraethoxysilane (TEOS) and a metallocene polyethylene–octene elastomer (POE) were chosen as the ceramic precursor and the continuous phase, respectively, for the preparation of new hybrids by an in situ sol–gel process. To obtain a better hybrid, a maleic anhydride‐grafted polyethylene–octene elastomer (POE‐g‐MAH), used as the continuous phase, was also investigated. Characterizations of POE‐g‐MAH/SiO₂ and POE/SiO₂ hybrids were performed by Fourier transform infrared (FTIR) and ²⁹Si solid‐state nuclear magnetic resonance (NMR) spectrometers, a differential scanning calorimeter (DSC), a thermogravimetry analyzer, and an Instron mechanical tester. The results showed that the POE‐g‐MAH/SiO₂ hybrid could improve the properties of the POE/SiO₂ hybrid because the interfacial force between the polymer matrix and the silica network was changed from hydrogen bonds into covalent Si? O? C bonds through dehydration of hydroxy groups in POE‐g‐MAH with residual silanol groups in the silica network. The existence of covalent Si? O? C bonds was proved by FTIR spectra. For the POE/SiO₂ and POE‐g‐MAH/SiO₂ hybrids, maximum values of the tensile strength and the glass transition temperature were found at 9 wt % SiO₂ since a limited content of silica might be linked with the polymer chains through the covalent bond. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 966–972, 2003