The rate acceleration in solid‐state polycondensation of PET by nanomaterials

The effect of nanomaterials on the solid‐state polycondensation (SSP) of PET was investigated using intrinsic viscosity measurement, wide‐angle X‐ray diffraction, differential scanning calorimetry, and polarizing microscope. The results showed that the montmorillonite nanomaterials could greatly increase the rate of solid‐state polycondensation of PET, probably due to the nucleation of montmorillonite nanomaterials for PET crystallization, which resulted in lower crystallinity, more small crystals, and more surfaces of the crystals. The surfaces of microcrystal and richer amorphous regions benefitted the polycondensation reaction of PET and diffusion of volatile by‐products, which led to the higher rate of SSP. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 971–976, 2004     

Fiber–matrix interactions in aramid‐short‐fiber‐reinforced thermoplastic polyurethane composites

The mechanical and dynamic mechanical properties of thermoplastic polyurethane (TPU) elastomers reinforced with two types of aramid short fibers, m‐aramid (Teijin‐Conex) and copoly(p‐aramid) (Technora), were investigated in this study with respect to the fiber loading. In general, both types of composites exhibited very similar stress–strain behaviors, except that Technora–TPU was stronger than Conex–TPU. This was primarily due to the intrinsic strength of the reinforcing fibers. Both types of fibers reinforced TPU effectively without any surface treatment. This could be attributed to good fiber–matrix interactions, which were revealed by the broadening of the tan δ peak in dynamic mechanical analysis. Furthermore, the morphologies of cryogenically fractured surfaces of the composites and extracted fibers, investigated with scanning electron microscopy, revealed possible polar–polar interactions between the aramid fibers and TPU matrices. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1059–1067, 2003     

Evaluation of tribological performance of surface‐treated carbon fiber‐reinforced thermoplastic polyimide composite

The effect of surface treatment [rare earth solution (RES) and air oxidation] of carbon fibers (CFs) on the mechanical and tribological properties of carbon fiber‐reinforced polyimide (CF/PI) composites was comparatively investigated. Experimental results revealed that surface treatment can effectively improve the interfacial adhesion between carbon fiber and PI matrix. Thus, the flexural strength and wear resistance were significantly improved. The RES surface treatment is superior to air oxidation treatment in promoting interfacial adhesion between carbon fiber and PI matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

锑系催化剂聚酯的熔融及固相聚合

对锑系催化剂中常用的醋酸锑(Sb(AC)3)、三氧化二锑(Sb2O3)和乙二醇锑(Sb2(EG)3)进行熔融及固相聚合试验,结果表明,三氧化二锑的有效锑含量比醋酸锑及乙二醇锑低;乙二醇锑在固相聚合时的催化作用略低于醋酸锑和三氧化二锑;3种锑系催化剂相比,乙二醇锑催化剂聚酯固相聚合速度略慢,但特性粘数增幅最为平稳;220℃下的反应速率常数以醋酸锑制得的聚酯最大。     

Surface modification and physical properties of various UHMWPE‐fiber‐reinforced modified epoxy composites

Two surface modification methods—plasma surface treatment and chemical agent treatment—were used to investigate their effects on the surface properties of ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers. In the analyses, performed using electron spectroscopy for chemical analysis, changes in weight, and scanning electron microscope observations, demonstrated that the two fiber‐surface‐modified composites formed between UHMWPE fiber and epoxy matrix exhibited improved interfacial adhesion and slight improvements in tensile strengths, but notable decreases in elongation, relative to those properties of the composites reinforced with the untreated UHMWPE fibers. In addition, three kinds of epoxy resins—neat DGEBA, polyurethane‐crosslinked DGEBA, and BHHBP‐DGEBA—were used as resin matrices to examine the tensile and elongation properties of their UHMWPE fiber‐reinforced composites. From stress/strain measurements and scanning electron microscope observations, the resin matrix improved the tensile strength apparently, but did not affect the elongation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 655–665, 2007     

Study on morphology development for in situ fiber–reinforced composites by blending polyolefin and polycaprolactone

The morphology developments and interfacial properties of extruded polyethylene/polycaprolactone and polypropylene/polycaprolactone blends were investigated. The interfacial thicknesses of both polymer blends were thin and this was investigated by interfacial tension measurement in the melt state. The aspect of boundary area was observed by AFM, and a clear line could be observed at the interface area as a result of thin interfacial thickness. The in situ fiber formation of the dispersed phase was remarkably generated under elongational flow (between die exit and solidification) rather than under shear flow (in the cylinder and die). Drawing ratio was varied at three levels to study its effect on elongation of the dispersed phases. The dispersions dramatically changed from spherical to spheroidal and filament shapes depending on the drawing ratio. Reduced capillary number (Ca*) was used to characterize droplet deformation. The deformation mode under shear flow was classified as nondeformation mode due to the fact that the Ca* was almost 0. On the other hand, the deformation mode under elongational flow was classified into filament shape mode (Ca* > 4). This classification was in agreement with the SEM images. The tensile properties were increased at the border line where the Ca* was 4.0. The melt interfacial tensions of polyolefin/polycaprolactone were relatively large, and a clear line could be observed at the interface area as a result of little affinity of polymer interface. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 500–508, 2005     

Effects of the carboxyl concentration on the solid‐state polymerization of poly(ethylene terephthalate)

There are two types of polycondensation reactions in the solid‐state polymerization (SSP) of poly(ethylene terephthalate) (PET), namely, transesterification and esterification. Transesterification is the reaction between two hydroxyl ends with ethylene glycol as the byproduct, and esterification is the reaction between a carboxyl end and a hydroxyl end with water as the byproduct. The SSP of powdered PET in a fluid bed is practically a reaction‐controlled process because of negligible or very small diffusion resistance. It can be proved mathematically that an optimal carboxyl concentration for reaction‐controlled SSP exists only if k₂/k₁ > 2, where k₂ and k₁ are the forward reaction rate constants of esterification and transesterification, respectively. Several interesting observations were made in fluid‐bed SSP experiments of powdered PET: (1) the SSP rate increases monotonously with decreasing carboxyl concentration, (2) k₂ < k₁ in the presence of sufficient catalyst, (3) k₁ decreases with increasing carboxyl concentration if the catalyst concentration is insufficient, and (4) the minimum catalyst concentration required to achieve the highest SSP rate decreases with decreasing carboxyl concentration. In the SSP of pelletized PET, both reaction and diffusion are important, and there exists an optimal carboxyl concentration for the fastest SSP rate because esterification, which generates the faster diffusing byproduct, is retarded less than transesterification in the presence of substantial diffusion resistance. The optimal prepolymer carboxyl concentration, which ranges from 25 to 40% of the total end‐group concentration in most commercial SSP processes, increases with increasing pellet size and product molecular weight. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1288–1304, 2002     

Study on the grafting of PET onto the glass fiber surface during in situ solid‐state polycondensation

An in situ solid‐state polymerization process was developed to produce long glass fiber reinforced poly(ethylene terephthalate) (PET) composites. As reported in our last article, one advantage of this new process is that the good wetting of reinforcing fiber can be obtained for using low‐viscosity oligomer as raw materials. In this article, the grafting of PET macromolecular chain onto the surface of reinforcing glass fiber during in situ solid‐state polycondensation (SSP) will be investigated, which was believed to be another advantage for this new process and should be very important for thermoplastic composite. The reinforcing glass fiber after removing ungrafted PET from a long glass fiber reinforced PET composite by solvent extraction was investigated by SEM, pyrolysis‐gas chromatography mass spectrometry (Py‐GC/MS), DSC, and FTIR. The information from morphology of SEM photos of glass fiber surface, the spectrum of Py‐GC/MS, the melt peak at differential scanning calorimetric (DSC) curve, and the spectrum of Fourier transform infrared Raman spectroscopy (FTIR) gave a series evidence to prove the presence of grafted PET layer on the surface of silane‐coupling‐treated glass fiber. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 775–781, 2006     

Hydrogen bonding effect on the poly(ethylene oxide), phenolic resin,and lithium perchlorate–based solid‐state electrolyte

The interaction behavior of solid‐state polymer electrolytes composed of poly(ethylene oxide) (PEO)/novolac‐type phenolic resin and lithium perchlorate (LiClO₄) was investigated in detail by DSC, FTIR, ac impedance, DEA, solid‐state NMR, and TGA. The hydrogen bonding between the hydroxyl group of phenolic and ether oxygen of the PEO results in higher basicity of the PEO. The higher basicity of the ether group can dissolve the lithium salts more easily and results in a greater fraction of “free” anions and thus higher ionic conductivity. DEA results demonstrated that addition of the phenolic increases the dielectric constant because of the partially negative charge on the ether group induced by the hydrogen bonding interaction between ether oxygen and the hydroxyl group. The study showed that the blend of PEO(100)/LiClO₄(25)/phenolic(15) possesses the highest ionic conductivity (1.5 × 10^?5 S cm^?1) with dimensional stability. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1207–1216, 2004     

Post‐extrusion solid‐state polymerization of fully drawn polyester yarns

Post‐extrusion solid‐state polymerization (SSP) of a commercial fully drawn filament yarn (FDY) of poly(ethylene terephthalate) was carried out at 220°C, 230°C, and 240°C for a duration of 30 min to 2 h under inert atmosphere. Molecular weight of the solid‐state polymerized polyester filaments was increased from 1.67 × 10⁴ gm/mol to a maximum of 2.61 × 10⁴ gm/mole for the sample subjected to 240°C for 2 h. The kinetics of the SSP in the highly oriented crystalline FDY polyester filaments was investigated using an empirical relation between initial molecular weight and time of SSP and was found to be greatly enhanced, compared to amorphous unoriented polyester chips. Though the free annealing (i.e., under no tension) of samples at high temperature during solid‐state polymerization had a detrimental effect on the orientation of the FDY yarn, the simultaneous increase in the molecular weight compensated the loss in mechanical properties to a great extent. Application of tension during SSP was found to improve the mechanical properties of the SSP yarn by a small value. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5113–5122, 2006     

聚酯固相缩聚等温结晶特性的研究

聚酯(PET)固相缩聚(SSP)中切片的结晶性能及其演变影响固相缩聚反应,采用差示扫描量热仪(DSC)和热台偏光显微镜研究了固相缩聚反应前后PET切片的等温结晶特性。结果表明:PET切片在DSC中的等温结晶符合Avrami 方程,等温结晶温度升高,结晶速率常数K值减小,即结晶速率降低;热台偏光显微镜中不同等温结晶温度下形成了不同的球晶形态:黑十字消光图以及环形消光图;随着PET特性粘数(平均分子质量)增大,结晶速率常数K值减小,球晶生长速率减小,Avrami指数n值增大,形成更加复杂的消光图。对于固相缩聚前PET基础切片,球晶最大结晶速率在190℃左右。     

Graphene‐reinforced biodegradable poly(ethylene succinate) nanocomposites prepared by in situ polymerization

In this study, poly(ethylene succinate)(PES)/graphene nanocomposites were facilely prepared by in situ melt polycondensation of succinic acid and ethylene glycol in which contained well dispersed graphene oxide (GO). Fourier transform infrared (FTIR), GPC, TGA, and XRD were used to characterize the composites. The FTIR spectra and TGA measurement confirmed that PES chains had been successfully grafted onto GO sheets along with the thermal reduction of GO to graphene during the polymerization. GPC results indicated that increasing amounts of graphene caused a slight decrease in number average molecular weight of PES matrix when polymerization time was kept constant. The content of grafted PES chains on graphene sheets was also determined by TGA and was to be about 60%, which made the graphene sheets homogeneously dispersed in the PES matrix, as demonstrated by SEM and XRD investigations. Furthermore, the incorporation of thermally reduced graphene improved the thermal stability and mechanical properties of the composites significantly. With the addition of 0.5 wt % graphene, onset decomposition temperature of the composite was increased by 12°C, and a 45% improvement in tensile strength and 60% in elongation at break were also achieved. The enhanced performance of the composites is mainly attributed to the uniform dispersion of graphene in the polymer matrix and the improved interfacial interactions between both components. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3212–3220, 2013     

Synthesis of high molecular weight poly(L‐lactic acid) via melt/solid polycondensation: Intensification of dehydration and oligomerization during melt polycondensation

Melt/solid state polycondensation (MP/SSP) is a cost‐effective route for synthesis of high molecular weight poly(L ‐lactic acid) (PLLA). However, the reaction rates in its four stages need to be enhanced greatly and the reaction times to be shortened largely before the MP/SSP technology can be industrialized. In this study, a new catalyst addition policy, i.e., adding TSA at the dehydration stage and SnCl₂·2H₂O at the MP stage, and more appropriate temperature and pressure programs were presented and applied in the MP process of LLA. The presence of TSA from dehydration appeared very effective for speeding up the dehydration and oligomerization stages as well as depressing racemization in the whole MP process. The polymerization degree (X_n) of oligomer was clearly increased, and the reaction time was shortened to a great extent. Direct using reduced pressure was also very helpful for intensifying the dehydration stage, only leading to LLA loss as little as 2%. A PLLA with M_w of 44,000 and optical purity of 96.8% suitable for subsequent SSP was produced after dehydration for 2 h, oligomerization for 2 h and MP for 4 h under appropriate conditions. And an interesting strong dependence of the M_w of final PLLA product on the X_n of the oligomer was observed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Isothermal cold crystallization and melting behaviors of poly(L‐lactic acid)s prepared by melt polycondensation

The isothermal cold crystallization and melting behaviors of poly(L ‐lactic acid)s (PLLAs, weight average molecular weight, M_w, 6000–80,000) prepared via melt polycondensation were studied with differential scanning calorimeter in this work. It is found that the crystallization rate increased with decreasing M_w, reached a maximum at M_w of ca. 21,000 and then decreased again. The crystallinity of PLLA can be controlled in the range 30–50% by crystallization temperature (T_c) and time to fulfill the requirement of subsequent solid state polycondensation. The melting behavior strongly depends on T_c. The samples crystallized at high T_c melted with a single peak but those crystallized at low T_c melted with double peaks. The higher melting point (T_mH) kept almost constant and the lower melting point (T_mL) increased clearly with T_c. But the T_mL changed in jumps and a triple melting peak appeared at the vicinity of a characteristic crystallization temperature T_b, possibly because of a change of crystal structure. The equilibrium melting temperature of PLLA with M_w of 21,300 was extrapolated to be 222°C with nonlinear Hoffman‐Weeks method. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

聚酯纤维固相缩聚和拉伸试验研究

对聚酯纤维进行固相缩聚,分别进行了纤维在松弛状态下和在紧张状态下的固相缩聚试验,成功制取了卷绕状态下的高黏度聚酯纤维,纤维特性黏度达到1.003dL/g。通过对这种高黏度聚酯纤维的拉伸试验,制取了强度达到7.03cN/dtex的高强纤维,而对比实验的纤维经过拉伸,强度只有5.40cN/dtex。     

Effect of rare earth elements surface treatment on tensile properties of aramid fiber‐reinforced epoxy composites

Solutions of rare earth modifier (RES) and epoxy chloropropane (ECP) grafting modification method were used for the surface treatment of aramid fiber. Tensile properties of both the aramid/epoxy composites and single fibers were tested. The effects of RES concentration on tensile properties of aramid/epoxy composites were investigated in detail to explore an optimum amount of rare earth elements in solution for modifying aramid fiber. The fracture surface morphologies of tensile specimens were observed and analyzed with the aid of SEM. The experimental results show that rare earth treatment is superior to ECP grafting treatment in promoting interfacial adhesion between the aramid fiber and epoxy matrix. Meanwhile, the tensile strengths of single fibers were almost not affected by RES treatment. The optimum performance is obtained when the content of rare earth elements is 0.5 wt %. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1037–1041, 2004     

Value‐added bioconversion of biomass by solid‐state fermentation

The value‐added bioconversion of biomass is necessary due to the depletion of fossil fuels and deterioration of the global environment situation. Based on the analysis of characteristics of solid materials and the applicability of solid agro‐industrial residues used as feedstock for solid‐state fermentation (SSF), the authors established a value‐added bioconversion system for biomass using the key technology SSF. This article gives an overview of biomass bioconversion by SSF and the corresponding advances achieved in recent years. Copyright © 2012 Society of Chemical Industry     

Investigation on the melt spinning fibers of PP/organoclay nanocomposites prepared by in‐situ polymerization

Fibers prepared by melt spinning process from the PP (polypropylene)/organoclay nanocomposite were characterized in details with the aid of SEM, FTIR, XRD, DSC, and mechanical measurements. The results suggested that the lower content of organoclay (0.1%) added to the PP matrix increased the crystallinity and mechanical property (tensile strength) of the PP/organoclay nanocomposite fiber. With increasing the content of organoclay (≥ 0.3%), the crystallinity and the tensile strength both a little decreased, and the fiber containing organoclay exhibited multi‐peaks at the same draw ratio during the heating process. Furthermore, the degree of orientation of the fiber increased a little with lower content of organoclay (0.1%) introduction to PP during the infrared dichroism measurement. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Phenol‐modified polypropylenes as adhesion promoters in glass fiber–reinforced polypropylene composites

This publication is based on research work done on functional phenol‐modified polypropylenes (PPs) as adhesion promoters in glass fiber–reinforced PP composites. The glass fiber roving was first impregnated with different combinations of functional polymers and polypropylene in a melt impregnation die attached to an extruder to obtain prepreg. The prepreg was then tested in many ways both macro‐ and micromechanically. The tests included notched tensile tests, optical and electron microscopy, and DMTA (dynamic mechanical thermal analyzer) and DSC (differential scanning calorimetry) analyses as well as determination of the glass content. The tests were run on prepregs containing pure PP, PP with a commercial adhesion promoter, and PP with a number of functional, mostly phenol‐based, polymers. Also, single‐fiber tests were performed on individual glass fibers to test the level of adhesion with the above‐mentioned material combinations. With these tests it could be seen that some of the phenol‐based functional polymers provided the prepreg with better adhesion between the fibers and the matrix than did the commercial adhesion promoter. Optical and electron microscopy also were used in determining the level of adhesion as well as the deformation and fracture mechanisms of the prepreg. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1203–1213, 2002; DOI 10.1002/app.10441