Reactive Blending Research Articles

Achieving simultaneously toughening and flame-retardant modification of poly(lactic acid) by in-situ formed cross-linked polyurethane and reactive blending with ammonium polyphosphate

Achieving simultaneously toughening and flame-retardant modification of poly(lactic acid) by in-situ formed cross-linked polyurethane and reactive blending with ammonium polyphosphate

Cationic Curing of Epoxy–Aromatic Matrices for Advanced Composites: The Assets of Radiation Processing

Cross-linking polymerization of multifunctional aromatic monomers initiated by exposure to high energy radiation continues to be explored as a promising alternative to thermal curing for the production of high-performance composite materials. High-energy radiation processing offers several advantages over thermosetting technology by allowing for fast and out-of-autoclave curing operations and for its adaptability in the manufacturing of large and complex structures at reduced energy costs. The present article covers the basic aspects of radiation curing by cationic polymerization of epoxy resins, providing a status report on recent investigations conducted in our group to improve the properties of epoxy matrices and gain better control over the process for producing composites. A selection of results based on blends prepared with different composition of epoxy aromatics, transfer agents, thermoplastic toughening agents and onium salt initiators exemplifies the importance of the composition on polymerization kinetics and on the properties of resulting materials. The superiority of radiation-triggered polymerization-induced phase separation of thermoplastic additives is emphasized by the obtained morphology of toughened materials. The low initial temperature and fast curing of the reactive blends limits the expansion of phase-separated thermoplastic domains, resulting in an enhancement of the toughness.

Modification of polylactide by reactive blending with polyhydroxybutyrate oligomers formed by thermal recycling through E1cB-elimination pathway

This study aimed to thermally recycle polyhydroxybutyrate (PHB), a microbial polyester with low thermal stability and limited re-processability, into crotonate-ended oligomers through the E1cB-elimination pathway. The resulting products were used as a functional additive to improve the mechanical and rheological properties of polylactide (PLA), which has intrinsic brittleness and low melt stability. The PLA was modified through a reactive blending process in an internal mixer. The quantitative 1H NMR analysis confirmed the crotonate functionality of the oligomers and their consumption during the reactive blending process. Tensile testing revealed that reactive blending 20 wt% PHB oligomers with PLA improve tensile toughness 24 times over pure PLA while keeping the elastic modulus above 1 GPa. Oscillatory-shear rheometry confirmed the improved shear-thinning behavior of reactive blends, while extensional viscosity measurements revealed a significant strain hardening behavior. The increase in melt stability was attributed to the formation of high molecular weight structures as a result of possible chain extension and branching reactions. DSC traces showed that branching and grafting points acted as nucleation sites, accelerating PLA melt crystallization. It was also found that increasing the PLA crystallinity above 44% gives rise to crystallization-induced phase separation, despite initial miscibility.

Effect of the reactive blend conditions on the thermal properties of waste biomass and soft coal as a reducing agent for silicon production

The reducing agents used for industrial silicon production often suffer from high coking and high consumption of coal, which is associated with high energy consumption, low efficiency, and low output. To overcome these issues, a mixture of biomass and soft coal (SC) was investigated as a new type of carbonaceous reducing agent for industrial silicon production. In this paper, TGA, SEM, XRD, and Raman spectroscopy were used to study the effects of the different proportions of banana peel (BP) and SC on the activity of carbon materials under different fermentation conditions and molding times. The results showed that the pyrolysis temperatures of fermented mixed carbon materials were decreased by 38–55 °C, and the activation energy was reduced by 68–74%. The pyrolysis temperature and activation energy of moldy mixed carbon materials decreased by 49–94 °C and 46–51%. There was a significant synergistic effect between the carbon materials, and the reactivity of SC was increased. The reduction of silica by fermented carbon materials was better than moldy carbon materials; therefore, the fermentation conditions were more conducive to the preparation of carbonaceous reducing agents for the production of industrial silicon.

Study on the Foaming Behaviors of PBS and Its Modification with PA6IcoT Assisted by scCO2

The foaming behaviors of a semicrystalline poly(butylenes succinate) (PBS) and its blends with an amorphous semiaromatic nylon poly(hexamethylene (iso‐co‐tere)phthalamide) (PA6IcoT) assisted by supercritical CO2 (scCO2) as blowing agent at 110–130 °C and 16–24 MPa are investigated. The results show that the average cell diameter and cell density of the pure PBS foam obtained at 24 MPa and 120 °C are 46 μm and 1.6 × 107 cells cm−3, respectively. The cell coalescence is prevented and heterogeneous nucleation is induced in the presence of PA6IcoT in the physical blends (mPBS), resulting smaller cell size as 12 μm and higher cell density as 1.6 × 109 cells cm−3 in the foams at 24 MPa and 120 °C. The reactive blends (rPBS) with PA6IcoT prepared by 2,2‐(1,3‐benzene)bis(2‐oxazoline) (PBO) as chain extender are promising for higher complex viscosity and lower crystallinity, resulting in higher melt strength and better foamability. The rPBS foams with cell size as small as 8 μm and cell density as high as 2.0 × 109 cells cm−3 are obtained at 24 MPa and 120 °C.

Effect of blending small amount of high-density polyethylene on molecular entanglements during melt-drawing of ultrahigh-molecular-weight polyethylene

The effect of blending a small amount of high-density polyethylene (HDPE) on molecular entanglements during melt-drawing of ultrahigh-molecular-weight polyethylene (UHMW-PE) was investigated in this study. UHMW-PE powders with a small amount of HDPE added and a bimodal MW distribution were synthesized by reactor blending. In situ wide-angle X-ray diffraction and small-angle X-ray scattering measurements during melt-drawing of UHMW-PE and UHMW-PE/HDPE films were performed to evaluate the state of molecular entanglements on the basis of the behavior of oriented crystallization and extended-chain crystal formation. The addition of a small amount of HDPE reduced the amount of tight molecular entanglements originating from UHMW-PE chains, and further addition reduced the amount of molecular entanglements that transmitted the applied stress. These results demonstrated that the addition of a small amount of HDPE significantly affected the amount of molecular entanglements of UHMW-PE chains during melt-drawing.

Reactive processing of poly(lactic acid)/poly(ethylene octene) blend film with tailored interfacial intermolecular entanglement and toughening mechanism

In order to obtain a uniform and effectively toughened poly (lactic acid) film by blending with low content of poly (ethylene octene) (POE) with high elasticity, the tailored interfacial intermolecular interaction and entanglement between the two phases of the PLA/POE blend was innovatively constructed via the facile reactive melt blending process through the reaction of the epoxy/anhydride groups grafted on the POE chains with the end groups of PLA chains (PLA/GPOE-MPOE). It was observed that POE domains were embedded tightly in PLA matrix with a fuzzy interface and abundant interface transition area, and the impact fractured surface of the blend showed an obvious plastic deformation with less occurrence of fibrillation of PLA matrix or interfacial de-bonding. Compared with neat PLA and directly blended PLA/POE blends, the PLA/GPOE-MPOE blend exhibited much higher complex viscosity/storage modulus, much lower tanδ values in the terminal region, and obvious strain-hardening behavior. The deviation in viscoelastic behavior of PLA/GPOE-MPOE from linear PLA indicated the enhanced molecular entanglement between the long-branched chains, resulting in an enhancement of the stretching ability during biaxial drawing of the blend. Uniform PLA/GPOE-MPOE films with draw ratio as high as 7 × 7 were obtained through biaxial stretching, which showed much higher tensile strength and the elongation at break than that of neat PLA and PLA/POE film. This work provides a facile method for fabricating toughening PLA films with application potentials.

A phase field model for dynamic simulations of reactive blending of polymers

A facile way to generate compatibilized blends of immiscible polymers is through reactive blending of end-functionalized homopolymers. The reaction may be reversible or irreversible depending on the end-groups and is affected by the immiscibility and transport of the reactant homopolymers and the compatibilizing copolymer product. Here we describe a phase-field framework to model the combined dynamics of reaction kinetics, diffusion, and multi-component thermodynamics on the evolution of the microstructure and reaction rate in reactive blending. A density functional with no fitting parameters, which is obtained by adapting a framework of Uneyama and Doi and qualitatively agrees with self-consistent field theory, is used in a diffusive dynamics model. For a symmetric mixture of equal-length reactive polymers mixed in equal proportions, we find that depending on the Flory χ parameter, the microstructure of an irreversibly reacting blend progresses through a rich evolution of morphologies, including from two-phase coexistence to a homogeneous mixture, or a two-phase to three-phase coexistence transitioning to a homogeneous blend or a lamellar copolymer. The emergence of a three-phase region at high χ leads to a previously unreported reaction rate scaling. For a reversible reaction, we find that the equilibrium composition is a function of both the equilibrium constant for the reaction and the χ parameter. We demonstrate that phase-field models are an effective way to understand the complex interplay of thermodynamic and kinetic effects in a reacting polymer blend.

Interfacial reaction-induced roughening in polymer thin films.

Reactive blending of immiscible polymers is an important process for synthesizing polymer blends with superior properties. We use a phase-field model to understand reaction dynamics and morphology evolution by diffusive transport in layered films of incompatible, end-reactive polymers. We thoroughly investigate this phenomenon over a large parameter space of interface shapes, layer thicknesses, reaction rates specified by a Damkohler number (Daf), and Flory-Huggins interaction parameter (χ), under static conditions with no external fields. For films of the same thickness, the dynamics of the system is not significantly influenced by the length of the film or the initial shape of the interface. The interface between the polymers is observed to roughen, leading to the formation of a spontaneous emulsion. The reaction progresses slower and the interface roughens later for thicker films, and systems with higher χ. Increasing Daf increases the reaction rate and hastens the onset of roughening. The quasi-static interfacial tension decreases with the extent of reaction, but does not become vanishingly small or negative at the onset of roughening. Simulations with reversible reactions and systems where only a fraction of the homopolymers have reactive end groups show that a critical diblock (reaction product) concentration exists, below which interfacial roughening and spontaneous emulsification is not observed. We also demonstrate that thermal fluctuations accelerate the onset of interfacial roughening, and help sustain the system in an emulsified state.

Effect of maleic anhydride grafted poly(lactic acid) on rheological behaviors and mechanical performance of poly(lactic acid)/poly(ethylene glycol) (PLA/PEG) blends.

A series of polylactic acid (PLA)/polyethylene glycol (PEG) blends was prepared by melt blending using PEG as a plasticizer to address the disadvantages of PLA brittleness. PEG can weaken the intermolecular chain interactions of PLA and improve its processing properties. PLA-grafted maleic anhydride (GPLA) was reactively blended with PLA/PEG to obtain a high tenacity PLA/PEG/GPLA blend. GPLA was prepared by melt grafting using diisopropyl peroxide as the initiator and maleic anhydride as the graft. The effects of different PEG molecular weights (1000-10 000 g mol-1) on the properties of PLA/PEG/GPLA blends were investigated. GPLA reacted with PEG1000 (M w = 1000 g mol-1) to form short PLA branched chains and reacted with PEG10000 (M w = 10 000 g mol-1) to form a small number of PLA branched chains, which was unconducive to increasing the intermolecular chain entanglement. The branched PLA formed by the reaction between PEG6000 (M w = 6000 g mol-1) and GPLA had a remarkable effect on increasing intermolecular chain entanglement. The complex viscosity, modulus, and melt strength values of PLA/PEG6000/GPLA blends were relatively large. The elongation at break of the blends reached 526.9%, and the tensile strength was 30.91 MPa. It provides an effective way to prepare PLA materials with excellent comprehensive properties.

High-entropy polymer blends utilizing in situ exchange reaction

High-entropy metal alloys comprising near-equimolar multiple elements have attracted considerable attention, and high configurational entropy is the main reason behind their outstanding performance. Analogical material design is expected to be applied for polymer blending; however, high-entropy polymer blends are still an undeveloped field owing to their long-chain structure. Increasing configurational entropy is essential for preparing high-entropy polymer blends, and to realize monomer unit dispersion beyond molecular chains, multi-component blending, utilizing an in situ exchange reaction, was investigated. Four types of aliphatic polyamides were employed as component polymers, and binary-to-quaternary blends were fabricated. Ternary and quaternary blends exhibited restricted crystallization behavior and high elongation at break. These characteristic behaviors were not observed in the reacted binary blends or unreacted quaternary blends. Numerical assessment revealed that the randomness of the molecular sequence in the reactive quaternary blend rapidly increased during melt mixing.

Fluorinated Phthalonitrile Resin with Excellent Thermal Stability and Low Dielectric Constant for High‐Frequency Electronic Packaging

AbstractPhthalonitrile (PN) resin promising material for preparing high‐speed and high‐frequency electronic packaging because of its unique hightemperature resistance and excellent insulation performance. A fluorinated PN oligomer (4,4’‐bis (p‐perfluoro‐phenol‐(bis(p‐phenol)perflouoropropane‐2,2‐diyl)‐p‐oxy‐diphthalonitrile) (PFDP)) containing trifluoromethyl and decafluorobiphenyl groups are designed, synthesized, and characterized. The oligomer is blended with 4‐(aminophenoxy) phthalonitrile (APPH), and then cured into polymers under the temperature‐programmed process. The reactive blend has good processability, and structures of isoindole, triazine ring, and phthalocyanine ring are found in the curing reactions. The fluorinated PN (P‐380) shows outstanding thermal stability and mechanical properties (5% thermal degradation temperature: 518 °C (N2); 516 (Air), THeat‐resistance index: 268 °C, activation energy of thermal decomposition: 334.89 kJ mol−1, glass transition temperature (Tg) > 400 °C). Meanwhile, the fluorinated PN simultaneously exhibited a superior low dielectric constant (Dk, 2.21) and dielectric loss (Df, 0.01) at 10 GHz. Moreover, the water absorption of the resin is as low as 0.74%, which meets the requirement of dielectric materials. These results would strongly suggest such PFDP PN resin as excellent packaging materials in those high‐tech applications such as aerospace and communication electronic devices.

Disentangled UHMWPE@silica powders for potential use in power bed fusion based additive manufacturing

Disentangled ultrahigh molecular weight polyethylene dUHMWPE (Mw ∼ 2.106Da) particles in a reactor blend with HDPE are catalytically prepared from ethylene, mediated by a new catalyst from N,N'-(2,6-pyridinediyl diethylidyne) bis[2,6-di-3-propenyl-benzenamine] iron dichloride and triethyl aluminum. These particles could be laser sintered, but not automatically processed in an SLS machine. The same catalyst supported on microsilica particles gives access to composite dUHMWPE@silica particle powder with particle sizes below 200 µm. Testing bars prepared by heat pressing have an Emod of 150 MPa, an elongation at break at 450 % and an ultimate strength of 39 ± 11 MPa. A SEM image indicates a silica induced crystallization into pseudo spherulites of 500 µm size. The dUHMWPE@silica composite particles have an fcc flowability value of 3.4 in a ring shear tester, and a low density of 150 kg.m−3. Additivation with nanosilica powder (1 wt%) and carbon black (0.25 wt%) allowed to process the composite in an SLS machine. The printed parts showed severe caking, but also a complete welding of the powder, albeit with voids on account of the low particle density.

Processing and rheological behavior of cross‐linked polyethylene containing disulfide bonds

AbstractVitrimers are a new class of materials that consist of chemically cross‐linked networks that engage in thermoactivated associative exchange reactions. These exchange reactions can impart malleability, healing, and recyclability properties to thermosets. In this study, a one‐step protocol to prepare linear low‐density polyethylene (LLDPE) vitrimer‐like materials with disulfide exchange bonds via reactive blending is presented. The cross‐linking reaction of maleic anhydride‐grafted‐linear low‐density polyethylene (LLDPE‐MAH) and 4,4′‐dithiodianiline was followed in a torque rheometer. The degree of MAH‐functionalization and its impact on the melt rheology, dynamic mechanical properties, and thermal properties of the vitrimer was studied. The cross‐linked LLDPE possessed a mostly elastic behavior, with storage modulus () higher than loss modulus () in the entire frequency range. The complex viscosity of cross‐linked LLDPE at high frequencies (>100 rad/s) was comparable to the thermoplastic LLDPE. The MAH‐groups and formation of cross‐links decreased the degree of crystallinity, which led to a decrease in the storage modulus at a temperature of 35°C. The storage modulus and dimensional stability of the materials improved with cross‐linking density, suggesting potential benefits of LLDPE vitrimers in secondary manufacturing processes. Finally, the reprocessing ability was demonstrated via internal mixing and the rheological and mechanical properties were retained.

Effects of Modified Thermoplastic Starch on Crystallization Kinetics and Barrier Properties of PLA.

This study reports on using reactive extrusion (REX) modified thermoplastic starch particles as a bio-based and biodegradable nucleating agent to increase the rate of crystallization, percent crystallinity and improve oxygen barrier properties while maintaining the biodegradability of PLA. Reactive blends of maleated thermoplastic starch (MTPS) and PLA were prepared using a ZSK-30 twin-screw extruder; 80% glycerol was grafted on the starch during the preparation of MTPS as determined by soxhlet extraction with acetone. The crystallinity of PLA was found to increase from 7.7% to 28.6% with 5% MTPS. The crystallization temperature of PLA reduced from 113 °C to 103 °C. Avrami analysis of the blends showed that the crystallization rate increased 98-fold and t1/2 was reduced drastically from 20 min to <1 min with the addition of 5% MTPS compared to neat PLA. Observation from POM confirmed that the presence of MTPS in the PLA matrix significantly increased the rate of formation and density of spherulites. Oxygen and water vapor permeabilities of the solvent-casted PLA/MTPS films were reduced by 33 and 19% respectively over neat PLA without causing any detrimental impacts on the mechanical properties (α = 0.05). The addition of MTPS to PLA did not impact the biodegradation of PLA in an aqueous environment.

Near-Infrared Light-Responsive Shape Memory Polymer Fabricated from Reactive Melt Blending of Semicrystalline Maleated Polyolefin Elastomer and Polyaniline.

A shape memory polymer was prepared by melt mixing a semicrystalline maleated polyolefin elastomer (mPOE) with a small amount of polyaniline (PANI) (up to 15 wt.%) in an internal mixer. Transmission electron microscopy (TEM), FTIR analysis, DMA, DSC, melt rheological analysis, and a tensile test were performed to characterize the structure and properties of the mPOE/PANI blends. The results revealed that the blends form a physically crosslinked network via the grafting of PANI onto the mPOE chains, and the PANI dispersed at the nanometer scale in the POE matrix served as a photo-thermal agent and provided increased crosslinking points. These structural features enabled the blends to exhibit a shape memory effect upon near-infrared (NIR) light irradiation. With increasing PANI content, the shape recovery rate of the blend under NIR stimulation was improved and reached 96% at 15 wt.% of PANI.

Preparation of a novel oligomer type compatibilizer for polypropylene/polystyrene blend

A polystyrene–g–2,2,6,6-tetramethylpiperidine 1-oxyl radical (PS–g–TEMPO) copolymer was formed during thermal-oxidative degradation of PS/hindered amine light stabilizer (HALS) under heat treatment by thermal equilibrium. The optimum preparation condition was identified at 150 °C for 21 h by assessment of the temperature and aging time dependences of the molecular weight and thermal properties. The optimized copolymer was reacted with polypropylene (PP). A PS–g–PP grafted copolymer-type compatibilizer was reactively prepared with the copolymer/PP at 200 °C melt mixing temperature. The tetrahydrofuran-soluble part of the PP/PS/PS–g–TEMPO blend was analyzed as the PS–g–PP copolymer. The PS–g–PP showed a broad melting peak in the range from 125 °C to 160 °C. The PP grafting ratio was approximately 4%, as calculated by pyrolysis gas chromatography mass spectrometry (Py-GC/MS) analysis. The reactive polymer blend of the PP/PS/PS–g–TEMPO showed significant improvement in mechanical properties and ductile fracture surface as compared with PP/PS. The HALS loading easily produced an excellent compatibilizer for PP/PS mechanical improvement.

Formulating Portland cement–reactive alumina blend through thermodynamic modeling to prevent the alkali–silica reaction

AbstractThis study aims to formulate solid and aqueous compositions of hydrated Portland cement incorporated with reactive alumina (RA) via thermodynamic modeling, with the goal to prevent alkali–silica reaction (ASR). Based on SEM/EDS point analysis, the uptake of Al into C–S–H was corrected in the thermodynamic modeling to improve the accuracy. The predicted solid and aqueous compositions were validated by means of XRD, TGA, and ICP. An accelerated mortar bar test was also carried out to confirm the ASR mitigating efficiency, and a preliminary relationship among the ASR expansion, solid assemblage, and aqueous species was established. The critical content for RA is around 5.75% in the studied systems, above which katoite precipitates, resulting in increased Al concentration in the pore solution (∼0.8 mmol/L); hence, ASR can be effectively inhibited.

Dynamic Interfacial Cross‐Linking Polymer Blends with Fiber‐Like Phase Structure by Recycling

AbstractThe properties of polymer blends strongly depend on their microstructure. Thus, tuning the phase structure and improving the interfacial interaction of blends are relatively crucial. Inspired by the breaking and reformation of dynamic covalent bonds in vitrimers, these special bonds are introduced into the phase interface of polymer blends in this work. Through reactive blending of epoxidized natural rubber (ENR), polylactic acid (PLA) and additives, polymer blends with dynamic interfacial cross‐linking are fabricated. The prepared blends with intensive interfacial interactions display excellent recycling capacity. Strikingly, after etching the dissolvable substances with a solvent, the porous phase structure of original polymer blends changes to a fiber‐like phase structure of the third recycled blends, entirely distinct from most reported phase structures in polymer blends. In addition, the composites show great enhancements in mechanical properties during recycling. This work provides an effective method to tune the phase structure and improve the interfacial interaction of polymer blends.

Superior toughened bio-compostable Poly(glycolic acid)-based blends with enhanced melt strength via selective interfacial localization of in-situ grafted copolymers

As an emerging bioplastic, poly(glycolic acid) (PGA) possesses excellent bio-compostability, gas barrier properties, mechanical strength and heat resistance. However, the inherent brittleness and inferior melt-strength of PGA severely limits its processability and application possibilities. In the present contribution, a two-step reactive melt blending of PGA and poly(butylene adipate-co-terephthalate) (PBAT) with epoxy functionalized copolymer (ethylene-methyl acrylate-glycidyl methacrylate) (EMAG) as compatibilizer was investigated to solve these shortcomings. The EMAG was first blended with PBAT and then with PGA to in-situ form PGA-g-EMAG-g-PBAT copolymers. These copolymers selectively locate at the interface between PGA and PBAT, which effectively improved the interfacial adhesion and the compatibility. Consequently, the PGA/(PBAT/EMAG) blends with 1 wt % EMAG exhibited high elongation at break (45 ± 4%) and a notched impact strength (14.4 ± 1.6 kJ/m2) respectively, which is about 1100% and 410% higher than that of PGA. Meanwhile, the viscosity and storage modulus of the PGA/(PBAT/EMAG) blends at 50.1 Hz were enhanced by 130% and 230% compared with PGA. This work provides a facile route to fabricate PGA-based blends with excellent toughness and melt strength, which could open up new possibilities for the application of PGA materials.