Chill Roll Temperature Research Articles

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.

Development of Breathable Films from Blends of Low-Density Polyethylene and Thermoplastic Polyester Elastomer

The main drawback of low-density polyethylene (LDPE) film for packaging of fresh fruit or vegetables is low moisture breathability. This study developed breathable films by blending LDPE with thermoplastic polyester elastomer (TPEE). LDPE and TPEE in the weight ratios of 95/5, 90/10, 80/20, 70/30, and 60/40 wt% were melt blended and then extruded into films using a cast film extruder. Clarity of films was characterized by UV-VIS spectroscopy. Tensile properties, tear resistance, the degree of crystallinity, and morphology of blend films were evaluated. Water vapour transmission rate (WVTR) was investigated using a desiccant method. The prepared films were transparent. However, the UV-VIS transmittance was reduced slightly. Blending TPEE of more than 10 wt% reduced the modulus but increased elongation at break. It did not impact on the tensile strength of the blends. Since LDPE and TPEE are immiscible, applied stress during extrusion pulled them apart at the interphase boundaries creating micro-pores. As a result, these micro-pores reduce tear resistance significantly but increase WVTR of the blend films. Using a blend ratio of 90/10 wt%, the effect of chill-roll temperature and nip-roll velocity on film properties were studied. It was found that nip-roll velocity had more influence on WVTR than chill-roll temperature due to elongation of the pores.

Crystal structure: a way to control properties in cast films of polypropylene

The efficiency of the degree of cooling and shear-induced crystallization on the formation of different crystal polymorphs and morphology development of isotactic polypropylene (iPP) and random propylene–ethylene copolymer was analysed in cast films. Wide-angle X-ray scattering was applied to evaluate the crystal structure formed in films solidified at different chill roll temperatures (15, 40, and 70 °C) and throughputs of the line (60 and 120 kg/h). The crystal geometry and morphology were visualized by atomic force microscopy. For films generated at 15 °C or at large supercooling together with the nodular domain additional grained round-shaped structures composed of mesophase were detected on the film surface. Increase of the chill roll temperature or lower supercooling allowed formation of the monoclinic phase of iPP. Higher drawing rate triggered crystal formation preferably on the surface of films quenched at 15 °C. The crystal structure and morphology were correlated to selected optical and mechanical properties. At close-to-identical crystallinity, the crystal aspect ratio and film roughness play a major role in controlling the film transparency and stiffness.

Control of Chain Orientation in Blends of Polypropylene and Polybutene‐1

An extruded sheet having unique molecular orientation is developed using a miscible blend of isotactic polypropylene (PP) and isotactic polybutene‐1 (PB). Blends containing a small amount of N,N′‐dicyclohexyl‐2,6‐naphthalenedicarboxamide are extruded from a ribbon‐shaped die onto a chill roll at various temperatures. It is found that form‐I crystals of PB become oriented in the flow direction, whereas β‐form crystals of PP become oriented perpendicular to the flow direction. The molecular orientation is the most obvious for the blend containing 60 wt% of PB extruded at a chill roll temperature of 80 °C. The anisotropy in the tensile modulus of the obtained extruded sheet is reduced by its extraordinary molecular orientation. image

Crystallization and Mechanical Properties of Polypropylene under Processing-Relevant Cooling Conditions with respect to Isothermal Holding Time

For semicrystalline thermoplastics, aside from pressure and shear, the temperature-time behavior while cooling the melt significantly affects the geometry and degree of ordered structures (e.g., spherulite size, degree of crystallization, and crystal modification) and, as a consequence, the resulting global component properties. Previous research has shown that a higher isothermal holding temperature (e.g., mold temperature and chill-roll temperature) leads to the formation of more distinct ordered structures and, therefore, can lead to greater stiffness and strength. Nevertheless, isothermal holding time during manufacturing is typically not taken into account. In this paper, fast scanning calorimetry (FSC) measurements were taken using polypropylene to analyze the crystallization during idealized temperature-time profiles based on the dynamic temperature process and to investigate the crystallization behavior at different temperatures and isothermal holding times analytically. Furthermore, iPP foils were extruded and tested mechanically to investigate the knowledge gained experimentally. Analytical and mechanical results show that foils produced at the same isothermal holding temperature can obtain significantly different ordered structures and mechanical properties depending primarily on the isothermal holding time.

Surface Quenching Induced Microstructure Transformations in Extrusion Foaming of Porous Sheets

Abstract In this article, a new technology is described to manufacture open cell thermoplastic foamed sheets with the aid of surface-quenching phenomenon during an extrusion process. As the gas laden polymer extrudate exits the slit die, its surface is rapidly quenched which results in freezing of cells on the surface, while the cells at the core continue to grow and leads to development of open-cellular microstructure at the core. Influence of chill roll temperature was found to be extremely significant in developing porous morphological attributes. Subsequently, synergistic effect of physical blowing agent (N2) content and chill roll temperature was examined for their expansion ratio and foam thickness. Fascinatingly, with reduced chill roll temperatures open-cell microstructure and high expansion ratio was obtained although its thickness was observed to decrease. Further, influence of chill roll rotating speed on foam microstructure and expansion ratio was studied. Lower chill roll rotational speed resulted in development of open-cellular microstructure; while at higher speeds, closed cell morphology was obtained. The results coherently demonstrate that by controlling the chill roll temperatures; open-cellular microstructure can be developed in sheet extrusion foaming process.

Influences of processing on the phase transition and crystallization of polypropylene cast films

ABSTRACTPhase transition and changes of properties of isotactic polypropylene (i‐PP) cast films with the processing conditions have been investigated by wide‐angle X‐ray diffraction, two‐dimensional small‐angle X‐ray scattering, and atomic force microscopy. It was found that chill roll temperature was a major factor, which influenced the formation of mesomorphic phase and its transition to spherulitic structure. Only mesomorphic phase was observed in the films produced under a chill roll temperature of below 40°C. When the roll temperature was increased to 60°C, mesomorphic phase coexisted with spherulitic crystal structure, and totally transformed to monoclinic structure at the roll temperature of 80°C. Differential scanning calorimetry, tensile, and optical tests were also performed on the films. The results showed that the observed structure changes were closely related to the thermal behavior, tensile, and optical properties of the PP films. The influence of die temperature on the films was also discussed, but the effect was much less than chill roll temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41100.

Erasure of the processing effects in polyamide 6 based cast films by the introduction of montmorillonite: Effect on water and oxygen transport properties

In this paper the influence of montmorillonite layers and of the processing conditions on the morphology and transport properties of polyamide 6 based films was investigated. Films were prepared by cast extrusion keeping all the extrusion parameters constant except the chill-roll temperature. Two chill-roll temperatures were used: 50°C and 125°C. The nanoclay amount contained in the different systems was low and varied from 0 to 1wt%. The state of dispersion of the nanoclays and the structure of the matrix crystalline phase were investigated as a function of the film processing conditions. The water sorption properties and the oxygen and water permeation were determined and a detailed analysis of the transport mechanism was proposed. For the neat PA6 films, a great dependency of the processing conditions on the morphology and the transport properties was observed. A significant improvement of barrier properties was obtained for the film elaborated with the high chill-roll temperature. For the nanocomposites, independently of the nanoclay amount and the processing conditions, the polymer matrix morphology and the barrier properties were close to each other. Moreover they were similar to those observed for the neat matrix elaborated with the high chill-roll temperature. From this result, the nanoclay can be considered as an efficient additive to make PA6 films properties much less processing dependent.

Morphological study of PVDF/PMMA/TiO2 blend films prepared by melt casting process

Abstract The influence of chill roll temperature and thermal annealing on the morphology and dynamic mechanical behavior of poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA)/titanium dioxide blend films prepared by a melt casting process was studied. The β phase of PVDF was formed at the chill roll temperature of 30°C. Furthermore, with the increase in this chill roll temperature, its structural conversion to the α phase was observed. No change in the crystal structure of either the β or α phase occurred on account of thermal annealing at 115°C for 24 h. The decrement in the storage modulus above the glass transition temperature ascribed to the mixed amorphous phase became smaller, as the chill roll temperature increased. Based on morphological observations, we deduced that the reason for this decrement is not that the film cast at 115°C was more crystalline than that cast at 30°C but that the actual weight fraction of PMMA in the mixed amorphous phase of the film cast at 115°C was lower than that of the one cast at 30°C.

Influence of montmorillonite and film processing conditions on the morphology of polyamide 6: Effect on ethanol and toluene barrier properties

Nanocomposite films were prepared by cast extrusion using two chill-roll temperatures from polyamide 6 and an organo-modified montmorillonite. The impact of the nanoclay amount in the range from 0 to 1wt%, as well as the processing conditions on the morphology and transport properties were investigated. The microstructure of the polymer highly depended on the films processing and the presence of the nanoclays. A detailed analysis of ethanol/toluene pervaporation properties was proposed for the all range of ethanol/toluene composition on the basis of thermodynamic and kinetic point of view. The transport mechanism was complex and resulted from a combination of different contributions involving the polymer–permeant and permeant–permeant interactions, the free-volume holes and the amount of γ phase in the crystalline part of the polymer. This study underlined the potentiality of using molecules differing in their interaction as an original way to probe the architecture of these systems.

Influence of film processing conditions on the morphology of polyamide 6: Consequences on water and ethanol sorption properties

Abstract Films based on polyamide 6 were prepared by cast extrusion keeping all the extrusion parameters constant except the chill-roll temperature. The impact of the process conditions on the morphology and transport properties was investigated. The structure of the matrix crystalline phase and the molecular mobility of the polymer chain in the amorphous phase highly depended on the films processing conditions. The gas permeation properties and the water and ethanol sorption properties were determined and a detailed analysis of the sorption mechanism was proposed on the basis of thermodynamic and kinetic modeling. The transport mechanism was shown to result from a combination of different contributions involving the size of the permeant, the free-volume holes distribution and the amount of γ phase in the crystalline part of the polymer. This study underlined also the potentiality of using molecules differing in their size as an original way to probe the architecture of these systems.

β-Crystal Development of Isotactic Polypropylene during Sheet Extrusion Process

The objective of this study is to correlate the crystal structure with material and processing parameters, in particular -nucleating agent and degree of supercooling. The selected -nucleating agent used in this study was “Quinacridone pigment, E3B” with concentration varied from 1 to 100 ppm. The degree of supercooling during sheet extrusion process was controlled by chill roll temperatures in a range of 60 to 115oC. Crystal structures in neat PP and PP-E3B samples were characterized using WAXD and DSC techniques. The selected PP-E3B, with optimum concentration of 5 ppm, was fabricated into sheets using chill roll temperatures of 60, 70, 80, 90, 100, 110 and 115oC; these sheets had -crystal content (K-value) of about 0.099, 0.214, 0.341, 0.430, 0.651, 0.754 and 0.892, respectively. The melting characteristics and physical properties of the nucleated iPP were also dependent upon -crystal content. Finally, it could be concluded that the development of -crystal structure was highly influenced by the concentration of nucleating agent and processing conditions during sheet extrusion.

Effect of processing on the crystalline orientation, morphology, and mechanical properties of polypropylene cast films and microporous membrane formation

Cast films of a high molecular weight linear polypropylene (L-PP) were prepared by extrusion followed by stretching using a chill roll. An air knife was employed to supply air to the film surface right at the exit of the die. The effects of air cooling conditions, chill roll temperature, and draw ratio on the crystalline orientation, morphology, mechanical and tear properties of the PP cast films were investigated. The crystallinity and crystal size distribution of the films were studied using differential scanning calorimetry (DSC). It was found that air blowing on the films contributed significantly to the uniformity of the lamellar structure. The orientation of crystalline and amorphous phases was measured using wide angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR). The amount of lamellae formation and long period spacing were obtained via small angle X-ray scattering (SAXS). The results showed that air cooling and the cast roll temperature have a crucial role on the orientation and amount of lamellae formation of the cast films, which was also confirmed from scanning electron microscopy (SEM) images of the films. Tensile properties and tear resistance of the cast films in machine and transverse directions (MD and TD, respectively) were evaluated. Significant increases of the Young modulus, yield stress, tensile strength, and tensile toughness along MD and drastic decreases of elongation at break along TD were observed for films subjected to air blowing. Morphological pictograms are proposed to represent the molecular structure of the films obtained without and upon applying air cooling for different chill roll temperatures. Finally, microporous membranes were prepared from annealed and stretched films to illustrate the effect of the PP cast film microstructure on the morphology and permeability of membranes. The observations of SEM surface images and water vapor transmission rate of the membranes showed higher pore density, uniform pore size, and superior permeability for the ones obtained from the precursor films prepared under controlled air cooling.

Effect of Chill-roll and Air-gap in Film Forming on Heat-sealability of Polypropylene Films Containing β-Form Nucleating Agent

Polypropylene (PP) films with β-form nucleating agent were prepared by T-die film extrusion. The relationship among extrusion conditions, crystal structure of the films and heat-sealability was studied. The following results were obtained: Fine crystallites formed more easily in films prepared at a chill-roll temperature of 25°C than in those at 75°C. The heat-sealabilities of the former films were better than those of the latter ones in a low heat-seal temperature range from 140°C to 144°C. The heat-sealability of PP film without additive prepared at a chill-roll velocity of 2.5m/min was better than that at 1.0m/min because of smaller size crystallites. On the other hand, the heat-sealability of the PP film with 0.10wt% β-form nucleating agent, prepared at 1.0m/min, was better than that at 2.5m/min due to the higher β-form crystal content. Accordingly, it may be said that the smaller sizes of α- and β-form crystals and the higher content of the β-form crystals both cause better heat-sealability due to the lower melting point of the crystals. It was also found that the air-gap distance negligibly affects the crystal structure and hence the heat-sealability of film.

THE EFFECTS OF PROCESSING CONDITIONS ON THE PHYSICAL PROPERTIES OF EXTRUDED HIGH IMPACT POLYSTYRENE SHEETS

The influence of various extrusion parameters on the physical properties of rubber modified polystyrene (HIPS) sheets is investigated. The extrusion parameters under consideration are melt temperature, chill-roll temperature, line speed and sheet thickness. Optimum extrusion conditions for producing quality polystyrene sheet feedstock are discussed. For sheet made with one HIPS resin, NOVA’s PS5100, the best gloss is obtained at a high melt temperature (230°C) and a high chill roll temperature setting of (102°C/102°C/102°C). The impact strength is maximized at a melt temperature of 220°C and at a low chill roll temperature setting of (90°C/90°C/90°C). To simultaneously optimize gloss and impact strength at a gauge of 940 μm and line speed of 2 m/min, the best conditions are melt temperature set at 220°C and chill roll temperature setting of (90°C/90°C/90°C).

Thermo-Oxidative Degradation of Polypropylene by Use of Screw Extruders

Films were cast from a polypropylene thermo-oxidatively degraded by use of a screw extruder and an undegraded polypropylene with a T-die extruder. The effect of casting conditions on the structures and properties of the films were studied.Films cast from the degraded polypropylene show superior transparency, dart impact strength, and heat sealability and show low stiffness and slipperiness. α-crystal phase is decreased and smectic and amorphous phases are increased by degradation. Although such tendency is also attained by decreasing the chill roll temperature or by increasing die temperature, it is more notable in films cast from the degraded polypropylene than in ones cast from the undegraded polypropylene under any casting conditions. Films cast from the degraded polypropylene have a feature that their inner structures are almost constant independent of the casting conditions.

Optimizing Sheet Extrusion Conditions to Minimize Internal Stresses in Thermoformed Sheet

This study was performed on an alloyed FPVC sheet which was extruded under controlled conditions. Some of the conditions consisted of draw ratio, die temperature, melt temperature before die, center chill roll temperature and bottom roll temperature on a three roll down-stack sheetline

Study on rough‐surface biaxially oriented polypropylene film. I. Formation of β‐form crystals in sheet cast with T‐die extruder

AbstractSheets were cast by extruding polypropylenes (PP) which contained γ‐quinacridone, a β‐crystal nucleator, at levels of 0–10 ppm using a 30 mm ϕ extruder with a T‐die at extrusion temperatures of 200–260°C and chill roll temperatures of 30–90°C. The influences of raw resin characteristics such as γ‐quinacridone content and MFI of the base PP and casting conditions such as extrusion temperature and chill roll temperature on the amount of β‐crystals formed in the sheet were studied. The amount of the β‐crystals formed was larger as the γ‐quinacridone content was higher and the extrusion temperature was lower and almost independent of the chill roll temperature. As for the influence of MFI of the base PP, the amount of the β‐crystals formed was maximum at MFI ≑ 8 dg/min.

Investigation Into the Production of Polyamide Film to Achieve Required Properties of PA/PE Laminate

Polyamide (PA) films made with nylon 6 for lamination—to polyethylene (PE) films, for example—require enhanced spherulite growth to prevent deformation of the flat film during removal of solvents in the drier. Several factors were considered in designing and performing tests which resulted in developing correlation equations for two of these factors—chill roll temperatures and film speed—for the test machine used to produce film suitable for use in packaging.