Effect of heat‐sealing temperature on the failure criteria of oriented polypropylene/cast polypropylene heat seal

Failure criteria of the heat‐sealed part of oriented polypropylene (OPP) and cast polypropylene (CPP) heat seals made by an impulse type heat‐sealing machine were investigated. Circular notches and precracks were introduced to direct failure to specific areas such as inside the seal, at the border, or at the unsealed part. The notched strength as a function of heat‐sealing temperature revealed that the seals were stronger in the transverse direction (TD) as compared with the machine direction (MD). Tensile failure that occurred inside the heat seal is more sensitive to sealing temperature, whereas that at the unsealed part is immune. The stress intensity factor (K₁) is generally higher along the TD. At high sealing temperatures, i.e. above 150°C, orientation in the OPP film is relaxed and this results in consistently low mechanical properties at this temperature range. This morphology was revealed by studies of crystalline orientation state and FTIR imaging. POLYM. ENG. SCI., 46:205–214, 2006. © 2005 Society of Plastics Engineers     

Effect of heat‐sealing temperature on the properties of OPP/CPP heat seals. Part II. Crystallinity and thermomechanical properties

The crystalline structure of the heat‐sealed part of oriented polypropylene (OPP) and cast polypropylene (CPP) films was investigated by differential scanning calorimetry, Fourier transform infrared spectroscopy, and thermal mechanical analysis (TMA). The relationship between the crystalline structure and the mechanical properties was analyzed. It was found that the high total crystallinity of both OPP and CPP gave rise to good mechanical properties and that the orientation of the crystalline structure in the OPP film also was an important factor. The optimum condition for heat sealing was the temperature at which total crystallinity was highest while still retaining the crystalline orientation of OPP. The assessment of crystalline orientation by TMA is an innovation initiated by the authors. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 513–519, 2006     

Development and characterization of a gelatin‐based coating with unique sealing properties

The experimental results on the development of thin (～ 1.5 μm) gelatin‐based coatings and the investigation on their sealing attribute when applied onto oriented polypropylene (OPP) are reported. The sealing performance, expressed as the strain energy required to separate the sealed joints, was studied as a function of three different influencing factors. pH of the hydrogel solution was varied between 5 and 11. The highest seal strength values were obtained for pH values beyond the isoelectric point (IEP) of the gelatin molecule. The effect of the plasticizer (glycerol) was studied by changing its concentration from 2.5 wt % to 7.5 wt % to the total weight of the hydrogel solution. Glycerol concentration = 7.5 wt % was found to be the best for achieving adequate strain energy values. The influence of a hydrophobic component on the capability of the coating to act as a sealant has also been assessed. The hydrophobic component had a positive effect only up to a certain level (1 wt %, weight percent), whereas beyond this value, it affected the seal strength attribute. According to the best setting conditions, seal strength values for the OPP biocoated films of ～ 61 N × mm were attained, with a corresponding maximum force required to break the joints of 2.4 N. These results are discussed by taking into consideration the modality of seals opening. Interestingly, the heat‐seal (temperature: 90°C; dwell time: 1 s; pressure: 4 bar) failed in both peeling and tearing mode failure, as confirmed by microscopy, spectrophotometric, and particle size analyzes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crosslinking of low‐density polyethylene by diisocyanates for superior barrier properties

The chemical modification of low‐density polyethylene (LDPE) resins with hexamethylene diisocyanate and toluene diisocyanate was achieved. The reaction of LDPE with diisocyanate was monitored by Fourier transform infrared spectroscopy, wherein the appearance of new peaks at 3326, 1620, and 1572 cm^?1 corresponding to ? N? H stretching, ? (C?O)? NH₂ stretching, and ? N? H bending in an amide moiety, respectively, was observed. Modified films of excellent clarity and uniform thickness were obtained by the solution casting of crosslinked polyethylene. The oxygen transmission rate (OTR), water vapor transmission rate (WVTR), grease resistance, and thermal properties of the modified films were studied. The results clearly indicate that the OTR was improved by 35% and that grease resistance was improved by 90–125% in the crosslinked LDPE films with little change in their strengths. The heat seal characteristics, however, showed that relatively higher temperatures were needed to achieve efficient sealing in these films. Differential scanning calorimetry showed a decrease in the melting temperature from 104°C for LDPE to 101°C for both of the crosslinked LDPE films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1193–1199, 2005     

Effect of heat treatment on dielectric relaxation of polyacrylonitrile: Reversible thermally induced structural change

The effect of heat treatment on the dielectric relaxation of polyacrylonitrile (PAN) was studied. Dielectric measurements, in the frequency range 0.1–100 kHz and temperature range 30–170°C, on PAN heat treated at two temperatures (120 and 160°C) and the untreated PAN are reported. The loss peak height, the dielectric relaxation strength, loss peak width, and the loss peak temperature were found to vary systematically with the temperature of the heat treatment. The changes in dielectric relaxation produced by heat treatment at the higher temperature (i.e., 160°C) were considerably less than those produced by heat treatment at 120°C. The results are discussed and attributed to the variation of the degree of bound nitrile groups (through their dipole–dipole interaction) with heat treatment temperature. Heat treatment of the higher temperature (160°C) results in lower degree of bound nitrile groups in the structure than heat treatment at the lower temperature (120°C).     

Evaluation of Polymethylmethacrylate Cohesion Behavior with a Gas-Assisted Thermal Bonding Method

By applying heat and pressure to thermoplastic materials, the overlap of the two pieces can be bonded to form hermetic systems. Polymethylmethacrylate (PMMA) is a thermoplastic used in commercial microfluidic devices; its advantages include low cost, ready fabrication, and high transparency. In order to gain an understanding of PMMA's relevant characteristics (thermal behavior, material strength, and hermetic sealing strength), we study its bulk properties and mechanical behavior. Experimental results of the cohesion behavior of PMMA sheets were collected and are presented here. Samples were bonded by subjecting a sample to elevated pressure and temperature in the glass transition range (85°C–165°C), which was determined beforehand by differential scanning calorimetry and literature. Five different bonding temperatures (140°C, 150°C, 160°C, 170°C, and 180°C) and three bonding pressures (1.2, 1.4, and 1.6 MPa) were applied for making samples; mechanical strength tests were then carried out to understand separately the bulk mechanical strength and the interfacial properties (shear strength and bonding strength) of a cohesive laminate at the temperatures near the glass transition range. POLYM. ENG. SCI., 60:161–167, 2020. © 2019 Society of Plastics Engineers     

Structure and properties of hard carbon films depending on heat treatment temperatures via polymer precursor

Phenylcarbyne polymer films were coated on silicon substrates and heat treated in 1 atm pressure of argon at various temperatures. The structural changes occurring during the heat treatment process of the polymer were investigated by Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The Raman and FTIR spectra features of the polymer showed a dependence on the heat treatment temperatures. At low temperatures (below 400°C), the Raman and IR spectra of the polymer were similar to those of the original polymer. The hardness and Young's modulus of the polymer films were below 1 and 50 GPa, respectively. With increasing temperature (above 400°C), thermal decomposition of the polymer occurred, resulting in structural changes of the polymer from soft amorphous hydrocarbon (400–600°C) phases to hard carbon phases (above 600°C). The hardness and Young's modulus increased from 1.5 and 65 GPa at 600°C to 9 and 120 GPa at 1000°C, respectively. It is assumed that the hard carbon film converted from the polymer might contain sp² and sp³ carbon phases; high temperature of heat treatment resulted in increasing sp² (glassy) carbon phase in the films.     

可热封双向拉伸聚酯薄膜简介

在聚酯生产过程中,采用第三或第四组分进行共聚改性,破坏或降低其结晶结构,便可具有可热封性能。以三层共挤结构为例,叙述了可热封双向拉伸聚酯薄膜的生产工艺,并将其主要性能与BOPP,CPP薄膜的进行对比。     

聚丙烯高档流延膜专用料的开发应用

聚丙烯流延膜是一类十分重要的薄膜品种。主要介绍了2008年茂名石化聚丙烯高档流延膜专用料CP9008的生产开发及应用情况。结果表明在海蒙特环管工艺生产高乙烯、高熔融指数产品是可行的。目前我们开发的CP9008热封温度为120℃-126℃,比以往的国内产品热封温度降低了10℃-20℃,但较进口料还是偏高。     

Tailored Polyethylene Nanocomposite Sealants: Broad-Range Peelable Heat-Seals Through Designed Filler/Polymer Interfaces

The heat sealing behavior of novel polyethylene-based nanocomposite films was investigated, as they relate to flexible packaging of fresh-cut vegetables, processed foods and biomedical devices. Appropriately designed sealant nanocomposites, which include dispersed montmorillonite nanofillers and ethyl vinyl acetate copolymer, produce a hermetic but peelable heat seal across a broad, 30–40°C, range of heat sealing temperatures, outperforming optimized commercial polyethylene-based sealants that achieve peelable seals in a much narrower heat sealing temperature range, of less than 15°C. Appropriate nanocomposite design leads to a general easy-open/peelable character of heat seals, which is: (a) independent of sealing conditions and apparatus — ranging from long dwell times at very high sealing pressures to very short heat impulses at very low sealing pressures; (b) markedly independent of the opposite side of the heat seal — for example, when sealed on itself, on unfilled sealant, or on high density polyethylene; and (c) rather insensitive to formulation variations of the sealant — for example, variations of the polyethylene of the ethyl vinyl acetate type and concentration, and of nanofiller loading. Insights from observations of the fracture seal surfaces by infrared spectroscopy and electron microscopy reveal that the underlying mechanism of this behavior is related to a synergistic effect of the ethyl vinyl acetate copolymer and the montmorillonite clay nanofiller, which introduces weak interfaces in the nanocomposite that lead to cohesive failure of the sealant.     

Influence of apple flavor absorption on physical and mechanical properties of poly(ethylene terephthalate) films

Poly(ethylene terephthalate) (PET) films (280‐μm film thickness), which are used in food packaging, were immersed into 160‐ and 320‐ppm apple flavor solution for 14, 28, and 56 days at 5, 25, and 40°C, respectively. At the end of this period, the changes in the PET films were investigated by measuring the mechanical and physical properties. The mechanical properties were determined by examining changes in the Young's modulus. The changes in the physical properties were investigated by Fourier transform IR spectroscopy and scanning electron microscopy (SEM). The formation of microcracks in the structure of PET films was observed by SEM. According to the results of those investigations, the apple flavor affects PET films, even at very low concentrations and temperatures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1802–1807, 2006     

Studies on the improvement of cured two-stage phenolics performance. III. Relation between conditions of heat treatment and properties of wood-flour-filled phenolics

The effect of heat treatment on the properties of cured two-stage phenolics was studied. Samples were compression-molded from the compound that was prepared from novolac, wood flour (100 phr), and hexamethylenetetramine (15 phr). Samples were heat-treated in conditions of four levels for temperature (150°C, 170°C, 190°C, and 210°C) and time (4, 8, 16, and 24 h). The properties of samples heat-treated, such as weight loss, dimensional stability, water absorption after boiling, and flexural properties were measured. The relation between the properties and the conditions of heat treatment was examined statistically. From the results, it was decided that the optimum conditions of heat treatment for practical use were: (i) to decrease water absorption and to heighten electrical resistance, 210°C, 24 h; (ii) to improve flexural properties at room temperature and at 160°C; 170°C, 8 h, and 170–190°C, 24 h, respectively. It was concluded that the decrease of water absorption of moldings was due to the increase of hydrophobic nature of wood flour included in moldings by heat treatment and that the improvement of flexural property of moldings at 160°C was due to an increase of crosslinking density by heat treatment. The reasons for the improvement of the electrical properties by heat treatment were also discussed.     

The influence of annealing treatment on the molecular structure and the mechanical properties of isotactic polypropylene fibers

An investigation was carried out on the effects of annealing treatment on the molecular structure and the mechanical properties of isotactic polypropylene fibers annealed in an air heated environment at temperatures ranging from 60 to 140°C. Analysis of the equatorial X‐ray diffraction traces showed the presence of a three phase system of amorphous‐smectic‐monoclinic forms and revealed the transformation of the metastable smectic form to the highly stable monoclinic form as the annealing temperature is increased, resulting in an enhanced degree of crystallinity and the crystallite size. The improvements in the degree of crystallinity and the crystallite size became more remarkable above 120°C. Evaluation of the crystallinity was carried out using an analysis of density, infrared spectroscopy, and X‐ray diffraction methods whereas the state of the molecular orientation was evaluated using polarized infrared spectroscopy measurements only. Polarized infra‐red spectroscopy measurements after the curve fitting procedure showed a slight increase of the molecular orientation of the helical chain segments present in the crystalline phase represented by the IR bands at 841 and 998 cm^?1 whereas the amorphous structure represented by the IR band at 974 cm^?1 showed no significant change with increasing annealing temperature. The improvement in the molecular orientation of the crystalline phase became more remarkable above 120°C. Tensile strength of the annealed fibers increased with increasing annealing temperature but the elongation at break and the initial modulus were not affected as much as the tensile strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Improvement of high-temperature mechanical properties of heat treated Cf/geopolymer composites by Sol-SiO2 impregnation

Unidirectional carbon fiber reinforced geopolymer composite was prepared by ultrasonic-assisted slurry infiltration method and heat treated at 1100 °C. Then it was impregnated with Sol-SiO₂ to seal the cracks and pores formed during heat treatment. The ambient strength of composite after impregnation was enhanced by 35.6% due to the increase relative density from the starting 79% to 93.6%. Composites both before and after impregnation fractured in a non-brittle manner at both ambient and high temperatures. Over an elevated temperature range from 700 to 900 °C, the strength of the two composites showed anomalous gains and reached their maximum values at 900 °C, 322.1 and 425.1 MPa, respectively. These values were 19.8% and 16.8% higher than their ambient ones. When the temperature was further increased to 1100 °C, the impregnated composite showed superior high-temperature properties, which was attributed to the improved fiber integrity due to the Sol-SiO₂ sealing effect.     

Molecular design,synthesis, and electro‐optic properties of novel Y‐type polyesters with high thermal stability of second harmonic generation

3,4‐Di‐(2′‐hydroxyethoxy)‐4′‐nitrostilbene was prepared and condensed with terephthaloyl chloride, adipoyl chloride, and sebacoyl chloride to yield novel Y‐type polyesters containing NLO‐chromophore dioxynitrostilbenyl groups, which constituted parts of the polymer backbone. Polymers were found soluble in common organic solvents such as acetone and N,N‐dimethylformamide. They showed thermal stability up to 300 °C in thermogravimetric analysis with glass‐transition temperatures obtained from differential scanning calorimetry in the range 110–152 °C. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films at a 1064 cm^?1 fundamental wavelength were around 3.51 × 10^?8 esu. The dipole alignment exhibited high thermal stability even at 10 °C higher than the glass‐transition temperature, and there was no SHG decay below 120 °C for one of these polymers due to the partial main‐chain character of polymer structure, which was acceptable for NLO device applications. Copyright © 2005 Society of Chemical Industry     

Synthesis and evaluation of mechanical and thermal properties of segmented condensation polyurethanes

Abstract

Condensation polyurethanes with different hard segment (HS) content were prepared by condensation reaction of urea, phenol sulphonic acid and formaldehyde and tested for their mechanical, physical and thermal properties. Obtained polyurethane (PUR) films were first heated at 50°C for 120 min and then treated at 135°C for 15 min or 160°C for 10 min. The tensile strength of samples thermally treated at 50°C then at 135°C was 120% higher than for samples treated only at 50°C. The obtained polyurethanes exhibited segmented structures with phase separation between HSs and soft segments (SSs). Films containing 19 and 21%HSs heated at 50°C then 135°C exhibited acceptable mechanical properties and water resistance. The lower and higher end use temperatures of PUR films were affected mainly by the polymer composition. Moreover, the polyurethane samples containing 19 and 21%HSs have shown the highest decomposition temperature (i.e. >165°C), compared to 80°C for polymers with 32%HSs.     

Structure and processability of iodinated poly(vinyl alcohol). IV. Drawability of the films iodinated at solution before casting

The drawability of iodinated at solution before casting (IBC) polyvinyl alcohol films prepared by casting aqueous solutions of 10 wt % PVA containing 15.2, 39.8, 83.2, 117.0, and 140.1% was examined with a tensile tester at 20–60°C. The tensile behavior of IBC films showed that the yield and breaking loads were much lower, and the breaking elongation was even higher than those of the unoriented iodinated after casting (IAC) films as well as the untreated PVA films. The maximum draw ratios of the films with the weight gain of 15.2, 39.8, 83.2, 117, and 140.1% were 4.5, 5.5, 8.5, 8.0, and 7.5, respectively, which were achieved at 20°C in all. The crystallinity of all films increased by the maximum draw, regardless of crystallinity before drawing. The crystalline structure was recovered to the original PVA crystalline lattice by deiodination. Amorphous orientation and initial moduli increased with the maximum draw ratio, while the orientation of crystals was constant. The orientation and moduli increased up to the weight gain of 83.2%, whose highest draw ratio and initial modulus were 8.5 and of 7.1 GPa, respectively, and then decreased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Effect of degree of neutralization of sodium-based ionomers on hot-tack properties

The hot-tack properties of ethylene-methacrylic acid copolymers neutralized with sodium (Na) cations to produce ionomers were investigated. Specimens with neutralization degrees of 20%, 54%, and 70% were examined. After testing at low sealing temperatures (<130°C), the highest hot-tack strength was obtained from a specimen with a neutralization degree of 20%. In contrast, at high sealing temperatures (>140°C), the hot-tack strength increased with an increasing degree of neutralization. Observations of the surfaces of samples tested at low sealing temperatures after hot-tack tests showed that specimens having a neutralization degree of 20% exhibited cohesive breakdown while the 54% and 70% specimens underwent interfacial delamination. The effect of sealing temperature on hot-tack strength was determined by assessing the rheological properties of molten ionomers. The results suggested that, when testing at low sealing temperatures, a low melt viscosity provided high hot-tack strength by allowing flow diffusivity of the resin at the sealed interface. At high sealing temperatures, uniaxial elongational viscosity related to strain hardening contributed to the high hot-tack strength of these Na-based ionomers. The present study highlights the important effect of ionic aggregates on hot-tack properties.     

Doubly oriented β-form films of poly(vinylidene fluoride)

PVDF sheets, rapidly quenched, were (1) two-step transversely stretched at various temperatures and (2) stretched at various temperatures, rolled at room temperature and then annealed. The orientation patterns of the β-form crystal (which contains the polar b-axis) in these films were analysed on the basis of X-ray diffraction photographs taken with flat and cylindrical cameras. In the case of (1), when both of the two-step transversely stretching temperatures were below 100°C, a doubly oriented film with the plar b-axis oriented parallel to the film surface was obtained. In the case of (2), when the stretching temperature was below 100°C, the sheets then rolled without annealing, another doubly oriented film with the polar b-axis preferentially oriented at 30° to the film surface was obtained. On the other hand, when these films were annealed above 100°C, or the stretching temperatures were above 100°C, orientation patterns in which the polar b-axis was partially rotated through 60° were obtained. The orientation mechanisms of these films are discussed using the measurements of the lattice spacings of the β-form crystal.     

Adsorption of chromium(VI) and nickel(II) ions on acid- and heat-activated deoiled spent bleaching clay

De-oiled spent bleaching clay was activated either by acid treatment followed by heat activation or by heat activation alone at temperatures between 200 and 800°C. The surface area of the heat-activated clay attained a maximal value of ≈120 m² g⁻¹ at temperatures between 400 and 500°C while the acid-heat-treated clay attained maximal surface area of ≈140 m² g⁻¹. The adsorption capacities of chromium [Cr(VI)] for both series studied increased as the activation temperature increased until 300°C and decreased again at higher temperatures. At lower pH, more than 95% of the Cr(VI) was absorbed in a solution with initial concentration of 1 mg L⁻¹ per gram of adsorbent activated at 300°C. The adsorption patterns followed Freudlich's isotherms. Two maximal values of adsorption capacities of nickel [Ni(II)] were observed at activation temperatures of 200 and 500°C for acid-treated samples, whereas these were at 200 and 700°C for the nonacid-treated samples. The amount of Ni(II) adsorbed increased with the pH of the solution for all samples studied. The maximal adsorption capacities of the adsorbents in solution containing initial Ni(II) concentration of 5 mg L⁻¹ per 0.5 g of adsorbent and at pH 6 were found to be 44 and 42%, respectively, for the acid-treated sample activated at 500°C and for the nonacid-treated sample activated at 700°C. They all obeyed both the Langmuir's and Freundlich's isotherms.