C.E. Park

Effects of morphology on toughening of tetrafunctional epoxy resins with poly(ether imide)

Abstract Tetraglycidyl-4,4′-diaminodiphenyl methane based resin with 30 phr diaminodiphenyl sulfone as curing agent was toughened with poly(ether imide) (PEI). The effects of morphology on the fracture toughness of modified epoxy resins were investigated. Morphology was controlled by changing the curing conditions. The co-continuous structure and morphology of the PEI spherical domain dispersed in the epoxy matrix were obtained. Phase-inversed morphology with PEI matrix was also obtained with 30 phr PEI content. The cured resin with phase-inversed morphology showed the highest fracture toughness. The modified epoxy resins with enhanced fracture toughness exhibited other improved mechanical properties such as flexural strength, flexural modulus and strain at break.

Adhesion improvement of epoxy resin/polyethylene joints by plasma treatment of polyethylene

Abstract Low density polyethylene (LDPE) and high density polyethylene (HDPE) were plasma-treated with N 2 and O 2 plasma. The wettability and polar component of surface free energy of plasma-treated polyethylene were investigated by contact angle measurement. The concentration of functional groups formed by plasma treatment such as hydroxyl and carbonyl groups was measured using attenuated total reflection Fourier transform infrared spectroscopy (ATR FT i.r.). The concentration of polar functional group increased rapidly with 5–10s of plasma treating time and then very slowly after that. The adhesion strength of epoxy resin/plasma-treated polyethylene joints was examined by a 90° peel test. The increase of the adhesion strength was similar to that of concentration of polar functional groups. The higher adhesion strength of epoxy resin/plasma-treated HDPE joints was observed than that of epoxy resin/plasma-treated LDPE joints since HDPE deformed more during the peel tests and had more polar functional groups on the surface.

Compatibilization mechanism of polymer blends with an in-situ compatibilizer

Abstract An in-situ compatibilizer of poly(styrene- ran -glycidyl methacrylate) (PS-GMA) was used to study the effect of blend compositions on the morphology of two different blend systems, i.e. poly(ethylene- ran -acrylic acid) (PE-AA) and polystyrene (PS) blend, and poly(butylene terephthalate) (PBT) and PS blend. The epoxy group in PS-GMA reacted easily with the carboxylic acid group in both PE-AA and PBT, thus PS- graft -PE (or PS- graft -PBT) copolymer as a compatibilizer was formed. We have shown that when there is no PS-GMA in both blend systems, the domain size of the dispersed phase in PE-AA/PS was larger than that in PBT/PS at the same blend composition. However, by increasing PS-GMA contents the reduction in the reduced domain size, defined by the ratio of the dispersed domain size with PS-GMA to the dispersed domain size without PS-GMA, in the PE-AA/PS blend system was greater than that in the PBT/PS blend system. These are attributed to the fact that Flory interaction parameter, χ, between PE-AA and PS was greater than that between PBT and PS. Based upon the experimental observation that the reduced domain size with PS-GMA contents was collapsed into one master curve regardless of blend compositions in each blend system, a compatibilization mechanism of blend with a reactive compatibilizer was proposed and discussed in terms of the interfacial area occupied by one compatibilizer chain at the interface.

Improvement of wettability and reduction of aging effect by plasma treatment of low-density polyethylene with argon and oxygen mixtures

To improve the hydrophilicity and reduce the aging effect, argon and oxygen mixtures were employed in the plasma treatment of low-density polyethylene (LDPE). Argon resulted in producing more oxygen ions and radicals in the plasma than only oxygen and forming cross-linked layers on the LDPE surface. Therefore, the water contact angle on plasma-treated LDPE decreased and the oxygen content measured by X-ray photoelectron spectroscopy (XPS) increased with the increase of argon content. The aging effect was also much reduced with the increase of argon content since argon induced cross-linking.

Toughening of cyanate ester resins with cyanated polysulfones

Abstract Bisphenol-A dicyanate (BADCy) resin was toughened by incorporating polysulfone (PSF) and cyanated polysulfone (CN-PSF). CN-PSF was synthesized by the bromination of PSF and cyanation. The effects of PSF content and interfacial adhesion between the matrix and the domain were investigated on the fracture toughness and morphology of BADCy/PSF blends. PSF formed a matrix phase when more than 20 parts per hundred of resin (phr) of PSF was incorporated. The particle size of BADCy decreased with increasing numbers of cyano groups in PSF. There was an optimum cyano group content for maximizing the fracture toughness of BADCy/CN-PSF blends with 30 phr of CN-PSF content. Toughening mechanisms were examined using scanning electron microscopy and transmission optical microscopy.

Adhesion improvement of epoxy resin/copper lead frame j oints by azole compounds

The adhesion strength of epoxy resin/copper joints is often very poor, due to the naturally formed copper oxide having a low mechanical strength. To improve the adhesion strength of epoxy resin/copper lead frame joints, copper lead frames were treated with azole compounds as adhesion promoters. The azole compounds used were benzotriazole (BTA), benzotriazole-5-carboxylic acid (CBTA), 8-azaadenine, imidazole, 2-methyl imidazole, urocanic acid, adenine, benzimidazole, and polybenzimidazole (PBI). The dependence of the adhesion strength of epoxy resin/azole-treated copper joints on the structure of the azole compound, the azole treatment time, and the azole treatment temperature was investigated. The surface coverage of azole-treated copper was examined by contact angle measurements, a surface defect test, optical microscopy, and scanning electron microscopy (SEM), and the locus of failure was studied by X-ray photoelectron spectroscopy (XPS). Triazole compounds such as CBTA and 8-azaadenine showed excellent...

Adhesion improvement of epoxy resin/polyimide joints by amine treatment of polyimide surface

Abstract Polyimide (PI) surfaces were modified to improve the adhesion strength of epoxy resin/PI joints by immersing in amine solutions. Adhesion strength of epoxy resin/amine-treated PI joints were measured depending on structure, molecular weight, concentration, treatment time and drying temperatures of amines. There was an optimum drying temperature for maximum adhesion strength after amine-treatment of PI surface. The optimum drying temperature and the maximum adhesion strength increased with increasing the molecular weight of diamines or polyamines. Poly(amic amide) was formed by the reaction of primary amine of diamines and imide group of PI, and the other primary amine of poly(amic amide) reacted with the imide groups of adjacent PI chains to form cross-linked structure. In this way, adhesion strength of epoxy resin/PI joints was improved by reinforcing the weak PI surface layer. Another additional adhesion mechanism could be the chemical reaction of epoxide in the epoxy resin and unreacted amine of poly(amic amide). Adhesion strength decreased at above the optimum drying temperature since poly(amic amide) was imidized. The adhesion mechanisms and existence of optimum drying temperature were investigated using FT i.r., contact angle goniometer, X-ray photoelectron spectroscopy and rheometric dynamic spectroscopy.

Phase separation behavior of cyanate ester resin/polysulfone blends

The composition of the blends and the curing temperature affect the morphology of the blends and the phase separation mechanism. The phase separation mechanism depends on the viscosity of medium at the initial stage of phase separation determined by the amount of thermoplastics and the curing temperature, and is closely related with the final morphology. When the homogeneous bisphenol A dicyanate (BADCy)/polysulfone (PSF) blends with low content of PSF (less than 10 wt %) were cured isothermally, the blends were phase separated by nucleation and growth (NG) mechanism to form the PSF particle structure. On the other hand, with more than 20 wt % of PSF content, the BADCy/PSF blends were phase separated by spinodal decomposition (SD) to form the BADCy particle structure. With about 15 wt % of PSF content, the blends were phase separated by SD and then NG to form a combined structure having both the PSF particle structure and the BADCy particle structure.

Effect of film formation process on residual stress of poly(p-phenylene biphenyltetracarboximide) in thin films

Abstract Soluble poly(p-phenylene biphenyltetracarboxamine acid) (BPDA-PDA PAA) precursor, which was synthesized from biphenyltetracarboxylic dianhydride and p-phenylene diamine in N-methyl-2-pyrrolidone (NMP), was spin-cast on silicon substrates, followed by softbake at various conditions over 80–185°C. Softbaked films were converted in nitrogen atmosphere to be the polyimide films of ca. 10 μm thickness through various imidizations over 120–400°C. Residual stress, which is generated at the polymer/substrate interface by volume shrinkage, polymer chain ordering, thermal history, and differences between properties of the polymer film and the substrate, was measured in situ during softbake and subsequent imidization processes. Polymer films imidized were further characterized in the aspect of polymer chain orientation by prism coupling and X-ray diffraction. Residual stress in the polyimide film was very sensitive to all the film formation process parameters, such as softbake temperature and time, imidization temperature, imidization step, heating rate, and film thickness, but insensitive to the cooling process. Softbaked precursor films revealed 9–42 MPa at room temperature, depending on the softbake temperature and time. That is, residual stress in the precursor film was affected by the amount of residual solvent and by partial imidization possibly occurring during softbake above the onset of imidization temperature, ca. 130°C. A lower amount of residual solvent caused higher stress in the precursor film, whereas a higher degree of imidization led to lower stress. Partially imidized precursor films were converted to polyimide films revealing relatively high stresses. After imidization, polyimide films exhibited a wide range of residual stress, 4–43 MPa at room temperature, depending on the histories of softbake and imidization. Relatively high stresses were observed in the polyimide films which were prepared from softbaked films partially imidized and by rapid imidization process with a high heating rate. The residual stress in films is an in-plane characteristic so that it is sensitive to the degree of in-plane chain orientation in addition to the thermal history term. Low stress films exhibited higher degree of in-plane chain orientation. Thus, residual stress in the film would be controlled by the alignment of polyimide chains via the film formation process with varying process parameters. Conclusively, in order to minimize residual stress and to maximize in-plane chain orientation, precursor films should be softbaked for 30 min-2 h below the onset imidization temperature, ca. 130°C, and subsequently imidized over the range of 300–400°C for 1–4 h by a two-step or multi-step process with a heating rate of ⩽ 5.0 K min−1, including a step to cover the boiling point, 202°C, of NMP. In addition, the final thickness of the imidized films should be

Residual stress and optical properties of fully rod‐like poly(p‐phenylene pyromellitimide) in thin films: Effects of soft‐bake and thermal imidization history

A soluble poly(amic acid) precursor solution of fully rod-like poly(p-phenylene pyromellitimide) (PMDA-PDA) was spin cast on silicon substrates, followed by soft bake at 80–185°C and subsequent thermal imidization at various conditions over 185–400°C in nitrogen atmosphere to be converted to the polyimide in films. Residual stress generated at the interface was measured in situ during imidization. In addition, the imidized films were characterized in the aspect of polymer chain orientation and ordering by prism coupling and X-ray diffraction. The soft-baked precursor film revealed a residual stress of 16–28 MPa at room temperature, depending on the soft bake condition: higher temperature and longer time in the soft bake gave higher residual stress. The stress variation in the soft-baked precursor film was not significantly reflected in the final stress in the resultant polyimide film. However, the residual stress in the polyimide film varied sensitively with variations in imidization process parameters, such as imidization temperature, imidization steps, heating rate, and film thickness. The polyimide film exhibited a wide range of residual stress, −7 MPa to 8 MPa at room temperature, depending on the imidization condition. Both rapid imidization and low-temperature imidization generated high stress in the tension mode in the polyimide film, whereas slow imidization as well as high temperature imidization gave high stress in the compression mode. Thus, a moderate imidization condition, a single- or two-step imidization at 300°C for 2 h with a heating rate of < 10 K/min was proposed to give a relatively low stress in the polyimide film of < 10 μm thickness. However, once a precursor film was thermally imidized at a chosen process condition, the residual stress–temperature profile was insensitive to variations in the cooling process. All the films imidized were optically anisotropic, regardless of the imidization history, indicating that rod-like PMDA-PDA polyimide chains were preferentially aligned in the film plane. However, its degree of in-plane chain orientation varied on the imidization history. It is directly correlated to the residual stress in the film, which is an in-plane characteristic. For films with residual stress in the tension mode, higher stress films exhibited lower out-of-plane birefringence, that is, lower in-plane chain orienta-tion. In contrast, in the compression mode, higher stress films showed higher in-plane chain orientation.