Janis Kajaks

Physical and mechanical properties of composites based on a linear low-density polyethylene (LLDPE) and natural fiber waste

The influence of the content and fiber length of textile waste (cotton, flax, and hemp) on the deformation and strength properties (in tension and bending) of a linear low-density polyethylene (LLDPE) was investigated. It was found that the tensile strength increased for all composites containing hemp fibers of up to 30 wt.%. The elongation at break rapidly decreased when the filler content was raised to 10 wt.%, but thereafter changed insignificantly. The flexural strength and modulus increased considerably with filler content in the composites. On the contrary, their deformability, as expected, decreased. The influence of hemp fibers on the physicalmechanical properties of the LLDPE was somewhat more pronounced. The optimum content of fibers in the composites (30 wt.%) was significantly smaller than that usually obtained (40-50 wt.% natural fibers) for other polyolefin composites, for example, with low-density polyethylene and polypropylene matrices. The highest values of strength parameters, both in tension and bending, were reached for systems with a fiber length of up to 1 mm. The melt flow index decreased considerably with increasing fiber content in the LLDPE matrix (from 4.4 dg/min for LLDPE to 0.05-0.14 dg/min for systems containing 30 wt.% fibers). Nevertheless, processing of the composites was possible by traditional methods, for example, extrusion.

Thermal and water sorption properties of polyethylene and linen yarn production waste composites

Composite materials were compounded from waste obtained at different stages of linen yarns production and both virgin and recycled polyethylene. Thermal and water sorption properties of selected polymer/linen waste combinations (filler content 10–50 wt.-%) without and with modifiers stearic acid and diphenylmethane diisocyanate were investigated. Effectiveness of diphenylmethane diisocyanate was well-founded.

Physical and mechanical properties of composites based on polypropylene and timber industry waste

Wood polymer composites (WPC) are widely used materials in different industries because of many application, processing and recycling advantages compared to traditional thermoplastic polymer composites containing mineral fillers [1]. However, the commercial success of these materials primarily depends on improvements in moisture performance, and ability to use recycled and waste material as a wood filler. The research regarding WPC is focused on the chemical interaction between dissimilar material components with an aim to provide strong adhesion to the surface of wood filler-polymer matrix [2]. The goal of this paper was to present results of investigations of exploitation properties of composites containing different plywood production industry byproducts and polypropylene. It was shown that modification of all composites with coupling agent maleated polypropylene (MAPP) considerably improve physical mechanical properties (tensile, flexural, impact strength) of WPC. MAPP (5 wt.%) additions also significantly improve water resistance of WPC. SEM investigations confirmed positive action of interfacial modifiers on strengthening of adhesion interaction between components wood and PP matrix that give considerable increase of exploitation properties of the WPC.

Wood Plastic Composites Made with Thermally Modified Birch Wood Residues

Thermally modified (TM) wood production has significantly increased in the last decade. The trend for TM wood residues should be similar – rapidly increasing, which has prompted this research on the possible efficient uses of these residues, such as sawdust. One of the possibilities could be the production of wood plastic composites (WPCs). In this work, three different hydrothermal modification regimes were used to modify birch boards. Modified and unmodified birch boards were milled to obtain sawdust. WPCs were made with a two-roll mill, and they consisted of 50 wt-% wood fibres + 50 wt-% polypropylene. Melt flow index (MFI), flexural properties, impact strength, microhardness water absorption and dimensional stability were tested. WPCs with TM wood showed improvement in flexural properties, MFI and other properties, however there was a decrease in impact strength. Scanning electron microscopy pictures of impact strength samples fracture surfaces were taken.

Rheological Properties of Wood-Plastic Composites Based on Polypropylene and Birch Wood Plywood Production Residues

Article summarizes investigation results of rheological and thermal stability properties of industrially prepared wood plastic composites, based on virgin polypropylene and birch wood plywood production residues-plywood sanding dust (PSD). WPCs PP+40 wt. % PSD contain different modifiers, such as lubricant Struktol TWP (blend of an aliphatic carboxylic acid salts and mono and diamides), sterically hindered phenolic antioxidant 1010, thermal stabilizer 168 (hydrolytically stable phosphite), UV stabilizer 770-low molecular weight hindered amine light stabilizer (HALS) and pigments based on LDPE. According to our studies, we could conclude that rheological properties studied by capillary rheometer method, strongly depends on WPCs composition. MFI values fluctuate in limits from 0.212 up to 0.724 g/10min. that is changes 3.4 times. Thermal and antioxidant stabilizers promote increase of thermal stability of WPCs noted by TGA. Curves of fluidity indicates character of typical pseudo-plastic liquids for which viscosity not only depends on temperature and shear stress and deformation rate, but also decrease with increase of shear rate. That confirms fluidity index n values which are smaller than 1.

Fungal Degradation of Wood Plastic Composites Made with Thermally Modified Wood Residues

Wood plastic composites (WPC) are mainly used as an outdoor material, so durability against fungal decay is one of the factors that should be analyzed and if necessary improved. WPC are susceptible to biodegradation, although these materials have limited water absorption because of the wood fiber encapsulation in polymer matrix. In the study two different water pretreatment methods (short-term and long-term) were used to ensure appropriate water content for fungal growth. Also in the paper thermally modified wood (different regimes) fiber influence on WPC fungal resistance is investigated. The results showed that long-term water pretreated WPC specimens had more suitable conditions for fungal degradation that led to higher weight loss. The results which were related to thermally modified wood fibers showed, that WPC with thermally modified wood fibers had improved resistance against fungi. Thermal modification regimes had an effect on WPC durability as well.

Some Exploitation Properties of Wood Plastic Composites Based on Polypropylene and Plywood Production Waste

Three types of birch wood plywood by-products: plywood sanding dust (PSD), plywood sawdust (PSWD) and refined plywood scrap fibres (RPSF) and polypropylene composites exploitation properties (tensile, flexural modulus), microhardness water resistance and fluidity of composite melts, were evaluated. These investigations showed possibility of usage as excellent reinforcements for polypropylene presented by-products. For example tensile modulus increase up to 5 times, but flexural modulus till 2.3 times. Optimal content of PSD in polypropylene composites is 40 wt%, but in the cases of PSWD and RPSF 50 wt%.

Influence of Hemp Fibers Pre-processing on Low Density Polyethylene Matrix Composites Properties

In present research with short hemp fibres reinforced LLDPE matrix composites with fibres content in a range from 30 to 50 wt% subjected to four different pre-processing technologies were produced and such their properties as tensile strength and elongation at break, tensile modulus, melt flow index, micro hardness and water absorption dynamics were investigated. Capillary viscosimetry was used for fluidity evaluation and melt flow index (MFI) evaluated for all variants. MFI of fibres of two pre-processing variants were high enough to increase hemp fibres content from 30 to 50 wt% with moderate increase of water sorption capability.

Recycled Thermoplastic Polymer Hot Melts Utilization for Birch Wood Veneer Bonding

Today, thermosetting polymer resins containing formaldehyde are mainly used in the production of plywood composites. These glues are toxic due to the generation of gaseous products, chiefly formaldehyde, during the production and exploitation of laminated materials, which pollute the environment. In order to decrease the emission of toxic products from these resins, natural product additives (lignins, tannins etc.) or fully biodegradable polymers such as starch, polylactides etc., are used. These glues are not toxic, but they have poor adhesion to wood, low water resistance and are more expensive. Our previous investigations have shown the possibility of using non-toxic virgin polyolefins as hot melts for plywood production. The aim of this work was to investigate the use of cheaper waste products, such as recycled thermoplastic polymers (polyolefins, polyamides), as glue hot melts for wood veneer bonding instead of traditional thermosetting resins, which are based on formaldehyde. Different recycled thermoplastic polymers produced from tetra package waste, domestic film waste, recycled polypropylene and recycled polyamide-6 were used as hot melts for birch wood veneer bonding. The content of the recycled adhesives was determined using differential scanning calorimetry (DSC) and the tetra package waste content of different types of polyethylenes, with additives of polypropylene and polyethylene terephthalate (PET), was fixed. Virgin high-density polyethylene and polypropylene were used as references. The fluidity of all the recycled materials, using melt flow index (MFI) measurements, was 1.96 g/10 min for polyethylenes and 1.94 g/10 min for polypropylene; this adhesive fluidity is sufficient to form full contact with the surface of the wood veneer sheets. Adhesive activity of the recycled hot melts was evaluated by preparing single overlap joints and specimens were tested for shear strength. The optimal technological parameters for producing samples were noted: pressure 2 MPa, contact time 1–2 min and a temperature for polyethylenes of 130°C, for polypropylene of 180°C, for PA-6 at 220°C. The highest values of shear strength were observed for specimens glued with recycled polypropylene (10 MPa), in the case of polyethylenes, the maximum was 5–6 MPa. The mixed fracture mechanism of adhesive joints was fixed after visually examining the surface of the broken samples. It was shown that to reach high adhesive strength it is also necessary to improve the cohesive strength of the adhesive layer. Polyethylene terephthalate fabric waste was used as reinforcement for strengthening the adhesive layer, which improved the bending strength and modulus of the two layers laminate bonded with recycled polypropylene. Direct correlation between high adhesive properties and high bending strength was not observed on all occasions. Water exposure experiments (23°C, 72 h) showed a decrease of adhesive strength to constant values of 2–2.2 MPa, for all investigated adhesives, which are similar to observations using 4 mm thick industrial plywood, corresponding to the 3rd class of water resistance. These investigations highlight the excellent prospects for the use of recycled polyolefins as hot melts for wood bonding.

Wood particle size influence on water resistance and mechanical properties of thermally modified wood-polypropylene composites

ABSTRACT The processing of wood produces large amounts and different types of wood residues. Currently, a part of these residues is used in the production of wood plastic composites (WPC). It is known that wood particle characteristics (size, length/diameter ratio, shape, etc.) significantly influence properties of WPC; however, for thermally modified wood, the information about these effects is limited. Therefore, the main objective of this research was to investigate how different size fractions of thermally modified wood particles influence mechanical and water resistance properties of WPC. The results showed that the particle size had a significantly smaller influence on the mechanical properties for WPC with thermally modified wood particles compared to WPC with unmodified wood particles. Additionally, the wood particle size had no effect on water absorption dynamics and ultimate water uptake in case of thermally modified wood particles. Finally, wood particle size did not affect changes in mechanical properties for re-dried WPC after 200 days of immersion in water.