Javier KM, Nadura R, Rengel CJ, Tumolva T. Evaluation of the sorption properties of a self-adhesive hydrogel wound dressing. Key Engineering Materials [Internet]. 2019;821 :10-16. Publisher's VersionAbstract

A novel self-adhesive wound dressing product was developed using a hydroxyethyl cellulose (HEC) hydrogel layered with a TAPE-gelatin bioadhesive. This wound dressing was then evaluated for its sorption properties through diffusion and swelling tests, and the parameters analyzed were hydrogel formulation, wound dressing thickness and adhesive layer thickness. Results showed that the wound dressing produced using 6% NaOH/5% thiourea in the crosslinking solution, with 2.5 mm hydrogel thickness, and 0.2 mm TAPE-gelatin thickness had the highest water absorbed. Lastly, analysis on swelling kinetics based on a previous study was conducted to determine the diffusion coefficients for the composite wound dressing.

Jamlang J, Marañon MT, Rigor GJ, Tumolva T. Developing a physically cross-linked hydroxyethyl cellulose hydrogel for wound dressing applications. Materials Science Forum [Internet]. 2019;947 :3-12. Publisher's VersionAbstract
Physically cross-linked hydroxyethyl cellulose (HEC) hydrogels of different concentrations are synthesized at room temperature, and the hydrogel films are evaluated for its antimicrobial and exudate absorption properties. Results showed that all the hydrogels inherently possess antimicrobial property for all the HEC concentrations tested. The maximum water uptake is determined to be 173.8% for the 13.75% HEC hydrogel. At the same HEC concentration, the hydrogel absorbed the largest amount of exudate. The rate of diffusion in the longitudinal direction is observed to be higher, but the exudate was observed to travel generally farther in the radial direction. The diffusion coefficient model reported by Kipcak, et al. in 2014 was observed to be valid and applicable for the HEC hydrogels. Lastly, scanning electron microscopy showed the microstructure of the fibers and pores of the hydrogels.
Nalzaro PJB, Doctor JNP, Domingo JRC, Madrid LLB, Tumolva TP. A modelling study on the degradation of hydroxypropyl cellulose/sodium alginate blend microcapsules for controlled drug delivery. Basic & Clinical Pharmacology & Toxicology [Internet]. 2019;124 (S3) :12. Publisher's VersionAbstract

Hydrogels are known suitable microencapsulating materials for the controlled delivery of active pharmaceutical ingredients in the body. To ensure biocompatibility and cost- effectiveness, the hydrogel microcapsules can be synthesized using naturally abundant biopolymers such as cellulose and its derivatives, as well as phycocolloids such as alginates that can be derived from locally indigenous seaweeds. This study focuses on a hydrogel developed from blending hydroxypropyl cellulose (HPC) with sodium alginate (NaAlg): with the combined chemical stability of HPC and NaAlg allows for the microcapsules to resist degradation along the digestive pathway up until the entry region of the small intestine, where the active ingredient should be released for optimal bioactivity. It is important to have a better understanding of the degradation phenomenon of the HPC- NaAlg hydrogel microcapsules so they can be more effectively used; hence, mathematical modeling is applied to provide significant insights and a deeper understanding on the blend ' s degradation behavior. In this study, it is desired to analyze the rate of degradation and obtain and validate a hydrogel degradation model by determining the associated kinetic parameters. Hydrogel samples were prepared from 50:50 HPC/NaAlg mixture using aqueous CaCl 2 solution as crosslinking agent. The samples were subjected into a diffusion test under different solutions to simulate the pH conditions throughout the gastrointestinal tract (pH 2, 4, 6 and 7). The diffusion- reaction behavior is mathematically modelled to determine pertinent diffusion kinetic parameters. Results show that only minimal swelling occurs under pH = 2, reaching only about 80.19% weight increase, and the hydrogel does not disintegrate despite the acidity, and there are no significant changes observed over the entire duration of the diffusion. For pH = 4, the weight of the hydrogel increases rapidly initially but slows down over time, with an observed maximum weight increase of 1385% around 70 minutes into the test. For pH = 7, the hydrogel samples are observed to quickly swell until they disintegrate in as early as 7 minutes, reaching around 973.1% in weight increase. Under basic conditions, the crosslinking bonds weaken since the calcium ions are drawn to the alkaline solution to form calcium hydroxide- thus, leading to swelling and disintegration. Using the diffusion data, the pH (concentration) dependence functions of the diffusion coefficient and plateau time parameter for a one- dimensional, combined diffusion and swelling kinetic model is established. These obtained functions are validated by the good agreement of the model with the experimental data taken for diffusion for pH = 6.

Ayapana CMN, Tumolva TP. Developing a gum arabic-citric acid bioadhesive for liquid bandage application. Basic & Clinical Pharmacology & Toxicology [Internet]. 2019;124 (S3) :11. Publisher's VersionAbstract

Open wounds resulting from either a surgical or a traumatic disruption of tissues layers should be sufficiently covered to prevent infection and promote fast healing and closing. At present, the application of bioadhesives as liquid bandages is being considered as alternative to conventional wound dressings such as dry gauzes since they provide several advantages such as reduced risk of infection and applicability in the different contours of the body. However, the current commercially available liquid bandages are relatively expensive; thus, there is still a need to develop novel bioadhesives that can be produced at a lower cost. This study aims to produce an inexpensive, sustainable, antimicrobial, biocompatible and effective external tissue liquid bandage using citric acid (CA) and gum Arabic (Gum). Gum- CA samples were prepared at different Gum-to-CA weight ratios and subjected under the following characterization tests: drying time, water swelling capacity, and surface hydrophilicity via water contact angle method. They were also subjected to antimicrobial and cytotoxicity test to establish antimicrobial activity and biocompatibility. The adhesion strengths of the Gum- CA samples were determined using T- peel test following ATSM F2256- 05 and were compared with that of a commercialized liquid bandage. Lastly, the cost effectiveness of Gum- CA as a liquid bandage is determined by calculating the total material cost in comparison to that for liquid bandages currently available in the market. Analysis shows that a 3:2 Gum- to- CA formulation gives a contact angle of 75.48°, which indicates a surface hydrophilicity that is reportedly favorable for optimal wound healing. The assays show that Gum- CA does not show antifungal activity against C. albicans but still exhibits antibacterial activity against E. coli, S. aureus, P. aeruginosa, and S. marcescens. The cytotoxicity test proves satisfactory, with a cell viability > 70% as required by ISO 1099 3- 5:2009. Water uptake is measured at 544.69% for 4:1 Gum- CA ratio and 300.31% for 3:2 Gum- CA ratio, which suggests the bioadhesive's ability to absorb exudate and provide a moist environment. The T- peel test shows that adhesion strength of a 2:3 Gum- CA sample is comparable with that of commercialized liquid bandage. Lastly, the calculated total material cost of Gum- CA is significantly lower than that of the liquid bandages currently available in the market, which indicates that this bioadhesive can be produced and sold commerciallyat a significantly lower price.

Tumolva T, Aquino SH, Cabeguin KM, Imperial JF. Development of a self-adhesive cellulosic hydrogel wound dressing. Key Engineering Materials [Internet]. 2019;801 :15-20. Publisher's VersionAbstract
In this study, a self-adhesive hydrogel wound dressing was developed by combining hydroxyethyl cellulose (HEC) hydrogel with a tannic acid-polyethylene glycol (TAPE) adhesive bioadhesive with gelatin. Test samples of the cellulosic wound dressing were prepared with three (3) different mixing ratios of the crosslinking solution, three (3) different adhesive formulation, and two different hydrogel/adhesive contact area (flat, ridged). Adhesion performances of these samples on porcine skin were evaluated by performing a T-peel test. Analysis of the HEC/TAPE-gelatin interface showed that the HEC cross-linking agent formulation, adhesive thickness, and presence of surface ridges showed significant three-way interaction effects, and these parameters were modeled using orthogonal polynomials and optimized via response surface methodology (RSM). The adhesion on the HEC-TAPE-gelatin interface was also investigated further using scanning electron microscopy (SEM), where it had been observed that greater adhesion occurred with a decrease in cross-linking density, thinner adhesive layer, and the presence of ridges. Lastly, disk diffusion testing indicated greater antimicrobial activity (mean inhibition zone = 12 mm) against S. aureus and P. aeruginosa in contrast to commercial hydrogel dressings (mean inhibition zone = 7.5 mm), while MTT assay on human lymphocytes resulted to a 98% cell survival rate. Based on these results, it was concluded that it is feasible to use HEC hydrogel with TAPE-gelatin adhesive for manufacturing self-adhesive wound dressing products.
Ramirez JCC, Tumolva TP. Analysis and optimization of water-based printing ink formulations for polyethylene films. Applied Adhesion Science [Internet]. 2018;6 (1). Publisher's VersionAbstract
Water-based ink formulations containing wax, surfactant, and defoamer additives were prepared and printed on polyethylene film substrates. Standard test methods for adhesion, rub resistance, and gloss were done on the printed polyethylene films. Quantitative methods for the assessment and evaluation of the three print properties were developed. Image analyses were done to quantify adhesion and rub resistance. Quantitative measurement was done to quantify gloss. Data were analyzed using mixture design modelling and optimization. Modelling results show that adhesion and gloss are described by special cubic model equations, while rub resistance is described by a linear model equation. Contour plots and 3D surface graphs were generated showing the response surfaces of the print properties. The effects of varying the mass fractions of wax, surfactant, and defoamer on adhesion, rub resistance, and gloss were determined. It was found that increasing wax increases rub resistance, while increasing surfactant increases gloss, and increasing defoamer increases adhesion. There is dependency found between the mass fraction of wax, surfactant and defoamer with respect to the rub resistance, adhesion and gloss. Multi-objective optimization revealed that optimum adhesion, rub resistance, and gloss is obtained by a formulation containing equal mass fractions of wax and surfactant but no defoamer.
Tumolva TP, Sabarillo NS. Characterization of MEPCM-incorporated paint as latent heat storage system. International Journal of Chemical Engineering and Applications [Internet]. 2017;8 (3) :203-209. Publisher's VersionAbstract
This study aimed to determine the effect of the mixing speed and pre-polymer dropping rate during synthesis of microencapsulated phase change materials (MEPCMs), and to assess the performance of MEPCM-incorporated paint as a latent heat storage (LHS) system. N-octadecane as phase change material was encapsulated with resorcinol-modified urea- melamine-formaldehyde at two different mixing speeds and four different pre-polymer dropping rates, and Fourier transform infrared (FTIR) spectroscopy was done to confirm success of microencapsulation. Scanning electron microscopy (SEM) revealed that increasing the homogenization speed and decreasing the pre-polymer dropping rate decreases the microcapsule size. Differential scanning calorimetry results showed that latent heat and encapsulation ratio increases with increasing mixing speed and decreasing pre-polymer dropping rate. The synthesized MEPCMs were incorporated into white paint at three different concentrations, and temperature profiling revealed that the paint’s temperature buffering capacity generally increases with increasing mixing speed, decreasing pre-polymer dropping rate and increasing MEPCM concentration.
Tumolva TP, Vito JKR, Ragasa JCR, Cruz RMCD. Mechanical properties of NFRP composites using anahaw (Saribus rotundifolius) fibers treated with sodium alginate. Journal of Chemical Engineering and Materials Science [Internet]. 2017;8 (7) :66-73. Publisher's VersionAbstract
Natural fiber reinforced polymer (NFRP) composites have been a focus of various research projects because of their advantages compared to traditional fiber reinforced plastics. In this study, Anahaw (Saribus rotundifolius) was used as fiber source because it is abundant in the Philippines. The fibers were treated by immersing in a sodium alginate solution and then in a calcium chloride solution. The treated fibers were used to reinforce the orthophthalic unsaturated polyester. Mechanical properties were tested using a universal testing machine (UTM) and the fracture surfaces were characterized using a scanning electron microscope (SEM). Sodium alginate treatment resulted in higher tensile and flexural strengths of the composites as compared to those reinforced with untreated fibers. On the other hand, the sodium alginate treatment was not able to show any improvement on the wet mechanical properties of the material. The increase in fiber load was also found to increase the stiffness of the composites. The measured stiffness and modulus of the treated Anahaw fiber-reinforced composite was found to be comparable to those of commercially available particle boards and fiber boards.
Tumolva TP, Jr. DE, Laus TJ, Requejo B. Mechanical properties of green composites from corn husk. MATEC Web of Conferences [Internet]. 2016;62. Publisher's VersionAbstract
This study explores the feasibility of using lignocellulosic waste and cellulosic fibers from corn husks in the production of green composites, with orthophthalic unsaturated polyester (ortho-UP) resin as a matrix. Lignocellulose was extracted from corn husk fibers by alkali treatment using 1M NaOH, and the dried lignocellulose extract was characterized using FTIR spectroscopy. Composites containing varying weight fractions of lignocellulose, treated fibers and ortho-UP were fabricated, and the tensile and flexural strengths and moduli were measured. Based on the results, it was observed that the composite containing 15wt% fiber possesses the highest tensile modulus, while the one with 20wt% lignocellulose showed the highest flexural modulus. The composites were also subjected to scanning electron microscopy to examine the fracture surfaces of the composites. Furthermore, the water sorption behavior of the composites was also studied, and it was observed that all the composites obey Fickian diffusion.
Vasquez JMG, Tumolva TP. Synthesis and characterization of a self-assembling hydrogel from water-soluble cellulose derivatives and sodium hydroxide/thiourea solution. American Journal of Chemistry [Internet]. 2015;5 (2) :60-65. Publisher's VersionAbstract
Hydrogels are hydrophilic polymers that can swell and absorb water without dissolving, provided that chemical or physical crosslinks exist among the macromolecular chains. The hydrogel can be derived from synthetic and natural polymers, the latter having desirable properties such as biocompatibility and biodegradation that do not produce adverse and reproductive and developmental effects. The aim of this study was to synthesize a physical hydrogel from a water-soluble cellulose derivative and a solution of 6 wt% sodium hydroxide/5 wt% thiourea. Physical hydrogels (also called self-assembling hydrogels) are formed when macromolecules self-assemble through non-covalent, secondary molecular interactions such as hydrophobic, electrostatic, and H-bonding. Hydroxyethyl cellulose, hydroxypropyl cellulose, and microcrystalline cellulose were used in this study. A hydrogel made from hydroxyethyl cellulose containing weight percentages of 5, 7.5, 10, and 12.5 wt% in the sodium hydroxide/thiourea solution. Hydroxypropyl cellulose only formed a cloudy yellow solution while microcrystalline cellulose did not dissolve at all in the solution. The hydroxyethyl cellulose/ sodium hydroxide/thiourea hydrogels were then characterized according to its functional groups present, physical structure, and mechanical properties, and biocompatibility.
Kubouchi, M., Tumolva TP, Shimamura Y. Biofiber-reinforced thermoset composites. In: Polymer Composites. Vol. 3. Weinheim, Germany: Wiley‐VCH Verlag GmbH & Co. KGaA ; 2014. pp. 213-237. Publisher's VersionAbstract

One way of generally classifying natural fiber-reinforced plastic (NFRP) composites is according to the type of polymeric resin used as matrix. The thermoplastic-based NFRP composites are presently obtaining a continually expanding range of applications; however, the major portion of the NFRP market is still comprised of biofiber reinforced thermoset-based composites. Thermoset matrix systems dominate the composites industry because they are more reactive and easier to impregnate with fillers. They also play an important role in the industry due to their high flexibility for tailoring desired ultimate properties. Various thermosetting resins have been utilized in the manufacture of composites for their excellent chemical stability, which allows the possibility of long-term applications such as pipes and chemical tank linings. They are also suitable for high temperature applications such as insulators. However, thermosetting resins are brittle at room temperature and have low fracture toughness- hence the necessity for reinforcements such as fibers.

This chapter reviews the recent studies on the manufacture of thermoset biocomposites, which may be produced either by using biothermoset matrices or by using biofiber reinforcements. Because natural fibers, though highly eco-friendly, have poor mechanical strength and low stability, the use of thermosetting matrices offer a distinct advantage when it comes to fabricating NFRP composites designed for very long service lifetime applications.

Tumolva T, Apayla RA, Dolor AM. Degradation behavior of CFB fly ash filled unsaturated polyester composites under acidic environment. Advanced Materials Research [Internet]. 2014;1051 :268-272. Publisher's VersionAbstract
In this study, the degradation behavior of circulating fluidized bed (CFB) fly ash reinforced unsaturated polyester composites at different loadings of 0%, 10%, 20%, 30%, and 40% CFB fly ash were observed at different temperatures of 30°C, 50°C, and 80°C under acidic environment. The mass uptakes of the samples were recorded at specified time intervals to determine the effects of fly ash content and temperature. Scanning electron microscopy was used to show if there were changes in the microstructure of the samples. Moreover, the glass transition temperature found from the differential scanning calorimetry showed that the types of diffusion behavior that may take place were the Fickian and non-Fickian (Case II). However, the empirical diffusion model used illustrated that only the Fickian diffusion had occurred.
Tumolva TP. Development and evaluation of natural fiber-reinforced thermoset-based composites for long-term carbon fixation. Graduate School of Science and Engineering, Tokyo Institute of Technology. 2011.Abstract

Thermoset-based natural fiber-reinforced polymeric composites (NFRPs) are developed to allow for long-term CO2 fixation. For long NFRPs (abaca and kenaf), better mechanical properties are achieved with orthophthalic-type unsaturated polyester by chemically-treating the fibers, increasing the fiber content, and applying cross-ply sheet stacking orientation. For bagasse NFRPs, mechanical strength is increased by creating hybrid NFRPs, with randomly-oriented chopped bagasse sandwiched between continuous sugarcane and abaca fibers. For the matrix, furan resin (polyfurfuryl alcohol)- a biosynthetic thermoset- is employed in lieu of common commercial resins to increase the NFRP’s carbon storage potential, the fiber-matrix adhesion in furan-based NFRPs is improved by applying acid fiber treatments. Finally, carbon storage potential is evaluated by performing mass and energy balance calculations and lifetime predictions based on thermogravimetric analysis. 

Tumolva T, Kubouchi M, Aoki S, Sakai T. Effect of fiber loading on the mechanical strength of NFR hybrid composites. ASEAN Journal on Chemical Engineering [Internet]. 2010;10 (1) :21-26. Publisher's VersionAbstract
Ortho-type UP resin is reinforced with long abaca and short bagasse fibers to produce a novel type of natural fiber-reinforced (NFR) hybrid composite material that is environment-friendly, has a long service life, possesses the properties of both long and short FRP’s, and has also acquired the advantages of utilizing two different types of natural fiber reinforcements. The abaca and bagasse fibers are treated in 5wt% NaOH(aq) solution at 80°C for 9 hours and pressed into continuous, unidirectional fiber sheets and random fiber mats, respectively. The fibers are then incorporated into the resin matrix by hand lay-up method, producing FRP laminates with the same uniform thickness but subjected to varying fiber loading conditions: (1) the stacking of long fiber sheets are done in cross-ply and parallel orientation; (2) the abaca and bagasse fibers are stacked in different alternating sequence patterns, and (3) the fibers are added into the ortho-UP matrix at increasing fiber fraction. The alkali-treated FRP laminates show an increase in fiber-matrix interfacial adhesion as compared to the untreated FRP’s, based on the overall improvement in the composite mechanical strength, as well as from the lesser visible fiber pull-out observed from SEM images on their fracture surfaces. Also, as expected, the tensile and flexural strengths of the abaca/bagasse hybrid FRP measures intermediate to those of abaca and bagasse FRP’s. The strength has also improved with increasing fiber content, although this increase has also caused an increased occurrence of void spaces that may consequently become detrimental to the NFR composite’s performance.
Tumolva TP. Development a predictive emission model for a diesel fuel-fired power plant. Department of Chemical Engineering, University of the Philippines Diliman. 2006.Abstract

Previous studies have demonstrated the feasibility of Predictive Emission Monitoring Systems (PEMS) as an alternative to the Continuous Emission Monitoring Systems (CEMS) in monitoring emissions from industrial plant operations. PEMS is more cost effective compared to CEMS and has the added feature of diagnostic and trending capabilities.  In view of its potential applicability in the country, a study was conducted in on the use of PEMS in a privately owned diesel power plant in the Philippines. A computer-based “first principles” PEMS model was developed to estimate emission concentrations levels for four criteria air pollutants, namely sulfur oxides (as SO2), nitrogen oxides (as NO2), particulate matter (PM) and carbon monoxide (CO). Using plant operations data as input, the model simulates the diesel engine operations and predicts the resulting emission characteristics using stoichiometric and thermodynamic principles. The model was validated by comparing emission concentrations calculated using the model with actual emissions data measured. The model was calibrated using historical plant operation data to increase the PEMS accuracy. Additional refinements in the computer model, such as emission data recording and storage, were also done to increase the model’s handiness and practicability in operation. The study showed that the PEMS model developed for the diesel power plant could effectively predict PM emissions.