Improving thermo‐oxidative degradation resistance of bamboo fiber reinforced polymer composites with antioxidants. Part II: Effect on other select properties

The first of this two‐article study showed that the addition of antioxidants can significantly improve the thermo‐oxidative resistance of bamboo fiber reinforced polypropylene composites (BFPCs). In this article, the effect of antioxidants on water absorption, thermal stability, crystallinity, and the dynamic mechanical properties of the composites were investigated. The results showed that the addition of antioxidants resulted in a slight increase in water absorption, but this increase can be reduced by controlling the ratio of the primary and secondary antioxidants. The glass transition temperature (T_g) of composites also slightly increased. However, the effects of antioxidants on the crystallinity as well as other thermal properties of BFPCs were small or even insignificant. The different combinations, ratios, and the adding amounts of antioxidants show tiny differences for all these properties. As a whole, the addition of minor antioxidants in the bamboo fiber (BF) polymer composites will not produce obvious negative effects on their overall performances. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44199.     

Structural effect of secondary antioxidants on mechanical properties and stabilization efficiency of polyamide 6/halloysite nanotube composites during heat ageing

Hindered phenol (Irganox 1010) was combined with two kinds of secondary antioxidants [i.e., tris(2,4‐di‐tert‐butylphenyl) phosphite (Irgafos168) and tris(nonylphenyl) phosphite (TNPP)] to form antioxidant mixtures, and their influences on mechanical properties and thermo‐oxidative degradation of polyamide 6 (PA6) and halloysite nanotube (HNT) filled composites were investigated. The results showed that the antioxidant combinations provided an improvement in the oxidative induction time, decomposition temperature (T_d), processability, and tensile properties of PA6. Irganox/TNPP (1:1) was found to exhibit the best thermal oxidative resistance. The study of heat ageing in the air oven at 130 °C showed that the stabilized composites with 5 wt % of HNT could retain 92% of strength without loss of modulus. The physical characteristics of antioxidants such as low volatility and possible interaction with filler in the composites played a crucial role in stabilizing efficiency during heat ageing. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45360.     

Development and characterization of green composites from bio‐based polyethylene and peanut shell

In the present work, different compatibilizers, namely polyethylene‐graft‐maleic anhydride (PE‐g‐MA), polypropylene‐graft‐maleic anhydride (PP‐g‐MA), and polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene‐graft‐maleic anhydride (SEBS‐g‐MA) were used on green composites derived from biobased polyethylene and peanut shell (PNS) flour to improve particle–polymer interaction. Composites of high‐density polyethylene/peanut shell powder (HDPE/PNS) with 10 wt % PNS flour were compatibilized with 3 wt % of the abovementioned compatibilizers. As per the results, PP‐g‐MA copolymer lead to best optimized properties as evidenced by mechanical characterization. In addition, best particle–matrix interface interactions with PP‐g‐MA were observed by scanning electron microscopy (SEM). Subsequently HDPE/PNS composites with varying PNS flour content in the 5–30 wt % range with PP‐g‐MA compatibilizer were obtained by melt extrusion and compounding followed by injection molding and were characterized by mechanical, thermal, and morphological techniques. The results showed that PNS powder, leads to an increase in mechanical resistant properties (mainly, flexural modulus, and strength) while a decrease in mechanical ductile properties, that is, elongation at break and impact absorbed energy is observed with increasing PNS flour content. Furthermore, PNS flour provides an increase in thermal stability due to the natural antioxidant properties of PNS. In particular, composites containing 30 wt % PNS powder present a flexural strength 24% and a flexural modulus 72% higher than the unfilled polyethylene and the thermo‐oxidative onset degradation temperature is increased from 232 °C up to 254 °C thus indicating a marked thermal stabilization effect. Resultant composites can show a great deal of potential as base materials for wood plastic composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43940.     

Properties of rice husk‐HDPE composites after exposure to thermo‐treatment

Natural fiber reinforced thermo‐plastic composite, with its often‐excellent properties, is well known as a material for external flooring and landscaping. Thermo‐treatment is considered as a method to improve the mechanical properties of these composites; however, oxidation might occur. In this article, thermo‐treatment is applied to a rice husk reinforced high density polyethylene (RH‐HDPE) composite. Variations in the mechanical properties, color, mass, and chemical constituents of the RH‐HDPE composite after thermo‐treatment were investigated. The results indicated that, with the extension of thermo‐treatment time, the color of the composites darkened; the composites underwent a gradual mass loss; during the early stages of thermo‐treatment the composite's flexural properties increased, and then remained stable after 128 h of treatment. Fourier transform infrared (FTIR) spectroscopy analysis showed wood indices of the RH‐HDPE composite decreased, indicating thermo‐degradation occurred during thermo‐treatment. Wide angle X‐ray diffraction (WAXD) results indicated an increased crystallinity of the RH‐HDPE composite in the first 128 h of thermo‐treatment, and increased crystalline grain size in the first 64 h of thermo‐treatment. Appropriate thermo‐treatment is essential to improve the mechanical properties of RH‐HDPE composites. POLYM. COMPOS., 35:2180–2186, 2014. © 2014 Society of Plastics Engineers     

Recycling of wood fiber‐reinforced HDPE by multiple reprocessing

The mechanical recycling of high‐density polyethylene (HDPE) reinforced with wood fiber was studied by means of repeated injection moulding. The change in properties during the recycling was monitored by tensile and flexural tests, Charpy impact tests, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), FTIR spectroscopy, and by measuring the fiber lengths. Tests were also done where injection moulding was combined with subsequent accelerated thermo‐oxidative ageing and thereafter repeated numerous times. The results showed that the HDPE composites were relatively stable toward both the ageing conditions and the repeated injection moulding. The change of the mechanical properties was mainly observed as an increased elongation at max. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43877.     

Thermo‐physical,thermal degradation,and flexural properties of betel nut husk fiber reinforced vinyl ester composites

This study aims to investigate the thermo‐physical, mechanical, and thermal degradation properties of betel nut husk (BNH) fiber reinforced vinyl ester (VE) composites. These properties were evaluated as a function of fiber maturity, fiber content, and fiber orientation. Thermo‐physical properties were analyzed experimentally using a hot disk TPS method. The introduction of BNH was found to reduce the thermal conductivity of neat VE. The thermal conductivity and thermal diffusivity of BNH reinforced VE composites decreased with the increase in fiber content. Short fiber BNH reinforced VE composites showed the lowest thermal conductivity as compared to the unidirectional and random nonwoven composites. The TGA analysis shows lower resin transition peak for the BNH reinforced VE composites than the peak of neat VE. Fiber maturity had a notable effect on the flexural modulus of the BNH fiber reinforced VE composites. Incorporation of 10 wt% BNH fibers into the composite has increased the composites' flexural modulus by 46.37%. However, further increases in the fiber content reduced both flexural strength and modulus of the composites. POLYM. COMPOS., 37:2008–2017, 2016. © 2015 Society of Plastics Engineers     

Biopolyamide hybrid composites for high performance applications

This study focuses on the performance characteristics of wood/short carbon fiber hybrid biopolyamide11 (PA11) composites. The composites were produced by melt‐compounding of the fibers with the polyamide via extrusion and injection molding. The results showed that mechanical properties, such as tensile and flexural strength and modulus of the wood fiber composites were significantly higher than the PA11 and hybridization with carbon fiber further enhanced the performance properties, as well as the thermal resistance of the composites. Compared to wood fiber composites (30% wood fiber), hybridization with carbon fiber (10% wood fiber and 20% carbon fiber) increased the tensile and flexural modulus by 168% and 142%, respectively. Izod impact strength of the hybrid composites exhibited a good improvement compared to wood fiber composites. Thermal properties and resistance to water absorption of the composites were improved by hybridization with carbon fiber. In overall, the study indicated that the developed hybrid composites are promising candidates for high performance applications, where high stiffness and thermal resistance are required. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43595.     

High‐density green polyethylene biocomposite reinforced with cellulose fibers and using lignin as antioxidant

Aiming to manufacture biomaterials using renewable resources, we prepared, using a corotating and intermeshing twin‐screw extruder, high‐density green polyethylene composites reinforced with 20, 30, and 40 wt % of bleached cellulose fibers. Injection molded test samples are characterized for mechanical and thermal properties using thermogravimetry (TGA) and differential scanning calorimetry (DSC). These composites present improved mechanical properties relative to the pure matrix; the elastic modulus increases by 240% for the composite with 30 wt % of fiber. We characterize this composite, additionally formulated with lignin and a secondary antioxidant, by tensile and flexural mechanical properties, DSC, TGA, and oxidation induction time (OIT). Lignin has no effect on the mechanical properties; however, for the composite, the OIT increases from 24 to 77 min, clearly evidencing its effect as a stabilizer. Aging the composites for 1000 h, in a QUV chamber, confirms the stabilizing effect of lignin. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45219.     

Mechanical and thermal properties of toughened polypropylene composites

The mechanical, thermal, and structural properties of a new flexible composite containing polypropylene fiber (PP) in a random poly(propylene‐co‐ethylene) (PPE) matrix with ethylene–propylene elastomer (EP) was investigated with emphasis on the effect of EP elastomer concentration. The intrinsic composition of the composites, toughening of the matrix with EP and the fiber–matrix interface determined the properties of the composites. Through the incorporation of EP elastomer into the polypropylene–poly (propylene‐co‐ethylene) (all‐PP) composite, tensile and storage modulus (E′) decreased, flexural modulus and loss modulus (E″, damping) increased slightly to 0.15 EP and then decreased. There was an increase in impact resistance for the toughened composites, with about 100% increase in comparison with an untoughened all‐PP composite. The composition corresponding to 0.20 weight fraction EP gave optimum impact and mechanical properties. Creep resistance of the composite decreased with increasing EP content, but recovery showed an increase with increasing EP content up to 0.20. Fracture surfaces of composites after impact tests were studied with scanning electron microscopy. Moreover, the use and limitation of theoretical equations to predict the tensile and flexural modulus of the flexible PP composite is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Thermal and mechanical evaluation of cyanate ester resin catalyzed by nonylphenol and stannous octoate

Nonylphenol (NP), stannous octoate [Sn(Otc)₂], and a mixture of NP and Sn(Otc)₂ were employed for catalyzing cyanate ester resin. The curing reaction was studied by differential scanning calorimetry. A water‐absorption test at 85 °C was utilized to study the resistance to warm and humid conditions. The thermal properties were evaluated through measuring thermal weight loss and the glass‐transition temperature (T_g), and the mechanical properties were evaluated through three‐point bending tests and tensile tests. The results show that the mixture of NP and Sn(Otc)₂ exhibits the best catalytic efficiency by decreasing the exothermic peak temperature by almost 148 °C. The mixture of NP and Sn(Otc)₂ has unfavorable effects on the thermal stability. Nevertheless, all catalyst systems have good water‐absorption resistance. The mechanical investigation confirms that the tensile properties show a little reduction that is due to the plasticization of the catalyst, while the excellent flexural properties are maintained. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43959.     

Local thermo‐oxidative degradation in injection molding

A loss in part properties and service life is caused by thermal, mechanical, and thermo‐oxidative stress during processing of thermoplastic materials. Process related thermal and mechanical stresses are inevitable. However, processing under exclusion of oxygen can reduce the thermo‐oxidative stress. A lower thermo‐oxidative stress can yield a higher transparency of optical parts, less reduction of average molecular weight for example in microinjection molding, and a longer service life due to less consumption of stabilizers during processing. For a cost‐effective and gentle process it is important to know at which step of processing the polymer is exposed to thermo‐oxidative degradation and where the oxygen comes from causing degradation. To study the local thermo‐oxidative stress, an injection molding machine was encapsulated and run under local exclusion of oxygen. As reported in this article, thermo‐oxidative degradation occurs in the plasticating unit due to oxygen from the surrounding air and oxygen dissolved in the polymer resin. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Effect of different additives and their mixtures on thermal stability of polyethylene synthesized using iron and titanocene hybrid catalysts

Traditionally, additives are introduced into a polymer matrix via extrusion process which consumes a high amount of energy. In this study, the use of different additives including antioxidants for the in‐reactor stabilization of polyethylene has been investigated in order to provide an energy saving system. Particular attention was dedicated to the efficiency of antioxidant influencing the catalysts activity and properties of polymers. The effect of the addition of Irganox 1330 and Irgafos 168 antioxidants and zinc stearate on the activities of metallocene, post‐metallocene, and their supported hybrid were studied. In addition, the effect of different additives on the thermal characteristics of the synthesized polymers and oxidative induction time (OIT) was evaluated. Our polymerization results exhibited that the factors such as chemical structure of antioxidant and its steric hindrance, type of catalysts, and their hybrid could affect the catalyst performance and OIT contents. The use of antioxidants mixture and hybrid of catalysts is a way that can increase oxidation resistance of polymers considerably. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45482.     

Enhancing the Thermal Stability of Polypropylene by Blending with Low Amounts of Natural Antioxidants

Natural antioxidants are added in very low amounts to protect a polypropylene (PP) matrix against thermo‐oxidative degradation during processing. Thus, PP is melt‐blended with caffeic, chlorogenic, trans‐ferrulic, and p‐coumaric acids, and also with flavone and 3‐hydroxyflavone at 0.1 wt% with respect to the PP matrix. Neat PP and PP blended with three traditional antioxidants are prepared for comparison. A complete structural, thermal, and mechanical characterization is conducted. Ferrulic acid and particularly caffeic acid increases the thermal stability, showing also the highest activation energy. The structural changes of PP‐based films due to the polymer thermal degradation at high temperature (i.e., 400 °C) followed by FTIR reveal that antioxidants effectively delay the thermal degradation process. The wettability and the mechanical performance are also studied to get information regarding the industrial application of such films. While caffeic acid provides a more flexible material, ferrulic acid provides higher water resistance. Finally, AFM‐QNM shows that PP with caffeic acid has the highest miscibility.     

Preparation and thermal and thermo‐oxidative stability of vinylidene chloride‐co‐vinyl chloride copolymer/synthetic hectorite nanocomposites

Poly(vinylidene chloride‐co‐vinylchloride)/organically modified hectorite (VDC‐VC/SPN) nanocomposites were prepared by melt blending VDC‐VC copolymer with SPN in the presence of dioctyl phthalate, which acted as a plasticizer. As a result, the exfoliated structure was found in the VDC‐VC/SPN nanocomposites. In nitrogen atmosphere, VDC‐VC/SPN nanocomposites exhibited a single‐step thermal degradation. The thermal stability of VDC‐VC/SPN nanocomposites is significantly influenced by the SPN, which was modified with long alkyl ternary ammonium salt. In air atmosphere, VDC‐VC/SPN nanocomposites revealed a two‐step thermo‐oxidative degradation behavior. At the first degradation stage, the weight loss pattern is similar to that of VDC‐VC composites in nitrogen, in which the thermo‐oxidative stability of VDC‐VC/SPN nanocomposites is affected by the ternary ammonium salt and oxygen rather than its morphology. At the second degradation stage, both the enhanced thermo‐oxidative stability and the flame‐retardation ability of VDC‐VC composites are strongly and closely related to the morphology of nanocomposites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci ,2009     

Influence of methacryl polyhedral oligomeric silsesquioxane on the thermal and mechanical properties of methylsilicone resin

A methacryl polyhedral oligomeric silsesquioxane (POSS)‐reinforced methylsilicone resin was prepared in this work. The structures of the obtained products were confirmed with Fourier transform infrared and atomic force microscopy. The influence of methacryl‐POSS on the thermal behavior of the methylsilicone resin was studied by thermogravimetric analysis and isothermal thermogravimetric analysis. The results showed that the thermal stability of the methylsilicone resin was improved, and the degree of thermooxidative degradation was lowered; this was due to the retardation of polymer chain motion and the formation of a protective layer of SiO₂. The interlaminar shear strength and flexural strength of quartz fiber/methylsilicone resin composites were tested to determine the effects of methacryl‐POSS on the mechanical properties of methylsilicone resin. The results revealed that the mechanical properties of the methylsilicone composites also increased obviously after the incorporation of methacryl‐POSS because of the increase in the cure degree and rigidity of the resin. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Miscibility,UV resistance,thermal degradation,and mechanical properties of PMMA/SAN blends and their composites with MWCNTs

Poly(methyl methacrylate)/poly(styrene‐co‐acrylonitrile) (PMMA/SAN) blends, with varying concentrations, were prepared by melt‐mixing technique. The miscibility is ensured by fixing the acrylonitrile (AN) content of styrene acrylonitrile (SAN) as 25% by weight. The blends were transparent as well. The Fourier transform infrared spectroscopic (FTIR) studies did not reveal any specific interactions, supporting the well accepted ‘copolymer repulsion effect’ as the driving mechanism for miscibility. Addition of SAN increased the stability of PMMA towards ultraviolet (UV) radiations and thermal degradation. Incorporation of even 0.05% by weight of multi‐walled carbon nanotubes (MWCNTs) significantly improved the UV absorbance and thermal stability. Moreover, the composites exhibited good strength and modulus. However, at higher concentrations of MWCNTs (0.5 and 1% by weight) the thermo‐mechanical properties experienced deterioration, mainly due to the agglomeration of MWCNTs. It was observed that composites with 0.05% by weight of finely dispersed and well distributed MWCNTs provided excellent protection in most extreme climatic conditions. Thus, PMMA/SAN/MWCNTs composites can act as excellent light screens and may be useful, as cost‐effective UV absorbers, in the outdoor applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43628.     

Pultruded fiber-reinforced poly(methyl methacrylate) composites. II. Static and dynamic mechanical properties,environmental effect,and postformability

This paper presents a novel process developed to manufacture poly(methyl methacrylate) (PMMA) pultruded composite. The mechanical, thermal, and dynamic mechanical properties, environmental effect, postformability of various fiber (glass, carbon, and Kevlar 49 aramid fiber) reinforced pultruded PMMA composites have been studied. Results show mechanical properties (i.e., tensile strength, specific tensile strength, tensile modulus, and specific flexural strength) and thermal properties (HDT) increase with fiber content. Kevlar fiber/PMMA composites possess the highest specific tensile strength and HDT, carbon fiber/PMMA composites show the highest tensile strength and tensile modulus, and glass fiber/PMMA composites show the highest specific flexural strength. Pultruded glass-fiber-reinforced PMMA composites exhibit good weather resistance. These composite materials can be postformed by thermoforming under pressure, and mechanical properties of postformed products can be improved. The dynamic shear storage and loss modulus (G′, G″) of pultruded glass-fiber-reinforced PMMA composites increased with decreasing pulling rate, and their shear storage moduli are higher than those of pultruded Nylon 6 and polyester composites.     

Bleached extruder chemi‐mechanical pulp fiber‐PLA composites: Comparison of mechanical,thermal, and rheological properties with those of wood flour‐PLA bio‐composites

An environmentally friendly bleached extruder chemi‐mechanical pulp fiber or wood flour was melt compounded with poly(lactic acid) (PLA) into a biocomposite and hot compression molded. The mechanical, thermal, and rheological properties were determined. The chemical composition, scanning electron microscopy, and Fourier transform infrared spectroscopy results showed that the hemicellulose in the pulp fiber raw material was almost completely removed after the pulp treatment. The mechanical tests indicated that the pulp fiber increased the tensile and flexural moduli and decreased the tensile, flexural, and impact strengths of the biocomposites. However, pulp fiber strongly reinforced the PLA matrix because the mechanical properties of pulp fiber‐PLA composites (especially the tensile and flexural strengths) were better than those of wood flour‐PLA composites. Differential scanning calorimetry analysis confirmed that both pulp fiber and wood flour accelerated the cold crystallization rate and increased the degree of crystallinity of PLA, and that this effect was greater with 40% pulp fiber. The addition of pulp fiber and wood flour modified the rheological behavior because the composite viscosity increased in the presence of fibers and decreased as the test frequency increased. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44241.     

Enhancement of physical and optical performances of polycarbonate‐based diffusers for direct‐lit LED backlight unit by incorporation of nanoclay platelets

Using twin‐extrusion compounding followed by compression molding processes, polycarbonate/clay nanocomposite optical diffusers with highly intercalated and exfoliated nanostructure could be prepared for application in direct‐lit LED backlight unit. The incorporation of nanoclay platelets with an appropriate level of content substantially improved thermal resistance, as well as thermo‐mechanical, and mechanical flexural properties. The optical property of luminance uniformity with respect to both location and viewing angle was also enhanced by the load of nanoclay platelets along with silicone bead, probably due to efficient scattering and diffusion action of the nanoclay. However, excess loading of nanoclay had insignificant effect on the improvement of properties for the nanocomposite diffusers. In addition, the presence of nanoclay platelets in the PC matrix effectively suppressed the moisture absorption rate, suggesting the feasibility of avoiding the warpage phenomena of the optical diffuser during use. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42973.     

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.