Major Project (2nd Draft)

The impact resistance development of cured epoxy by addition of poly(ethylene oxide)

Sixun et al. (1994) conducted a study to blend epoxy resin (diglycidyl ether of bisphenol A or DGEBA) and poly(ethylene oxide) or PEO and cure them with an aromatic amine curing agent. The epoxy resin had epoxide equivalent weight 185 – 210 and PEO terminated with hydroxyl group had molecular weight of 20,000; moreover, the aromatic amine curing agent was 4,4’-diaminodiphenylmethane (DDM). DGEBA and PEO were first blended at 80^oC (above the melting point of PEO) by continuous stirring. The curing agent DDM was added to the mixture by continuous stirring until a homogeneous ternary mixture was formulated. The samples of mixture were cured completely by 80^oC for 2 h plus 150^oC for 2 h. The glass transition temperature (T_g) of all samples was investigated with thermal analysis by differential scanning calorimeter (DSC) and dynamic mechanical analysis (DMA) and the Fox equation was used to compare with the T_g – composition behaviors. The results showed that addition of PEO to the system can decrease T_g of all compositions. However, the cure reaction was incomplete and there was larger negative deviation between the experimental and Fox T_gs because of the dilution effect of PEO as miscible inactive cure reaction, when there was more PEO content in the blends. The researchers suggested that PEO might make toughen epoxy resins with low glass transition temperature because of plasticization effect of PEO.

            This study provides investigating toughen epoxy resins with low Tg by blending PEO in epoxy resin. However, there are some limitations.

1)      The researchers did not study the crystallization and melting point of the mixture which could be effect from PEO or thermoplastic polymer blend. The crystallization could be formed when there is more PEO content in system and it could decrease and hinder the cure reaction (Guo et al., 2001). In addition, the melting point may reduce the thermal stability if the cured sample is applied in an extensively non-isothermal situation.

2)      The study did not inspect the change of functional group by Fourier-transform infrared (FTIR) in order to determine hydrogen-bonding interaction between the hydroxyl groups of cured epoxy and the ether oxygen of PEO in the blends. The hydrogen-bonding interaction may be an important driving force for the miscibility of the epoxy-PEO blends. This can confirm that cured epoxy-PEO blends are completely miscible (Guo et al., 2001).

3)      This study used only DSC and DMA to confirm the homogeneous ternary mixture. It should study the morphology of the mixture by scanning electron microscope (SEM) (Horng and Woo, 1997) or real-time SAXS measurement (Guo et al., 2001) to support and confirm the result from DSC and DMA.

            The strength of this study is that the addition of PEO in epoxy resins can improve the main disadvantage of epoxy resins which is low impact resistance with highly crosslinked structures. Although there are several modifiers, such as carboxyl- terminated butadiene-acrylonitrile rubber, amine- terminated butadiene-acrylonitrile rubber and silicone to improve the problems, these modifiers may make to toughen epoxy resins with high modulus and T_g. Therefore, the addition of PEO in epoxy resins may be a good way to improve impact resistance.

References

Guo, Q., Harrats, C., Groeninckx, G., & Koch, M. H. J. (2001). Miscibility, crystallization kinetics and real-time small-angle X-ray scattering investigation of the semicrystalline morphology in thermosetting polymer blends of epoxy resin and poly(ethylene oxide). Polymer, 42(9), 4127-4140.

Horng, T. J., & Woo, E. M. (1998). Effects of network segment structure on the phase homogeneity of crosslinked poly (ethylene oxide)/epoxy networks. Polymer, 39(17), 4115-4122.

Sixun, Z., Naibin, Z., Xiaolie, L., & Dezhu, M. (1995). Epoxy resin/poly(ethylene oxide) blends cured with aromatic amine. Polymer, 36(18), 3609-3613.

Major Project (1st draft)

The impact resistance development of cured epoxy by addition of poly(ethylene oxide)

Sixun et al. (1994) conducted a study to blend epoxy resin (diglycidyl ether of bisphenol A or DGEBA) and poly(ethylene oxide) or PEO and cure them with an aromatic amine curing agent. The epoxy resin had epoxide equivalent weight 185 – 210 and PEO terminated with hydroxyl group had molecular weight of 20,000; moreover, the aromatic amine curing agent was 4,4’-diaminodiphenylmethane (DDM). DGEBA and PEO were first blended at 80^oC (above the melting point of PEO) by continuous stirring. The curing agent DDM was added to the mixture by continuous stirring until a homogeneous ternary mixture was formulated. The samples of mixture were cured completely by 80^oC for 2 h plus 150^oC for 2 h. The glass transition temperature (T_g) of all samples was investigated with thermal analysis by differential scanning calorimeter (DSC) and dynamic mechanical analysis (DMA) and the Fox equation was used to compare with the T_g – composition behaviors. The results showed that addition of PEO to the system can decrease T_g of all composition. However, the cure reaction was incomplete and there was larger negative deviation between the experimental and Fox T_gs because of the dilution effect of PEO as miscible inactive cure reaction, when there was more PEO content in the blends. The researchers suggested that PEO might make toughen epoxy resins with low glass transition temperature because of plasticization effect of PEO.

            This study provides investigating toughen epoxy resins with low Tg by blending PEO in epoxy resin. However, there are some limitations.

1)      The researchers did not study the crystallization and melting point of the mixture which could be effect from PEO or thermoplastic polymer blend. The crystallization could be formed when there is more PEO content in system and it could decrease and hinder the cure reaction (Guo et al., 2001). In addition, the melting point may reduce the thermal stability if the cured sample is applied in an extensively non-isothermal situation.

2)      The study did not inspect the change of functional group by Fourier-transform infrared (FTIR) in order to determine hydrogen-bonding interaction between the hydroxyl groups of cured epoxy and the ether oxygen of PEO in the blends. The hydrogen-bonding interaction may be an important driving force for the miscibility of the epoxy-PEO blends. This can confirm that cured epoxy-PEO blends are completely miscible (Guo et al., 2001).

3)      This study used only DSC and DMA to confirm the homogeneous ternary mixture. It should study the morphology of the mixture by scanning electron microscope (SEM) (Horng and Woo, 1997) or real-time SAXS measurement (Guo et al., 2001) to support and confirm the result from DSC and DMA.

            The strength of this study is that the addition of PEO in epoxy resins can improve the main disadvantage of epoxy resins which is low impact resistance with highly crosslinked structures. Although there are several modifiers, such as carboxyl- terminated butadiene-acrylonitrile rubber, amine- terminated butadiene-acrylonitrile rubber and silicone to improve the problems, these modifiers may make to toughen epoxy resins with high modulus and T_g. Therefore, the addition of PEO in epoxy resins may be a good way to improve impact resistance.

References

Guo, Q., Harrats, C., Groeninckx, G., & Koch, M. H. J. (2001). Miscibility, crystallization kinetics and real-time small-angle X-ray scattering investigation of the semicrystalline morphology in thermosetting polymer blends of epoxy resin and poly (ethylene oxide). Polymer, 42(9), 4127-4140.

Horng, T. J., & Woo, E. M. (1998). Effects of network segment structure on the phase homogeneity of crosslinked poly (ethylene oxide)/epoxy networks. Polymer, 39(17), 4115-4122.

Sixun, Z., Naibin, Z., Xiaolie, L., & Dezhu, M. (1995). Epoxy resin/poly (ethylene oxide) blends cured with aromatic amine. Polymer, 36(18), 3609-3613.

Minor Project

Minor Project

            My research question is whether type of amine curing agent is affecting curing temperature of epoxy system for read-write head in hard disk drive (HDD). The amine curing agent is an important component in epoxy adhesive because it induces the curing reaction and continues to complete reaction. However, there are several types of amine curing agents and they affect the curing temperature. Therefore, the amines are studied in order to formulate the epoxy adhesive whose curing temperature is match with temperature of process in HDD production.

            Researchers who have looked at this subject are Tanmoy Maity and Hongyang Cai. The former formulated epoxy adhesive with aromatic amine and the latter used aliphatic amine as curing agent.

            Maity et al (2007) reports that the curing behavior of epoxy adhesive with aromatic amine curing agents is investigated by differential scanning calorimetry (DSC) analysis. The curing temperature is widely about 150 – 210^oC.

            Cai et al (2008) reports that the DSC thermograms of aliphatic amine-epoxy systems show the curing temperature about 115 – 125^oC. This temperature is lower and narrower than results of Maity because the structure of aliphatic amines is more mobility than structure of aromatic amines at the same temperature.

            Debate centers on the basic issue of process temperature. The epoxy adhesive can be react if the temperature of production is not less than curing temperature of epoxy system.

            My work will be closer to the research of Cai et al (2008) because the temperature of production is 120 – 130^oC and the curing temperature of aliphatic amine-epoxy systems is about 115 – 125^oC. Moreover, the temperature of production should not be more than 150^oC because the read-write head will be damaged at high temperature.

            Finally, I expect my contribution will be the way to choose and formulate the amine-epoxy systems whose the curing reaction is appropriate for HDD production in order to increase the productivity and especially reduce any problem during operation. (318 words)

Reference List

Cai, H., Li, P., Sui, G., Yu, Y., Li, G., Yang, X., Ryu, S. (2008). Curing kinetics study 
               of epoxy resin/flexible amine toughness systems by dynamic and isothermal 
               DSC. Thermochimica Acta, 473, 101-105.

Maity, T., Samanta, B.C., Dalai, S., Banthia, A.K. (2007). Curing study of epoxy
              resin by new aromatic amine functional curing agents along with
              mechanical and thermal evaluation. Materials Science and
              Engineering: A, 464, 38-46.

Assignment#2: Writing an introduction

The Development of Epoxy Adhesive whose Properties are Suitable
for Head Gimbal Assembly Process

by

Tossapol Boonlert-uthai

Stage 1: The head gimbals assembly process (HGA) operates in a hard disk drive manufacturing plant. HGA is made by assembling slider (read-write head) on a suspension with adhesive in which it is an important part in a hard disk drive. According to the Head Gimbal Assembly Process in Western Digital (Bang Pa-in) Co., Ltd. (2012), there are two assembly lines. In the first assembly line, semi automation, is divided into two steps, which are dispensing glue from a syringe on a suspension in the area that will be adhered to the slider via an auto adhesive dispensing (ATD) machine. After that, the slider is then put down on the glue-dispensed area of a suspension and radiated ultraviolet (UV) light to cure an adhesive for setting via an optical system corporation (OSC)-automation slider bond. In this stage, an adhesive is partially cured to be able to hold a slider. On the second assembly line, automation one, auto core adhesion machine (ACAM) proceeds all steps in one machine. After that, the part is put in an IR oven to enable an adhesive to be completely solidified and dried. Finally, HGA is sent to the further stages such as quality control, cleaning and packing process.

Stage 2: The adhesive used for HGA process is an epoxy type. The component of epoxy adhesive depends on HGA process, UV curing and thermal curing. Therefore there are epoxy monomer, photoinitiator (for UV curing) and curing agent (for thermal curing) which are the main composition. Decker (1996) proposed the mechanism of UV curing in which a photoinitiator absorbs UV-radiation to cleave the radical or reactive species, such as free radicals and protonic acid that initiate cross-linking polymerization with a monomer according to a radical and cationic mechanism, respectively, and then obtains the polymer network. For the thermal curing reaction, epoxy or oxirane group reacts with amine group of curing agent is called polyaddition reaction (Petri, 2006, p.64). Furthermore, Golaz et al. (2013) reported that ambient temperature can influence rate of polymerization. When operating temperature increases, the adhesive’s viscosity decreases in which it can accelerate the rate of polymerization due to higher mobility of adhesive molecules.

Stage 3: There are several problems relating to process, for example, instability of adhesive’s viscosity, air bubbles in adhesive and degree of cure, have been encountered. Causes of the problems of epoxy adhesive have not been thoroughly studied. Data were collected from production line and inquiring the problems from authorities and engineers. After that, the problems are analyzed and some hypotheses are considered.

Stage 4&5: Therefore, this research aims to characterize the epoxy adhesive used in HGA process in terms of thermal, rheological and chemical properties of uncured and cured adhesive. After that the characteristics of epoxy adhesive are applied with the HGA process to use epoxy adhesive properly and efficiently. Afterwards, formulating epoxy adhesive whose properties are suitable for head gimbals assembly process than current adhesive will be performed.