外文翻译:UV固化曝光时间对机械的影响和物理性能的环氧、乙烯基酯...

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VOL. 6, NO. 4, APRIL 2011 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences ©2006-2011 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 104 EFFECTS OF UV CURING EXPOSURE TIME TO THE MECHANICAL AND PHYSICAL PROPERTIES OF THE EPOXY AND VINYL ESTER FIBER GLASS LAMINATES COMPOSITES J. Ramli1, A. R. Jeefferie2 and M. M. Mahat3 1Faculty of Mechanical Engineering, University Malaysia Pahang, Lebuhraya Tun Razak, Kuantan, Pahang Darul Makmur, Malaysia 2Engineering Materials Department, Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, Durian Tunggal, Melaka, Malaysia 3Faculty of Applied Sciences, Universiti Teknologi MARA, 40450, Shah Alam, Selangor Darul Ehsan, Malaysia E-Mail: [email protected] ABSTRACT Ultra-violet (UV) curing process is introduced in the curing of polymer matrix composites (PMC) for the application in producing bullet proof vest. Two types of adhesives or matrix materials were used: epoxy and vinyl ester. Each of them were mixed together with different types of photoinitiator; Bisacyl Phosphine Oxide (BaPO) and Alpha Hydroxyl Ketone Peroxide (AHK) at 1.0 per hundred of resin (phr) from the total proportion of the mixture. Sandwich construction of the PMC was done by hand lay-up process where the mixture was wiped on the fiber layers. Samples were then cured under various duration times which are 3, 6, 9 and 12 minutes to compare the overall quality of produced composites under the exposure of the UV light. The laminate was then tested to determine its characteristics of physical properties and its behavior to the applied loads. Morphological observation through Scanning Electron Microscope (SEM) was performed in order to evaluate the quality of adhesion between each fiber layer and matrix wetting behavior. Vinyl ester is not recommended to be used as the matrix since two days is required to make it fully cured unlike epoxy which was cured rapidly once exposed under UV light. On the other hand, the effect of curing time shows the optimum result for density was obtained at 12 minutes of curing time. Curing time between 6 to 9 minutes is found to be optimum for tensile strength value. Three minutes of curing under UV light exposure caused maximum value in penetration resistance or hardness for the resulted composite laminates. Keywords: UV curing, epoxy, vinyl ester, photoinitiator, curing time effects, mechanical, physical, morphological. INTRODUCTION Ultraviolet (UV) curing is known to be a hardening process of liquid material when it is exposed to UV radiation. The curing process of polymeric material by using UV light has played an important role in the processing of polymer material since the process is more advantageous than heat cure. Although curing by this technique is relatively slow compared to heat curing, the result is high strength and high impact properties of Polymer Matrix Composites (PMC) due to crystallinity enhancement of the polymers through cross-linking mechanism. One of the applications of the curing process of polymeric material by ultraviolet light can be seen in producing personal protective equipment (PPE) for instance bullet proof vest. This research is conducted as the preliminary stage in producing the bullet proof vest where the PMC will be used to wrap an alumina plate in order to act as holder when high ballistic impact hit the bullet proof vest. This will avoid alumina plate break into pieces once bullet is triggered to hit them. The objective of this research is to develop an outside part of bullet proof vest and to assess the ability of the UV light in converting the thermosetting material to become harden or cure under the UV exposure with the assistance of photoinitiator. In addition, it is also to study the parameter of curing time in the UV curing process of polymeric materials and its effects to the properties of the resulted products. This study has its own importance and benefits, which are to provide the fundamental understanding on the effects of UV curing to the physical and mechanical properties for the application of bullet proof vest manufacturing technique. The output of the cured PMC will then be studied and analyzed. Although a particular substance to be processed may vary widely depending upon its application and the final use, they are basically composed of polymer. UV curing, a conversion process of polymeric materials from a liquid to solid by UV light is a popular alternative instead of conventional drying. The number and variety of applications for UV curable inks, coatings, and adhesives, continue to expand at a rapid pace and pose new design challenges to increase cure efficiency, speed, and the physical properties of the cured polymer film. UV curing is highly adaptable to painting and coating, decorating, and assembling of a great variety of products owing to some of its key attributes. It is a low temperature process where heat is not required and a high speed process cure is nearly instantaneous. In addition, it is energy efficient processes whereby energy is invested only in the curing reaction, not in heating [1]. UV curing adhesive also have two components. One part is the adhesive resin itself and the second part already mixed in is called a photoinitiator. The secret of the photoinitiator is that, it will not react with the resin by itself. The photoinitiator must absorb UV light before anything can happen. When the UV light is delivered, the photoinitiator will undergo a chemical reaction and produce products that cause the adhesive to harden better. One type of photoinitiator used in this study VOL. 6, NO. 4, APRIL 2011 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences ©2006-2011 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 105 is BAPO with Irgacure 819 as its trade name. BAPO is a versatile photoinitiator for radical photo polymerization of unsaturated resins upon exposure to UV light. It has demonstrated useful application in white pigmented formulations, the curing of glass fiber reinforced polyester/styrene systems and for clear coats for outdoor use with light stabilizers. The outstanding absorption properties of BAPO also allow curing of thick sections [2]. On the other hands, AHK is the second photoinitiator that used in this research with trade name Irgacure 184. This is highly efficient non yellowing photoinitiator, which is used to initiate the photopolymerisation of chemically unsaturated prepolymers in combination with mono or multifunctional vinyl monomers [2]. UV light has two important characteristics which are wavelength and intensity. For the photoinitiator to react correctly, it must be exposed to light of the correct wavelength and of sufficient intensity. Otherwise, the chemical reaction may not happen completely. The result will be poor or inconsistent in the adhesive performance [3]. UV curing is dependent on photon molecule collision. The successful implementation of any UV curing process is dependent on the ease or difficulty of projecting photons into a curable material [1]. The optical properties of the curable material (polymeric resin) and the optical characteristics of the lamp must be matched to produce an effective UV curing system. The UV energy striking the surface causes the photoinitiator to trigger the polymerization reaction. The material is usually solidified or dried when it exits the UV cure zone. The time, and consequently the space, required for cure is significantly less than thermal drying methods. Because the process relies on UV light to initiate the crosslinking of molecules, it does not evaporate any solvents nor significantly heat the substrate [4]. The application, particularly the end product it produces, will determine the requirements of the physical properties of the cured photochemistry [2]. UV processing offers several advantages over other finishing methods. Typical product lines involve coatings (on wood, metal, paper and plastic), inks (for letterpress, lithographic, gravure and screen printing) and adhesives (for film, foil or paper substrates). The industries using these technologies are diverse and varied, including automotive components, medical products, electronics, CDs and DVDs, two piece and three piece can print, pipe and tube coating, furniture, fiber optics, flooring, packaging and containers [4]. MATERIALS AND METHODS Raw materials and sample preparation Polymeric resins are the main raw material that was mixed together with photoinitiator. Both epoxy and vinyl ester was act as binder in the mixture. It has been bought from Wee Tee Tong Chemicals Pte. Ltd, Singapore. Meanwhile, photoinitiator material has been sponsored by Ciba Specialty Chemicals, Singapore. The photoinitiator was added to the matrix materials in the amount of part per hundred of resin (phr), with ratio of 1:3. There are two types of samples that involved in this research. Sample B is a series of sample with vinyl ester as the matrix material while sample C is the sample with epoxy as the matrix material. Details on sample formulation are described in the following Table-1. Each sample B and C was mixed together and stirred to obtain homogenous solution. The total weight of resin is 120 gram. The composition ratio of BAPO to AHK is 1:3 and added in the amount of 1.0 phr from the total mixture. At the first stage of sweeping process, a layer of woven roving was placed on a flat surface. Once mixture of resin and photoinitiator is homogenized, it was swept over the top of the glass using brush. After that, another layer was put on the first glass laminate and the same procedure was repeated until the laminate of l0 layers is produced. This laminates construction was done repeatedly for another sample. After the 10 layers of woven roving stick together, the laminate was then undergoing vacuum bagging process where it was put in a vacuum chamber. By performing this step, the adhesion between the layers was improved and the entrapped air was expelled. After the vacuum bagging stage, the glass laminate was exposed to UV light. Once the process completed, sample was taken out and ready for testing. Table-1. Details on sample formulation and curing strategy. Sample Details for each sample B Woven roving + Vinyl ester + BAPO + AHK ; (BAPO + AHK = 1.0 phr) 3 minutes 6 minutes 9 minutes 12 minutes C Woven roving + Epoxy + BAPO + AHK ; (BAPO + AHK = 1.0 phr) 3 minutes 6 minutes 9 minutes 12 minutes VOL. 6, NO. 4, APRIL 2011 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences ©2006-2011 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 106 Sample testing Density test Density test was carried out in order to study the physical properties of UV cured laminate composites produced with parameter that has been varied for instance type of adhesive used to develop sandwich construction between each layer of glass as well as the time of exposure under UV light. This test was conducted by applying the Archimedes principle. Tensile test Tensile test was carried out in accordance to ASTM D 3039 standards. The test was carried out at a crosshead speed of 2 mm per minute. Specimens for the tensile test were produced by cutting out laminate strips measuring 200 mm x 25 mm. The specimens were cut 3 mm oversize and final dimensions obtained by grinding and using sand paper to produce smoother end surface. Aluminum end tabs of 3.2 mm thick and measuring 50 mm x 25 mm was locally bonded onto the both ends of each laminate. A total of 8 specimen strips were cut from each of the composite laminates produced. For this testing, two series of sample were produced. Series B produced with vinyl ester as the matrix material while series C has epoxy as the matrix material. The purpose of this testing is to study the effects of resin used and to study the effects in curing by increasing the exposure time under UV light. Figure-1 below shows samples for tensile testing. Figure-1. Specimen for tensile test ASTM D 3039. Hardness test Hardness test was performed to the samples in order to know the resistance of surface penetration to the glass laminates that has been cured under UV light. The hardness test was conducted in the Brinell hardness test mode with diameter of indenter is 10 mm and 100 N of loads. Morphological observation by Scanning Electron Microscope (SEM) The purpose of this observation is to determine if proper adhesion and fiber wet out occurred in each of the laminates. SEM used for this observation is the variable pressure scanning electron microscope. RESULTS AND DISCUSSIONS Physical testing of density behavior The purpose of the density test is to observe the effect on the physical properties of UV cured laminate composites produced by different type of resin and to study if variability exists in the variation of curing time under the UV light. Generally, the density of the vinyl ester used is 1.35 g/cm3 while for the epoxy; the density is 1.50 g/cm3. The samples using epoxy as an adhesive have greater density as compared to samples using vinyl ester. This result is in accordance with the density data of both virgin resins where epoxy’s density has greater value than vinyl ester. Figure-2 shows the density behavior of PMC in function of curing time under the UV light to produce composites of samples B and C. Based on the plot, the density value for sample B and C seems to increase constantly with the increasing of curing duration. For both sample B and C, the plotted data shows an increment as a time of curing increased. This indicates that the exposure time under the UV light affects the density value of UV cured laminates. It may caused by the atom of resin that might have enough energy to move, in order to make better arrangement between them while curing is in progress. In addition, this will allow the fibers to make better linkage due to curing with polymer chain as time of UV light exposure increased. Chain in the resin will have more time to arrange the fiber closer to each other. Thus, the probability for the void to exist was minimized by longer exposure time of UV light. The void occurred preferentially at the ply interfaces and grew quite large [5]. Density (g/cm3) vs. Time of Curing (Minutes) 1.1 1.2 1.3 1.4 2345678910111213 Time of Curing (Minutes) Density (g/cm3) Sample B Sample C Figure-2. Density of samples at various curing time exposure. Mechanical testing of tensile strength Figure-3 shows the plotted data for tensile strength versus time of curing for both samples in group B and C. From the graph, both of the tensile strength curves showed the strength peaks at certain value of exposure VOL. 6, NO. 4, APRIL 2011 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences ©2006-2011 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 107 time. Therefore, in overall, distribution data shows that, series of sample C have greater tensile strength compared to the series of sample B. From the plotted graph, the value of tensile strength for 3 minutes of curing exposure is the lowest compared to all data obtained in the testing result for the series of sample B. This might due to not enough curing time of 3 minutes for the adhesive to complete the transformation phase from liquid to solid under the UV light exposure. Thus, it produces weak bonding between each fiber between the polymer matrixes. The glass fiber woven roving inside the laminate is still wet, thus not strongly bonded between each other. For 6 minutes of exposure time, the mechanical tensile strength of composites for both polymer matrixes were getting stronger compared to 3 minutes of curing exposure. The wet fibers become completely dried, making the adhesion bonded strongly. For further 3 minutes of curing exposure, for the sample B3, the tensile strength was found to increase further, however for curing time up to 12 minutes, the tensile strength decreased. At 12 minutes of curing time the fibers become charred where it will not act as reinforcement and the ability to bond between each particle become limited. Tensile Strength (N/mm2) vs. Time of Curing (Minutes) 0 50 100 150 200 250 2345678910111213 Time of Curing (Minutes) Tensile Strength (N/mm2) Sample B Sample C Figure-3. Tensile strength of samples at different curing time exposure. For sample C1, 3 minutes of curing under the UV light exposure shows greater tensile strength. This is due to the type of adhesive where epoxy has better properties compared to vinyl ester. The adhesive between the fibers is strongly bonded for epoxy resin. However, the limitation of the epoxy is that, it will not cure as rapid as vinyl ester. After UV curing step, it needs another 2 days of drying period at room temperature to be fully cured and hardened. After another 3 minutes of curing exposure, the tensile strength was increased further. This means that, higher force is needed to break the sample because better properties were achieved for sample C2. As the exposure time increased, the result showed a constant value of tensile strength but there was a bit reduction occurred at 9 minutes of exposure time. This means that for epoxy resin, the sample achieves peak value between 6 to 9 minutes of exposure time. As the exposure time increased until 12 minutes, the value of tensile strength was decreased. Hardness test evaluation Figure-4 shows the plotted data for hardness of produced composites that was cured under the UV light with different exposure time. Series of sample B represent samples that were wiped with vinyl ester as adhesive resin and series of sample C represent samples that were wiped by epoxy as adhesive material. Based on Figure-4, the plotted graph shows that epoxy which is represented as series of sample B have greater hardness value. For series of vinyl ester sample B1 shows that, with 3 minutes of exposure time, the hardness is better compared to sample B2 even B2 was exposed under the UV light for longer period which is 6 minutes. The comparison can be clarified by the idea of uneven adhesive distribution on glass laminate during the wiping process. The resin of adhesive was probably wiped on the glass layers in an uneven condition where the resin distribution may slightly varied at different places on the same plate. Hardness (HB) vs. Time of Curing (Minutes) 5 8 11 14 17 20 2345678910111213 Time of Curing (Minutes) Hardness (HB) Sample B Sample C Figure-4. Hardness of samples at different curing time. In addition, void may exist in the fiber layers that resulted in lower hardness value. Thus, during the hardness test, the result obtained shows that the variation in hardness is depends on the resin distribution on glass laminate. Thicker adhesive wiped on glass laminate may have greater hardness value. For sample B3, which is 9 minutes of exposure time under UV light, there is a bit increment in hardness values as compared to 6 minutes of curing time. Hardness value was increased further when cured until 12 minutes of UV exposure for sample B4. On the other hand, sample C1 has highest value of hardness among other sample in series C. However, for 6 minutes of curing time, the value of hardness for sample C2 shows a bit decrement. The value increases slightly at 9 minutes of curing time for sample C3 but decreases again for sample C4 down to 16.7 HB. Thus, from the data obtained, it is indicated that, with the increasing of curing time, only series of sample that used vinyl ester as adhesive shows an increment in term of hardness. In contrast, the value of hardness for epoxy is dec 展开阅读全文