Reactive Melt Processing Research Articles

Chemical-free Reactive Melt Processing of Biosourced Poly(butylene-succinate-adipate) for Improved Mechanical Properties and Recyclability.

Biosourced and biodegradable polyesters like poly(butylene succinate-co-butylene adipate) (PBSA) are gaining traction as promising alternatives to oil-based thermoplastics for single-use applications. However, the mechanical and rheological properties of PBSA are affected by its thermomechanical sensitivity during its melt processing, also hindering PBSA mechanical recycling. Traditional reactive melt processing (RP) methods use chemical additives to counteract these drawbacks, compromising sustainability. This study proposes a green reactive method during melt compounding for PBSA based on a comprehensive understanding of its thermomechanical degradative behavior. Under the hypothesis that controlled degradative paths during melt processing can promote branching/recombination reactions without the addition of chemical additives, we aim to enhance PBSA rheological and mechanical performance. An in-depth investigation of the in-line rheological behavior of PBSA was conducted using an internal batch mixer, exploring parameters such as temperature, screw rotation speed, and residence time. Their influence on PBSA chain scissions, branching/recombination, and cross-linking reactions were evaluated to identify optimal conditions for effective RP. Results demonstrate that specific processing conditions, for example, twelve minutes processing time, 200 °C temperature, and 60 rpm screw rotation speed, promote the formation of the long chain branched structure in PBSA. These structural changes resulted in a notable enhancement of the reacted PBSA rheological and mechanical properties, exhibiting a 23% increase in elastic modulus, a 50% increase in yield strength, and an 80% increase in tensile strength. The RP strategy also improved PBSA mechanical recycling, thus making it a potential replacement for low-density polyethylene (LDPE). Ultimately, this study showcases how finely controlling the thermomechanical degradation during reactive melt processing can improve the material's properties, enabling reliable mechanical recycling, which can serve as a green approach for other biodegradable polymers.

Joncryl chain extender reactivity with polylactide: Effect of d-lactide content, Joncryl type, and processing temperature

In this study, a highly crystallizable and an amorphous polylactide (i.e., cPLA and aPLA) with, respectively, low (0.5 mol. %) and high (12 mol. %) d-lactic acid contents and similar molecular weights were melt compounded with two different multifunctional epoxy-based Joncryl chain extenders (CEs, i.e., ADR 4400 and 4468) at 190 °C. Reactivity of Joncryl grades with aPLA was also explored at melt processing temperatures of 150, 170, and 210 °C. Small amplitude oscillatory shear rheological analysis was conducted to understand the extent of the Joncryl reaction with PLA molecules, and the results were confirmed with molecular weight determination using gel permeation chromatography. Extensional viscosity of the processed samples was also compared to control their strain hardening behavior. Results showed that the Joncryl reaction with cPLA and aPLA differs in terms of preference for chain extension or branching, indicating that molecular regularity affected the interactions with both Joncryl grades during reactive melt processing. Moreover, although the increase in processing temperature accelerated PLA degradation, it noticeably increased the reactivity of both Joncryl grades with aPLA. In all cases, ADR 4468 was more reactive in molecular chain extension/branching due to its higher functionality than ADR 4400. Differential scanning calorimetry results also revealed that the crystallization of cPLA was differently affected by the change in the Joncryl content and type.

A Sustainable Multi‐Dimensional Printable Material

AbstractPolymeric materials are usually tailored for specific functionality. A single polymer exhibiting multiple simultaneous functionalities often requires intricate molecular architecture, which is difficult to manufacture at scale because of its complex synthesis routes. Herein, a facile, partly renewable composition―prepared via reactive melt processing―that induces tunable functionalities such as 3D printability, shape recovery, and self‐healing while exhibiting satisfactory mechanical properties is reported. The system with a hydrogen‐bonded 3D network consists of thermally reversible nano‐scale agglomerates of sustainable, rigid phenolic oligomers and crystallizable flexible polymer. Local molecular mobility and temperature‐dependent relaxation and recovery of the non‐equilibrium networked states enable exploiting these simultaneous functionalities. Transitions involving solidification and structure stabilization at ambient temperature spanning several hours after preheating only at 70 °C directly contrast typical thermoplastic or thermoplastic elastomer behaviors. Results from this study can inform the design of future rheology modifiers and materials for soft robotics.

Lignin valorization in thermoplastic biomaterials: from reactive melt processing to recyclable and biodegradable packaging

Lignin valorization in thermoplastic biomaterials: from reactive melt processing to recyclable and biodegradable packaging

Impact-Resistant Poly(3-Hydroxybutyrate)/Poly(ε-Caprolactone)-Based Materials, through Reactive Melt Processing, for Compression-Molding and 3D-Printing Applications.

Biobased and biocompatible polymers, such as polyhydroxyalkanoates (PHAs), are of great interest for a large range of applications in the spirit of green chemistry and upcoming reuse and recycling strategies. Polyhydroxybutyrate (PHB), as a promising biocompatible polymer belonging to PHAs, is subject to increased research concern regarding the high degree of crystallinity and brittle behavior of the resulting materials. Therefore, the improvement of PHB's physico-mechanical properties aims to decrease the Young's modulus values and to increase the ductility of samples. Here, we proposed an ambitious approach to develop melt-processed materials, while combining PHB characteristics with the ductile properties of poly(ε-caprolactone) (PCL). In order to compatibilize the poorly miscible PHB/PCL blends, dicumyl peroxide (DCP) was used as a free-radical promotor of polyester interchain reactions via the reaction extrusion process. The resulting PHB/PCL-DCP materials revealed a slight increase in the elongation at break, and significant improvement in the impact resistance (7.2 kJ.m-2) as compared to PHB. Additional decrease in the Young's modulus values was achieved by incorporating low molecular polyethylene glycol (PEG) as a plasticizer, leading to an important improvement in the impact resistance (15 kJ.m-2). Successful 3D printing using fused deposition melting (FDM) of the resulting PHB/PCL-based blends for the design of a prosthetic finger demonstrated the great potential of the proposed approach for the development of next-generation biomaterials.

Reactive melt crosslinking of cellulose nanocrystals/poly(ε-caprolactone) for heat-shrinkable network

Focusing on the challenge of non-biodegradable plastics replacement, we propose a design for peroxide-initiated crosslinking of biodegradable poly(ε-caprolactone) (PCL) and renewable cellulose nanocrystals (CNCs) bionanocomposites. An industrially scalable water-assisted reactive melt-processing (REx) is studied to explore the hypothesis of synergy between simultaneous effects of water on improving CNC dispersion and boosting PCL branching/crosslinking. We demonstrate that the melt processing control enables the preparation of targeted thermoplastic/thermoset bionanocomposites with gel content up to ≈ 40 %, identified as the limit of their melt-processability. Structural characterization reveals that ≈ 70 wt% of the initial CNC content is irreversibly incorporated in a percolating network, enhancing the crosslinked bionanocomposites properties. The bionanocomposites' complex viscosity and elastic character increase with the gel content, thus improving PCL melt performance. Furthermore, the irreversible entrapment of CNCs in the 3D percolating network provides heat-shrinkability, indicating a potential of the reacted bionanocomposites for heat-triggered shape-memory.

Lignin Valorization in Thermoplastic Biomaterials: From Reactive Melt Processing to Recyclable and Biodegradable Packaging

Lignin Valorization in Thermoplastic Biomaterials: From Reactive Melt Processing to Recyclable and Biodegradable Packaging

Substantial Effect of Water on Radical Melt Crosslinking and Rheological Properties of Poly(ε-Caprolactone).

One-step reactive melt processing (REx) via radical reactions was evaluated with the aim of improving the rheological properties of poly(ε-caprolactone) (PCL). In particular, a water-assisted REx was designed under the hypothesis of increasing crosslinking efficiency with water as a low viscous medium in comparison with a slower PCL macroradicals diffusion in the melt state. To assess the effect of dry vs. water-assisted REx on PCL, its structural, thermo-mechanical and rheological properties were investigated. Water-assisted REx resulted in increased PCL gel fraction compared to dry REx (from 1–34%), proving the rationale under the formulated hypothesis. From dynamic mechanical analysis and tensile tests, the crosslink did not significantly affect the PCL mechanical performance. Dynamic rheological measurements showed that higher PCL viscosity was reached with increasing branching/crosslinking and the typical PCL Newtonian behavior was shifting towards a progressively more pronounced shear thinning. A complete transition from viscous- to solid-like PCL melt behavior was recorded, demonstrating that higher melt elasticity can be obtained as a function of gel content by controlled REx. Improvement in rheological properties offers the possibility of broadening PCL melt processability without hindering its recycling by melt processing.

Rheological/thermal properties of poly(ethylene terephthalate) modified by chain extenders of pyromellitic dianhydride and pentaerythritol

AbstractDue to low molecular weight and wide molecular weight distribution, polyethylene terephthalate (PET) shows weak melt strength properties. In this study, the synergistic effect of using different types of chain extenders and catalyst on rheological behavior of PET has been investigated. Long‐chain branching is known as a suitable method for developing the structure of PET during reactive melt processing. Thus, pyromellitic dianhydride (PMDA) and pentaerythritol (PENTA) were added to the fiber grade PET. The best formulation was determined based on rheological results, which revealed an improvement in both storage modulus and complex viscosity of PMDA‐modified samples. Samples containing 1.5% PMDA and 0.5% PENTA exhibited the best rheological properties. Also, dibutyltin dilaurate (DBTDL) acted as an accelerator for chain extension reaction during reactive melt blending. Subsequently, the rheological properties were improved by increasing the chain extending rate. Moreover, thermal properties such as crystallization and melting temperatures and the degree of crystallinity for modified PET were investigated by differential scanning calorimetry.

Crystallization kinetics of chain extended poly(L-lactide)s having different molecular structures

Poly(l-lactide)s (PLLAs) with different chain structures were prepared by reactive melt processing and using Joncryl ADR as chain extender. Results of gel permeation chromatography (GPC) revealed that chain extended PLLAs had high molecular weights and two differentiated molecular weight distributions. Linear rheology was sensitive to the obtained molecular structures and revealed as the increase on the amount of chain extender gradually led to a decrease of the loss factor in the whole frequency region and to an increase of melt viscosity and both storage and loss moduli. In addition, the entanglement density increased significantly with addition of chain extender and had a significant influence on crystallization kinetics. Correlation of molecular weight, viscosity and entanglements changed the crystallinity and crystallization kinetics of chain extended PLLAs in both isothermal and non-isothermal crystallizations. Specifically, samples prepared from 1 wt-% of Joncryl (PLLA1R) revealed the highest nucleation and the fastest crystallization rate.

Reactive melt processing of poly (L-lactide) in the presence of thermoplastic polyurethane and carboxylated carbon nanotubes

In this study, two types of polymeric nanocomposite blends based on poly(l-lactide) (PLLA) and a thermoplastic polyurethane were prepared by reactive and non-reactive melt mixing. Multiwalled carbon nanotubes (MWCNTs) participated in reactive melt mixing and changed in both cases the morphology of blends. Melt rheology was used to study the influence of reactive melt mixing and localization of MWCNTs in terms of melt viscoelastic properties and relaxation time spectrum. Two relaxation times were observed for both types of blends due to reptation and stress release mechanism, although blends prepared by reactive melt mixing showed another relaxation mechanism associated with the generated interphase. Solid-state viscoelasticity determined by dynamical mechanical analysis showed significant influences of both MWCNTs and reactive melt mixing on storage modulus of the blends. Thermogravimetric analysis showed several degradation steps for polymer blends that contrast with the single step determined for both pure PLLA and PLLA nanocomposites.

Polyamide 6/reduced graphene oxide nano-composites prepared via reactive melt processing: formation of crystalline/network structure and electrically conductive properties

In this work, polyamide 6 (PA6)/reduced graphene oxide (RGO)- toluene-2,4-diisocyanate (TDI) composites were fabricated by reactive melt processing, and effect of formation of crystalline/network structure on electrically conductive properties of the composites was studied. The molecular bridge effect of exfoliated RGO-TDI resulted in the homogeneous dispersion of RGO in PA6 matrix. Crystallization analysis shows that RGO facilitated the crystallization of PA6 matrix mainly via accelerating the generation of crystal nucleus, reaching maximum of Xc and minimum of crystal grain size upon RGO level of 1.66 vol.%, which confirmed the formation of most perfect crystalline structure. According to the dynamic rheological analysis, both frequency-independence of G’ and sharply reduce phase angle at low-frequency region with RGO loading level of 1.66 vol.% indicate the transition from liquid-like to solid-like rheological behavior, where terminal to non-terminal transition as well as Cole-Cole arc and rapidly increasing entanglement density confirm the formation of percolation network structure with RGO as a crosslinking center. Corresponding to the analysis above, the electrical conductivity of the nano-composites increased rapidly to the equilibrium value, resulting from the formation of perfect conductive network at RGO loading level of 1.66 vol.%, which was confirmed by TEM analysis.

Preparation of long‐chain branched poly(ethylene terephthalate): Molecular entanglement structure and toughening mechanism

Poly(ethylene terephthalate) (PET) was long‐chain branched (LCB) by ring‐opening reaction with both pyromellitic dianhydride and tetrahydrophthalic acid diglycidyl ester as chain extenders through reactive melt processing. It was found that with the increase of chain extenders dosage, the intrinsic viscosity of PET increased and melt index decreased greatly, while both the tensile strength and impact strength of PET were remarkably improved. The elastic modulus (G′) and viscous modulus (G″) were enhanced by chain branching. Compared with PET, the complex viscosities of LCB‐PET were much higher at full frequency range, and obvious shear thinning was presented. The Cole–Cole curve deviated from the semicircular shape and the curve end was inclined to upward in high viscosity region, indicating the formation of the multiple hierarchical structures. The molecular weight of the branch (MB) was much greater than critical entanglement molecular weight (M e), which essentially confirmed the existence of LCB structure and fairly strong molecular entanglement in the LCB‐PET molecular chain. When subjected to external force, the entanglement point, acting as physical crosslinking point between the molecules, was in favor of increasing the molecular interaction, reducing the molecular slippage, and bearing a large deformation. POLYM. ENG. SCI., 59:1190–1198 2019. © 2019 Society of Plastics Engineers

Fabrication of polyamide 6/reduced graphene oxide nano-composites by conductive cellulose skeleton structure and its conductive behavior

Benefited from hierarchical porous structure of Loofah sponge (LS) fibers, a 3D electrically and thermally conductive network structure termed conductive cellulose skeleton (Cellulose-RGO-TDI) was fabricated. In addition, PA6 molecular chains were covalently bonded with conductive cellulose skeleton by reaction between imino groups of PA6 and isocyanate groups of Cellulose-RGO-TDI. As a result, PA6/Cellulose-RGO-TDI nano-composite with high electrical and thermal conductivity was fabricated via reactive melt processing. Both RGO outside the fiber and RGO inside the 3D-bundled micro-channel work together to assemble omnibearing trans-scale conductive networks in the whole hierarchical porous structure of the cellulose skeleton. Finally, more integral conductive pathways are established by RGO along the cellulose fiber, which is more beneficial to transmission of charge carrier and phonons in the whole cellulose skeleton. Exfoliated RGO nano-sheets homogeneously dispersed between matrix and cellulose skeleton and a good interface forms, which promoted formation of electrically and thermally conductive network, resulting in the remarkably improved electrically conductivity of 5.8 × 10−1 S/m and thermally conductivity of 0.419 W m−1 K−1 of the composite with 1.2 vol% RGO loading.

Reactive melt processing of polyamide 6/reduced graphene oxide nano-composites and its electrically conductive behavior

Based on the industrialized reduced graphene oxide (RGO) product, the graphene precursor of RGO-TDI with reactive sites of isocyanate groups was prepared with high grafting ratio, and a series of PA6/RGO-TDI composites were prepared via reactive melt processing. The PA6 molecules were confirmed to reactively intercalate into RGO layers through covalent and hydrogen bonding, which had high grafting ratio and layer thickness, exhibiting almost monolayer dispersion state. The molecular bridge effect of exfoliated RGO-TDI lowered activation energy of electrically conductive network formation, which resulted in a rapid increase of electrical conductivity of the composites with a low threshold percolation.

Water‐dispersive PLA‐based materials: from reactive melt processing to properties

Melt blending of poly(l‐lactide) (PLLA) and water‐soluble polymers was carried out through reactive melt processing with the objective to prepare water‐dispersible PLLA‐based materials. For this purpose, both polyvinyl alcohol (PVOH) and hydroxyethyl cellulose (HEC) were considered. Prior to melt blending, the preparation of plasticized PVOH and plasticized HEC was performed. The so‐obtained blends have been characterized in terms of morphology and thermomechanical properties. The morphological analysis evidenced the possibility to prepare co‐continuous PLLA/plasticized HEC blends. Nevertheless, their low melt strength did not allow producing monofilaments by melt spinning. Thus, PVOH was considered as an alternative to HEC. The results showed that using maleic anhydride‐grafted polylactide as a compatibilizer for PLLA/plasticized PVOH 40/60 (w/w) blends allowed preparing co‐continuous blends leading to tough monofilaments with high ultimate elongation. Moreover, the assessment of the water dispersiveness revealed that the monofilaments readily swelled in water and started to break up after 30 min. A full fragmentation of the monofilaments was observed within 1 hr. Copyright © 2015 John Wiley & Sons, Ltd.

Study of Reactive Melt Processing Behavior of Externally Plasticized Cellulose Acetate in Presence of Isocyanate.

Two types of externally plasticized cellulose acetate (CA) were chemically modified using 4,4'-methylene diphenyl diisocyanate (MDI) as crosslinking agent. Crosslinking was performed in the molten state by means of melt mixing in an internal mixer. The viscoelastic properties of the non-crosslinked, externally plasticized CA show typical temperature dependence, similar to conventional thermoplastics. A strong increase in storage modulus is observed with increasing crosslink density indicating that the crosslinked compounds exhibit predominately elastic response. The complex viscosity also increases considerably with increasing crosslink density and does not reach the typical Newtonian plateau at low radial frequencies any more. The viscoelastic properties correlate well with the data recorded online during reactive melt processing in the internal mixer. In comparison to the non-crosslinked CA, the crosslinked compounds show higher glass transition temperature, higher VICAT softening temperatures, improved thermal stability and lower plasticizer evaporation at evaluated temperatures.

Peroxide induced cross‐linking by reactive melt processing of two biopolyesters: Poly(3‐hydroxybutyrate) and poly(l‐lactic acid) to improve their melting processability

ABSTRACTPoly(3‐hydroxybutyrate) (PHB) and poly(l‐lactic acid) (PLLA) were individually cross‐linked with dicumyl peroxide (DCP) (0.25–1 wt %) by reactive melt processing. The cross‐linked structures of the polymer gel were investigated by nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopies. The size of the polymer crystal spherulites, glass transition temperature (Tg), melting transition temperature (Tm), and crystallinity were all decreased as a result of cross‐linking. Cross‐linking density (νe) was shown to increase with DCP concentration. Based on parallel plate rheological study (dynamic and steady shear), elastic and viscous modulus (G″ and G′), complex viscosity (η*) and steady shear viscosity (η) were all shown to increase with cross‐linking. Cross‐linked PHB and PLLA showed broader molar mass distribution and formation of long chain branching (LCB) as estimated by RheoMWD. Improvements in melt strength offer bioplastic processors improved material properties and processing options, such as foaming and thermoforming, for new applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41724.

Grafted d/l-lactide to cellulose acetate by reactive melt processing: Its role as CA/PLA blend compatibilizer

Cellulose acetate (CA) with a degree of substitution (DS) of 2.5 and polylactic acid (PLLA) were plasticized by melt extrusion using triacetin. Blends of resulting thermoplastic materials were then prepared and characterized by their tensile strength and differential scanning calorimetry (DSC). Thermal analysis revealed the invariability of the PLLA glass transition temperature in all blends, indicating that the compounds were immiscible. Grafted d/l lactide to CA copolymers were prepared by reactive melt processing using CA with different degree of substitution i.e. 2.1 and 2.5 and evaluated as CA/PLLA blend compatibilizer. The compatibility of the blends was investigated by scanning electron microscopy (SEM). Results showed that blend compatibility was improved evidencing the best performance of grafted copolymers with long grafted chains as blend compatibilizer of CA/PLLA blends. Finally, compatibilized blends compositions with enhanced ultimate elongation were achieved by using plasticized PLLA instead of neat PLLA.

Novel poly(ester-urethane)s based on polylactide: From reactive extrusion to crystallization and thermal properties

The synthesis of novel poly(ester-urethane)s (PEUs) based on polylactide was carried out. It was performed by a catalysed two-step reaction process, i.e., ring-opening polymerization (ROP) and chain extension reaction in bulk. For this purpose, α,ω-dihydroxyl PLA macrodiols were synthesized by catalysed ROP and employed as precursors that reacted in the melt with 4,4′-diisophenylmethane diisocyanate (MDI) and 4,4′-diaminodiphenylmethane (MDA) as coupling agent and chain extender, respectively. The PEUs were characterized by DSC, Polarized Light Optical Microscopy and X-ray techniques. The PEUs were generally characterized by higher cold crystallization temperature, lower melting temperature and slower cold crystallization kinetics as compared to the PLA precursors. The Avrami equation modelled the entire isothermal cold crystallization process. The synthesis variables that had the largest impact on the crystallization and thermal properties of the PEUs were the molecular weight of the PLA precursors and the [NCO]/[OHPLA + NH2] ratio, which could be readily tailored by the investigated reactive melt-processing.