The effect of γ‐irradiation on thermal strain of high strength polyethylene fiber at low temperature

To understand the contribution to negative thermal expansion by the length of the molecular chains in high‐strength ultra‐high‐molecular‐weight polyethylene (UHMW‐PE) fiber, the thermal expansion coefficient in the range of low temperature was investigated for high‐strength UHMW‐PE fiber (Toyobo, Dyneema®; hereinafter abbreviated to DF), irradiated by γ‐rays (γ‐rays treatment) that induce the molecular scission. The molecular weight of DF decreased by γ‐ray treatment. X‐ray diffraction behavior did not change by γ‐ray treatment. The melting behavior observed by DSC showed the main chain scission of DF by γ‐ray treatment. The DFs, with and without γ‐ray treatment, expand by cooling down (negative thermal expansion). The change of negative thermal expansion of DF by γ‐ray treatment was small. It is suggested that negative thermal expansion does not change by only the molecular chain scission. These results suggested that the effect of negative thermal expansion of DF in the temperature range from 213 to 303 K by the molecular chain scissions is small and that the length of extended molecular chains contributes to a negative thermal expansion a little. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 204–209, 2006     

An analytical approach to evaluate the coefficients of thermal expansion of textile composite materials

An analytical approach is developed to evaluate the coefficients of thermal expansion (CTE) of textile reinforced composites. At the micro level, a cylindrical composite model is employed to model the fiber/matrix thermal and mechanical interactions. The effects of voids and fiber coating on the thermal expansion coefficients of composites are considered at this level. The cylindrical model was then embedded in a macro hybrid finite element solutio structure to calculate the value of the CTE for textile composites. AS‐4/epoxy balanced plain weave textile composites were manufactured. Five different fiber volume fractions were tested for CTE. Evaluatio of the thermal expansion coefficients using the current model was compared to experimental data for in‐plane and out‐of‐plane directions.     

The effect of paraffin on fiber dispersion and mechanical properties of polyolefin–sawdust composites

This article reports on the influence of the paraffin (PAR) on the wood fiber (WF) dispersion in different polyethylene (low‐density polyethylene, high‐density polyethylene, recycled polyethylene) matrices, as well as on the melt flow behavior and mechanical properties of WF‐reinforced polyethylene (PE) composites. In the presence of paraffin, the composites showed improved tensile and flexural strength and modulus, but lower impact strength and elongation at break. The extent of improvement in mechanical properties depends on paraffin content and type of polyethylene; the most effective paraffin was in LDPE‐based composites. Paraffin‐treated WF showed lower moisture absorption ability in comparison with unmodified wood fiber. The phase segregation process was investigated for PE/PAR blends by DSC method. It was shown that an increase of paraffin concentration in the PE/PAR blend leads to a decrease of PE melting temperature and an increase of paraffin melting temperature; it indicates a net exchange of material from paraffin towards polyethylene. However, generally both components of PE/PAR blends remain immiscible. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2385–2393, 2004     

Enhancement of wood/polyethylene composites via compatibilization and incorporation of organoclay particles

Despite many advantages of wood–polyethylene composites, the shortcomings of this kind of composite include relatively low modulus, low notched impact resistance, relatively large thermal expansion, as well as substantial creep. In this article, in addition to using maleic anhydride grafted polyethylene as compatibilizer, organoclay was introduced into the polyethylene matrix so as to further enhance the thermal and mechanical performance. First, the influence of maleic anhydride grafted polyethylene type and loading on the morphology and properties of wood/HDPE composites was studied. Then, the effects of organoclay loading and of the compounding procedure on the wood/HDPE composites were investigated. The compatibilization was found to result in better polymer impregnation on the wood, reduced linear thermal expansion coefficients, and significantly improved mechanical properties. Incorporation of organoclay further reduced the thermal expansion and elevated the heat deflection temperature. More compatibilizer is needed to maintain the mechanical properties with the presence of clay. POLYM. ENG. SCI., 47:797–803, 2007. © 2007 Society of Plastics Engineers     

Effect of polypyrrole deposition of carbon fiber on the thermal expansion of carbon fiber-epoxy composites

Polypyrrole (PPy) was deposited onto carbon fibers via continuous electrochemical deposition (ECD). Composites of PPy-deposited carbon fiber and epoxy were prepared. The thermal expansion coefficients of these materials were determined using either a thermal mechanical analyzer or an imbeded strain gauge. The results show that PPy has a negative thermal expansion coefficient while carbon fiber and epoxy have positive thermal expansion coefficients. The resulting composite has a smaller thermal expansion coefficient, higher interlaminar shear stress and a smaller critical fiber length than the composite using untreated carbon fiber. This suggests that the deposition of PPy can effect an improvement in the fiber-matrix interfacial bonding of the composite.     

Wood‐fiber/high‐density‐polyethylene composites: Compounding process

The compounding process directly influenced the compounding quality of wood–polymer blends and finally affected the interfacial bonding strength and flexural modulus of the resultant composites. With 50 wt % wood fiber, the optimum compounding parameters for the wood‐fiber/high‐density‐polyethylene blends at 60 rpm were a temperature of 180°C and a mixing time of 10 min for the one‐step process with a rotor mixer. The optimum compounding conditions at 90 rpm were a temperature of 165°C and a mixing time of 10 min. Therefore, a short compounding time, appropriate mixing temperatures, and a moderate rotation speed improved the compounding quality of the modified blends and the dynamic mechanical properties of the resultant composites. The melt torque and blend temperature followed a polynomial relationship with the loading ratio of the wood fiber. The highest melt torque and blend temperature were obtained with 50% wood fiber. The coupling treatment was effective for improving the compatibility and adhesion at the interface. The two‐step process was better than the one‐step process because the coupling agents were more evenly distributed at the interface with the two‐step process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2570–2578, 2004     

Influence of fly ash cenospheres on performance of coir fiber‐reinforced recycled high‐density polyethylene biocomposites

Recycled high‐density polyethylene (RHDPE)/coir fiber (CF)‐reinforced biocomposites were fabricated using melt blending technique in a twin‐screw extruder and the test specimens were prepared in an automatic injection molding machine. Variation in mechanical properties, crystallization behavior, water absorption, and thermal stability with the addition of fly ash cenospheres (FACS) in RHDPE/CF composites were investigated. It was observed that the tensile modulus, flexural strength, flexural modulus, and hardness properties of RHDPE increase with an increase in fiber loading from 10 to 30 wt %. Composites prepared using 30 wt % CF and 1 wt % MA‐g‐HDPE exhibited optimum mechanical performance with an increase in tensile modulus to 217%, flexural strength to 30%, flexural modulus to 97%, and hardness to 27% when compared with the RHDPE matrix. Addition of FACS results in a significant increase in the flexural modulus and hardness of the RHDPE/CF composites. Dynamic mechanical analysis tests of the RHDPE/CF/FACS biocomposites in presence of MA‐g‐HDPE revealed an increase in storage (E′) and loss (E″) modulus with reduction in damping factor (tan δ), confirming a strong influence between the fiber/FACS and MA‐g‐HDPE in the RHDPE matrix. Differential scanning calorimetry, thermogravimetric analysis thermograms also showed improved thermal properties in the composites when compared with RHDPE matrix. The main motivation of this study was to prepare a value added and low‐cost composite material with optimum properties from consumer and industrial wastes as matrix and filler. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42237.     

Effect of thermal cycling on carbon fiber‐reinforced PPS composites

Calorimetry, coefficient of thermal expansion (CTE), and tensile modulus were recorded to investigate the effect of thermal cycling on polyphenylene sulfides (PPS) carbon fiber composites. Thermal cycling at higher temperatures increased the degree of crystallinity of PPS, as indicated by increasing heat of melting. CTE measurements during thermal cycling were used to study the anisotropy of the composites in directions parallel and transverse to the fiber orientation. It was noted that increasing crystallinity enhanced the tensile modulus of unidirectional composites, while reducing the tensile modulus of quasi‐isotropic composites. The latter reduction may be due to internal damage or interlaminar slippage associated with the residual thermal stresses caused by thermal mismatch between multiply oriented plies. POLYM. COMPOS., 26:713–716, 2005. © 2005 Society of Plastics Engineers     

辐照交联中密度聚乙烯中空纤维管的结构与性能

研究了加工条件对辐照交联中密度聚乙烯中空纤维管凝聚态结构和力学性能的影响,特别是辐照剂量与中空纤维管抗拉性能和耐扩张性能的关系,并研究了中空纤维管的交联度、结构、晶形和热性能。结果表明:辐照交联聚乙烯中空纤维管的结构和性能可以通过辐照工艺来调控,辐照剂量升高,中空纤维管的凝胶含量提高,抗拉强度增加。     

Recycled milk pouch and virgin LDPE‐LLDPE‐based jute fiber composites

The present investigation deals with the thermo‐mechanical recycling of post consumer milk pouches (LDPE‐LLDPE blend) and its use as jute fiber composite materials for engineering applications. The mechanical, thermal, morphological, and dynamic‐mechanical properties of recycled milk pouch‐based jute fiber composites with different fiber contents were evaluated and compared with those of the virgin LDPE‐LLDPE/jute fiber composites. Effect of artificial weathering on mechanical properties of different formulated composites was determined. The recycled polymer‐based jute fiber composites showed inferior mechanical properties as well as poor thermal stability compared to those observed for virgin polymer/jute fiber composites. However, the jute‐composites made with (50:50) recycled milk pouch‐virgin LDPE‐LLDPE blend as polymer matrix indicated significantly superior properties in comparison to the recycled milk pouch/jute composites. Overall mechanical performances of the recycled and virgin polymeric composites were correlated by scanning electron microscopy (SEM). The dynamic mechanical analysis showed that storage modulus values were lower for recycled LDPE‐LLDPE/jute composites compared to virgin LDPE‐LLDPE/jute composites throughout the entire temperature range, but an increase in the storage modulus was observed for recycled‐virgin LDPE‐LLDPE/jute composites. POLYM. COMPOS. 28:78–88, 2007. © 2007 Society of Plastics Engineers     

Thermomechanical properties of a magnetically and mechanically oriented liquid crystalline copolyester,xydar

Elastic moduli and linear coefficients of thermal expansion (CTE) of a random thermotropic liquid crystalline copolyester, oriented in a magnetic field and by mechanical methods were measured in the directions parallel and perpendicular to the orientation direction. The axial elastic modulus of the magnetically oriented film was lower than that of the uniaxially stretched film. The elastic modulus measured in the transverse direction was higher for the magnetically oriented film. In the axial direction, both the mechanically stretched and magnetically oriented films exhibited shrinkage at low temperatures (CTE ≈ -2 · 10^?5 K^?1) and exhibited expansion at elevated temperatures. In the transverse direction, expansion was observed except for the biaxially stretched film at low temperatures. The magnetically oriented film showed the lowest axial CTE at elevated temperatures.     

Structure and properties of UHMWPE fiber/carbon fiber hybrid composites

Ultrahigh molecular weight polyethylene (UHMWPE) fiber/carbon fiber hybrid composites were prepared by inner‐laminar and interlaminar hybrid way. The mechanical properties, dynamic mechanical analysis (DMA), and morphologies of the composites were investigated and compared with each other. The results show that the hybrid way was the major factor to affect mechanical and thermal properties of hybrid composites. The resultant properties of inner‐laminar hybrid composite were better than that of interlaminar hybrid composite. The bending strength, compressive strength, and interlaminar shear strength of hybrid composites increased with an increase in carbon fiber content. The impact strength of inner‐laminar hybrid composite was the largest (423.3 kJ/m²) for the UHMWPE fiber content at 43 wt % to carbon fiber. The results show that the storage modulus (E′), dissipation factor (tan δ), and loss modulus (E″) of the inner‐laminar hybrid composite shift toward high temperature remarkably. The results also indicate that the high‐performance composite with high strength and heat resistance may be prepared by fibers' hybrid. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1880–1884, 2006     

Young's modulus,thermal expansion coefficient and fracture behavior of selected Si–B–C based carbides in the 20–1200 °C temperature range as derived from the behavior of carbon fiber reinforced microcomposites

The Young's modulus, thermal expansion coefficient and fracture behavior of different ceramic phases in the Si–B–C system have been determined from room temperature up to 1200 °C using results of tests performed on matrix-dominated carbon fiber reinforced microcomposites by means of a specific high temperature testing apparatus. Results have shown that the boron-rich materials had higher stresses to failure and thermal expansion coefficients than silicon-rich materials whereas all the boron containing materials exhibited a viscoplastic time-dependant mechanical behavior over 1000 °C. The thermoelastic values of the Si–B–C based carbides thus obtained have been used to compute thermal residual stresses in model composite systems, in view of understanding some results reported in the literature regarding the implantation of layered matrices in ceramic matrix composites.     

Thermal Sensor to Monitor Mechanical Properties in Polymer/Fiber Composite Molding

Multi‐layered samples of 1) continuous fiber axially aligned and 2) random oriented mat glass fiber composites were manually prepared for a fiber content ranging from zero to 20% (vol.). The uniaxially aligned samples displayed linear relations between both normalized elastic modulus and normalized thermal conductivity, and fiber content, for axially applied load and heat flux. For the random mat composite samples, similar results were obtained, with symmetry displayed in the plane of the mat. In both cases, measured axial thermal conductivity permits an evaluation of the axial elastic modulus. The Mathis surface probe used (US patent #5,795,064) is demonstrated as a non‐intrusive indirect method of obtaining thermal conductivity for heat flux parallel (i.e. axial or transverse) to the plane of a sample. The method shows potential for use as an in‐line monitoring device for the mechanical properties of molded composites.     

Preparation of a nanosilica‐modified negative‐type acrylate photoresist

A new type of negative photoresist, which incorporated nanosized silica into a photosensitive acrylic resin, was developed. First, free‐radical polymerization was employed to synthesize the acrylic resin, poly[methyl methacrylate/methacrylic acid/3‐(trimethoxysilyl) propyl methacrylate], and then a silica precursor, prepared by hydrolysis and condensation of tetraethoxysilane in a sol–gel process, was introduced into the as‐formed resin solution. After the addition of photosensitive monomers and photoinitiators, a negative‐type organic–inorganic photoresist was produced. The morphology of the UV‐cured photoresist, as observed by field emission scanning electron microscopy, indicated that the size of the silica domain in the material could be reduced from 300 to about 50 nm by appropriate dosage of 3‐(trimethoxysilyl) propyl methacrylate. Thermogravimetric analysis, dynamic mechanical analysis, differential scanning calorimetry, and thermal mechanical analysis were used to evaluate the thermal and dimensional stabilities of the cured photoresists. It was found that the thermal decomposition temperature and glass‐transition temperature increased, whereas the thermal expansion coefficients before and after the glass transition decreased, with increasing silica content. The incorporation of 3‐(trimethoxysilyl) propyl methacrylate also enhanced the thermal and dimensional stabilities; however, the level of enhancement was moderate for the thermal decomposition temperature and thermal expansion coefficient and low for the glass‐transition temperature. In addition, a photoresist coated on a copper substrate demonstrated high hardness (5H) and strong adhesion (100%) with a resolution of 30 μm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Polyethylene fibers-polyethylene matrix composites: Preparation and physical properties

Drawing on the difference in melting points of UHMPE fiber (150°C) and HDPE matrix (130°C), single-polymer composites were fabricated under various processing conditions. Because of the chemical similarity of the composite components, good bonding at the fiber-matrix interface could be expected. The matrix, the fiber, and unidirectional composite laminae were studied using TMA and DSC analyses, a hot-stage crystallization unit attached to a polarizing microscope, and an universal tensile testing machine. The TMA showed negative thermal expansion of the fiber over the complete temperature range of the experiment. Three regimes of contraction according to the values of the thermal expansion coefficient were detected. DSC analyses of either the fiber or the composite specimens did not show any appreciable changes after various thermal treatments. They also showed no evidence of fiber relaxation during manufacture, probably because of the pressure-related transverse constraint. The tensile strength and modulus values of the composite appeared to be fairly high and close to those reported for other composites reinforced with polyethylene (PE) fibers. An apparent maximum on the temperature dependencies of tensile properties was observed. A study of the matrix microstructure did not give any proof of transcrystalline growth at the fiber-matrix interface even for chemical or plasma surface-treated fibers. © 1993 John Wiley & Sons, Inc.     

Effect of different film preparation procedures on the thermal,morphological and mechanical properties of pure and calcite‐filled HDPE films

The effect of different film preparation procedures on the thermal, morphological and mechanical properties of high density polyethylene (HDPE) films have been studied using differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and ultimate tensile testing. Film preparation procedures included variation in cooling methods, including quenching, forces (fanning) and natural cooling and techniques such as extrusion followed by melt squeezing and compression molding. The heat of fusion (from DSC), the degree of crystallinity (from WAXRD) and the crystallite size (from WAXRD and AFM) were found to be highest for naturally cooled specimens, followed by fan‐cooled and quenched ones. AFM images of surface topology exhibit stacked lamellar morphology for forcefully cooled (fan‐cooled and quenched) samples and spherulitic ‘lozenges’ for naturally cooled ones. The Young's modulus and yield stress [from the universal testing machine (UTM)] were highest for naturally cooled samples, followed by fan‐cooled and quenched ones. Among the calcite‐filled composites, the ‘base film,’ which was prepared by extrusion followed by melt squeezing and natural cooling, exhibited the lowest heat of fusion and degree of crystallinity and a similar crystallite size relative to compression‐molded films. Lower yield stress, tensile strength and Young's modulus and higher elongation at break were observed for the base film in comparison to the naturally cooled composite film. The low degree of crystallinity and crystallite size in the ‘base film’ explain all of its mechanical and morphological properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1427–1434, 2004     

Recycled milk pouch and virgin low‐density polyethylene/linear low‐density polyethylene based coir fiber composites

The viability of the thermomechanical recycling of postconsumer milk pouches [a 50 : 50 low‐density polyethylene/linear low‐density polyethylene (LDPE–LLDPE) blend] and their use as polymeric matrices for coir‐fiber‐reinforced composites were investigated. The mechanical, thermal, morphological, and water absorption properties of recycled milk pouch polymer/coir fiber composites with different treated and untreated fiber contents were evaluated and compared with those of virgin LDPE–LLDPE/coir fiber composites. The water absorption of the composites measured at three different temperatures (25, 45, and 75°C) was found to follow Fickian diffusion. The mechanical properties of the composites significantly deteriorated after water absorption. The recycled polymer/coir fiber composites showed inferior mechanical performances and thermooxidative stability (oxidation induction time and oxidation temperature) in comparison with those observed for virgin polymer/fiber composites. However, a small quantity of a coupling agent (2 wt %) significantly improved all the mechanical, thermal, and moisture‐resistance properties of both types of composites. The overall mechanical performances of the composites containing recycled and virgin polymer matrices were correlated by the phase morphology, as observed with scanning electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Evaluation of the thermal and mechanical properties of poly(ε‐caprolactone), low‐density polyethylene,and their blends

The thermal and mechanical properties of low‐density polyethylene (LDPE), poly(ε‐caprolactone) (PCL), and their blends were evaluated. Differential scanning calorimetry showed that increasing the PCL content of the blend did not change the LDPE melting temperature, but reduced the crystallinity by up to 16.8%. This behavior was related to interactions between the PCL chains and the crystalline phase of LDPE. Tensile strength and elongation at break values for the blends were lower than those for the pure polymers, which suggested an incompatibility between the polymers. The values for Young's modulus under tensile increased when PCL was added to LDPE. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3909–3914, 2004     

Implications of melt compatibility/incompatibility on thermal and mechanical properties of metallocene and Ziegler–Natta linear low density polyethylene (LLDPE) blends with high density polyethylene (HDPE): influence of composition distribution and branch content of LLDPE

In this paper, the implications of melt compatibility on thermal and solid‐state properties of linear low density polyethylene/high density polyethylene (LLDPE/HDPE) blends were assessed with respect to the effect of composition distribution (CD) and branch content (BC). The effect of CD was studied by melt blending a metallocene (m‐LLDPE) and a Ziegler‐Natta (ZN) LLDPE with the same HDPE at 190 °C. Similarly, the effect of BC was examined. In both cases, resins were paired to study one molecular variable at a time. Thermal and solid‐state properties were measured in a differential scanning calorimeter and in an Instron mechanical testing instrument, respectively. The low‐BC m‐LLDPE (BC = 14.5 CH₃/1000 C) blends with HDPE were compatible at all compositions: rheological, thermal and some mechanical properties followed additivity rules. For incompatible high‐BC (42.0 CH₃/1000 C) m‐LLDPE‐rich blends, elongation at break and work of rupture showed synergistic effects, while modulus was lower than predictions of linear additivity. The CD of LLDPE showed no significant effect on thermal properties, elongation at break or work of rupture; however, it resulted in low moduli for ZN‐LLDPE blends with HDPE. For miscible blends, no effect for BC or CD of LLDPE was observed. The BC of LLDPE has, in general, a stronger influence on melt and solid‐state properties of blends than the CD. Copyright © 2004 Society of Chemical Industry