Study of the Physical and Mechanical Properties of Thermoplastic Starch/Poly(Lactic Acid) Blends Modified with Acid Agents

In this work, we present a functionalization strategy of starch-poly(lactic acid) (PLA) blends with organic acids. Lactic and acetic acid were used as acid agents, and oleic acid was also included in the previous acids, with the aim of finding a synergy that thermodynamically benefits the products and provides hydrophobicity. The ratio of starch and sorbitol was 70:30, and the added acid agent replaced 6% of the plasticizer; meanwhile, the thermoplastic starch (TPS)–PLA blend proportion was 70:30 considering the modified TPS. The mixtures were obtained in a torque rheometer at 50 rpm for 10 min at 150 °C. The organic acids facilitated interactions between TPS and PLA. Although TPS and PLA are not miscible, PLA uniformly dispersed into the starch matrix. Furthermore, a reduction in the surface polarity was achieved, which enabled the wettability to reach values close to those of neat PLA (TPS–L-PLA increased by 55% compared to TPS–PLA). The rheological results showed a modulus similar to that of TPS. In general, there were transitions from elastic to viscous, in which the viscous phase predominated. The first and second-order thermal transitions did not show significant changes. The structural affinity of lactic acid with biopolymers (TPS–L-PLA) allowed a greater interaction and was corroborated with the mechanical properties, resulting in a greater resistance with respect to pure TPS and blended TPS–PLA (28.9%). These results are particularly relevant for the packaging industry.

Rheological, Thermal, Superficial, and Morphological Properties of Thermoplastic Achira Starch Modified with Lactic Acid and Oleic Acid

The modification of achira starch a thermoplastic biopolymer is shown. Glycerol and sorbitol, common plasticizers, were used in the molten state with organic acids such as oleic acid and lactic acid obtaining thermodynamically more stable products. The proportion of starch:plasticizer was 70:30, and the acid agent was added in portions from 3%, 6%, and 9% by weight. These mixtures were obtained in a torque rheometer for 10 min at 130 °C. The lactic acid managed to efficiently promote the gelatinization process by increasing the available polar sites towards the surface of the material; as a result, there were lower values in the contact angle, these results were corroborated with the analysis performed by differential scanning calorimetry and X-ray diffraction. The results derived from oscillatory rheological analysis had a viscous behavior in the thermoplastic starch samples and with the presence of acids; this behavior favors the transitions from viscous to elastic. The mixture of sorbitol or glycerol with lactic acid promoted lower values of the loss module, the storage module, and the complex viscosity, which means lower residual energy in the transition of the viscous state to the elastic state; this allows the compounds to be scaled to conventional polymer transformation processes.

PENGARUH JUS JERUK DAN MINUMAN BERKARBONASI TERHADAP KEKERASAN PERMUKAAN RESIN KOMPOSIT

Background: Orange juice and Carbonat drink contains an acid agent which can affect the surface hardness of composite resin. Changes of surface hardness of composite resin is caused by infiltration of water containing the acid agent that affect the bonding of matrix to filler composite resin. This study purpose to determine the effect of immersed orange juice and carbonat drink on surface hardness of composite resin. Method: This was experimental laboratory study with a pre and post test control group design. The samples of composite resin had 12 mm in diameters and 2 mm in thickness (n=27). Composite resin used is FiltexTM Z350 XT shades A2. Samples were divided into three groups : group A immersed with orange juice, group B immersed with carbonat drink, and group C immersed with aquadest as the negative control. Samples were immersed for 24 hours. The pre and post immertion of composite resin surface hardness were measured with Micro Vickers Hardness Tester. Results: Post immertion Vickers hardness was compared by using one way anova test. The result showed that immersed orange juice and carbonat drink significantly reduced the surface hardness of composite resin (p < 0,05). Concluision: The conclusion Immersed carbonat drink more reduced the surface hardness of composite than orange juice. It is suggested to reduce the duration direct exprossure of consumption carbonat drink.

UJI KEKERASAN KOMPOSIT TERHADAP RENDAMAN BUAH JERUK NIPIS (CITRUS AURANTIFOLIA)

Lime (Citrus aurantifolia) contains an acid agent which can affects the surface hardness of composite. Change of surface hardness of composite is caused by infiltration of water containing the acid agent that affects the bonding of matrix to filler of composite.This study aimed to determine the effect of immersed lime on surface hardness of composite. This was an experimental laboratory study with a pre and post test control group design. The samples of resin composite had 5 mm in diameters and 4 mm in thickness (n = 24). Samples were divided into two groups: mineral water as the control group and immersed lime as the trial group. Samples were alternately immersed for 30, 60, 120 minutes. Post immersion, the changes of composite hardness were measured with Mico Vickers Hardness Tester. Post immersion Vickers hardness was compared by using paired t-test. The result showed that immersed lime significantly reduced the surface hardness of composite (p<0.05). Duration of 60 and 120 minutes of lime immersion reduced significantly the surface hardness of composite (p<0.05). It is suggested to reduce the duration of acidic fruit exposure such as lime to the composite.Keywords: resin composite, surface hardness changes, limeAbstrak: Buah jeruk nipis (Citrus aurantifolia) mempunyai kandungan asa m yang dapat memengaruhi kekerasan komposit. Perubahan kekerasan komposit disebabkan oleh menyerapnya air yang mengandung asam pada komposit yang memengaruhi ikatan matriks dan filler. Penelitian ini bertujuan untuk mengetahui pengaruh perendaman buah jeruk nipis terhadap perubahan kekerasan komposit. Jenis penelitian ini ialah eksperimental laboratorium dengan desain pre and post test control group. Jumlah sampel penelitian ialah 24 resin komposit dengan diameter 5 mm dan tebal 4 mm. Sampel dibagi menjadi 2 kelompok yaitu kelompok kontrol air mineral dan kelompok perlakuan yang direndam dalam sari jeruk nipis dengan 3 durasi waktu yang berbeda 30, 60, dan 120 menit. Setelah perendaman diukur nilai perubahan kekerasan dengan Mico Vickers Hardness Tester. Hasil perendaman berdasarkan uji Vickers diuji banding secara statistik menggunakan uji paired sample t test. Hasil penelitian menunjukkan adanya pengaruh perendaman buah jeruk nipis terhadap perubahan kekerasan komposit (p<0,05). Pada durasi waktu 60 dan 120 menit terdapat pengurangan yang bermakna dari kekerasan permukaan resin komposit (p<0,05). Disarankan untuk mengurangi durasi paparan komposit terhadap buah-buahan yang mengandung asam seperti jeruk nipis.Kata kunci: resin komposit, perubahan kekerasan permukaan, jeruk nipis