Katerina Chryssou* and Eugenia Lampi
General Chemical State Laboratory, B’ Chemical Division of Athens, Department A’ Tsocha 16, Greece
*Corresponding author:Katerina Chryssou, General Chemical State Laboratory, B’ Chemical Division of Athens, Department A’ Tsocha 16, 11521 Athens, Greece
Submission: December 26, 2024;Published: January 16, 2025
Volume5 Issue1January 16, 2025
The determination of dry tensile properties of a paper wrapping plastic film was performed as well as the percent strain at break, the elongation in mm, in both directions, the machine direction, and the counter machine direction. We observed a correlation between stress and tensile strain in % by linear function. Also, the thickness of the plastic film was measured and was found to be 0.16mm. The dry tensile strength in the machine direction increased linearly with decreasing film thickness. The tensile strain at break in % increased linearly with increasing film thickness in the machine direction. The dry tensile strength across the cross-machine direction increased linearly with increasing film thickness. Also, the geometrical mean of the tearing resistance in mN was calculated and was correlated linearly with film thickness. The elongation at break in % in both directions increased as the film thickness increased. Finally, the plastic film was considered isotropic.
Keywords: Paper wrapping thin plastic film; Tensile strength; Thickness; Tearing resistance; Geometrical mean tearing resistance
The need for soft, elastic materials to resemble the elastic nature of soft tissues has driven the development of various biodegradable elastomeric polymers in tissue engineering and drug delivery. These materials are mechanically weak with a tensile strength at dry state, not more than 10MPa. Effectively balancing the mechanical properties and biodegradation of the plastic films, especially bio-functionalisation, to regulate cell/tissue biomaterial interactions is a challenge [1]. In general polymer thin films are difficult to be handled, and their mechanical properties have been poorly understood [2]. In this work a paper wrapping plastic film’s dry tensile and other mechanical properties are studied. The tensile properties vary with specimen thickness, specimen width, the rate of grip separation, and the initial gauge length. The tensile properties indicate anyway how well the plastic film can withstand tension [3]. Generally, tensile strength and elongation are seen as important barometers in later estimating photo-degradability, and the ultimate tensile strength and elongation values at the break point would be later statistically compared to determine photo-degradability. Elongation is more closely related to degradability. Changes in average elongation of the test sample toward cross direction (CD), and machine direction (MD) can be tested during periods of UV-irradiation [4].
Instruments and materials
Ten or more test pieces 21cm x 1.5cm were cut from the plastic film sample by a guillotine IDEAL 1043 GS. These test pieces were conditioned at 23 °C and 50% RH for 16hr in a conditioning chamber [5]. The tensile testing machine Zwick Roell Z2.5 BT1-FR 2.5th D14/2008, S.N. 181435/2008, was used for measuring the tensile strength [TS (MPa)] and percentage elongation at break (%) [E (%)] and elongation in (mm) of the wrapping plastic film, according to ASTM Standard Method D 882-10 [6]. The machine extended the plastic test pieces at 500mm/min constant rate of elongation (cross head speed), and measured both the tensile force and the elongation produced. Two clamps holded the plastic test pieces of 15mm width and grab them along a straight line across the full width of the plastic test pieces. The initial grip to grip separation was set at 50mm [6].
The thickness of the plastic film sample was measured using the digital precision micrometer TMI Model No 49-61-01-0002, S.N. 33421-01, with range 0-1.270mm. Twenty measurements were made on each test piece of 10cm x 10cm dimensions and mean thickness was calculated [7]. These test pieces were also conditioned at 23 °C and 50% RH for 16hr in a conditioning chamber [5].
The tearing resistance, Elmendorf method, was measured in a Lorentzen & Wettre, Stockholm Sweden, pendulum-type manual tearing tester with serial number 1210, code:009, type:95021, No:5529. The test piece dimensions were 7.6cm x 6.3cm and it was a pack of four rectangular sheets of the same size (7.6cm x 6.3cm), that it was tested according to ISO 1974:2012 [8]. These test pieces were also conditioned at 23 °C and 50% RH for 16hr in a conditioning chamber [5].
As in a model where the polymer molecules and the bonds were simplified as homogeneous and isotropic continua, the tensile properties of the plastic film were determined. The method used was specified in ASTM D882-10 [6]. Ten replicates were measured in the machine direction (MD) and eleven replicates were measured in the counter machine direction (CD) [9] (Figure 1).
Figure 1:Tensile force curves in Newton versus strain in mm, for the ten specimens of the paper wrapping plastic film tested in the machine direction (MD), and the relevant statistics.
The elongation at break values, of several hundred found during testing were common for film packaging plastics [10].
In Figure 2 we had correlation between stress and tensile strain in % by a linear function [11].
Figure 2:Linear in plane dry tensile stress-strain curve in the MD direction of a wrapping plastic film (Table 1).
Table 1:MD stress in MPa and the corresponding values of MD strain at break in%, and in mm, of a sample of paper wrapping plastic film [9].
Figure 3:Linear in plane dry tensile stress-elongation at break curve in the MD direction of a wrapping plastic film (Table 1).
Figure 4:Linear dry tensile stress in the MD direction-thickness curve of a wrapping plastic film (Table 2).
Table 2:MD stress in MPa and the corresponding values of thickness in mm, of a sample of paper wrapping plastic film.
The dry tensile strength across the machine direction increased linearly with decreasing polymer film thickness within the film thickness range studied [13].
Tensile strain at break in % increased linearly with increasing film thickness within the range studied (Figure 5 & Figure 6) [14].
Figure 5:Linear dry tensile strain at break in % in the MD direction-thickness curve of a wrapping plastic film (Table 2).
Figure 6:Tensile force curves in Newton versus strain in mm, for the eleven specimens of the paper wrapping plastic film tested in the counter machine direction (CD), and the relevant statistics.
Eleven replicates were measured in the counter machine direction as specified in ASTM D882-10 [6] (Figure 7).
Figure 7:Linear in plane dry tensile strength-strain curve in the CD direction of a wrapping plastic film (Table 3).
The mechanical properties helped us to understand the workability and applicability of the paper wrapping polymer film and were understood in terms of the tensile strength and strain at failure (flexibility) also in the counter-machine direction (CD) [15] (Figure 8).
Figure 8:Linear in plane dry tensile strength-elongation in mm curve in the CD direction of a wrapping plastic film (Table 3).
Table 3:CD stress in MPa and the corresponding values of CD strain at break in%, and in mm, of a sample of wrapping plastic film.
From the results of the tensile tests the conclusion could be drawn that the film with an average thickness of 159μm could be considered isotropic [16].
The tensile strength in the CD direction of the film was offset by the increase in the film thickness [17]. The dry tensile strength across the cross-machine direction (CD) increased linearly with increasing film thickness within the film thickness range studied (Figure 9 & Figure 10).
Figure 9:Linear dry tensile strength in the CD direction-thickness curve of a wrapping plastic film (Table 4).
Figure 10:Linear dry tensile strain at break in % in the CD direction-thickness curve of a wrapping plastic film (Table 3 and Table 4).
Table 4:CD stress in MPa and the corresponding values of thickness in mm, of a sample of wrapping plastic film.
Tearing was one of the most critical mechanical properties of polymeric films. The tearing process of ductile films was very similar to the tensile process because of the large deformation in the direction of loading [18,19].
The performance of the Elmendorf tearing test was an important end-use test of the plastic film and was used to determine the range of the film application, as well as the price of the film-grade resin, and to compare polymerization catalysts, and also the processes employed for the synthesis of the respective polymer [20].
The tearing strength depended strongly on the thickness of the film, as could be seen in Figure 11.
Figure 11:Geometrical mean tearing versus thickness curve, of a wrapping plastic film (Table 5).
Table 5:MD Tearing in mN and CD tearing in mN, Geometrical mean tearing, and the corresponding values of thickness in mm, of a sample of wrapping plastic film [19].
The elongation at break in % (E) values for the film varied linearly with the tensile strength in MPa (TS). The elongation at break (%) (E) in general increased as the film thickness increased, so in general comparison of (E) should also include film thickness. No anisotropy effect was observed. Isotropy was expected and, was observed, since there was the same molecule orientation in all directions of the plastic film.
© 2025 Katerina Chryssou. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and build upon your work non-commercially.