Improvement of Polypropylene Adhesion by Kraft Lignin Incorporation

Abstract

Low surface energy and poor adhesion are well-known characteristics of polypropylene (PP). Surface treatments such as plasma, corona, and laser are usually applied to overcome these limitations. However, current studies highlight the incorporation of hydrophilic or amphiphilic polymers into hydrophobic low-surface-energy polymers as an alternative for increasing surface energy and thus improving adhesion. Lignin could be a promising amphiphilic polymer for use in increasing surface energy. In this work, PP/kraft lignin composites were obtained by incorporating up to 5 wt% of kraft lignin (KL) into a PP matrix. Corona treatment was applied to pristine PP and composites surfaces. Contact angle measurements and peeling tests were carried out to investigate the effects of KL incorporation and corona treatment on the surface energy and the mechanical strength of adhesion. Differential scanning calorimetry (DSC) was used to evaluate the PP's crystallinity index and recrystallization temperature and to dismiss their effects on the surface energy changes. Scanning electron microscopy (SEM) was applied to investigate the lignin dispersion. The results show that KL incorporation has potential as a method to improve the surface energy of PP, improve its poor adhesion, and enhance the effects of corona treatment.

Polyurethane adhesives from castor oil and modified lignin via reaction with propylene carbonate

“…The mechanical property deterioration that was verified for PU_30HKL_PC is probably due to the emergence of a second phase in this concentration, which was revealed and discussed in the DMA results. The interfaces between the primary and the lignin‐rich secondary phase can act as stress concentration sites, which can lead to premature failure and thus could possibly explain the reduction of ultimate tensile strength and elongation at break for the PU_30HKL_PC sample 57,58 …”

“…The interfaces between the primary and the ligninrich secondary phase can act as stress concentration sites, which can lead to premature failure and thus could possibly explain the reduction of ultimate tensile strength and elongation at break for the PU_30HKL_PC sample. 57,58…”

Valorization of Hemp Core Residues: Impact of NaOH Treatment on the Flexural Strength of PP Composites and Intrinsic Flexural Strength of Hemp Core Fibers

“…In that work, optimal amounts of lignin were proved to secure the stress transferring between the phases promoting the strengthening of the composite. Additionally, other authors suggested the use of lignin as binder between the fibers and hydrophobic matrices [ 40 , 41 ]. In general, there seems to be a balance between the lignin content, which provides a good dispersion of the reinforcement inside the matrix, and the hydroxyl groups in cellulose, ensuring a good interfacial bonding with the coupling agent.…”

Polypropylene/lignin blend monoliths used as sorbent in oil spill cleanup

“…Consequently, partial replacement of Polypropylene by Lignin is economically and ecologically gained attention for versatile applications [ 35 ]. Lignin combination in the Polypropylene matrix at various loading levels was presented [ 36 , 37 , 38 , 39 ]. The development of novel synthetic strategies to simplify miscible polymer/lignin blends with massive efforts has been made to recognize the potential advantages of Lignin for the growth and develop new thermoplastic polymer mixture [ 40 ].…”