Tailoring the thermal and mechanical properties of injection-molded poly (lactic acid) parts through annealing

The effect of cold-crystallization on poly (lactic acid) (PLA) injection-molded parts was systemically investigated at different annealing temperatures (80/100/120°C) and annealing times (0.5/1/1.5/2 hr). The relative crystallinity (X_c) and crystal form (α' and α) of samples was investigated by differential scanning calorimetry (DSC) and wide X-ray angle diffraction (WAXD). The dependence of the thermal and mechanical performance on relative crystallinity and crystal form/morphology was discussed in detail. A linear relationship between the increment of heat distortion temperature (HDT) and that of X_c was found. The tensile strength, tensile modulus and storage modulus all increased with annealing time and annealing temperature, while the tensile toughness presented a different behavior. The elongation at break for specimens reached a maximum value of 16.9% after annealing at 80°C for 2 hr, which is a threefold improvement compared to PLA samples prepared without annealing. This work suggests that annealing is an effective method for tailoring the physical properties of PLA products.     

Long chain branched poly(butylene succinate‐co‐terephthalate) copolyesters using pentaerythritol as branching agent: Synthesis,thermo‐mechanical,and rheological properties

Incorporating long chain branching (LCB) structure into biodegradable copolyesters can effectively improve their melt strength and film blowing processability. However, branching also results in deterioration of crystallizability which is also important for copolyester properties and processing. In this study, pentaerythritol (PER) was used as branching agent (BA) instead of previous used in‐situ BA, diglycidyl 1,2,3,6‐tetrahydrophthalate (DGT), to synthesize LCB poly(butylene succinate‐co‐terephthalate) (PBST) copolyesters. The chain structure was characterized and the effects of branching on thermal transition, mechanical, and rheological properties were investigated. Similar to DGT, copolymerizing small amount of PER (0.1–0.4 mol %) generates LCB structure and, therefore, improves the melt elasticity or strength and tensile modulus but reduces the elongation at break. Differing from DGT, PER showed higher branching efficiency, and PER‐branched PBSTs exhibited unchanged or even improved crystallization ability compared with linear PBST. The improved melt strength coupled with good crystallizability will endow PER‐branched PBSTs with better film blowing processability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44544.     

Structure,thermal, and mechanical properties of DDM‐hardened epoxy/benzoxazine hybrids: Effects of epoxy resin functionality and ETBN toughening

Bifunctional, trifunctional, and tetrafunctional epoxy (EP) resins were hardened with stoichiometric amount of 4,4′‐diaminodiphenyl methane in presence and absence of benzoxazine (BOX). The EP/BOX ratio of the hybrid systems was constant, viz. 50/50 wt %. For the bifunctional EP, the EP/BOX range covered the ratios 75/25 and 25/75 wt %, as well. Epoxy‐terminated liquid nitrile rubber (ETBN) was incorporated in 10 wt % in the systems with trifunctional and tetrafunctional EP, and in 10, 15, and 20 wt % in the EP/BOX with bifunctional EP to improve their toughness. Information on the structure and morphology of the hybrid systems was received from differential scanning calorimetric, dynamic‐mechanical thermal analysis, atomic force microscopic, and scanning electron microscopic studies. The flexural, fracture mechanical properties, thermal degradation, and fire resistance of the EP/BOX and EP/BOX/ETBN hybrids were determined. It was found that some homopolymerized BOX was built in the EP/BOX conetwork in form of nanoscale inclusions, whereas ETBN formed micron scaled droplets of sea‐island structure. Incorporation of BOX improved the charring and fire resistance, enhanced the flexural modulus and strength, reduced the glass transition (T_g), the fracture toughness, and energy. Additional modification with ETBN decreased the charring, fire resistance, flexural modulus and strength, as well as T_g, however, improved the fracture toughness and especially the fracture energy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Development of multiwalled‐carbon‐nanotube‐welded carbon fibers and evaluation of the interfacial strength in epoxy composites

Multiwalled carbon nanotube (MWCNT)‐welded carbon fibers (CFs) were prepared by a three‐step process, which included polyacrylonitrile (PAN) coating, MWCNT absorption, and heat treatment. The structure of these materials was characterized by scanning electron microscopy, Fourier‐transform infrared spectroscopy, and Raman spectroscopy. The MWCNTs were uniformly assembled on the surface of the PAN‐coated CFs and welded by a PAN‐based carbon layer after heat treatment. The contact angle of the MWCNT‐welded CFs in the epoxy resins was 41.70°; this was 22.35% smaller than that of the unsized CFs. The interfacial shear strength (IFSS) of the MWCNT‐welded CF–epoxy composite was 83.15 MPa; this was 28.89% higher than that of the unsized CF–epoxy composite. The increase in the IFSS was attributed to the enhancement of adhesions between the CFs and polymer matrix through the welding of the MWCNTs on the CFs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45027.     

Curing kinetics,thermal, and adhesive properties of acetylene‐terminated benzoxazine

The acetylene‐terminated benzoxazine monomer (BB‐apa) has been synthesized using 2,2‐bis(4‐hydroxyphenyl)butane, 3‐aminophenylacetylene, and paraformaldehyde. The structure of the monomer was characterized by FTIR spectroscopy and ¹H NMR spectra, which indicated that the reactive oxazine ring and acetenyl groups existed in molecular structure of BB‐apa. The polymerization behavior was monitored by FTIR and non‐isothermal differential scanning calorimetry (DSC), which showed that the BB‐apa had completely cured with multiple polymerization mechanisms according to oxazine ring‐opening and ethynyl addition polymerization. The curing kinetics results revealed that the introduction of ethynyl groups can accelerate the ring‐opening polymerization of benzoxazine, leading to a lower curing temperature and apparent activation energy. Moreover, the thermoset derived from the BB‐apa exhibits higher thermal stability and lap shear strength (at 350 °C) with the glass transition temperature of 353 °C compared with the traditional benzoxazine polymer without ethynyl groups (BB‐a). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44547.     

Preparation and properties of novel hybrid resins based on acetylene‐functional benzoxazine and polyvinylsilazane

A serial of addition‐curable hybrid resins for resin matrix of advanced composites are prepared by thermal prepolymerization between acetylene‐functional benzoxazine(BZ) and polyvinylsilazane(PSN) with various weight ratios. Processing capability of BZ‐PSN resin is investigated by measuring viscosity. Cure behavior is investigated by differential scanning calorimetry (DSC) and Fourier transform infrared (FT‐IR) spectra. Thermal property of cured BZ‐PSN resin is investigated by Thermogravimetric analysis (TGA) and Dynamic mechanical analysis (DMA). BZ‐PSN resin shows a low viscosity of 40–180 mPa·s between 60 and 90°C, and maintains the low viscosity for 6 h, indicating that the resin is suitable for resin transfer molding (RTM) process to fabricate composites. DSC results show that BZ‐PSN resin can be cured completely at about 250°C without adding any other curing additives. FT‐IR shows the reaction between BZ and PSN take place. TGA shows that thermal stability of cured BZ‐PSN resin is increased with the content of polyvinylsilazane increasing both in nitrogen and in air. DMA shows cured hybrid resins have excellent thermal properties. The excellent processability and thermal properties suggest that BZ‐PSN resin is a promising candidate for resin matrix of advanced composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3794–3799, 2013     

Preparation of a branched amine and physical and thermal studies of epoxy compositions including the amine compound

A branched amine, abbreviated as EATP, was synthesized by reacting ethylene diamine with methyl acrylate, followed by reaction with xylylene diamine via a two‐step process. The prepared EATP (in the range of 5–30 parts per resin) was added to epoxy compositions with bisphenol A epoxy resin and a curing agent, xylylene diamine. The epoxy compositions were cured at high temperatures and processed for flexural strength testing and dynamic mechanical analysis. The results showed that the flexural strength was improved by 13% when 10% EATP was present in the epoxy matrix, but there was a decrease in tan δ and storage modulus values. Moreover, the degree of fire hazard of the epoxy compositions and EATP was studied by measuring the heat release rate (HRR). The reduction in the HRR with higher amounts of EATP in the epoxy indicated that the xylylene groups of EATP enhance the thermal stability of the resin. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46233.     

Electrical,thermal, and mechanical properties of silicone foam composites filled with carbon-based nanofillers

It is critical to develop a new method to prepare engineered carbon-based fillers for high-performance applications. In this article, the functional nanocarbon-based fillers (FG-M) composed of multiwalled carbon nanotubes (MWNTs) and graphene oxide (GO) was synthesized by a simple self-assembly reaction under the existence of triethoxyvinylsilane. Based on the FG-M fillers, the silicone foam composites (FG-M/SF) were prepared, and the electrical, thermal, and mechanical properties of the composites were studied. Results showed that the FG-M could effectively improve the electrical, thermal, and mechanical properties of the composites compared with the single-filler system (GO/SF and MWNTs/SF). Especially, the composites exhibited the best synergistic effect on electrically, thermal and mechanical enhancement while the ratio of MWNTs and GO was close to 1:1. Moreover, the effect of type and content of fillers on the rheological properties and density of the composites was also studied. The result showed that the FG-M/SF system has good thixotropic and foaming performance. The FG-M filler will have a good application prospect in the preparation of high-performance SF composites.     

Modulating silica‐rubber interface by a biorenewable urushiol derivative. Synthesis,surface modification,and mechanical and dynamic mechanical properties of vulcanizates therefrom

Hydrogenated urushiol (i.e., 3‐pentadecylcatechol) can be used to directly modify silica particles via surface complexation with silicon. The degree of surface coverage can be varied by experimental conditions. Mooney viscosity and Payne effect studies of uncured rubber compounds show that dispersion of silica filler completely covered by hydrogenated urushiol in the absence of coupling agent bis[3‐(triethoxysilyl)propyl] tetrasulfide (TESPT) is as effective as dispersion of standard unmodified silica in the presence of TESPT under otherwise identical mixing conditions. Low bound rubber content and observation of filler flocculation at the early stage of vulcanization demonstrate that the filler‐rubber interaction is physical in nature as the result of surface modification by hydrogenated urushiol. When silica is partially covered by hydrogenated urushiol, it can be used in conjunction with TESPT. Judicial combination of partially covered silica and TESPT can give optimal properties to the resultant vulcanizate, including reduced Payne effect and improved cut resistance while maintaining other key parameters the same in comparison with a standard silica‐TESPT reinforced rubber. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45937.     

Extrusion of polypropylene/chitosan/poly(lactic-acid) films: Chemical,mechanical, and thermal properties

Development of extruded films composed of biopolymers blended with synthetic polymers aims to minimize the environmental impact of plastic waste-materials and lead to the sustainable plastic industry. To produce biodegradable polymeric blends, the weight content of biopolymers must be maximum without compromising the performance properties of the extruded films. Using a solvent-free extrusion method, films composed of polypropylene, poly(lactic-acid), and Chitosan, can be obtained with the use of polypropylene-graft-maleic anhydride and glycerol as compatibilizer and plasticizer, respectively. Extruded films with up to a 50 wt% content of biopolymers show acceptable thermal and mechanical properties, where the use of compatibilizer improves the processing characteristics and homogeneous distribution of chitosan throughout the films. Therefore, the extruded films can be considered as alternatives to conventional synthetic-polymer films, due to their acceptable mechanical and thermal properties with direct potential applications in extrusion-method mass production of biodegradable polymers.     

Effects of polycaprolactone molecular weights on thermal and mechanical properties of polybenzoxazine

Polymer blends of polybenzoxazine (PBA‐a) and polycaprolactone (PCL) of different molecular weights (M_n = 10,000, 45,000, and 80,000 Da) were prepared at various PBA‐a/PCL mass ratios and their properties were characterized. The results from dynamic mechanical analyzer (DMA) revealed two glass transition temperatures implying phase separation of the two polymers in the studied range of the PCL contents. Moreover, a synergistic behavior in glass transition temperature (T_g) was evidently observed in these blends with a maximum T_g value of 281°C compared with the T_g value of 169°C of the PBA‐a and about ?50°C of the PCL used. The blends with higher M_n of PCL tended to provide greater T_g value than those with lower M_n of PCL. The modulus and hardness values of PBA‐a were decreased while the elongation at break and area under the stress?strain curve were increased with an increase of the content and M_n of PCL, suggesting an enhancement of toughness of the PBA‐a. Scanning electron micrographs (SEM) of the sample fracture surface are also used to confirm the improvement in toughness of the blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41915.     

Influences of diallyl phthalate as chain extender on the properties of high molecular weight poly(vinyl chloride) resin

A higher porosity with better thermostability is desirable for poly(vinyl chloride) (PVC) resin. In this study, high molecular weight PVC resins are prepared by vinyl chloride monomer (VCM)‐diallyl phthalate (DAP) suspension copolymerization in a 20‐L reactor at 50 °C using DAP as chain extender. SEM, BET, and analyses of plasticizer absorption results show the high molecular weight poly(vinyl chloride) (HPVC) by DAP‐VCM copolymerization is loose and porous. With increasing DAP content when the mass ratio of DAP/VCM (ω) is below the gel point, the porosity and the degree of polymerization increase. Nevertheless, the bulk density and particle size decrease. When more than the gel point, these relationships are reversed. Thermogravimetric analysis revealed that the HPVC had better thermostability than that of commercial PVC, and its thermostability increases with increasing ω before it reaches the gel point. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45093.     

Effect of functionalized graphene oxide with phosphaphenanthrene and isocyanurate on flammability,mechanical properties,and thermal stability of epoxy composites

Maleic anhydride, 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and 1, 3, 5-triglycidyl isocyanurate functionalized graphene oxide (GO) was prepared in this paper. The resultant phosphorus-nitrogen functionalized GO called GOMT was homogeneously dispersed and incorporated into diglycidyl ether of bisphenol A to prepare composites. The char residue of GOMT/EP composites increased and its LOI value increased to 28.1% with UL-94 V-1 rating. T _g of composite containing 1 phr GOMT increases to 165.6 °C, and the storage modulus of the sample with 3 phr GOMT was increased by 19% compared with pure EP. Furthermore, the elastic modulus and flexural strength of epoxy composite with 5 phr GOMT were increased by 17.9 and 26.7% at room temperature, respectively. Besides, the incorporation of GOMT into EP significantly reduces the PHRR and THR of the matrix. Therefore, the as-designed GOMT not just obviously enhances the flame retardancy with low loading but raises the mechanical behavior and thermal stability of epoxy resins. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48761.     

Characterization of hemicellulose-carboxymethyl cellulose blend films: Enhancement of the physicochemical,thermal, and mechanical properties

This study investigates the influence of hemicellulose (Hc) on the chemical composition, thermal stability, mechanical properties, and morphology of carboxymethyl cellulose (CMC). Hc was isolated from oil palm trunk and then added into CMC at 10–30 wt% to prepare Hc-CMC films via solution casting method. The addition of Hc resulted in reduced visual transparency, rendering the blend films opaque. Fourier transform infrared spectroscopy verified the chemical interaction between Hc and CMC by revealing persistent and robust hydrogen bonding at specific spectral peaks (3483–3045 cm⁻¹). The interaction between Hc and CMC was further indicated by the rougher interfacial structure as revealed in scanning electron microscopy (SEM). Thermal analysis via differential scanning calorimetry and thermogravimetry analysis indicated a decrement in thermal stability as Hc loadings increased in the CMC films. The highest tensile properties were observed in Hc-CMC blend films at a 20 wt% Hc loading, showcasing notable enhancement about 23%. The 20 wt% Hc-CMC blend films appeared as more suitable blending composition which having an enhanced physicochemical, thermal, and mechanical properties. This finding underscores its potential applicability in diverse industrial sectors, particularly in packaging applications.     

Novel propargylether‐terminated monomers containing pyridine and phenyl pendent group: Synthesis,cure, and properties

Two novel propargylether‐terminated resins containing pyridine and bulky phenyl pendent group were prepared from propargyl bromide and different diphenols, and highly thermal stable polymers were obtained by the thermal cure of the monomers. The chemical structures of these novel monomers were well confirmed by FTIR, ¹H‐NMR and elemental analysis. Curing and thermal behavior of the resins were investigated using differential scanning calorimetry (DSC) and dynamic thermogravimetry in argon atmosphere. DSC curves of these two monomers showed a single endothermic peak corresponding to the conformation of chromene ring and homopolymerization of the chromene ring. The temperature at 5% weight loss (T_d5) was higher than 440°C under argon and the highest glass transition temperature (T_g) reached 362°C. The rheological behavior and solubility of the monomer were also investigated. The monomers showed excellent flow‐ability, broad processing window, and great solubility. These results showed that the two resins could be ideal candidates for high‐temperature resistant resins. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40469.     

Remarkable improvement of thermal stability of main‐chain benzoxazine oligomer by incorporating o‐norbornene as terminal functionality

A new main‐chain benzoxazine oligomer with o‐norbornene functionality as end groups has been designed and synthesized. As compared to traditional main‐chain type benzoxazine polymers, this benzoxazine oligomer with o‐norbornene terminal functionality can undergo further crosslinking polymerization after general ring‐opening polymerization of oxazine rings. Another main‐chain benzoxazine oligomer has also been designed based on the reaction of bisphenol‐A, 4,4′‐diaminodiphenylmethane, paraformaldehyde, and phenol for comparison. The structure of the synthesized oligomers is confirmed by ¹H nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy (FTIR). The molecular weight has been determined by using gel permeation chromatography (GPC). The benzoxazine oligomer containing o‐norbornene functionality can polymerize with multiple polymerization mechanisms rather than the single mechanism common to traditional 1,3‐benzoxazine resins. The polymerization mechanisms are monitored by in situ FTIR and differential scanning calorimetry (DSC). Moreover, the thermoset derived from the benzoxazine oligomer containing o‐norbornene functionality exhibits high thermal stability with the transition temperature of 360 °C and a high T_d5 of 404 °C. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45408.     

Ultrahigh molecular weight polyethylene/polypropylene/organo‐montmorillonite nanocomposites: Phase morphology,rheological, and mechanical properties

Phase morphology, rheological, and mechanical properties of ultrahigh molecular weight polyethylene (UHMWPE)/PP/organo‐montmorillonite nanocomposites were investigated in this work. The results of TEM and XRD indicated that the organo‐montmorillonite PMM prepared with the complex intercalator [2‐methacryloyloxyethyldodecyldimethylammonium bromide/poly(ethylene glycol)] were exfoliated and dispersed into UHMWPE matrix, and the synergistic effect of the complex intercalator on the exfoliation and intercalation for montmorillonite occurred. Besides, the presence of PMM in UHMWPE matrix was found able to lead to a significant reduction of melt viscosity and enhancement in tensile strength and elongation at break of UHMWPE, except that izod‐notched impact strength was without much obvious change. The dispersed PMM particles exhibited a comparatively large two‐dimensional aspect ratio (L_clay/d_clay = 35.5), which played an important role in determining the enhancement of mechanical properties of UHMWPE nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of ball milling on the mechanical properties and crystallization of graphene nanoplatelets reinforced short chain branched-polyethylene

Short-chain-branched-polyethylene (SCB-PE) is extensively used in domestic hot and cold piping systems. SCB-PE nanocomposites using graphene nanoplatelets (GNPs) as a filler, were prepared in this work. The effect of ball-milling as a premixing technique prior to melt-mixing, on the crystallization and the nanomechanical properties of the composites has been studied. Two sets of SCB-PE/GNPs nanocomposites with various filler loadings were prepared; one with and one without the ball-milling step. The dispersion of the filler was evaluated by optical microscopy while the crystallization process was studied using differential scanning calorimetry. The nonisothermal crystallization's experimental data were analyzed using various methods. The materials' nanomechanical behavior was investigated by conducting nanoindentation tests. A finite element analysis process was developed to extract the composites' stress–strain behavior. The composites prepared with ball-milling presented improved dispersion of GNPs in the SCB-PE matrix, which affected the crystallization, while nanoindentation tests showed significantly enhanced mechanical properties.     

Decoration of graphene oxide nanosheets with amino silane‐functionalized silica nanoparticles for enhancing thermal and mechanical properties of polypropylene nanocomposites

Graphene oxide nanosheets were decorated by amino‐silane modified silica nanoparticles. An electrostatic interaction between the negative charge of oxygen‐containing groups of graphene oxide and the positive charge of amino‐silane functional groups on the surface of silica nanoparticles plays a major role for the interfacial interaction of these two materials. The hybrid material was then used as a reinforcement in polypropylene (PP) composite. The increasing tensile strength at yield, tensile, and flexural modulus of the PP composite at a graphene oxide‐ amino‐silane silica loading content of 20 wt % are about 24.81, 55.52, and 30.35%, respectively, when compared with those of PP. It is believed that GO assists the dispersion of SiO₂ nanoparticles to the polymer matrix because of its unique structure having hydrophilicity due to its oxygen functional groups and hydrophobicity owing to its backbone graphitic carbon structure. This hybrid material may also be used as the reinforcement in other polyolefins. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44382.     

Stille cross‐coupling applied to get higher molecular weight polymers: Synthesis,optoelectronic, Voc properties,and solar cell application

Conjugated polymers are highly desirable for the photovoltaic applications. We report the synthesis, characterization, optoelectronic properties, and solar cell application of two polymers, namely, poly[(9,9‐didodecylfluorene‐2,7‐diyl)‐alt‐(2,2′:5′,2″‐terthiophene‐5,5″‐diyl)] (P1) and poly[(1,4‐bis(dodecyloxy)benzene‐2,5‐diyl)‐alt‐(2,2′:5′,2″‐terthiophene‐5,5″‐diyl)] (P2). The polymers were synthesized via Stille cross‐coupling reaction, and were characterized by the gel permeation chromatography, nuclear magnetic resonance, Fourier transform infrared, UV–vis, thermogravimetric analysis, and cyclic voltammetry analyses. The two copolymers are processable due to their good solubility in organic solvents (tetrahydrofuran, CHCl₃, toluene, chlorobenzene, and o‐dichlorobenzene). The optical band gaps (UV–vis, film, and E_g^opt) of the P1 and P2 are 2.04 and 2.00 eV, respectively. The density functional theory output structures showed that S ^… O space interaction is likely responsible for the higher planarity of P2. The polymers showed low HOMO energy levels (P1: −5.33 eV, P2: −5.05 eV). The E_HOMO for P1 is close to the E_HOMO (−5.4 eV) of an ideal polymer, which is an important, rare, and main origin of the observed higher V_oc (801–808 mV). The onset decomposition temperatures (T_d) for the P1 and P2 are 418°C and 365°C, respectively. The polymer solar cell based on the P1: C₆₀ (1: 1) and P2: C₆₀ (1: 1) blend showed a power conversion efficiency (PCE) of 0.94 and 0.71%, respectively. The composite polymer : PC₆₀BM = 1 : 2 increased PCE of the P1 (1.65%) and P2 (1.09%) under AM 1.5 illumination (100 mW/cm²). The study provided important examples to design donor–donor (D–D) polymers for the photovoltaic applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42147.