Enhancement of interfacial adhesion and engineering properties of polyvinyl alcohol/polylactic acid laminate films filled with modified microfibrillated cellulose

This work was done to improve the interfacial adhesion and engineering performance of polyvinyl alcohol/polylactic acid laminate film by altering the polyvinyl alcohol phase surface properties via incorporating microfibrillated cellulose modified by propionylation. Incorporating the modified microfibrillated cellulose into polyvinyl alcohol film improved adhesion between film layers during the laminating process. Improved peel strength and tensile properties confirmed that modified microfibrillated cellulose can produce better bonding between polyvinyl alcohol and polylactic acid via mechanical interlocking and cohesive forces at the film interface. Modified microfibrillated cellulose (3 wt%) increased the peel strength by 40% comparing with the neat polyvinyl alcohol/polylactic acid laminate film.The reduction of both moisture absorption and diffusion rate of the modified microfibrillated cellulose–polyvinyl alcohol/polylactic acid to 20 and 23%, respectively, also indicated that the modified microfibrillated cellulose could inhibit moisture permeation across the film. This was because the modified microfibrillated cellulose is hydrophobic. Furthermore, the addition of modified microfibrillated cellulose also increased the decomposition temperature of the laminate film up to 10% as observed at 20% of remaining weight, while the storage modulus substantially increasing to 72% relative to the neat laminate film.The superior interfacial adhesion between the polylactic acid and modified microfibrillated cellulose–polyvinyl alcohol layers, observed by scanning electron microscopy, confirmed the improved compatibility between the polyvinyl alcohol and polylactic acid phases.

Experimental Investigation of Thermal Management of Tablet Computers Using Phase Change Materials (PCMs)

This paper presents a study of thermal management of tablet computers (tablet PCs) using phase change materials (PCMs) encapsulated in aluminized laminated film under continuous operation. The experimental setup consists of original tablet PC parts and a simplified dummy printed circuit board (PCB) with a thermal response similar to the original PCB. Two PCMs were used in the experiments, n-eicosane and PT-37 (a commercial PCM from PureTemp). These PCMs have similar melting temperatures (n-eicosane – 35.6 °C; PT-37 – 36.3 °C) but different latent heats of fusion (n-eicosane – 236 kJ/kg; PT-37 – 206 kJ/kg). Two encapsulations with different sizes (6″ × 2.6″, 7″ × 1.5″) but the same thickness (0.0792″ (2 mm)) were used in this study. The effects of inclination and power input level on the thermal behavior of the tablet were investigated. Experiments showed that PCM encapsulated in laminate film led to lower back cover temperature for constant heat flux applications. As much as a 20 °C temperature reduction of the back cover hotspot was achieved with encapsulated PCM. It was also observed that better thermal behavior was achieved both by the melting of PCMs and heat spreading through the laminate film. It was found that the rate of PCM melting is directly related to the power input. No significant effect on PCM melting and temperature history was observed in relation to the system inclination.

Numerical and experimental analysis of heat sealing of multi-layered laminate films used in lithium polymer battery packaging

The packaging of a lithium polymer secondary battery involves a wrapping process of an aluminum/polymer laminate film that uses heat sealing. Heat sealing time and sealing block width are important variables in creating packaging requirements for optimal battery performance and safety. In this study, a heat transfer analysis is performed using finite element method to investigate the temperature distribution of the sealing block over the course of the heat sealing process. Heat sealing time and sealing block width were the variables of interest for the heat transfer simulation in order to identify optimal manufacturing conditions. Through the analysis, we successfully identified a minimum heat sealing time less than 3 s and 1.5 mm width of the sealing block that optimizes both the rate of battery production and lithium polymer battery capacity. To validate the quality of heat sealing properties, visual inspection and restrained packaging tests were performed.

THERMO-VISCOELASTIC CHARACTERIZATION OF POLYMER LAMINATE FILMS

The investigated material - laminate is intended as a substrate for small electronic components, electrodes and printed circuits, which are processed onto the laminate prior to thermoforming. The placement of the electronic components and the connecting circuits must be carefully designed to prevent damage during the thermoforming. The thermo-viscoelastic behavior of a polymer laminate film was characterized by mechanical measurements to obtain data for material modeling. The strain was measured using digital image correlation. The film is anisotropic and is able to deform to strains up to 60%.

Thermoforming of Polymer Laminate Films: Thermo-Viscoelastic Characterization

The thermo-viscoelastic behavior of a polymer laminate film was characterized by mechanical measurements to obtain data for material modeling. The strain was measured using digital image correlation. The film is anisotropic and sustains uniaxial strains up to 60%. Additionally, the thermal expansion was measured for both materials that form the laminate.

Photopatternable Laminate BCB Dielectric

Divinylsiloxane-bis-benzocyclobutene (DVS-bis-BCB, or BCB) is a well-known dielectric material that has been used in high volume manufacturing for many years (Dow's CYCLOTENE™ 3000/4000-series Advanced Electronic Resins). Typically, the application of these products has been by spincoating or spray coating of the dielectric material from a solvent-based formulation. However, for certain applications - for example, those involving large area, square substrates such as glass panels - it is desirable to be able to apply the BCB-based dielectric material using a dry film coating process, such as vacuum or hot roll lamination. In this paper, we describe the concept of creating a laminate film utilizing DVS-bis-BCB as the primary dielectric material component. In creating the laminate dielectric material, it is important to maintain the unique combination of thermal and electrical properties of DVS-bis-BCB, including high thermal stability, excellent copper barrier properties, low moisture uptake, low dielectric constant, and low dielectric loss. However, DVS-bis-BCB alone is too rigid to produce a high quality laminate film, therefore, it is necessary to modify the formulation to improve flexibility and lamination quality. As the flexibility of the film is increased, higher fracture toughness (K1C) and higher elongation values should result. Novel formulation adjustments to the base DVS-bis-BCB polymer system have resulted in an experimental laminate dielectric product that will be the focus of this discussion. Depending on the application, laminate films can vary in thickness from 2μm to 50μm or even thicker. A typical laminate film construct includes the BCB-based dielectric film with a base sheet of an optically-clear polyester (PET) film and a polyethylene (PE) cover sheet. The DVS-bis-BCB-based laminate can be tuned with appropriate additives to either pattern with UV exposure from a tool such as a Süss MicroTec Mask Aligner (50mJ/cm2 – 100mJ/cm2 exposure energy) or laser pattern with a tool such as a Süss MicroTec 248nm Excimer Laser. Aspect ratios of 1:1.5 have been achieved with a photopatternable DVS-bis-BCB film and aspect ratios of >1:1 are possible with a laser-patterned film. Beside the photopackage added to the film to enable UV patterning, toughening additives have also been incorporated to enhance the fracture toughness (K1C) and elongation properties. K1C for the laminate has been improved to 0.55Mpa·m1/2 vs. 0.35Mpa·m1/2 for DVS-bis-BCB. Elongation has been improved to 13% for the laminate vs. 8% for DVS-bis-BCB. Electrical properties are similar to DVS-bis-BCB. An additional attribute of the laminate dielectric is the ability to tent over and protect vias. Vias >100μm diameter have successfully been tented with a 10μm thick film. A DVS-bis-BCB-based laminate has been demonstrated with continued optimization and evaluation to follow.