A Comprehensive Review on Process and Technological Aspects of Wood-Plastic Composites

This review deals with recent works on the process and technological aspects of wood-plastic composites (WPCs) manufacturing.WPCs relate to any composites that are built from wood and non-wood fibers and thermoplastic polymers. Recent progress relevant to wood-plastic composites has been reviewed in this article. The process and technological aspects of WPC, such as raw materials, fabrication, mechanical, physical, thermal, and morphological properties, were outlined comprehensively. The manufacturing process of WPCs is an important aspect of WPCs production. Manufacturing methods like compression molding and pultrusion have some limitations. Extrusion and injection molding processes are the most widely used in WPCs due to their effectiveness. Recent developments dealing with WPCs and the use of different kinds of nanofillers in WPCs have also been presented and discussed. Nanoclays are widely used as nanofillers in WPCs because they represent an eco-friendly, readily available in large quantity, and inexpensive filler. WPCs can be found in a wide range of applications from construction to the automotive industry.Keywords: additive manufacturing, adhesion, fabrication techniques, mechanical and physical properties, wood-plastic composite

Effects of Hydrolysis on the Removal of Cured Urea-Formaldehyde Adhesive in Waste Medium-Density Fiberboard

The vast production of medium-density fiberboard (MDF) in the world is expected to generate a large quantity of waste MDF after its service life, which requires the recycling of waste MDF (wMDF). This work attempted to investigate the removal of cured urea-formaldehyde (UF) resins adhesive in wMDF using hydrolysis for a possible way of recycling wMDF. The wMDFs were fabricated with two kinds of recycled fibers (RFs): refiner recycled fibers (RRFs) and hammer mill recycled fibers (HRFs) from red and radiata pine. The wMDFs were also produced at different RFs contents, such as 0, 5, 10, 20, 30, 50, and 100%. The panels were then hydrolyzed with water and oxalic acid solution to remove the cured UF resins. The Kjeldahl method was applied to determine the nitrogen (N) content in the panel before and after hydrolysis. Regardless of the wood species and recycling process, the mass loss, pH, and formaldehyde liberation of wMDFs after hydrolysis were greater for oxalic acid than those in water, confirming a greater N content had been extracted by oxalic acid than water. The resin removal became greater as the RFs content increased. In addition, the resin removal was slightly greater in wMDFs made of HRFs than the RRFs. Moreover, red pine RFs gave higher resin removal than radiata pine. These results suggested that a proper combination of the recycling process and additives could make it possible to recycle wMDF panels in the future.Keywords: cured urea-formaldehyde, hydrolysis, medium-density fiberboard, oxalic acid, recyclin

Utilization of Lignin from the Waste of Bioethanol Production as a Mortar Additive

Lignin is the second most abundant biopolymer, exceeded only by cellulose, and comprises 15-25% of the dry weight of woody plants, with around 285,000 tons/year of production capacity globally. This study aims to utilize the lignin obtained from the waste of bioethanol production from oil palm empty fruit bunches (OPEFB) as a mortar additive. The use of mortar as a material for road construction is increasing, but its long time hardening is causing problems such as traffic jams. Lignin can be used as an additive to shorten the hardening time of mortar. Lignin was isolated at various NaOH concentrations and temperatures of OPEFB pretreatment for bioethanol production. The workability of the slump and compressive strength of mortars generated were further tested. Lignin from OPEFB  can be used as a water reducer in the mortar with improved workability as much as 24.4% compared to controls. The addition of lignin could also increase the compressive strength at the mortar age of 7 and 28 days compared to the commercial lignosulfonate and control on the various water-cement ratios. The setting time of mortar with the lignin addition increased rapidly, reaching up to 80% at the 7 days, indicating that curing time is getting shorter. The most remarkable improvement of compressive strength with suitable workability and high-quality concrete was reached by 1% lignin addition and 0.45 water-cement ratio with compressive strength 38.81 N/mm2 at 28 days.Keywords: compressive strength, lignin, mortar, OPEFB, water reduce

Characteristics of Eco-Friendly and Sustainable Plywood Adhesive derived from Low-Quality Cat’s Eye Damar Resin

Wood panel products mainly use formaldehyde-based adhesives that release free formaldehyde and potentially cause health problems. This study aimed to develop a free-formaldehyde adhesive from cat’s eye damar (CED) resin as an alternative adhesive for plywood production. The low-quality CED resin was used to increase the added value of the resin. The adhesive formulation consists of a ratio of 30:70 (CED:benzene) dissolved for 15 minutes at 45°C. The plywood was manufactured using glue spread rates of 200, 250, and 300 g/m2 with an addition of 10% tapioca flour and hot pressed using a pressure of 2.45 MPa at 120°C for 6 minutes. The CED-based adhesive produced has a solid content of 28.76%, a pH value of 5.93, a gel time value of 70.05 minutes, and a viscosity value of 4.02 mPa.s. Fourier-transform infrared spectroscopy analysis stretching of the C-H group, indicating an alkane compound. Plywood’s physical and mechanical properties bonded with CED-based adhesive increased with higher glue spread application. Utilizing a glue spread of 300 g/m2 could produce plywood with comparable physical and mechanical properties to the urea-formaldehyde-bonded plywood. Keywords: cat’s eye damar, dynamic mechanical analysis, formaldehyde-free adhesive, plywood, Shorea javanic

Lignin as an Active Biomaterial: A Review

Lignin is the second most naturally abundant biopolymer in the cell wall of lignocellulosic compound (15-35%) after cellulose.Lignin can be generated in massive amounts as by-products in biorefineries and pulp and paper industries through differing processes. Most lignin is utilized as generating energy and has always been treated as waste. Due to the high amount of phenolic compounds in lignin, it is considered as a potential material for various polymers, building blocks, and biomaterials production. Even though lignin can be utilized in the form of isolated lignin directly, the modification of lignin can increase the wide range of lignin applications. Lignin-based copolymers and modified lignin show better miscibility with another polymeric matrix, outstanding to the enhanced performance of such lignin-based polymer composites.This article summarizes the properly updated information of lignin’s potential applications, such as bio-surfactant, active packaging, antimicrobial agent, and supercapacitor.Keywords: active packaging, antimicrobial agent, bio-surfactant, lignin, supercapacito

Characteristics of Polyurethane Cross-Laminated Timber Made from a Combination of Pine and Coconut

The objective of this study was to assess the properties of cross-laminated timber (CLT) fabricated from the combination of Sumatran pine (P) and coconut trunk (C) bonded with polyurethane adhesive. The basic properties of raw materials and adhesives were characterized. The CLT panels’ length, width, and thickness are 100 cm by 30 cm by 3.6 cm, respectively. Three-layer CLT was made with 4 combinations of face/core/back lamina, i.e., PPP, CCC, PCP, and CPC, which are arranged perpendicular to each other. The laminae were bonded using PU adhesive on 160 g.m-2 glue spread. The CLT’s delamination and wood failure percentages (WFP) were assessed following the JAS 3079 (2019) standard. The study’s results demonstrated that the PU adhesive employed in this investigation could curl ideally at 30°C for 200 min. Solid pine and coconut’s physical and chemical characteristics differed, but their wettability to polyurethane adhesives was identical. Hybrid pine CLT has greater attributes compared to single pine CLT. Single coconut CLT, on the other hand, offers better features than hybrid coconut CLT. All CLT samples failed to fulfil the JAS 3079 (2019) requirement for delamination (== 90%). Keywords: Coconut trunk, cross-laminated timber, layer combination, pine wood, polyurethane adhesiv

Bio-Polyurethane Resins Derived from Liquid Fractions of Lignin for the Modification of Ramie Fibers

In this study, technical lignin from black liquor was used as a pre-polymer for the preparation of bio-polyurethane (Bio-PU) resins. Briefly, the isolated lignin was fractionated using ethyl acetate (EtAc) and methanol (MeOH). The liquid fractions of lignin, such as lignin-EtAc (L-EtAc) and lignin-methanol (L-MeOH), were mixed with 10% of polymeric isocyanate (based on the weight of liquid fractions) to obtain Bio-PU resins. The isolated lignin, fractionated lignin, and lignin-derived Bio-PU resins were characterized using several techniques. The obtained Bio-PU resins were then used to modify ramie fibers using vacuum impregnation method. Fourier Transform Infrared (FTIR) spectroscopy, Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA) revealed that the isolated lignin had quite similar characteristics to the lignin standard. Fractionation of lignin with EtAc and MeOH altered its characteristics. FTIR, DSC, and TGA showed that solid fractions of lignin had similar characteristics to lignin standard and isolated lignin, while the liquid fractions had characteristics from lignin and the solvents. The absorption band of isocyanate (−N=C=O) groups was shifted to 2285 cm−1 from 2240 cm−1 owing to the reaction with the −OH groups in lignin, forming urethane (R−NH−C=O−R) groups at 1605 cm−1 in Bio-PU resins. Thermal properties of Bio-PU resins derived from L-EtAc exhibited greater endothermic reaction compared to Bio-PU-L-MeOH. As a result, the free −N=C=O groups in Bio-PU resins have reacted with –OH groups on the surface of ramie fibers and improved its thermal properties. Modification of ramie fibers with Bio-PU resins improved the fibers’ thermal stability by 15% using Bio-PU-LEtAc for 60 min of impregnation.Keywords: Bio-polyurethane resins, Impregnation, Lignin fractions, Ramie fibers, Thermal stabilit

The Removal of Cured Urea-Formaldehyde Adhesive towards Sustainable Medium Density Fiberboard Production: A Review

Medium density fiberboard (MDF) is an engineered wood product that has density and specific gravity similar to solid wood, ranging from 600 to 800 kg/m3 of density and 0.6 to 0.8 of specific gravity. This makes MDF suitable to partially replace solid wood, particularly for interior application. Approximately over than 100 million m3 of MDF are produced in 2020, resulting in a large amount of waste MDF will be generated in the next 20 years. MDF is produced using urea-formaldehyde (UF) resins adhesive. UF resins adhesive is a poly-condensation product of urea and formaldehyde via an alkaline acid two-step reaction. Sustainable MDF production is required as the world is facing climate change and deforestation. Recycling is a way to support sustainable production in the engineered wood products manufacturing. Many attempts have been done to find ways to recycle waste MDF. The main problem is UF resins, which bond the MDF panel fibers. In order to re-manufacture the waste MDF into new recycled MDF, UF resins should be eliminated from the waste MDF before being used. The presence of UF resins in MDF can interfere with the utilization of the recycled fibers, whether it will be used as a raw material for new MDF or other composite products. This paper reviews the process of removal of cured UF resins from waste MDF panel by considering the hydrolytic stability of cured UF resins for MDF recycling, providing a comprehensive review of how cured UF resins can be removed from waste MDF and characterization of recycled fibers obtained from recycling prior to re-manufacturing of recycled MDF panel.Keywords: hydrolysis, medium density fiberboard, resin, recycling, resin removal, urea-formaldehyd

Pengaruh Lama Penyimpanan dan Pengenceran Lindi Hitam Terhadap Karakteristik Lignin Kraft Acacia mangium

This study aimed to investigate the effects of storage time and dilution of black liquor (BL) from Acacia mangium kraft pulping on the characteristics of isolated Lignin. Lignin isolation was carried out by 1 and 2 steps of isolation using HCL 1M to precipitate Lignin, diluted before isolation. Isolated Lignin was analyzed for its acid-soluble Lignin (ASL), insoluble acid lignin (AIL), functional groups by FTIR, solubility in dioxane and NaOH and thermal properties. The effect of BL storage time was also evaluated on the characteristics of the Lignin produced. The results suggest that the longer BL is stored, the higher the lignin yield. When compared to the isolation approach without dilution, the dilution process produced a higher yield and ash content up to 84% and 21%, respectively. Without dilution, the AIL isolated was lower than the dilution during BL storage. The longer the storage duration, the higher the lignin purity. Compared to two-step lignin isolation, dilution treatment in single-step isolation improves yield and purity. The thermal stability of lignin isolation without dilution (184 ⁰C and 167 ⁰C for 1 and 2 steps, respectively) was higher than that of isolated Lignin with dilution (154.8 ⁰C and 160.9 ⁰C for 1 and 2 steps, respectively), according to thermal study. Both lignin isolates with and without dilution have comparable functional groups, as shown by FTIR spectra. Due to the high yield and purity of isolated Lignin, BL dilution could be a viable alternative in lignin isolation from BL. Moreover, the properties of isolated Lignin are also influenced by BL storage

Effects of Compression Ratio and Phenolic Resin Concentration on the Properties of Laminated Compreg Inner Oil Palm and Sesenduk Wood Composites

Due to its inferior properties, oil palm wood (OPW) extracted from the inner layer of the oil palm (Elaeis guineensis) trunk, referred as inner OPW in this study, is frequently regarded as a waste. Phenolic resin treatment and lamination of inner OPW with other hardwoods may be an excellent way to improve the properties of the inner OPW. In this study, inner OPW were treated with two different concentrations (15% and 20%) of low molecular weight phenol formaldehyde resin (LmwPF) and compressed at different compression ratios (10%, 20%, and 30%). The physical and mechanical properties of the modified inner OPW’s were evaluated according to British Standards (BS) 373: 1957. The results revealed that inner OPW treated with the highest compression ratio (30%) and resin concentration (20%) exhibited the highest weight percent gain, polymer retention and density. In the following phase of the research, the treated inner OPW was used as the core layer in the fabrication of a three-layer laminated compreg hybrid composites, with untreated and treated sesenduk (Endospermum diadenum) wood serving as the face and back layers. The compression ratios of 10% and 20% and resin concentrations of 10% and 20% were used in this phase of study as laminated boards made with 30% compression ratio failed. The findings showed that resin concentration had a significant impact on both the inner OPW and the laminated compreg hybrid panels. Markedly, higher resin concentrations (20%) resulted in improved physical properties, i.e., thickness swelling and water absorption, as well as enhanced mechanical properties (modulus of rupture and modulus of elasticity). Although compression ratios had no significant effect on the properties of the laminated products, those compressed at higher compression ratios (20%) performed slightly better than the panels compressed at lower compression ratios (10%)