Cast Film Extrusion Research Articles

Characterization, processing, and modeling of industrial recycled polyolefins

AbstractThis study aims to establish a systematic approach for characterizing recycled polyolefins of unknown composition, with a specific focus on predicting their performance in film extrusion. We explore various characterization techniques, including differential scanning calorimetry (DSC), Fourier‐transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and rheometry to assess their effectiveness in identifying the polyethylene (PE) fractions within polypropylene (PP) recyclates. By integrating experimental data with modeling techniques, we aim to provide insights into the predictive capabilities of these techniques in determining processing behaviors. The research highlights the superior fidelity of DSC in predicting the relative fraction and type of PE in a PP recyclate. FTIR is also identified as a high‐fidelity approach, albeit requiring application‐specific calibration. TGA, capillary, and oscillatory rheometry are recognized for their ability to distinguish between grades of recycled polyolefins but provide aggregate behaviors rather than detailed constituent information. 3D flow simulation of the cast film extrusion investigated the effect of the viscosity characterization method, non‐isothermal assumption, and process settings but could not fully replicate the observed variations in the cast film processing of two industrial polyolefins with similar melt flow rates and viscosity behaviors. This underscores the practical challenge of predicting processing issues prior to actual processing, necessitating reliance on reliable instrumentation suites and human expertise for diagnosing and remedying variations.Highlights Two industrial recycled polypropylene materials having similar melt flow rates exhibit drastically different cast film processing behaviors. DSC and FTIR provide reasonable approaches for identifying constituent materials. Modeling of the melt viscosities characterized by capillary and parallel plate rheology suggests that viscosity variations relative to the power‐law behavior assumed in the coat hanger die design is a predominant driver of cast film instabilities.

Progress in the Preparation and Application of Breathable Membranes.

Breathable membranes with micropores enable the transfer of gas molecules while blocking liquids and solids, and have a wide range of applications in medical, industrial, environmental, and energy fields. Breathability is highly influenced by the nature of a material, pore size, and pore structure. Preparation methods and the incorporation of functional materials are responsible for the variety of physical properties and applications of breathable membranes. In this review, the preparation methods of breathable membranes, including blown film extrusion, cast film extrusion, phase separation, and electrospinning, are discussed. According to the antibacterial, hydrophobic, thermal insulation, conductive, and adsorption properties, the application of breathable membranes in the fields of electronics, medicine, textiles, packaging, energy, and the environment are summarized. Perspectives on the development trends and challenges of breathable membranes are discussed.

Effect of screw speed in compounding of poly(butylene adipate‐co‐terephthalate)/thermoplastic starch blends and their processability by cast extrusion

AbstractBlends of bio‐polyesters cover a wide percentage of the market share and possess properties comparable to the ones of conventional polymers. Poly(butylene adipate‐co‐terephthalate) (PBAT) is a fossil‐based compostable bioplastic, which possess good mechanical properties and processability. Blending PBAT with thermoplastic starch (TPS) allows to lower the cost of the final products and to increase the amount of bioderived material. The influence of the processing parameters on the morphology and on the mechanical properties of PBAT/TPS blends is studied. The compounds were produced via twin‐screw extrusion and then films were produced via cast film extrusion. The quality of the dispersion is strongly related to the screw speed adopted during the compounding process. The quality of the film and their processability depend on the parameters adopted during the compounding process.

Kinetic migration of PBS and PBSA biopolymers prepared by cast film extrusion and biaxial stretching: A combined experimental and modeling approach

AbstractThe kinetic migration of poly(butylene succinate) (PBS) and poly(butylene succinate‐co‐adipate) (PBSA) biopolymers, prepared by cast film extrusion (thin film) and biaxial stretching (biaxially oriented [BO] film) techniques, were investigated based on experimental and mathematical modeling. MATLAB coding was used to fit the migration data to a diffusion model. BO films significantly reduced the migration rate compared with thin films, with reductions of 29% and 41% for BO‐PBS and BO‐PBSA, respectively, due to the increased degree of molecular crystallinity. Higher ethanol content increased the quantity of substance diffusing from plastic film. PBS and PBSA are more suitable for packaging hydrophilic foods than alcoholic beverages. PBS exhibited a lower migration rate than PBSA due to its more rigid polymer matrix. Remarkably, BO‐films exhibited 31% and 41% lower diffusion coefficients (D) compared with thin films, but significantly higher partition coefficients (KP,F) by 44% and 267% for BO‐PBS and BO‐PBSA, respectively. This suggests a stronger affinity of migrant for BO film matrix. However, at 70°C, PBSA films may be hydrolyzed with a high ethanol, resulting in an inadequate diffusion model. The diffusion–reaction concept should be implemented for a better fit. These findings provide valuable insights for selecting appropriate packaging materials and predicting migration under diverse conditions, ultimately promoting consumer safety.

Upcycling of post-industrial starch-based thermoplastics and their talc-filled sustainable biocomposites for single-use plastic alternative

This study utilized post-industrial wheat starch (biological macromolecule) for the development of poly(butylene adipate-co-terephthalate) (PBAT) based thermoplastic starch blend (TPS) and biocomposite films. PBAT (70 wt%) was blended with plasticized post-industrial wheat starch (PPWS) (30 wt%) and reinforced with talc master batch (MB) (25 wt%) using a two-step process, consisting of compounding the blend for pellet preparation, followed by the cast film extrusion at 160 °C. The effect of the chain extender was analyzed at compounding temperatures of 160 and 180 °C for talc-based composites. The incorporation of talc MB has increased the thermal stability of the biocomposites due to the nucleating effect of talc. Moreover, tensile strength and Young's modulus increased by about 5 and 517 %, respectively as compared with the TPS blend film without talc MB. Thermal, rheological, and morphological analyses confirmed that the use of talc in the presence of chain extender at a processing temperature of 160 °C has resulted in an enhanced dispersion of talc and chain entanglement with PBAT and PPWS than PBAT/PPWS blend and PBAT/PPWS/Talc composite films. On the other hand, at 180 °C, the talc-containing biocomposite with chain extender tended to form PPWS agglomerates, thereby weakening its material properties.

Real-time structural characterization of isotactic polypropylene during cast film extrusion

Understanding the crystallization behavior of semi-crystalline polymers during processing is key to achieve the desired material performances. Isotactic polypropylene characteristics are highly tunable and easy to adjust by changing the processing conditions thanks to its structural versatility and polymorphic behavior. Hereby, we performed for the first time ever a challenging real-time X-ray characterization of isotactic polypropylene during the cast film extrusion process by interfacing a compact cast film extruder machine with a synchrotron line.We report data of excellent quality recorded from the contact point between the just extruded polymer melt and the water-refrigerated cooling roll further down to the cooling roll line by using a grazing incidence scattering geometry. The explored cooling roll temperatures (from 70 °C to 15 °C) allowed to produce iPP films with defined structural composition, from α to mesophase.Evolution of the phase crystallinity as a function of the contact time between the polymer melt and the cooling roll clearly shows the presence of three crystallization zones: 1) an amorphous zone, 2) a frostline zone and lastly 3) a high-crystallinity zone. In the end, the experimental data have been matched with simulated data using a simple crystallization kinetics model, finding a good agreement in terms of crystalline development over the investigated time scale.As a closing remark, we hope that our effort will spark new interest in the real-time characterization of semi-crystalline materials and that will ultimately be utilized as a starting point to optimize and expand the characterization of these extremely important materials.

Oxygen Scavenger and Antioxidant LDPE/EVOH/PET-Based Films Containing β-Carotene Intended for Fried Peanuts (Arachis hypogaea L.) Packaging: Pilot Scale Processing and Validation Studies.

The aim of this study was to develop an oxygen scavenger and antioxidant active packaging material for fried peanuts. The packaging solution, which has been made at the laboratory previously, has been developed by cast film extrusion and is composed of low-density polyethylene-ethylene vinyl alcohol-polyethylene terephthalate (LDPE/EVOH/PET)-based films containing β-carotene (CAR). In comparison with film without additive, developed film presented an orange colouring (higher L* and b* values and lower a* values) and an increase in oxygen induction time (OIt) from 4.5 to 14.1 min. The incorporation of β-carotene to the formulation also brings about a significant effect on the thermal stability as maximum degradation temperatures increased around 1%. Regarding the oxygen absorption capacity of the films, values of 1.39 ± 0.10 mL O2 per g of film at laboratory scale and 1.7 ± 0.3 mL O2 per g of multilayer (ML)/LDPE_CAR were obtained, respectively, after 3 days, proving the suitability of the packaging solutions as oxygen absorbers. To validate the packaging solution, the oxidative stability of fried peanuts packed in fabricated multilayer β-carotene bags was evaluated for 3 months at 40 °C. The hexanal content remained constant during this period. Meanwhile, peanuts packed in ML without β-carotene increased their hexanal content to 294%. This fact indicated a lower extent of oxidation in fried peanuts compared to food samples packaged in control films, suggesting the potential of ML/LDPE_CAR films as sustainable and antioxidant food packaging systems to offer protection against lipid oxidation in foods. Sensory evaluation confirmed that ML/LDPE_CAR films provided the peanut samples with an extra aroma due to the volatile degradation products of β-carotene (such as β-cyclocitral or 6-methyl-5-hepten-2-ol).

Stretchability and Deformation Behavior of Polybutylene Adipate-co-terephthalate Blend Films

The single use packaging is widely used in various products; ranging from food to non-food contact, from commodity to specialty purposes. Most of these materials are derived from non-renewable fossil resources. In a sustainable manner, it needs to be recyclable or compostable. Good mechanical properties together with biodegradability can make the product more recyclable. In this study, the elasticity for films consisting of polybutylene adipate-co-terephthalate (PBAT) blended with polylactic acid (PLA) (10, and 20 %wt), additive and reactive agents were evaluated. The blends were prepared via a twin-screw extruder. The film specimens were prepared by cast film extrusion. The films were then stretched with different ratios (1.5, 2 and 2.5 times) by the uniaxial machine. The mechanical properties, elasticities and surface morphology of uniaxially stretched PBAT and PBAT blend films were characterized by tensile testing and scanning electron microscope (SEM), respectively. The tensile strength of stretched films tended to improve while the elongation at break reduced at higher stretching ratios. The surface morphology of stretched films revealed that the degree of orientation was increased after higher stretching ratios. The ability to recover in the plastic deformation region of stretched films was increased at the higher stretching ratios.

Enhanced Performance of Polylactide Film via Simultaneous Biaxial Stretching and Silane Coupling Agent as a Thermal Shrinkable Film

Biaxial stretching technique has been known to improve the toughness of polylactide (PLA) film. Furthermore, blending with an additive is another way to control the mechanical properties of the product. The integrated effect of simultaneous biaxial stretching and blending with silane coupling agent on the properties of PLA film is examined in this study. The PLA pellets are melt compounded with various amounts of 3-aminopropyltriethoxy silane (APS). Then, the films are prepared by cast film extrusion and simultaneous biaxial stretching process with a stretching speed of 75 mm s–1. The relationships among the crystallinity, tensile properties, and thermal shrinkage of the prepared films are investigated. The crystallinity of PLA is significantly induced in the film by the stretching technique. An increase in the additive content also facilitates the polymeric crystallinity. The elongation at the break of the biaxially stretched film increases with the additive content, which corresponds with the PLA crystallinity. Compared to the pristine PLA film, the addition of 1% APS improves tensile strength in a transverse direction of the film about 10 times. The thermal shrinkage of the obtained films was evaluated to assess their applications as heat-shrinkable films. The prepared films show a thermal shrinkage of 45%, which are comparable to that of a commercial shrink film.

Production of a PET//LDPE Laminate Using a Reversibly Crosslinking Packaging Adhesive and Recycling in a Small-Scale Technical Plant

Multilayer packaging is an important part of the packaging market, but it is not recyclable with conventional methods since it is made of different thermodynamically immiscible materials. In this work, it was shown that it is possible to produce a PET//LDPE laminate in a pilot plant for lamination by using an adhesive consisting of maleimide- and furan-functionalized polyurethane prepolymers that cure through the Diels–Alder reaction. The material could then be delaminated in a small-scale recycling plant using a solvent-based recycling process by partially opening the Diels–Alder adducts through the influence of temperature. The PET and LDPE could be recovered without any adhesive residues before each material was regranulated, and in the case of the PE, a film was produced via cast film extrusion. The obtained PET granulate exhibited a slight, approximately 10%, decrease in molecular weight. However, since small amounts of LDPE could not be separated, compatibilization would still be required here for further use of the material. The obtained LDPE film was characterized by means of infrared spectrometry, differential scanning calorimetry, tensile testing, determination of the melt index, and molecular weight. The film showed lower crosslinking than usual for LDPE recycling and exhibited good mechanical properties. In this work, it was thus shown that upscaling of the laminate production with the modified adhesive and also its recycling at the pilot plant scale is possible and thus could be an actual option for recycling multilayer packaging.

Double-Function Oxygen Scavenger and Aromatic Food Packaging Films Based on LDPE/Polybutadiene and Peanut Aroma.

The aim of this study was to develop a double function active packaging material for nuts. The packaging solution, on the one hand, integrated polybutadiene (PB) as an oxygen scavenger and, on the other hand, it incorporated peanut aroma (PA) to improve customer’s sensorial experience. Different formulations based on low density polyethylene (LDPE), commercial PA (5 wt %) and PB at two levels (5 wt % and 13 wt %) were obtained by cast film extrusion. The obtained films were compared in terms of their mechanical, structural, optical and thermal properties confirming a plasticizing effect of PA and PB resulting in an increase in the ductility of the polymer and in a slight decrease in the thermal properties, maintaining their transparency. Regarding the oxygen capacity of the films, values of 4.4 mL and 2.7 mL O2 g−1 film were obtained for PE/PA/PB13 and PE/PA/PB5, respectively, after 6 days proving the suitability of the UV irradiation treatment in improving the oxygen absorption capacity of PB without the need of a metal catalyst. The aroma retention capacity into the polymer matrix was also evaluated in the developed formulations. The incorporation of PB in 13 wt % into a LDPE matrix improved the PA retention. This behavior was attributed to the ability of PB in enhancing cross-linking of LDPE as the concentration of PB increases. The results suggested the potential of PE/PB/PB13 films as oxygen scavenger and aromatic food packaging system to offer protection against lipid oxidation in nuts.

Structure-property-processing relationships in extruded liquid crystal polymer film

Liquid crystal polymers (LCPs) derive favorable mechanical, chemical, and electrical behavior from long-range molecular ordering. The microstructure gives rise to anisotropic bulk properties that are problematic for industrial applications, and thus the ability to model the polymer directionality is essential to the design of isotropic material manufacturing processes. This investigation proposes a modeling methodology to simulate the 3D director field in full-scale film extrusion geometries. Wide-angle x-ray scattering (WAXS) is used to validate the predicted orientation for a standard coat-hanger die, and is compared with macroscopic mechanical, thermal, and dielectric testing of LCP film to illustrate the morphological dependence of the polymer properties. The highly anisotropic orientation state resulting from cast film extrusion is both predicted by the model and confirmed experimentally, and this preferred orientation is shown to correlate with observed anisotropy in the bulk properties. Additionally, a practical implementation of the modeling tool is presented to simulate directionality in two alternative die geometries designed to improve bulk isotropy, and it is demonstrated that the model is capable of simulating the resulting order for large, irregular domains typical of industrial processing.

Multi-Micro/Nanolayer Films Based on Polyolefins: New Approaches from Eco-Design to Recycling

This paper describes a future-oriented approach for the valorization of polyethylene-based multilayer films. The method involves going from eco-design to mechanical recycling of multilayer films via forced assembly coextrusion. The originality of this study consists in limiting the number of constituents, reducing/controlling the thickness of the layers and avoiding the use of tie layers. The ultimate goal is to improve the manufacturing of new products from recycled multilayer materials by simplifying their recyclability. Within this framework, new structures were developed with two polymer systems: polyethylene/polypropylene and polyethylene/polystyrene, with nominal micro- and nanometric thicknesses. Hitherto, the effect of the multi-micro/nanolayer architecture as well as initial morphological and mechanical properties was evaluated. Several recycling processes were investigated, including steps such as: (i) grinding; (ii) monolayer cast film extrusion; or (iii) injection molding with or without an intermediate blending step by twin-screw extrusion. Subsequently, the induced morphological and mechanical properties were investigated depending on the recycling systems and the relationships between the chosen recycling processes or strategies, and structure and property control of the recycled systems was established accordingly. Based on the results obtained, a proof of concept was demonstrated with the eco-design of multi-micro/nanolayer films as a very promising solution for the industrial issues that arise with the valorization of recycled materials.

Effect of Filler Synergy and Cast Film Extrusion Parameters on Extrudability and Direction-Dependent Conductivity of PVDF/Carbon Nanotube/Carbon Black Composites.

In the present study, melt-mixed composites based of poly (vinylidene fluoride) (PVDF) and fillers with different aspect ratios (carbon nanotubes (CNTs), carbon black (CB)) and their mixtures in composites were investigated whereby compression-molded plates were compared with melt-extruded films. The processing-related orientation of CNTs with a high aspect ratio leads to direction-dependent electrical and mechanical properties, which can be reduced by using mixed filler systems with the low aspect ratio CB. An upscaling of melt mixing from small scale to laboratory scale was carried out. From extruded materials, films were prepared down to a thickness of 50 µm by cast film extrusion under variation of the processing parameters. By combining CB and CNTs in PVDF, especially the electrical conductivity through the film could be increased compared to PVDF/CNT composites due to additional contact points in the sample thickness. The alignment of the fillers in the two directions within the films was deduced from the differences in electrical and mechanical film properties, which showed higher values in the extrusion direction than perpendicular to it.

Systematic Investigation on the Structure-Property Relationship in Isotactic Polypropylene Films Processed via Cast Film Extrusion.

The effect of cast film extrusion processing conditions, such as the chill-roll temperature, temperature of the melt, and line speed, on the structure of different isotactic polypropylene homo- and random copolymers has been investigated by means of Small- and Wide-Angle X-ray Scattering (SAXS and WAXS) and correlated to stiffness and haze. Stiffness and transparency have been found to be strongly dependent on the temperature of the chill-roll. Interestingly, line speed has been found to affect the total crystallinity when the chill-roll temperature is increased, while an overall minor effect of the melt temperature was found for all cast films. The polymer characteristics, defined by the catalyst nature and comonomer content, affect the final material performance, with the single-site catalyzed grades performing better in both mechanics and optics. Haze levels were found to correlate with the mesophase content rather than to α-crystallinity and to be dependent on the domain size for all grades. The remarkably low haze levels reached by the single-site grade with higher isotacticity can arise from high nucleation rate and orientational effects, which ultimately yield smaller and smoother scattering domains.

A Novel Simple Approach to Material Parameters from Commonly Accessible Rheometer Data.

When characterizing the viscoelastic properties of polymers, shear rheological measurements are commonly the method of choice. These properties are known to affect extrusion and nozzle-based processes such as fiber melt spinning, cast film extrusion and 3D-printing. However, an adequate characterization of shear thinning polymers can be challenging and still insufficient to not only describe but predict process relevant influences. Furthermore, the evaluation of rheological model systems in literature is mostly based on stress–relaxation experiments, which are rarely available for various polymeric materials. Therefore, a simple approach is presented, that can be used to evaluate and benchmark a wide range of rheological model systems based on commonly accessible frequency sweep data. The approach is validated by analyzing alginate PH176 solutions of various concentrations, a thermoplastic poly-urethane (TPU) Elastollan 1180A melt, the liquid silicon rubber Elastosil 7670 and a polycaprolactone (PCL) fiber-alginate composite system. The used rheological model systems, consisting of simple springs and dashpots, are suitable for the description of complex, viscoelastic material properties that can be observed for polymer solutions and gel-like systems. After revealing a suitable model system for describing those material properties, the determination and evaluation of relevant model parameters can take place. We present a detailed guideline for the systematic parameter revelation using alginate solutions of different concentrations as example. Furthermore, a starting point for future correlations of strut spreading in 3D-bioprinting and model parameters is revealed. This work establishes the basis for a better understanding and potential predictability of key parameters for various fabrication techniques.

Reactive extrusion of sustainable PHBV/PBAT-based nanocomposite films with organically modified nanoclay for packaging applications: Compression moulding vs. cast film extrusion

The mechanical, thermal and barrier properties of a sustainable PHBV/PBAT blend was investigated under the influence of organically modified nanoclay (0.6, 1.2 and 1.8 wt%) after processing by two different techniques i.e. compression moulding and cast film extrusion. Firstly, a pelletized nanoclay masterbatch was fabricated by blending PBAT with 20% nanoclay using melt extrusion. The masterbatch was used as a reinforcement phase for the PHBV/PBAT blend matrix to fabricate nanocomposite pellets using a melt extrusion process. The prepared PHBV/PBAT/Nanoclay nanocomposite pellets were used to fabricate films using compression moulding and cast film extrusion. The cast extruded PHBV/PBAT nanocomposite films showed improved barrier properties (oxygen and water vapour) as compared to compression moulded films because of the chain orientation during the high-speed stretching. The barrier properties results showed significant improvement of ~79 and ~70% in oxygen and water vapour permeability respectively in cast PHBV/PBAT composite films after adding 1.2 wt% nanoclay, which indicates a good dispersion of nanoclay and strong interfacial adhesion between the matrix and filler. The intercalation/exfoliation of nanoclay in PHBV, as well as at the interface of the PHBV and PBAT blend matrix, was confirmed by transmission electron microscopy (TEM). The % elongation at break (567.6 ± 0.1) of the cast PHBV/PBAT/Nanoclay(1.2%) nanocomposite film was highly improved as compared to that of the PHBV/PBAT blend due to better stress transfer ability as compared to the compression moulded film. The rheological properties also support better dispersion of nanoclay and interaction between the matrix and filler. Hence, the cast extruded nanocomposite film with 1.2% nanoclay is a potential candidate to be used in flexible packaging.

Fabrication of Poly(Butylene Succinate) Composite Films with Silver Doped ZSM-5: Effect of Silver ZSM-5 on Antibacterial Activity and Biodegradable Behavior

This work was focused on the effects of filler concentration on the antibacterial activity and biodegradable behavior of poly (butylene succinate) (PBS) composite films containing silver exchanged zeolite ZSM-5 (SZSM-5). The composite films were prepared by chill roll cast film extrusion, by varying the silver zeolite content from 0.5 to 4 %wt. The silver content in zeolite was examined by energy dispersive X-ray spectroscopy (EDX). The morphology and crystal structure of silver zeolite were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) technique, respectively. The incorporation of silver did not influence the zeolite morphology and its crystal structure. The antibacterial action of composite films was investigated against gram-negative Escherichia coli and gram-positive Staphylococcus aureus. The results revealed that the PBS composite films containing SZSM-5 showed 99.9% of bacterial reduction. The optimal SZSM-5 content in PBS composite films was 0.5%wt because it was the lowest concentration that showed high efficiency of antibacterial behavior. In case of biodegradable ability, PBS composite films incorporated with 0.5%wt of SZSM-5 exhibited the degradation after three-month of soil burial test, although they exhibited slower rate than neat PBS films. The SEM micrographs of the films after soil burial test displayed the cavity on film surface, indicating the biodegradable properties of the films. PBS composite films incorporated with 0.5%wt of SZSM-5 showed the potential to be used as the food packaging.

Thermal and barrier properties of poly(butylene adipate-coterephthalate) incorporated with zeolite doped potassium ion for packaging film

In this research, the works were focused on development of film packaging of poly(butylene adipate-co-terephthalate) (PBAT) incorporated with modified zeolite using (3-aminopropyl) trimethoxysilane. PBAT composites were compounded by melt mixing using twin screw extrusion then molded into film by cast film extrusion process. Effects of zeolite 13X at 1 wt% and zeolite doped potassium ion (K+) on thermal properties, permeability of gases (oxygen, carbon dioxide and water vapor) and also absorption of ethylene gas of PBAT composites films have been studied. Typically, zeolite would act as a nucleating agent. Therefore, adding zeolite would increase the degree of crystallinity of PBAT. Comparing zeolite with and without cation exchange, the degree of crystallinity in film tended to increase for the one doped with potassium ion. Either zeolite with or without potassium exchange had no impact on thermal stability of composite films. Gas permeation of PBAT/zeolite film possessed lower permeation of oxygen and carbon dioxide whereas the water vapor transmission showed relatively higher rate than the neat PBAT. After cation exchange with zeolite, the permeation of oxygen and carbon dioxide has reduced 21.04% and 21.90% respectively but the effect of K+ exchange had no effect on water vapor transmission compared with PBAT. Film of PBAT and zeolite doped with cation could absorb ethylene gas more than the one with zeolite.

Transparent, Lightweight, and High Strength Polyethylene Films by a Scalable Continuous Extrusion and Solid‐State Drawing Process

AbstractThe continuous production of transparent high strength ultra‐drawn high‐density polyethylene films or tapes is explored using a cast film extrusion and solid‐state drawing line. Two methodologies are explored to achieve such high strength transparent polyethylene films; i) the use of suitable additives like 2‐(2H‐benzotriazol‐2‐yl)‐4,6‐ditertpentylphenol (BZT) and ii) solid‐state drawing at an optimal temperature of 105 °C (without additives). Both methodologies result in highly oriented films of high transparency (≈91%) in the far field. Maximum attainable modulus (≈33 GPa) and tensile strength (≈900 MPa) of both types of solid‐state drawn films are similar and are an order of magnitude higher than traditional transparent plastics such as polycarbonate (PC) and poly(methyl methacrylate). Special emphasis is devoted to the effect of draw down and pre‐orientation in the as‐extruded films prior to solid‐state drawing. It is shown that pre‐orientation is beneficial in improving mechanical properties of the films at equal draw ratios. However, pre‐orientation lowers the maximum attainable draw ratio and as such the ultimate modulus and tensile strength of the films. Potential applications of these high strength transparent flexible films lie in composite laminates, automotive or aircraft glazing, high impact windows, safety glass, and displays.